2026

1. journal

   A Sliding Mode Approach to Asymptotic Recovery of Nominal Performance for Uncertain Linear Systems

   Hyuntae Kim, Hyungbo Shim, Nam Hoon Jo, Mohammad Ataei, and Gyunghoon Park

   IEEE Transactions on Industrial Electronics, 2026

   Abs DOI

   This article presents a new structure of a sliding mode disturbance observer (SM-DOB) for handling model uncertainty and unmodeled disturbances. The proposed SM-DOB is composed of two key components. First, a Levant’s differentiator is used to estimate the high-order time derivatives of the output. To satisfy the conditions required for the effective operation of Levant’s differentiator, we employ an integral SM technique so that on the sliding surface, the real plant’s dynamics are substituted with the nominal dynamics. With this structure, the proposed SM-DOB can achieve robust disturbance rejection and recover nominal performance in finite time. The stability and the finite time convergence of the proposed SM-DOB are rigorously proved by the Lyapunov stability method. Finally, to show the superiority and verify the validity of the proposed SM-DOB, we conduct both numerical simulations and laboratory experiments with brushless dc (BLdc) motor drives. It is observed that the proposed SM-DOB guarantees satisfactory performance in rejecting both input disturbance and plant uncertainty while remaining robust in the presence of noisy measurement.

2. conference

   On Asymptotic Stability of Hybrid Systems with Frequent Updates and Sampled-Data Observers

   Aneel Tanwani, Hyungbo Shim, and Andrew Teel

   In European Control Conference (ECC), 2026

   HTML
3. journal

   Low-Power Disturbance Observer for Linear Systems of High Relative Degree with Robust Stability Condition

   Donghyeon Song, Hyuntae Kim, and Hyungbo Shim

   International Journal of Control, Automation, and Systems, Apr 2026

   Abs DOI

   The disturbance observer (DOB)-based control is a powerful robust control technique characterized by external disturbance rejection and nominal performance recovery. However, the conventional DOB encounters numerical challenges in implementation when the plant has a high relative degree. This is due to its high-gain observer structure inside which requires gains that scale with the reciprocal of the time constant, and the gain is further powered up to the relative degree, leading to a potential numerical instability. To address this issue, we propose a modified DOB whose gains are limited to at most the second order of the high-gain parameter, regardless of how large the relative degree is. The key idea is replacing the original high-gain observer with the so-called ‘low-power” high-gain observer. The proposed “low-power” DOB not only preserves the original capability of DOB that allows the outer-loop controller to be designed without consideration about robustness, but also provides estimated state of the plant for the outer-loop controller without numerical issues. A robust stability condition is analyzed via singular perturbation theory, and a systematic design methodology for the design coefficients is developed based on Kharitonov theorem and root locus techniques. The numerical simulation results are provided to validate the theoretical results.

4. journal

   A Learning with Errors Based Encryption Scheme for Dynamic Controllers That Discloses Residue Signal for Anomaly Detection

   Yeongjun Jang, Joowon Lee, Junsoo Kim, Takashi Tanaka, and Hyungbo Shim

   IEEE Transactions on Control of Network Systems, 2026

   Abs DOI

   Although encrypted control systems ensure confidentiality of private data, it is challenging to detect anomalies without the secret key as all signals remain encrypted. To address this issue, we propose a homomorphic encryption scheme for dynamic controllers that automatically discloses the residue signal for anomaly detection, while keeping all other signals private. To this end, we characterize the zero-dynamics of an encrypted dynamic system defined over a finite field of integers and incorporate it into a Learning With Errors (LWE) based encryption scheme. We then present a method to further utilize the disclosed residue signal for implementing dynamic controllers over encrypted data, without requiring re-encryption even when they have non-integer state matrices.

2025

1. journal

   Two Algorithms for Distributed Mode Computing Based on Blended Dynamics Approach

   Chao Huang, Siliang Yu, Hyungbo Shim, and Brian D.O. Anderson

   Systems & Control Letters, 2025

   Abs DOI

   This paper studies the distributed mode computing problem in a multi-agent system, in which each individual agent possesses a certain attribute and the agent group aims to agree upon the mode (the most frequent attribute owned by the agents) via distributed computing. Two algorithms are proposed, the first one estimates the frequency of all attributes at every agent, and then identifies the most frequent attribute as the mode; the second is based on a distributed consensus protocol that renders all the agents agreeing on an attribute whose frequency is no less than a given threshold. This protocol is then used as the main building block to compute the mode via a branch-and-bound algorithm. Analysis of both algorithms establishes finite time convergence and is based on the blended dynamics approach.

2. journal

   Robust Disturbance Rejection for Uncertain Linear System with Time-Varying Exo-System: A Disturbance Observer Approach

   Hyuntae Kim, Gyunghoon Park, and Hyungbo Shim

   Automatica, 2025

   Abs DOI

   This paper addresses the problem of completely eliminating modeled disturbance that enters linear minimum-phase systems having parametric uncertainty and is generated by a linear time-varying exo-system. Motivated by the internal model principle (IMP), the core is to append a filter in front of the plant, such that (a) the disturbance model is embedded into the filter dynamics and (b) the filter is of minimum phase. Then the cascade connection of the plant and the filter is robustly stabilized by employing a disturbance observer (DOB)-based controller. In addition to simplicity in the design over the existing IMP-based approaches, the proposed controller also enjoys benefits of the DOB techniques, such as robustness against large parametric uncertainty and additional unmodeled disturbance, and guaranteeing a pre-defined nominal tracking performance in both transient and steady-state. Stability and performance of the controller are analyzed by the singular perturbation theory.

3. journal

   Encrypted Dynamic Control Exploiting Limited Number of Multiplications and a Method Using RLWE-Based Cryptosystem

   Joowon Lee, Donggil Lee, Junsoo Kim, and Hyungbo Shim

   IEEE Transactions on Systems, Man, and Cybernetics: Systems, 2025

   DOI
4. journal

   Stability of Linear Systems with Slow and Fast Time Variation and Switching: General Case

   Hyungbo Shim and Daniel Liberzon

   Nonlinear Analysis: Hybrid Systems, 2025

   Abs DOI

   This paper studies exponential stability of linear systems with slow and fast time variation and switching. We use averaging to eliminate the fast dynamics and only retain the slow dynamics. We then use a recent stability criterion for slowly time-varying and switched systems, combined with perturbation analysis, to prove stability of the original system. The analysis involves working with an impulsive system in new coordinates, which enables us to treat a more general class of systems compared to previous work.

5. journal

   Singularly Perturbed Hybrid Systems for Analysis of Networks with Frequently Switching Graphs

   Aneel Tanwani, Hyungbo Shim, and Andrew R. Teel

   IEEE Transactions on Automatic Control, 2025

   Abs DOI

   For a class of hybrid systems, where jumps occur frequently, we analyze the stability of system trajectories in view of singularly perturbed dynamics. The specific model we consider comprises an interconnection of two hybrid subsystems, a timer which triggers the jumps, and some discrete variables to determine the index of the jump maps. The flow equations of these variables are singularly perturbed differential equations and, in particular, a smaller value of the singular perturbation parameter leads to an increase in the frequency of the jump instants. For the limiting value of this parameter, we consider a decomposition that comprises a quasi-steady-state system modeled by a differential equation without any jumps and a boundary-layer system described by purely discrete dynamics. Under appropriate assumptions on the quasi-steady-state system and the boundary-layer system, we derive results showing practical stability of a compact attractor when the jumps occur sufficiently often. As an application of our results, we discuss the control design problem in a network of second-order continuous-time coupled oscillators, where each agent communicates the information about its position to some of its neighbors at discrete times. Using the results developed in this article, we show that if the union of the communication graphs being used for information exchange between agents is connected, then the oscillators achieve practical consensus.

6. journal

   A Distributed Observer Accommodating a Broad Range of Intermittent Communication Scenarios

   Sunghyun Koo, Jin Gyu Lee, and Hyungbo Shim

   IEEE Control Systems Letters, 2025

   Abs DOI

   This paper proposes a distributed observer that utilizes intermittent communication and accommodates a broad range of scenarios, including asynchronous operation, unidirectional communication, packet loss, and communication delays. An analysis over jointly connected switching topology supports this and provides a condition for exponential convergence of the estimation error. This condition can be used to determine a communication rate. The analysis is valid when the unobservable subspace of each agent admits an invariant orthogonal complement. This is a property that is always achievable via a coordinate transformation when the system matrix is diagonalizable over the complex field.

7. journal

   Data-Driven Displacement-Based Formation Control with Range-Only Measurements

   Soojeong Hyeon, Hyuntae Kim, and Hyungbo Shim

   IEEE Access, 2025

   Abs DOI

   This paper proposes an algorithm to coordinate a displacement-based formation of a multi-agent system when their local frames are not aligned. Agents can measure neither the relative positions nor orientations, but only the range (distance) to their neighbors. We demonstrate that persistently exciting data exchanged between two agents can be used to infer relative positions and orientations. In the proposed method, we address discrete-time distributed orientation estimation based on an averaging consensus protocol. An asymptotic stability analysis of the desired formation shape is presented and the proposed strategy is validated through simulation results.

8. conference

   Adaptation of Parameters in Heterogeneous Multi-Agent Systems

   Hyungbo Shim, Jin Gyu Lee, and Brian D. O. Anderson

   In IEEE Conference on Decision and Control (CDC), 2025

   Abs DOI arXiv

   This paper proposes an adaptation mechanism for heterogeneous multi-agent systems to align the agents’ internal parameters, based on enforced consensus through strong couplings. Unlike homogeneous systems, where exact consensus is attainable, the heterogeneity in node dynamics precludes perfect synchronization. Nonetheless, previous work has demonstrated that strong coupling can induce approximate consensus, whereby the agents exhibit emergent collective behavior governed by the so-called blended dynamics. Building on this observation, we introduce an adaptation law that gradually aligns the internal parameters of agents without requiring direct parameter communication. The proposed method reuses the same coupling signal employed for state synchronization, which may result in a biologically or sociologically plausible adaptation process. Under a persistent excitation condition, we prove that the linearly parametrized vector fields of the agents converge to each other, thereby making the dynamics asymptotically homogeneous, and leading to exact consensus of the state variables.

9. conference

   A Polynomial-Based QCQP Solver for Encrypted Optimization

   Sebastian Schlor, Andrea Iannelli, Junsoo Kim, Hyungbo Shim, and Frank Allgöwer

   In IEEE Conference on Decision and Control (CDC), Dec 2025

   Abs DOI

   In this paper, we present a novel method for solving a class of quadratically constrained quadratic optimization problems using only additions and multiplications. This approach enables solving constrained optimization problems on private data since the operations involved are compatible with the capabilities of homomorphic encryption schemes. To solve the constrained optimization problem, a sequence of polynomial penalty functions of increasing degree is introduced, which are sufficiently steep at the boundary of the feasible set. Adding the penalty function to the original cost function creates a sequence of unconstrained optimization problems whose minimizer always lies in the admissible set and converges to the minimizer of the constrained problem. A gradient descent method is used to generate a sequence of iterates associated with these problems. For the algorithm, it is shown that the iterate converges to a minimizer of the original problem, and the feasible set is positively invariant under the iteration. Finally, the method is demonstrated on an illustrative cryptographic problem, finding the smaller value of two numbers, and the encrypted implementability is discussed.

10. conference

    Distributed Q-Learning on Multi-Agent Markov Decision Process with Heterogeneous State Transition Probabilities

    Yong Joo Do, Deuksun Hong, and Hyungbo Shim

    In IEEE Conference on Decision and Control (CDC), 2025

    Abs DOI

    This paper presents a distributed Q-learning (DQ-learning) algorithm within the framework of Multi-agent Markov Decision Process characterized by heterogeneous state transition probabilities and a common reward function. By communicating during learning, each agents experiencing different state transition probabilities, do not converge to their own local optimal Q-functions. Instead, the interaction forces their learning dynamics to align, and every agent converges to the optimal Q-function corresponding to the average over these heterogeneous state transition probabilities. Further analyzing its behavior, we reformulate the update algorithm of DQ-learning as a continuous time dynamics using modified ODE based stochastic approximation. Through the blended dynamics approach, the asymptotics of such dynamics is analyzed, theoretically guaranteeing the emergent behavior of DQ-learning.

11. journal

    구조에 관한 사전지식을 활용하는 반매개변수화 커널 릿지 회귀

    Heein Park, Hamin Chang, Yeongjun Jang, Hyeonyeong Jang, and Hyungbo Shim

    제어로봇시스템학회 논문지, 2025

    DOI

2024

1. journal

   Robust Stability Condition and Simplified Design of Filter-Embedded Disturbance Observer

   Hamin Chang, Donghyeon Song, Chanhwa Lee, and Hyungbo Shim

   International Journal of Control, Automation, and Systems, 2024

   DOI
2. journal

   Maintaining and Steering a Formation in an Unknown Dynamic Environment via a Consistent Distributed Dynamic Map

   Miao Guo, Bayu Jayawardhana, Jin Gyu Lee, and Hyungbo Shim

   International Journal of Robust and Nonlinear Control, 2024

   Abs DOI

   Abstract In this paper, we study the problem of maintaining a stable mobile robot formation, steering and localizing all robots in an unknown dynamic environment consisting of multiple periodically moving objects, without the presence of a global positioning system or a robot tracking system. We propose a distributed observer such that each agent can estimate global positions of all mobile robots and that of moving landmarks in an unknown environment. By combining the proposed distributed observer with the distributed formation control and centroid tracking control law, we show that the formation shape can be maintained by utilizing its available relative measurements and the estimated relative measurements to its neighbors, and the group’s centroid follows a desired trajectory. We present stability analysis of the closed‐loop system. Finally, we validate the proposed methods in a simulation result where a group of mobile robots can maintain a robust formation and maneuver in an unknown dynamic environment.

3. conference

   Multi-Agent Target Position Estimation Using Bearing-Only Measurements via Spatial Excitation

   Soojeong Hyeon, Iman Shames, and Hyungbo Shim

   In American Control Conference (ACC), 2024

   DOI
4. journal

   Path Generating Inverse Gaussian Process Regression for Data-Driven Ultimate Boundedness Control of Nonlinear Systems

   Yeongjun Jang, Hamin Chang, Heein Park, and Hyungbo Shim

   IEEE Control Systems Letters, 2024

   DOI
5. journal

   A Design Method of Distributed Algorithms via Discrete-Time Blended Dynamics

   Jeong Woo Kim, Jin Gyu Lee, Donggil Lee, and Hyungbo Shim

   Automatica, 2024

   Abs DOI

   We develop a discrete-time version of the blended dynamics theorem for the use of designing distributed computation algorithms. The blended dynamics theorem enables to predict the behavior of heterogeneous multi-agent systems. Therefore, once we get a blended dynamics for a particular computational task, design idea of node dynamics for individual heterogeneous agents can easily occur. In the continuous-time case, prediction by blended dynamics was enabled by high coupling gain among neighboring agents. In the discrete-time case, we propose an equivalent action, which we call multi-step coupling in this paper. Compared to the continuous-time case, the blended dynamics can have more variety depending on the coupling matrix. This benefit is demonstrated with three applications; distributed estimation of network size, distributed computation of the PageRank, and distributed computation of the degree sequence of a graph, which correspond to the coupling by doubly-stochastic, column-stochastic, and row-stochastic matrices, respectively.

6. journal

   Asymptotic Output Tracking in a Class of Non-Minimum Phase Nonlinear Systems via Learning-Based Inversion

   Namguk Kim and Hyungbo Shim

   International Journal of Robust and Nonlinear Control, 2024

   Abs DOI

   Abstract Asymptotic output tracking of non‐minimum phase (NMP) nonlinear systems has been a popular topic in control theory and applications. Many approaches have focused on finding solutions under minimal assumptions either in the target system or desired trajectories, as there is no general solution available. In this article, we propose a practical and simple solution for cases where the reference trajectory is periodic in time. Our approach employs a learning‐based scheme to iteratively determine the desired feedforward input. Unlike previous learning‐based frameworks, our method only requires the output tracking error to update the feedforward input iteratively and can be applicable to NMP systems. Our method retains the key advantages of the learning‐based framework, including robustness to parameter uncertainties and periodic disturbances. We evaluate the effectiveness of our algorithm using simulation results with an inverted pendulum on a cart, a typical NMP nonlinear system.

7. journal

   Evaluating MR-GPR and MR-NN: An Exploration of Data-Driven Control Methods for Nonlinear Systems

   Hyuntae Kim, Hamin Chang, and Hyungbo Shim

   International Journal of Control, Automation, and Systems, 2024

   DOI
8. conference

   Reference-Tracking Sliding-Mode Control Robust to Mismatched Exogenous Disturbances

   Sunghyun Koo and Hyungbo Shim

   In 14th Asian Control Conference (ASCC), 2024

   Abs HTML

   A dynamic state-feedback sliding-mode controller (SMC) based on the internal model principle (IMP) is proposed for the tracking of exogenous signals. The proposed SMC is robust to both matched disturbances and mismatched exogenous disturbances. It also achieves robustness to matched parametric uncertainties and a certain degree of mismatched parametric uncertainties. The stability of the closed-loop system and the existence of a global solution are theoretically guaranteed by a specific initialization of the internal model. Its performance is demonstrated through numerical simulations.

9. journal

   On Existence of Uniformly Marginally Stable Zeros of Linear Sampled-Data Systems and Its Application to Stable Inversion-Based Control

   Gyunghoon Park, Hyungbo Shim, and Tomomichi Hagiwara

   IEEE Access, 2024

   DOI
10. conference

    Further Results on Stability of Linear Systems with Slow and Fast Time Variation and Switching

    Hyungbo Shim and Daniel Liberzon

    In 27th ACM International Conference on Hybrid Systems: Computation and Control (HSCC), 2024

    DOI
11. journal

    A Lyapunov Characterization of Prescribed Performance Control Systems

    Yutian Wang, Tengfei Liu, Hyungbo Shim, George A. Rovithakis, and Zhong-Ping Jiang

    IEEE Transactions on Automatic Control, 2024

    DOI
12. conference

    Disturbance Observer with Switched Output Redefinition for Robust Stabilization of Non-Minimum Phase Linear Systems

    Hamin Chang, Donghyeon Song, Stephan Trenn, and Hyungbo Shim

    In IEEE Conference on Decision and Control (CDC), 2024

    Abs DOI

    Q-filter-based disturbance observer (DOB) has emerged as a powerful robust control technique renowned for its effectiveness in mitigating disturbances and addressing plant uncertainties. Despite its advantage, a key limitation of the Q-filter-based DOB lies in its requirement for plants to be of minimum phase. In this paper, we introduce an approach allowing the utilization of the Q-filter-based DOB as a stabilizing controller for non-minimum phase linear systems based on switched output redefinition of the systems. By redefining the output of systems to be controlled periodically, the approach stabilizes unstable internal dynamics of the systems as well as the original output. The proposed method is verified by an illustrative example.

13. conference

    Authentication of Multi-Agent System with Verifiable Computation and Distributed Aggregation

    Seungbeom Lee, Dongwoo Kim, Heewon Chung, Junsoo Kim, and Hyungbo Shim

    In IEEE Conference on Decision and Control (CDC), 2024

    Abs DOI

    We propose an authentication scheme for a multiagent system over integers, based on verifiable computation primitives. The naive approach, employing Freivalds’ algorithm in centralized way, faces several challenges. Specifically, unreliability of the network introduces the risk of information tampering by other agents. To this end, it requires locally updating and merging the proofs of the individual states in a distributed manner. Our proposed method addresses these issues with assuming presence of a leader agent who is responsible for validating the correctness of all the states of the agents. This can be achieved by a distributed protocol that aggregates proofs from the individual agents, relying on the well-known knowledge-of-exponent assumption. By using this distributed protocol, computational complexity and communication cost are reduced compared to centralized verification. Furthermore, we incorporate a clustering technique to distribute storage requirements.

14. conference

    New Results on Finite Convergence Time Mode Consensus: A Summary

    Chao Huang, Hyungbo Shim, Siliang Yu, and Brian D. O. Anderson

    In IEEE Conference on Decision and Control (CDC), 2024

    Abs DOI

    This paper studies the distributed mode consensus problem in a multi-agent system. Three algorithms are proposed to find the most frequent attribute (the mode) owned by the agents via distributed computation. The first algorithm computes the frequency of each attribute using consensus protocols rooted in blended dynamics, then identifies the most frequent attribute as the mode. The second algorithm, under the assumption that each agent possesses a priori knowledge of a minimum frequency for the mode, can decrease the frequency computations required at each agent for large lower bounds. In contrast, the third algorithm eliminates the necessity for such information by implementing an adaptive updating mechanism. These algorithms successfully determine the mode within a finite time frame, and predictive estimates for convergence time are included. Moreover, the first and second algorithms demonstrate plug-and-play property with a dwell time.

15. conference

    Fully Distributed EV Charging Scheduling for Load Flattening in V2G Systems

    Jinwook Heo, Soojeong Hyeon, Hyungbo Shim, and Jinsung Kim

    In IEEE Conference on Decision and Control (CDC), 2024

    Abs DOI

    This paper presents a fully distributed algorithm for scheduling electric vehicle (EV) charging and discharging to flatten the total load of the grid, while considering constraints on grid transmission capacity. As a fully distributed solution, the proposed algorithm operates without the need for a central unit. Instead, each agent only communicates a single dual variable with its neighboring agents based on a communication graph, and thus no private information is shared. In particular, the algorithm does not rely on initial conditions, ensuring robustness in online changes of operational conditions. Simulation results verify the effectiveness of the proposed algorithm.

16. journal

    군집은 어떻게 동기화를 통해 창발성을 발현하는가?

    Hyungbo Shim

    제어로봇시스템학회 논문지, Apr 2024

    DOI
17. conference

    Stability of Nonlinear Systems with Slow and Fast Time Variation and Switching: The Common Equilibrium Case

    Daniel Liberzon and Hyungbo Shim

    In IEEE Conference on Decision and Control (CDC), 2024

    DOI

2023

1. journal

   A Toolkit for Globally Robust Observer-Based Feedback with Relaxed Characterization of iISS/ISS

   Hiroshi Ito and Hyungbo Shim

   IEEE Transactions on Automatic Control, 2023

   DOI
2. journal

   Decentralized Design and Plug-and-Play Distributed Control for Linear Multi-Channel Systems

   Taekyoo Kim, Donggil Lee, and Hyungbo Shim

   IEEE Transactions on Automatic Control, 2023

   DOI
3. journal

   Dynamic Controller That Operates Over Homomorphically Encrypted Data for Infinite Time Horizon

   Junsoo Kim, Hyungbo Shim, and Kyoohyung Han

   IEEE Transactions on Automatic Control, 2023

   DOI arXiv
4. journal

   Edge-Wise Funnel Output Synchronization of Heterogeneous Agents with Relative Degree One

   Jin Gyu Lee, Thomas Berger, Stephan Trenn, and Hyungbo Shim

   Automatica, 2023

   DOI
5. conference

   Conversion of Controllers to Have Integer State Matrix for Encrypted Control: Non-Minimal Order Approach

   Joowon Lee, Donggil Lee, Seungbeom Lee, Junsoo Kim, and Hyungbo Shim

   In IEEE Conference on Decision and Control (CDC), 2023

   Abs DOI

   To implement an encrypted dynamic controller based on homomorphic encryption that operates for an infinite time horizon, it is essential for every component of the controller’s state matrix to be an integer. In this paper, we tackle the challenge of converting a pre-designed controller into a new one with an integer state matrix while preserving its control performance in the closed-loop system. This enables encrypted dynamic systems to be realized without re-encryption and approximation of control parameters, compared to the previous results. To achieve this, we propose two approaches and provide sufficient conditions on the design parameter for each. The first approach is to design the new controller as an estimator of the original closed-loop system, and the conditions on the estimator gain are derived. Our second approach is to formulate a problem of finding certain polynomials, whose solution leads to the design of the new controller. In a special case when the numerator of the plant transfer function is a constant, we provide a constructive method to obtain such solution.

6. journal

   Distributed Resilient Observer: Blended Dynamics Theory Meets L1-Minimization Approach

   Donggil Lee, Junsoo Kim, and Hyungbo Shim

   IEEE Control Systems Letters, 2023

   Abs DOI

   This letter presents a distributed resilient observer for continuous-time linear time-invariant plants that remains functional even under sensor attacks. The proposed method aims to determine the estimation outcome that matches the majority of sensor measurements, which is formulated as an l1-minimization problem considering all the observable components of each sensor measurement. A distributed observer based on the blended dynamics theory is then proposed to solve the l1-minimization problem in a distributed manner. As a result, the distributed resilient estimation is enabled for a broader class of systems compared to previous works. The design procedure is constructive with parameters obtained from a specified condition that is equivalent to the well-known null-space property.

7. conference

   User-Friendly Vehicle-to-Grid Optimal Scheduling Problem and Distributed Implementation for Plug-and-Play Operation

   Seungbeom Lee, Jinwook Heo, Soojeong Hyeon, Jiyeon Nam, Hyungbo Shim, and Jinsung Kim

   In International Conference on Control, Automation and Systems (ICCAS), 2023

   Abs DOI

   In this paper, we propose an optimization method of charging scheduling algorithm based on preference of vehicle owners. To suffice various desires for vehicle charging, we design objective function of optimization problem as weighted sum of some objective function to reflect various desires. To solve the problem without aggregating weight coefficient, distributed optimization based on dynamic average consensus method is implemented. By initialization-free property of dynamic average consensus, plug-and-play operation of electric vehicle is applicable. Finally, we simulate the proposed algorithm to enlighten the meaning of weighted sum for objective function and plug-and-play scenario.

8. conference

   Exponential Synchronization of Heterogeneous Multi-Agent Systems via Linear-Signum-Type Diffusive Coupling: Blended Dynamics Approach

   Jeong Mo Seong, Donggil Lee, and Hyungbo Shim

   In International Conference on Control, Automation and Systems (ICCAS), 2023

   Abs DOI

   This paper investigates the behavior of heterogeneous agents that interact through diffusive coupling, resulting in emergent blended dynamics that may not be observed in the dynamics of individual agents. In particular, we propose a linear-signum-type diffusive coupling to achieve exponential synchronization among heterogeneous agents. This finding offers a notable advantage over previous research, which primarily focused on linear-type diffusive coupling with remaining steady-state error in synchronization. We provide conditions of both linear and signum coupling strengths for achieving the exponential synchronization and analyze the associated convergence rate. Furthermore, simulation results validate the effectiveness of the proposed approach.

9. conference

   Data-Driven Inverse of Linear Systems and Application to Disturbance Observer

   Yongsoon Eun, Jaeho Lee, and Hyungbo Shim

   In American Control Conference (ACC), 2023

   Abs DOI

   This work develops a data-based construction of inverse dynamics for LTI systems. Specifically, the problem addressed here is to find an input sequence from the corresponding output sequence based on pre-collected input and output data. The problem can be considered as a reverse of the recent use of the behavioral approach, in which the output sequence is obtained for a given input sequence by solving an equation formed by pre-collected data. The condition under which the problem gives a solution is investigated and turns out to be L-delay invertibility of the plant and a certain degree of persistent excitation of the data input. The result is applied to form a data-driven disturbance observer. The plant dynamics augmented by the data-driven disturbance observer exhibits disturbance rejection without the model knowledge of the plant.

10. conference

    Model Reference Gaussian Process Regression: Data-Driven Output Feedback Controller

    Hyuntae Kim, Hamin Chang, and Hyungbo Shim

    In American Control Conference (ACC), 2023

    Abs DOI

    Data-driven controls using Gaussian process regression have recently gained much attention. In such approaches, system identification by Gaussian process regression is mostly followed by model-based controller designs. However, the outcomes of Gaussian process regression are often too complicated to apply conventional control designs, which makes the numerical design such as model predictive control employed in many cases. To overcome the restriction, our idea is to perform Gaussian process regression to the inverse of the plant with the same input/output data for the conventional regression. With the inverse, one can design a model reference controller without resorting to numerical control methods. This paper considers single-input single-output (SISO) discrete-time nonlinear systems of minimum phase with relative degree one. It is highlighted that the model reference Gaussian process regression controller is designed directly from pre-collected input/output data without system identification.

2022

1. journal

   Comparison of Encrypted Control Approaches and Tutorial on Dynamic Systems Using Learning with Errors-Based Homomorphic Encryption

   Junsoo Kim, Dongwoo Kim, Yongsoo Song, Hyungbo Shim, Henrik Sandberg, and Karl H. Johansson

   Annual Reviews in Control, 2022

   DOI
2. journal

   Blended Dynamics Approach to Distributed Optimization: Sum Convexity and Convergence Rate

   Seungjoon Lee and Hyungbo Shim

   Automatica, 2022

   DOI
3. book chapter

   Design of Heterogeneous Multi-Agent System for Distributed Computation

   Jin Gyu Lee and Hyungbo Shim

   In Trends in Nonlinear and Adaptive Control, edited by Jiang, Z. P. and Prieur, C. and Astolfi, A., Springer, 2022

   A Tribute to Laurent Praly for his 65th Birthday

   Abs DOI arXiv

   A group behavior of a heterogeneous multi-agent system is studied which obeys an “average of individual vector fields” under strong couplings among the agents. Under stability of the averaged dynamics (not asking stability of individual agents), the behavior of heterogeneous multi-agent system can be estimated by the solution to the averaged dynamics. A following idea is to “design” individual agent’s dynamics such that the averaged dynamics performs the desired task. A few applications are discussed including estimation of the number of agents in a network, distributed least-squares or median solver, distributed optimization, distributed state estimation, and robust synchronization of coupled oscillators. Since stability of the averaged dynamics makes the initial conditions forgotten as time goes on, these algorithms are initialization-free and suitable for plug-and-play operation. At last, nonlinear couplings are also considered, which potentially asserts that enforced synchronization gives rise to an emergent behavior of a heterogeneous multi-agent system.

4. journal

   Synchronization with Prescribed Transient Behavior: Heterogeneous Multi-Agent Systems Under Funnel Coupling

   Jin Gyu Lee, Stephan Trenn, and Hyungbo Shim

   Automatica, 2022

   DOI
5. conference

   Stability of Linear Systems with Slow and Fast Time Variation and Switching

   Daniel Liberzon and Hyungbo Shim

   In IEEE Conference on Decision and Control (CDC), 2022

   DOI
6. book chapter

   Zero-Dynamics Attack, Variations, and Countermeasures

   Hyungbo Shim, Juhoon Back, Yongsoon Eun, Gyunghoon Park, and Jihan Kim

   In Security and Resilience of Control Systems, edited by Ishii, Hideaki and Zhu, Quanyan, Springer, 2022

   Abs DOI arXiv

   This chapter presents an overview of actuator attacks that exploit zero dynamics, and countermeasures against them. First, zero-dynamics attack is reintroduced based on a canonical representation called normal form. Then it is shown that the target dynamic system is at elevated risk if the associated zero dynamics is unstable. From there on, several questions are raised in series to ensure when the target system is immune to an attack of this kind. The first question is: Is the target system secure from zero-dynamics attack if it does not have any unstable zeros? An answer provided for this question is: No, the target system may still be at risk due to another attack surface emerging in the process of implementation. This is followed by a series of questions, and in the course of providing answers, variants of the classic zero-dynamics attack are presented, from which the vulnerability of the target system is explored in depth. In the end, countermeasures are proposed to render the attack ineffective. Because it is known that zero dynamics in continuous-time systems cannot be modified by feedback, the main idea of the countermeasure is to relocate any unstable zero to a stable region in the stage of digital implementation through modified digital samplers and holders. Adversaries can still attack actuators, but due to the relocated zeros, they are of little use in damaging the target system.

7. conference

   Initialization-Free Algorithm for Discrete-Time Dynamic Average Consensus and Its Application to Distributed Optimization

   Jiyeon Nam, Jinwook Heo, Jeong Woo Kim, Hyungbo Shim, Jae Sung Bang, and Jinsung Kim

   In International Conference on Control, Automation and Systems (ICCAS), 2022

   Abs DOI

   In this paper, we address the problem of dynamic average consensus in a discrete-time setting. The objective of dynamic average consensus problem is for each state of agent to track the average of reference input signals of each agent in a distributed manner. Without initialization process, the proposed algorithm renders the state of each agent converge practically to the average of time-varying reference signals with any given bound. It is a simple time-domain algorithm based on two-time scale. Finally, by applying our algorithm to an distributed optimization problem, we provide two simulation results that converge correctly when the initial conditions are perturbed and that converge within certain amount of small error when numerical errors are injected every time step.

8. journal

   Development and Evaluation of Haltere-Mimicking Gyroscope for Three-Axis Angular Velocity Sensing Using a Haltere-Mimicking Structure Pair

   Chulhong Kim, Junghyun Park, Taeyup Kim, Jee-Seong Kim, Jeong Mo Seong, Hyungbo Shim, Hyoungho Ko, and Dongil Dan Cho

   Bioinspiration & Biomimetics, 2022

   Abs DOI

   This paper presents a three-axis biomimetic gyroscope, mimicking the haltere of Diptera. Diptera use a club-shaped mechanosensory organ called the haltere to get the three-axis angular velocity information, namely roll, pitch and yaw axes, for flight control. One pair of halteres is physically connected to the wings of Diptera that vibrate in antiphase to the flapping wings in ambient air. They sense the Coriolis force and relay angular velocity information to the Diptera. As an alternative to the conventional micro-electro-mechanical system gyroscopes which are widely used in robotics, many research groups have attempted to mimic the haltere. However, no previous study succeeded in measuring all three-axis components of angular velocity, due to various shortcomings. In this paper, we developed the first three-axis haltere-mimicking gyroscope. Two perpendicularly positioned haltere-mimicking structures that can vibrate at a 180\textdegree amplitude were mechanically integrated into a robot actuator. Two accelerometers, placed at the tip of each structure, were employed to measure the Coriolis force. The performance of the novel biomimetic gyroscope was measured in all rotational directions, using a motion capture system as the ground truth. One-axis input experiments were performed 240 times at different input magnitudes and directions, and the measured orientation error was less than \textpm2.0% in all experiments. In 80 three-axis input experiments, the orientation error was less than \textpm3.5%.

2021

1. journal

   Distributed Dynamic Quantile Solver with Plug-and-Play Operation

   Jeong Mo Seong, Jeong Woo Kim, Seungjoon Lee, and Hyungbo Shim

   IEEE Access, 2021

   DOI
2. conference

   Lyapunov Functions for Singularly Perturbed Hybrid Systems with Frequent Jump Dynamics

   Aneel Tanwani and Hyungbo Shim

   In IEEE Conference on Decision and Control (CDC), 2021

   DOI
3. conference

   Method for Running Dynamic Systems Over Encrypted Data for Infinite Time Horizon Without Bootstrapping and Re-Encryption

   Junsoo Kim, Hyungbo Shim, Henrik Sandberg, and Karl H. Johansson

   In IEEE Conference on Decision and Control (CDC), 2021

   Abs DOI

   In this paper, we propose a method for dynamic systems to operate over homomorphically encrypted data for an infinite time horizon, where we do not make use of reset, re-encryption, or bootstrapping for the encrypted messages. The given system is first decomposed into the stable part and the anti-stable part. Then, the stable part is approximated to have finite impulse response, and by a novel conversion scheme, the eigenvalues of the state matrix of the anti-stable part are approximated to algebraic integers. This allows that the given system can be implemented to operate for an infinite time horizon using only addition and multiplication over encrypted data, without re-encrypting any portion of data. The performance error caused by the approximation and quantization can be made arbitrarily small, with appropriate choice of parameters.

2020

1. journal

   Robust Feedback Stabilization Using High-Gain Observer via Event-Triggering

   Abhisek K. Behera and Hyungbo Shim

   International Journal of Robust and Nonlinear Control, 2020

   Abs DOI

   Summary In this article, the problem of robust output feedback stabilization of single‐input single‐output nonlinear systems is studied in the event‐triggering framework. In this work, an event‐triggered output feedback law based on a high‐gain observer is constructed, which guarantees the stability of closed‐loop system. First, the high‐gain observer with a triggering scheme is designed to estimate the plant state in the presence of external disturbances subject to any satisfactory accuracy of the estimation error. The observer‐based triggering mechanism decides the transmission of plant output to the observer by observing a certain event condition. Similarly, another triggering mechanism is designed using the estimated state of observer that triggers the control signal to be updated only when it is satisfied. Under this proposed event‐triggering framework, the stability of closed‐loop system is then analyzed. Here, we provide the simplified design technique, in which the high‐gain parameter and the triggering thresholds can be selected independently to achieve any desired bound for the plant trajectory. The results are finally demonstrated through simulation of a numerical example.

2. conference

   Simultaneous Distributed Localization, Mapping and Formation Control of Mobile Robots Based Local Relative Measurements

   Miao Guo, Bayu Jayawardhana, Jin Gyu Lee, and Hyungbo Shim

   In IFAC World Congress, 2020

   DOI
3. journal

   Completely Decentralized Design of Distributed Observer for Linear Systems

   Taekyoo Kim, Chanhwa Lee, and Hyungbo Shim

   IEEE Transactions on Automatic Control, 2020

   DOI
4. journal

   Neutralizing Zero Dynamics Attack on Sampled-Data Systems via Generalized Holds

   Jihan Kim, Juhoon Back, Gyunghoon Park, Chanhwa Lee, Hyungbo Shim, and Petros G. Voulgaris

   Automatica, 2020

   DOI
5. book chapter

   Comprehensive Introduction to Fully Homomorphic Encryption for Dynamic Feedback Controller via LWE-Based Cryptosystem

   Junsoo Kim, Hyungbo Shim, and Kyoohyung Han

   In Privacy in Dynamical Systems, edited by Farokhi, Farhad, Springer, 2020

   DOI arXiv
6. conference

   Toward Nonlinear Dynamic Control Over Encrypted Data for Infinite Time Horizon

   Junsoo Kim, Farhad Farokhi, Iman Shames, and Hyungbo Shim

   In IFAC World Congress, 2020
7. journal

   A Distributed Algorithm That Finds Almost Best Possible Estimate Under Non-Vanishing and Time-Varying Measurement Noise

   Jin Gyu Lee and Hyungbo Shim

   IEEE Control Systems Letters, 2020

   DOI
8. journal

   Fully Distributed Resilient State Estimation Based on Distributed Median Solver

   Jin Gyu Lee, Junsoo Kim, and Hyungbo Shim

   IEEE Transactions on Automatic Control, 2020

   DOI
9. journal

   A Tool for Analysis and Synthesis of Heterogeneous Multi-Agent Systems Under Rank-Deficient Coupling

   Jin Gyu Lee and Hyungbo Shim

   Automatica, 2020

   DOI
10. conference

    Utility of Edge-Wise Funnel Coupling for Asymptotically Solving Distributed Consensus Optimization

    Jin Gyu Lee, Thomas Berger, Stephan Trenn, and Hyungbo Shim

    In European Control Conference (ECC), 2020

    DOI
11. book chapter

    Disturbance Observers

    Hyungbo Shim

    In Encyclopedia of Systems and Control, edited by Baillieul, John and Samad, Tariq, Springer, 2020

    Abs DOI arXiv

    Disturbance observer is an inner-loop output-feedback controller whose role is to reject external disturbances and to make the outer-loop baseline controller robust against plant’s uncertainties. Therefore, the closed-loop system with the DOB approximates the nominal closed-loop by the baseline controller and the nominal plant model with no disturbances. This article presents how the disturbance observer works under what conditions, and how one can design a disturbance observer to guarantee robust stability and to recover the nominal performance not only in the steady-state but also for the transient response under large uncertainty and disturbance.

12. conference

    Authenticated Computation of Control Signal from Dynamic Controllers

    Jung Hee Cheon, Dongwoo Kim, Junsoo Kim, Seungbeom Lee, and Hyungbo Shim

    In IEEE Conference on Decision and Control (CDC), Dec 2020

    Abs DOI

    Significant concerns on networked control systems are modifications on the control signals caused by a compromise on the network or the controller, since it can cause a devastating behavior or even entire failure of the system. In this paper, we present a fundamental solution to this problem by proposing a new authenticated computation that checks the matrix-vector multiplications-the main arithmetic of a controller-and verifies the updates on the states of the controller. It enables the plant-side not only to check the computation of the controller with much less computational cost than that required for the computation itself, but also to detect any modifications on the control signals.

13. conference

    Distributed Aggregation Over Homomorphically Encrypted Data Under Switching Networks

    Donggil Lee, Junsoo Kim, and Hyungbo Shim

    In IEEE Conference on Decision and Control (CDC), Dec 2020

    Abs DOI

    This paper presents a distributed algorithm for additive aggregation over encrypted data. Our algorithm allows networked systems to compute the sum of all individual data without revealing each node’s private contribution. To conceal the private data, the local computations on each node and the communications with neighbor nodes are conducted by utilizing the additively homomorphic cryptosystem. As a consequence, the leader node which has the secret key of the cryptosystem recovers the correct outcome after decryption in a finite time. Moreover, the leader cannot learn the private data of the other nodes. Furthermore, the proposed algorithm can operate on encrypted data for an infinite time horizon even when the network varies intermittently with time.

2019

1. conference

   Study on Realizable Generalized Hold Functions as a Countermeasure Against Zero Dynamics Attack

   Jongsoo Ha and Hyungbo Shim

   In IEEE Conference on Decision and Control (CDC), 2019

   DOI
2. journal

   Detection of Sensor Attack and Resilient State Estimation for Uniformly Observable Nonlinear Systems Having Redundant Sensors

   Junsoo Kim, Chanhwa Lee, Hyungbo Shim, Yongsoon Eun, and Jin H. Seo

   IEEE Transactions on Automatic Control, 2019

   DOI arXiv
3. journal

   Masking Attack for Sampled-Data Systems via Input Redundancy

   Jihan Kim, Gyunghoon Park, Hyungbo Shim, and Yongsoon Eun

   IET Control Theory & Applications, 2019

   Abs DOI

   This study discovers a new vulnerability of cyber‐physical systems to malicious attack. It arises when the physical plant, that is modelled as a continuous‐time LTI system, is controlled by a digital controller with periodic sampling and actuation. In the sampled‐data framework, most anomaly detectors monitor the plant’s output only at discrete time instants. Consequently, abnormal behaviour between sampling instants cannot be detected if output behaves normally at every sampling instant. This implies that if an actuator attack drives the plant’s state to pass through the kernel of the output matrix at each sensing time, then the attack compromises the system while remaining stealthy. It is shown that this type of attack always exists when the sampled‐data system has an input redundancy, i.e. the number of inputs being larger than that of outputs and/or the sampling rate of the actuators being higher than that of the sensors. Simulation results for the X‐38 vehicle and other numerical examples illustrate this new attack strategy may result in disastrous consequences.

4. journal

   State Estimation and Tracking Control for Hybrid Systems by Gluing the Domains

   Jisu Kim, Hyungbo Shim, and Jin Heon Seo

   IEEE Transactions on Automatic Control, 2019

   DOI arXiv
5. conference

   A Countermeasure Against Zero-Dynamics Sensor Attack via Generalized Hold Feedback

   Jihan Kim and Hyungbo Shim

   In IEEE Conference on Decision and Control (CDC), 2019

   DOI
6. conference

   Encrypted State Estimation in Networked Control Systems

   Junsoo Kim and Hyungbo Shim

   In IEEE Conference on Decision and Control (CDC), 2019

   DOI
7. conference

   On Improving the Robustness of Reinforcement Learning-Based Controllers Using Disturbance Observer

   Jeong Woo Kim, Hyungbo Shim, and Insoon Yang

   In IEEE Conference on Decision and Control (CDC), 2019

   DOI
8. journal

   Output Feedback Based Event-Triggered Sliding Mode Control for Delta Operator Systems

   Kiran Kumari, Bijnan Bandyopadhyay, Kyung-Soo Kim, and Hyungbo Shim

   Automatica, 2019

   DOI
9. journal

   On Redundant Observability: From Security Index to Attack Detection and Resilient State Estimation

   Chanhwa Lee, Hyungbo Shim, and Yongsoon Eun

   IEEE Transactions on Automatic Control, 2019

   DOI arXiv
10. conference

    Behavior of a Network of Heterogeneous Lienard Systems Under Output Coupling

    Jin Gyu Lee and Hyungbo Shim

    In IFAC Symposium on Nonlinear Control Systems (NOLCOS), 2019

    DOI
11. journal

    Distributed Algorithm for Economic Dispatch Problem with Separable Losses

    Seungjoon Lee and Hyungbo Shim

    IEEE Control Systems Letters, 2019

    DOI
12. journal

    Disturbance Observer Approach for Fuel-Efficient Heavy-Duty Vehicle Platooning

    Gyujin Na, Gyunghoon Park, Valerio Turri, Karl H. Johansson, Hyungbo Shim, and Yongsoon Eun

    Vehicle System Dynamics, 2019

    Special Issue on Connected and Automated Vehicles

    DOI
13. journal

    Stealthy Adversaries Against Uncertain Cyber-Physical Systems: Threat of Robust Zero-Dynamics Attack

    Gyunghoon Park, Chanhwa Lee, Hyungbo Shim, Yongsoon Eun, and Karl H. Johansson

    IEEE Transactions on Automatic Control, 2019

    DOI
14. journal

    Initialization-Free Privacy-Guaranteed Distributed Algorithm for Economic Dispatch Problem

    Hyeonjun Yun, Hyungbo Shim, and Hyo-Sung Ahn

    Automatica, 2019

    DOI

2018

1. conference

   DO-DAT: A MATLAB Toolbox for Design & Analysis of Disturbance Observer

   Hamin Chang, Hyuntae Kim, Gyunghoon Park, and Hyungbo Shim

   In 9th IFAC Symp. on Robust Control Design (ROCOND), 2018

   DOI
2. journal

   Toward a Secure Drone System: Flying with Real-Time Homomorphic Authenticated Encryption

   Jung Hee Cheon, Kyoohyung Han, Seong-Min Hong, Hyoun Jin Kim, Junsoo Kim, Suseong Kim, Hosung Seo, Hyungbo Shim, and 1 more author

   IEEE Access, 2018

   DOI
3. conference

   Practical Synchronization of Heterogeneous Multi-Agent System Using Adaptive Law for Coupling Gains

   Seungjoon Lee, Hyeonjun Yun, and Hyungbo Shim

   In American Control Conference (ACC), 2018

   DOI
4. conference

   Preliminary Result on Distributed Solution to Economic Dispatch Problemwith Power Losses

   Seungjoon Lee and H. Shim

   In International Conference on Control, Automation and Systems (ICCAS), 2018
5. conference

   A Posteriori Detection of Momentum of Attack on Cyber-Physical Systems: A Back-and-Forth Observer Approach

   Jiyeon Nam, Gyunghoon Park, Taekyoo Kim, and Hyungbo Shim

   In IFAC Workshop on Distributed Estimation and Control in Networked Systems (NecSys), 2018

   DOI
6. journal

   Guaranteeing Almost Fault-Free Tracking Performance from Transient to Steady-State: A Disturbance Observer Approach

   Gyunghoon Park and Hyungbo Shim

   Science China Information Sciences, 2018

   Special Issue on Advances in Disturbance/Uncertainty Estimation and Attenuation Techniques with Applications

   DOI
7. journal

   Recovering Nominal Tracking Performance in Asymptotic Sense for Uncertain Linear Systems

   Gyunghoon Park, Hyungbo Shim, and Youngjun Joo

   SIAM Journal on Control and Optimization, 2018

   DOI
8. conference

   On Stealthiness of Zero-Dynamics Attacks Against Uncertain Nonlinear Systems: A Case Study with Quadruple-Tank Process

   Gyunghoon Park, Chanhwa Lee, and Hyungbo Shim

   In International Symposium on Mathematical Theory of Networks and Systems (MTNS), 2018
9. conference

   Adaptable iISS Small-Gain Formulation and Its Application to Observer-Based Output Feedback Design

   Hiroshi Ito and Hyungbo Shim

   In IEEE Conference on Decision and Control (CDC), 2018

   DOI
10. conference

    Heterogeneous Van Der Pol Oscillators Under Strong Coupling

    Jin Gyu Lee and Hyungbo Shim

    In IEEE Conference on Decision and Control (CDC), 2018

    DOI
11. conference

    Distributed Algorithm for the Network Size Estimation: Blended Dynamics Approach

    Donggil Lee, Seungjoon Lee, Taekyoo Kim, and Hyungbo Shim

    In IEEE Conference on Decision and Control (CDC), 2018

    DOI
12. conference

    Local Identification of Sensor Attack and Distributed Resilient State Estimation for Linear Systems

    Junsoo Kim, Jin Gyu Lee, Chanhwa Lee, Hyungbo Shim, and Jin Heon Seo

    In IEEE Conference on Decision and Control (CDC), 2018

    DOI
13. conference

    Need for Controllers Having Integer Coefficients in Homomorphically Encrypted Dynamic System

    Jung Hee Cheon, Kyoohyung Han, Hyuntae Kim, Junsoo Kim, and Hyungbo Shim

    In IEEE Conference on Decision and Control (CDC), 2018

    DOI

2017

1. conference

   Enhancement of Security Against Zero Dynamics Attack via Generalized Hold

   Juhoon Back, Jihan Kim, Chanhwa Lee, Gyunghoon Park, and Hyungbo Shim

   In IEEE Conference on Decision and Control (CDC), 2017

   DOI
2. conference

   Singular Perturbation for Sampled-Data Systems with Fast Subsystems

   Hyeonjun Yun, Hyungbo Shim, and H.J. Chang

   In IFAC World Congress, 2017

   DOI
3. journal

   Noise Reduction Disturbance Observer for Disturbance Attenuation and Noise Suppression

   Nam Hoon Jo, Chanyoung Jeon, and Hyungbo Shim

   IEEE Transactions on Industrial Electronics, 2017

   DOI
4. journal

   Robust Control of an Equipment-Added Multirotor Using Disturbance Observer

   Suseong Kim, Seungwon Choi, Hyeonggeun Kim, Jongho Shin, Hyungbo Shim, and H. Jin Kim

   IEEE Transactions on Control Systems Technology, 2017

   DOI
5. conference

   Consensus of Linear Time-Invariant Multi-Agent System Over Multilayer Network

   Seungjoon Lee and Hyungbo Shim

   In International Conference on Control, Automation and Systems (ICCAS), 2017

   DOI
6. conference

   Synchronized Behavior of Heterogeneous Multi-Agent Systems Under Funnel

   Jin Gyu Lee and Hyungbo Shim

   In SWARM 2017: The Second Int. Symp. on Swarm Behavior and Bio-Inspired Robotics, 2017
7. journal

   Robust Estimation Algorithm for Both Switching Signal and State of Switched Linear Systems

   Zhaowu Ping, Chanhwa Lee, and Hyungbo Shim

   International Journal of Control, Automation, and Systems, 2017

   DOI
8. conference

   Consensus-Based Distributed Coordination for Optimal Energy Generation of Hierarchical Systems

   Hyeonjun Yun, Seungjoon Lee, and Hyungbo Shim

   In SICE Annual Conference, 2017

   DOI

2016

1. conference

   SoC Regulator and DOB-Based Load Frequency Control of a Microgrid by Coordination of Diesel Generator and Battery Storage

   Takuto Hiranaka, Hyungbo Shim, and Toru Namerikawa

   In IEEE Conference on Control Applications (CCA) in Multi-Conference on Systems and Control, 2016

   DOI
2. journal

   Resilient State Estimation for Control Systems Using Multiple Observers and Median Operation

   Heegyun Jeon, Sungmin Aum, Hyungbo Shim, and Yongsoon Eun

   Mathematical Problems in Engineering, 2016

   Abs DOI

   This paper addresses the problem of state estimation for linear dynamic systems that is resilient against malicious attacks on sensors. By “resiliency” we mean the capability of correctly estimating the state despite external attacks. We propose a state estimation with a bank of observers combined through median operations and show that the proposed method is resilient in the sense that estimated states asymptotically converge to the true state despite attacks on sensors. In addition, the effect of sensor noise and process disturbance is also considered. For bounded sensor noise and process disturbance, the proposed method eliminates the effect of attack and achieves state estimation error within a bound proportional to those of sensor noise and disturbance. While existing methods are computationally heavy because online solution of nonconvex optimization is needed, the proposed approach is computationally efficient by using median operation in the place of the optimization. It should be pointed out that the proposed method requires the system states being observable with every sensor, which is not a necessary condition for the existing methods. From resilient system design point of view, however, this fact may not be critical because sensors can be chosen for resiliency in the design stage. The gained computational efficiency helps real-time implementation in practice.

3. journal

   Robustness of Synchronization of Heterogeneous Agents by Strong Coupling and a Large Number of Agents

   Jaeyong Kim, Jongwook Yang, Hyungbo Shim, Jung-Su Kim, and Jin Heon Seo

   IEEE Transactions on Automatic Control, 2016

   DOI
4. conference

   Arbitrarily Large Gain/Phase Margin Can Be Achieved by DOB-Based Controller

   Hyuntae Kim, Gyunghoon Park, Hyungbo Shim, and Nam Hoon Jo

   In International Conference on Control, Automation and Systems (ICCAS), 2016

   DOI
5. conference

   Detection of Sensor Attack and Resilient State Estimation for Uniformly Observable Nonlinear Systems

   Junsoo Kim, Chanhwa Lee, Hyungbo Shim, Yongsoon Eun, and Jin H. Seo

   In IEEE Conference on Decision and Control (CDC), 2016

   DOI
6. conference

   On Distributed Optimal Kalman-Bucy Filtering by Averaging Dynamics of Heterogeneous Agents

   Jaeyong Kim, Hyungbo Shim, and Jingbo Wu

   In IEEE Conference on Decision and Control (CDC), 2016

   DOI
7. conference

   Distributed Luenberger Observer Design

   Taekyoo Kim, Hyungbo Shim, and Dongil Dan Cho

   In IEEE Conference on Decision and Control (CDC), 2016

   DOI
8. conference

   Tracking Control for Hybrid Systems with State Jumps Using Gluing Function

   Jisu Kim, Hyungbo Shim, and Jin Heon Seo

   In IEEE Conference on Decision and Control (CDC), 2016

   DOI
9. conference

   Zero-Stealthy Attack for Sampled-Data Control Systems: The Case of Faster Actuation Than Sensing

   Jihan Kim, Gyunghoon Park, Hyungbo Shim, and Yongsoon Eun

   In IEEE Conference on Decision and Control (CDC), 2016

   DOI
10. conference

    When Adversary Encounters Uncertain Cyber-Physical Systems: Robust Zero-Dynamics Attack with Disclosure Resources

    Gyunghoon Park, Hyungbo Shim, Chanhwa Lee, Yongsoon Eun, and Karl H. Johansson

    In IEEE Conference on Decision and Control (CDC), 2016

    DOI
11. journal

    Nonlinear Observers Robust to Measurement Disturbances in an ISS Sense

    Hyungbo Shim and Daniel Liberzon

    IEEE Transactions on Automatic Control, 2016

    DOI
12. journal

    Yet Another Tutorial of Disturbance Observer: Robust Stabilization and Recovery of Nominal Performance

    Hyungbo Shim, Gyunghoon Park, Youngjun Joo, Juhoon Back, and Nam Hoon Jo

    Control Theory and Technology, 2016

    Special Issue on Disturbance Rejection: A Snapshot, A Necessity, and A Beginning

    DOI arXiv
13. conference

    State-Space Analysis of Discrete-Time Disturbance Observer for Sampled-Data Control Systems

    Hyeonjun Yun, Gyunghoon Park, Hyungbo Shim, and H. J. Chang

    In American Control Conference (ACC), 2016

    DOI
14. conference

    Encrypting Controller Using Fully Homomorphic Encryption for Security of Cyber-Physical Systems

    Junsoo Kim, Chanhwa Lee, Hyungbo Shim, Jung Hee Cheon, Andrey Kim, Miran Kim, and Yongsoo Song

    In IFAC Workshop on Distributed Estimation and Control in Networked Systems (NecSys), 2016

    DOI

2015

1. journal

   Embedding Internal Model in Disturbance Observer with Robust Stability

   Youngjun Joo, Gyunghoon Park, Juhoon Back, and Hyungbo Shim

   IEEE Transactions on Automatic Control, 2015

   DOI
2. journal

   Design of Stable Parallel Feedforward Compensator and Its Application to Synchronization Problem

   Hongkeun Kim, Seongjun Kim, Juhoon Back, Hyungbo Shim, and Jin Heon Seo

   Automatica, 2015

   DOI
3. conference

   Three-Dimensional Time-Space Grid Allocation Algorithm for Traffic Control of Autonomous Vehicles at an Intersection

   Jaeyong Kim, Jin Gyu Lee, Seungjoon Lee, Hyuntae Kim, Hyungbo Shim, Yongsoon Eun, and Kangwon Lee

   In International Conference on Control, Automation and Systems (ICCAS), 2015

   Abs DOI

   Two-dimensional (2-D) time-space diagram have been widely used to analyze the flow of the traffic. However, it has limitations to make a plan that guarantees the collision avoidance of vehicles at the intersections. In this paper, we introduce the three-dimensional (3-D) time-space diagram and demonstrate its effectiveness in describing the movements of vehicles at the intersections. We also propose an algorithm based on the grid allocation of 3-D time-space diagram to avoid collision between vehicles to achieve the autonomous intersection.

4. conference

   A Secure and Robust State Estimation Under Sensor Attacks, Measurement Noise, and Process Disturbances: Observer-Based Combinatorial Approach

   Chanhwa Lee, Hyungbo Shim, and Yongsoon Eun

   In European Control Conference (ECC), 2015

   DOI
5. journal

   An Asymptotic Ratio Characterization of Input-to-State Stability

   Daniel Liberzon and Hyungbo Shim

   IEEE Transactions on Automatic Control, 2015

   DOI
6. conference

   On Robust Stability of Disturbance Observer for Sampled-Data Systems Under Fast Sampling: An Almost Necessary and Sufficient Condition

   Gyunghoon Park, Youngjun Joo, Chanhwa Lee, and Hyungbo Shim

   In IEEE Conference on Decision and Control (CDC), 2015

   DOI
7. journal

   Comments on “Observability of Switched Linear Systems: Characterization and Observer Design”

   Aneel Tanwani, Hyungbo Shim, and Daniel Liberzon

   IEEE Transactions on Automatic Control, 2015

   DOI
8. book chapter

   Observer Design for Switched Linear Systems with State Jumps

   Aneel Tanwani, Hyungbo Shim, and Daniel Liberzon

   In Hybrid Dynamical Systems. Lecture Notes in Control and Information Sciences, edited by Djemai, M. and Defoort, M., Springer, 2015

   DOI
9. journal

   Consensus of Output-Coupled Linear Multi-Agent Systems Under Deterministic and Markov Switching Networks

   Dmitry Vengertsev, Hongkeun Kim, Jin H. Seo, and Hyungbo Shim

   International Journal of Systems Science, 2015

   Abs DOI

   Consensus problem for high-order multi-agent systems is considered under deterministic and Markovian switching topologies. Only relative output information of agents is assumed to be available through the networks. First, a necessary and sufficient condition for achieving a consensus under a fixed communication network is presented. Based on this result and the stability of switched systems, a high-order multi-agent system with the proposed low-gain controller is shown to reach a consensus under deterministic switching network if the total time when the network is disconnected is, in some senses, smaller than the total time of the network being connected. Furthermore, the conditions sufficient for a high-order multi-agent system to reach an almost sure and mean-square consensus, under Markovian switching networks, are presented. Finally, illustrative examples are given to demonstrate the results.

10. conference

    A Preliminary Result on Frequency-Shaped Model Predictive Control

    Hyeonjun Yun, H. J. Chang, Hyungbo Shim, and Jin Heon Seo

    In IEEE Conference on Decision and Control (CDC), 2015

    DOI
11. conference

    A Generalized Framework for Robust Stability Analysis of Discrete-Time Disturbance Observer for Sampled-Data Systems: A Fast Sampling Approach

    Gyunghoon Park and Hyungbo Shim

    In International Conference on Control, Automation and Systems (ICCAS), 2015

    DOI
12. conference

    Robust Synchronization for High-Order Heterogeneous Multi-Agent Systems

    Jaeyong Kim and Hyungbo Shim

    In SWARM 2015: The First Int. Symp. on Swarm Behavior and Bio-Inspired Robotics, 2015

2014

1. journal

   Reduced-Order Implementation of Disturbance Observers for Robust Tracking of Nonlinear Systems

   Juhoon Back and Hyungbo Shim

   IET Control Theory & Applications, 2014

   Abs DOI

   The disturbance‐observer‐based control (DOBC) is a well‐known robust control scheme and recently its non‐linear version has been developed. Observing that two components (so‐called Q‐filters) in the conventional DOBC structure have the same transfer function, the authors propose a reduced‐order DOBC for uncertain non‐linear systems. It is shown that the proposed controller also guarantees the same robust transient response as those developed before. Numerical simulations using a magnetic levitation system are included to illustrate the detailed design procedure and validate the performance of the proposed controller.

2. journal

   A Study of Disturbance Observers with Unknown Relative Degree of the Plant

   Nam H. Jo, Youngjun Joo, and Hyungbo Shim

   Automatica, 2014

   DOI
3. journal

   Adaptive Add-on Output Regulator for Rejection of Sinusoidal Disturbances and Application to Optical Disc Drives

   Hyungjong Kim, Hyungbo Shim, and Nam Hoon Jo

   IEEE Transactions on Industrial Electronics, 2014

   DOI
4. journal

   Linear Systems with Hyperbolic Zero Dynamics Admit Output Regulator Rejecting Unknown Number of Unknown Sinusoids

   Hyungjong Kim and Hyungbo Shim

   IET Control Theory & Applications, 2014

   Abs DOI

   This study presents an off‐the‐shelf error feedback controller that can completely rejects the sinusoidal disturbances whose magnitudes, phases, bias, frequencies and even the number of frequencies are all unknown. A closed‐form solution is given under the assumptions that the plant has no uncertainty and has hyperbolic zero dynamics (i.e. there is no zero on the imaginary axis of the complex plane), and that the number of unknown frequencies has upper bound which is known. A non‐minimum phase plant can be dealt with. The proposed controller is tested by a simulation, which verifies its effectiveness.

5. conference

   Consensus Under Time-Delayed Information on States and Network

   Jin Gyu Lee and Hyungbo Shim

   In IEEE Conference on Decision and Control (CDC), 2014

   DOI
6. conference

   Asymptotic Rejection of Sinusoidal Disturbances with Recovered Nominal Transient Performance for Uncertain Linear Systems

   Gyunghoon Park, Youngjun Joo, and Hyungbo Shim

   In IEEE Conference on Decision and Control (CDC), 2014

   DOI
7. journal

   Hybrid-Type Observer Design Based on a Sufficient Condition for Observability in Switched Nonlinear Systems

   Hyungbo Shim and Aneel Tanwani

   International Journal of Robust and Nonlinear Control, 2014

   Special Issue on High-Gain Observers in Nonlinear Feedback Control

   Abs DOI

   This paper presents a sufficient condition for observability of continuous‐time switched nonlinear systems that also involve state jumps. Without the assumption of observability of individual modes, the sufficient condition is based on gathering partial information from each mode so that the state is completely recovered after several switchings. Based on the sufficient condition, a hybrid‐type observer is designed, which comprises a copy of the actual plant and an error correction scheme at discrete time instants. In order to execute the proposed design, the observable component of the state at each mode needs to be estimated without transients or ‘peaking’ (caused by high‐gain observers), and this motivates us to introduce a back‐and‐forth estimation technique. Under the assumption of persistent switching, analysis shows that the estimate thus generated converges asymptotically to the actual state of the system. Simulation results validate the utility of the proposed algorithm.

8. journal

   Robust Cascade Control of Electric Motor Drives Using Dual Reduced-Order PI Observer

   Young Ik Son, In Hyuk Kim, Dae Sik Choi, and Hyungbo Shim

   IEEE Transactions on Industrial Electronics, 2014

   DOI

2013

1. conference

   Disturbance Observer with Noise Reduction Capability

   Nam H. Jo and Hyungbo Shim

   In European Control Conference (ECC), 2013

   DOI
2. conference

   Robustness of Synchronization in Heterogeneous Multi-Agent Systems

   Jaeyong Kim, Jongwook Yang, Hyungbo Shim, and Jung-Su Kim

   In European Control Conference (ECC), 2013

   DOI
3. journal

   Consensus of Output-Coupled Linear Multi-Agent Systems Under Fast Switching Network: Averaging Approach

   Hongkeun Kim, Hyungbo Shim, Juhoon Back, and Jin Heon Seo

   Automatica, 2013

   DOI
4. conference

   Real Time Switching Signal Estimation of Switched Linear Systems with Measurement Noise

   Chanhwa Lee, Zhaowu Ping, and Hyungbo Shim

   In European Control Conference (ECC), 2013

   DOI
5. journal

   On the Stability of Critical Point for Positive Systems and Its Applications to Biological Systems

   Joo-Won Lee, Nam Hoon Jo, Hyungbo Shim, and Young Ik Son

   Journal of Electrical Engineering & Technology, 2013

   DOI
6. conference

   Back-and-Forth Operation of State Observers and Norm Estimation of Estimation Error

   Hyungbo Shim, Aneel Tanwani, and Zhaowu Ping

   In IEEE Conference on Decision and Control (CDC), 2013

   DOI
7. journal

   Observability for Switched Linear Systems: Characterization and Observer Design

   Aneel Tanwani, Hyungbo Shim, and Daniel Liberzon

   IEEE Transactions on Automatic Control, 2013

   DOI My Comment

   See the erratum of this paper: Comments on “Observability of switched linear systems: Characterization and observer design," A. Tanwani, H. Shim, and D. Liberzon, IEEE Trans. on Automatic Control, vol. 60, no. 12, pp. 3396-3400, 2015

2012

1. conference

   A Note on Disturbance Observer with Unknown Relative Degree of the Plant

   Nam H. Jo, Youngjun Joo, Hyungbo Shim, and Young Ik Son

   In IEEE Conference on Decision and Control (CDC), 2012

   DOI
2. conference

   Practical Consensus for Heterogeneous Linear Time-Varying Multi-Agent Systems

   Jaeyong Kim, Jongwook Yang, Jung-Su Kim, and Hyungbo Shim

   In International Conference on Control, Automation and Systems (ICCAS), 2012

   Abs HTML

   This paper studies practical consensus (PC) problem for linear multi-agent systems (MAS) under a fixed, connected, and undirected communication network. PC means that the difference between any two agents remains in an arbitrarily chosen neighborhood of the origin after some time by using a suitable control law. All the agents, which are heterogeneous first-order linear time-varying (LTV) systems, can collect only relative state information from their neighborhoods. According to the assumptions of MAS, we divide the problem into two cases; one is a class of homogeneous LTV MAS with heterogeneous disturbances where the difference between any two disturbances is bounded, and the other is a class of heterogeneous LTV MAS with heterogeneous bounded disturbances. Finally, we show that PC for each case is always achieved if the control gain is sufficiently large.

3. journal

   Disc Margins of the Discrete-Time LQR and Its Application to Consensus Problem

   Jinyoung Lee, Jung-Su Kim, and Hyungbo Shim

   International Journal of Systems Science, 2012

   DOI
4. conference

   Analysis of Discrete-Time Disturbance Observer and a New Q-Filter Design Using Delay Function

   Chanhwa Lee, Youngjun Joo, and Hyungbo Shim

   In International Conference on Control, Automation and Systems (ICCAS), 2012

   Abs HTML

   In industrial applications, the disturbance observer (DOB) approach has been widely used due to its robustness and simple structure, and its results in a continuous-time fashion are frequently encountered in many literatures. Although most of DOBs are implemented in a discrete-time form with digital devices, a rigorous analysis on the discrete-time DOB is still insufficient compared to the continuous-time DOB. Therefore, in this paper, we mainly focus on the application of the DOB to discrete-time systems and some phenomena that are not observed in continuous-time systems. In particular, the time constant of the discrete-time Q-filter should have a lower bound, while the continuous-time DOB does not have this constraint. The time constant to sampling time ratio of the discrete-time Q-filter plays a crucial role in the discrete-time DOB, and it is suggested that this ratio be one for stability. Based on the above analysis, a new design method of the discrete-time Q-filter using a delay function is proposed. Furthermore, a robust stability condition for discrete-time systems using the delay function Q-filter is presented. Finally, simulation with an optical disk drive (ODD) model demonstrates the effectiveness of the newly proposed Q-filter.

5. conference

   Rejection of Polynomial-in-Time Disturbances via Disturbance Observer with Guaranteed Robust Stability

   Gyunghoon Park, Youngjun Joo, Hyungbo Shim, and Juhoon Back

   In IEEE Conference on Decision and Control (CDC), 2012

   DOI
6. journal

   Output Feedback Consensus for High Order Linear Systems Having Uniform Ranks Under Switching Topology

   J.H. Seo, J. Back, H. Kim, and H. Shim

   IET Control Theory & Applications, 2012

   Abs DOI

   This study addresses a challenging problem on the consensus of multi-agent systems, that is, simultaneously deals with the high-order linear multi-agent systems (including single and double integrators, and harmonic oscillators) and time-varying interaction topology. The interaction topology is assumed to switch among a finite number of connected undirected graphs having a non-vanishing dwell time. It is also constrained that each agent can use only the system outputs of its neighbouring agents for the purpose of feedback. Under these conditions, the authors propose two high-gain dynamic consensus protocols, one with multiple time-scale based and the other single time-scale, for the uniform rank systems without finite zeros. An example is provided to validate the proposed protocols.

2011

1. journal

   A Control Theoretic Approach to Malaria Immunotherapy with State Jumps

   H. Chang, Alessandro. Astolfi, and Hyungbo Shim

   Automatica, 2011

   Special Issue on Systems Biology

   DOI
2. journal

   Output Consensus of Heterogeneous Uncertain Linear Multi-Agent Systems

   Hongkeun Kim, Hyungbo Shim, and Jin Heon Seo

   IEEE Transactions on Automatic Control, 2011

   DOI
3. journal

   A Constrained Consensus Problem Using MPC

   Jinyoung Lee, Jung-Su Kim, Hwachang Song, and Hyungbo Shim

   International Journal of Control, Automation, and Systems, 2011

   DOI
4. journal

   Reduced-Order Consensus Controllers for Output-Coupled SISO Linear Systems

   Jin Heon Seo, Hyungbo Shim, and Juhoon Back

   International Journal of Control, Automation, and Systems, 2011

   DOI
5. journal

   Finite-Time Stabilizing Dynamic Control of Uncertain Multi-Input Linear Systems

   S. Seo, H. Shim, and J. H. Seo

   IMA Journal of Mathematical Control and Information, 2011

   DOI
6. conference

   Robust Tracking by Reduced-Order Disturbance Observer: Linear Case

   Juhoon Back and Hyungbo Shim

   In IEEE Conference on Decision and Control (CDC), 2011

   DOI
7. conference

   Can a Fast Disturbance Observer Work Under Unmodeled Actuators?

   Nam H. Jo, Youngjun Joo, and Hyungbo Shim

   In International Conference on Control, Automation and Systems (ICCAS), 2011

   PDF
8. conference

   Stabilizability of a Group of Single Integrators and Its Application to Decentralized Formation Problem

   Hongkeun Kim, Hyungbo Shim, Juhoon Back, and Jin Heon Seo

   In IEEE Conference on Decision and Control (CDC), 2011

   DOI
9. conference

   On a Sufficient Condition for Observability of Nonlinear Switched Systems and Observer Design Strategy

   Hyungbo Shim and Aneel Tanwani

   In American Control Conference (ACC), 2011

   DOI
10. conference

    Observability Implies Observer Design for Switched Linear Systems

    Aneel Tanwani, Hyungbo Shim, and Daniel Liberzon

    In ACM International Conference on Hybrid Systems: Computation and Control (HSCC), 2011

    DOI

2010

1. journal

   Robust Tracking and Vibration Suppression for a Two-Inertia System by Combining Backstepping Approach with Disturbance Observer

   Jae Sung Bang, Hyungbo Shim, Sang Kyun Park, and Jin H. Seo

   IEEE Transactions on Industrial Electronics, 2010

   DOI
2. journal

   Disturbance Observer for Non-Minimum Phase Linear Systems

   Nam Hoon Jo, Hyungbo Shim, and Young Ik Son

   International Journal of Control, Automation, and Systems, 2010

   DOI
3. journal

   Note on Differential Regulator Equation for Non-Minimum Phase Linear Systems with Time-Varying Exosystems

   Hyungbo Shim, Jung-Su Kim, Hongkeun Kim, and Juhoon Back

   Automatica, 2010

   DOI Supp
4. journal

   Further Extensions on a Stability Property with Slowly Varying Inputs

   Hyungbo Shim and Nam H. Jo

   Dynamics of Continuous, Discrete and Impulsive Systems, 2010

   Special issue in honor of Prof. Hassan K. Khalil’s 60th birthday

   Abs PDF

   In this paper we present three extended results on the stability property with slowly varying inputs that has been studied in, e.g., Khalil and Kokotovic (1991). The stability property has played an important role in control methodologies such as gainscheduling controls or robust controls for systems having slowly varying parameters. We begin with a review of the first extension, which shows that the inputs may vary fastly, but once its ‘average’ is slowly varying, then the same stability property still holds. The second extension deals with the case when a (transcritical) bifurcation occurs so that the assumptions of the stability property are violated. We propose a Jump & Wait strategy which will still guarantee the stability property even under this case. Finally we prove that the Jump & Wait strategy can be employed not with the input itself but with the average of the input if the proposed structural condition is satisfied.

5. conference

   Immunisation Against HIV and Malaria: Control Theoretic Approach with State Jump

   H. Chang, Alessandro Astolfi, and Hyungbo Shim

   In American Control Conference (ACC), 2010
6. conference

   A Control Theoretic Approach to Venom Immunotherapy with State Jumps

   H. Chang, Alessandro Astolfi, and Hyungbo Shim

   In Annual International Conference of IEEE Engineering in Medicine and Biology Society (EMBC), 2010

   DOI
7. conference

   Reduced-Order Dynamic Observer Error Linearization

   J. Yang, Juhoon Back, Jin Heon Seo, and Hyungbo Shim

   In IFAC Symposium on Nonlinear Control Systems (NOLCOS), 2010

   DOI
8. conference

   Consensus of Output-Coupled Linear Multi-Agent Systems Under Frequently Connected Network

   Dmitry Vengertsev, Hongkeun Kim, Hyungbo Shim, and Jin Heon Seo

   In IEEE Conference on Decision and Control (CDC), 2010

   DOI
9. conference

   Consensus of Multi-Agent Systems Under Periodic Time-Varying Network: Averaging Approach

   Hongkeun Kim, Hyungbo Shim, Juhoon Back, and Jin Heon Seo

   In IFAC Symposium on Nonlinear Control Systems (NOLCOS), 2010

   DOI

2009

1. journal

   An Inner-Loop Controller Guaranteeing Robust Transient Performance for Uncertain MIMO Nonlinear Systems

   Juhoon Back and Hyungbo Shim

   IEEE Transactions on Automatic Control, 2009

   DOI
2. journal

   Consensus of High-Order Linear Systems Using Dynamic Output Feedback Compensator: Low Gain Approach

   Jin Heon Seo, Hyungbo Shim, and Juhoon Back

   Automatica, 2009

   DOI
3. journal

   A System Theoretic Study on a Treatment of AIDS Patient by Achieving Long-Term Non-Progressor

   Hyungbo Shim, Nam H. Jo, H. Chang, and Jin Heon Seo

   Automatica, 2009

   Abs DOI

   There has been much recent interest in the long-term non-progressor (LTNP), who has been infected with human immunodeficiency virus (HIV) but does not proceed to AIDS. Under the assumption that a mathematical model describing the HIV infection and drug effects is true for real systems, we claim that it is possible to steer the state of any patients to that of LTNP if the model parameters belong to the proposed parameter intervals. Once the state is transferred close to LTNP, CTL memory is established and the viral load remains very low level even after the medication is stopped. In order to justify the claim, we first analyze the stability and the bifurcation of the model and show that there exists an equilibria curve towards LTNP, which is stable for all fixed constant inputs except some singular points. Then, we propose a new treatment strategy based on a useful property of Non-vanishing Basin of Attraction (NvBA)-stability. An extensive simulation study is also included to validate the proposed treatment for various initial conditions and to show the robustness against the parameter uncertainty. From a practical perspective, it deserves further investigation whether the proposed treatment strategy could switch a patient into LTNP in the real world.

4. journal

   An Almost Necessary and Sufficient Condition for Robust Stability of Closed-Loop Systems with Disturbance Observer

   Hyungbo Shim and Nam H. Jo

   Automatica, 2009

   DOI
5. journal

   Low-Pass Filter Property of an Input-Dimensional Output Feedback Passification Controller for Rotary Inverted Pendulum

   Young Ik Son, Nam Hoon Jo, Hyungbo Shim, and Goo-Jong Jeong

   IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences, 2009

   DOI
6. conference

   Control of Infection Dynamics with Application to HIV/AIDS Model

   H. Chang, Alessandro Astolfi, and Hyungbo Shim

   In IEEE Conference on Decision and Control (CDC), 2009

   DOI
7. conference

   HIV Treatment: With or Without Consideration of the Immune System

   H. Chang, Alessandro Astolfi, and Hyungbo Shim

   In European Control Conference (ECC), 2009
8. conference

   Quasi-ISS Reduced-Order Observers and Quantized Output Feedback

   Hyungbo Shim, Daniel Liberzon, and Jung-Su Kim

   In IEEE Conference on Decision and Control (CDC), 2009

   DOI
9. conference

   Consensus and Synchronization of Linear High-Order Systems via Output Coupling

   Jin Heon Seo, Hyungbo Shim, and Juhoon Back

   In European Control Conference (ECC), 2009
10. conference

    High-Order Consensus of MIMO Linear Dynamic Systems via Stable Compensator

    Jin Heon Seo, Hyungbo Shim, and Juhoon Back

    In European Control Conference (ECC), 2009

2008

1. journal

   Adding Robustness to Nominal Output Feedback Controllers for Uncertain Nonlinear Systems: A Nonlinear Version of Disturbance Observer

   Juhoon Back and Hyungbo Shim

   Automatica, 2008

   DOI
2. journal

   Locally Optimal and Robust Backstepping Design for Systems in Strict Feedback Form with C1 Vector Fields

   Juhoon Back, Sejin Kang, Hyungbo Shim, and Jin Heon Seo

   International Journal of Control, Automation, and Systems, 2008

   HTML
3. journal

   Switching Adaptive Output Feedback MPC for a Class of Input-Constrained Linear Plants

   J.-S. Kim, T.-W. Yoon, H. Shim, and J.H. Seo

   IET Control Theory & Applications, 2008

   DOI
4. journal

   Determination of Stability with Respect to Positive Orthant for a Class of Positive Nonlinear Systems

   Hyungbo Shim and Nam H. Jo

   IEEE Transactions on Automatic Control, 2008

   DOI Supp
5. conference

   An Inner-Loop Controller Guaranteeing Robust Transient Performance for Uncertain MIMO Linear Systems

   Juhoon Back, Hyungbo Shim, and Youngjun Joo

   In IFAC World Congress, 2008

   DOI
6. conference

   A New Disturbance Observer for Non-Minimum Phase Linear Systems

   Hyungbo Shim, Nam H. Jo, and Young I. Son

   In American Control Conference (ACC), 2008

   DOI
7. conference

   Global Finite-Time Stabilization of a Nonlinear System Using Dynamic Exponent Scaling

   S. Seo, Hyungbo Shim, and Jin Heon Seo

   In IEEE Conference on Decision and Control (CDC), 2008

   DOI
8. conference

   Locally Optimal and Globally Inverse Optimal Controller for Multi-Input Nonlinear Systems

   H. Kim, Juhoon Back, Hyungbo Shim, and Jin Heon Seo

   In American Control Conference (ACC), 2008

   DOI

2007

1. journal

   Nonsmooth Feedback Stabilizer for Strict-Feedback Nonlinear Systems That May Not Be Linearizable at the Origin

   J. Back, S.G. Cheong, H. Shim, and J.H. Seo

   Systems & Control Letters, 2007

   DOI
2. journal

   Perfect Tracking Control for Linear Systems with State Constraint

   Dane Baang, Jin Young Choi, and Hyungbo Shim

   International Journal of Control, Automation, and Systems, 2007

   HTML
3. conference

   Design of a Disturbance Observer-Based Controller for DC/DC Boost Converter

   S.-J. Kim, Young I. Son, Hyungbo Shim, and Y.-S. Jeong

   In IASTED International Conference on Intelligent Systems and Control, 2007
4. conference

   Design of Disturbance Observer for Non-Minimum Phase Systems Using PID Controllers

   Young I. Son, Hyungbo Shim, Nam H. Jo, and S.-J. Kim

   In SICE Annual Conference, 2007

   DOI
5. conference

   Analysis and Synthesis of Disturbance Observer as a Tool for Nonlinear Robust Control

   Juhoon Back and Hyungbo Shim

   In IFAC Symposium on Nonlinear Control Systems (NOLCOS), 2007

   Awarded DOI

   Presented as a semi-plenary talk

6. conference

   State Space Analysis of Disturbance Observer and a Robust Stability Condition

   Hyungbo Shim and Youngjun Joo

   In IEEE Conference on Decision and Control (CDC), 2007

   DOI
7. conference

   Locally Optimal and Robust Backstepping Design for C1 Vector Fields

   Sejin Kang, Juhoon Back, Hyungbo Shim, and Jin Heon Seo

   In International Conference on Control, Automation and Systems (ICCAS), 2007

   DOI

2006

1. journal

   Discussion on: An Adaptive Gradient Law with Projection for Non-Smooth Convex Boundaries

   Juhoon Back and Hyungbo Shim

   European Journal of Control, 2006

   DOI
2. conference

   An Application of Gradual Reduction of Drug Dose to HIV Infection Model in Consideration of Drug Resistance and Drug Dose

   H. Chang, Nam H. Jo, and Hyungbo Shim

   In SICE-ICASE International Joint Conference, 2006

   DOI
3. conference

   Adaptive Regulation for Nonlinear Systems with Unknown Virtual Control Coefficient and Nonlinear Parameterization

   S. Seo, Hyungbo Shim, and Jin Heon Seo

   In SICE-ICASE International Joint Conference, 2006

   DOI
4. conference

   Improving LaSalle’s Invariance Principle Using Geometric Clues

   Hyungbo Shim and Jin Heon Seo

   In SICE-ICASE International Joint Conference, 2006

   DOI
5. conference

   Output Regulation Problem and Solution for LTV Minimum Phase Systems with Time-Varying Exosystem

   Hyungbo Shim, J.H. Lee, Jung-Su Kim, and Juhoon Back

   In SICE-ICASE International Joint Conference, 2006

   DOI

2005

1. journal

   A New Approach to Design of a Dynamic Output Feedback Stabilizing Control Law for LTI Systems

   Young-Ik Son, Hyungbo Shim, Nam-Hoon Jo, and Kab-II Kim

   Journal of Mechanical Science and Technology, 2005

   DOI
2. conference

   Track Following Controller for Optical Disk Drives Based on Adaptive Output Regulation

   H. J. Kim, W. H. Kim, C. C. Chung, and Hyungbo Shim

   In IFAC World Congress, 2005

   DOI
3. conference

   Non-Smooth Feedback Stabilizer for Strict-Feedback Nonlinear Systems Not Even Linearizable at the Origin

   S. G. Cheong, Juhoon Back, Hyungbo Shim, and Jin Heon Seo

   In American Control Conference (ACC), 2005

   DOI
4. conference

   An Algorithm for System Immersion Into Nonlinear Observer Form: Forced System

   Juhoon Back, Hyungbo Shim, and Jin Heon Seo

   In IFAC World Congress, 2005

   DOI
5. conference

   Switching Adaptive Output Feedback MPC for Input-Constrained Neutrally Stable Linear Plants

   Jung-Su Kim, T.W. Yoon, and Hyungbo Shim

   In IEEE Conference on Decision and Control (CDC), 2005

   DOI
6. conference

   A Simple Condition for Checking Non-Vanishing Basin of Attraction Stability for a Class of Positive Nonlinear Systems

   Hyungbo Shim and Nam H. Jo

   In IEEE Conference on Decision and Control (CDC), 2005

   DOI
7. conference

   On a Stability Property of Nonlinear Systems with Periodic Inputs Having Slowly Varying Average

   Y.U. Choi, Hyungbo Shim, and Jin Heon Seo

   In IFAC World Congress, 2005

   DOI
8. conference

   A Stability Property of Nonlinear Systems with Inputs Having Slowly Varying Average and Its Application to HIV Problem

   Y.U. Choi, Hyungbo Shim, and Jin Heon Seo

   In American Control Conference (ACC), 2005

   DOI

2004

1. journal

   Nonlinear Observer Design via Approximate Normal Form: Ball and Beam System on a Vibrating Frame

   Juhoon Back, Nam H. Jo, Young I. Son, Hyungbo Shim, and Jin H. Seo

   IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences, 2004

   DOI
2. journal

   Further Results on Robustness of (Possibly Discontinuous) Sample and Hold Feedback

   C.M. Kellett, H. Shim, and A.R. Teel

   IEEE Transactions on Automatic Control, 2004

   DOI
3. journal

   A Dynamic Output Feedback Control Law for Elastic Joint Robots via Feedback-Passivity Approach

   Young I Son, Hyungbo Shim, and Jin H Seo

   Journal of the Franklin Institute, 2004

   DOI
4. journal

   Feedback Passivity Approach to Output Feedback Disturbance Attenuation for Uncertain Nonlinear Systems

   Y. I. Son, J. W. Yang, N. H. Jo, H. Shim, and J. H. Seo

   International Journal of Systems Science, 2004

   DOI
5. conference

   Control of Immune Response of HIV Infection Model by Gradual Reduction of Drug Dose

   H. Chang, Hyungbo Shim, and Jin Heon Seo

   In IEEE Conference on Decision and Control (CDC), 2004

   DOI
6. conference

   Design and Experiment of Add-on Track Following Controller for Optical Disc Drives Based on Robust Output Regulation

   Hyungbo Shim, H. J. Kim, and C. C. Chung

   In American Control Conference (ACC), 2004

   DOI
7. conference

   Non-Vanishing Basin of Attraction with Respect to a Parametric Variation and Center Manifold

   Hyungbo Shim, H.J. Chang, and Jin Heon Seo

   In IEEE Conference on Decision and Control (CDC), 2004

   DOI

2003

1. journal

   Design of an Adaptive Observer for a Class of Nonlinear Systems

   Y.U. Choi, H. Shim, Y.I. Son, and J.H. Seo

   International Journal of Control, Automation, and Systems, 2003
2. journal

   Recursive Observer Design Beyond the Uniform Observability

   Hyungbo Shim and J.H. Seo

   IEEE Transactions on Automatic Control, 2003

   DOI
3. journal

   An Adaptive Algorithm Applied to a Design of Robust Observer

   Young-Ik Son, Hyungbo Shim, Juhoon Back, and Nam-Hoon Jo

   KSME International Journal, 2003

   DOI
4. journal

   Asymptotic Controllability and Observability Imply Semiglobal Practical Asymptotic Stabilizability by Sampled-Data Output Feedback

   Hyungbo Shim and A.R. Teel

   Automatica, 2003

   DOI
5. journal

   Nonlinear Observer Design via Passivation of Error Dynamics

   H. Shim, J.H. Seo, and A.R. Teel

   Automatica, 2003

   DOI
6. journal

   Optimal Scheduling of Drug Treatment for HIV Infection: Continuous Dose Control and Receding Horizon Control

   H. Shim, S.J. Han, C.C. Chung, S.W. Nam, and J.H. Seo

   International Journal of Control, Automation, and Systems, 2003

   DOI
7. journal

   A Design Method of an SPR System for Stabilization of a Crane Without Velocity Measurement

   Young Ik Son, Hyungbo Shim, and Kab-Il Kim

   IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences, 2003

   HTML
8. journal

   Output Feedback Passification of Nonlinear Systems Not in Normal Form

   Young Ik Son, Hyungbo Shim, Nam Hoon Jo, and Jin H. Seo

   IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences, 2003

   HTML
9. journal

   Further Results on Passification of Non-Square Linear Systems Using an Input-Dimensional Compensator

   Young Ik Son, Hyungbo Shim, Nam Hoon Jo, and Jin H. Seo

   IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences, 2003

   HTML
10. conference

    Optimal Scheduling of Drug Treatment for HIV Infection: Continuous Dose Control and Receding Horizon Control

    Hyungbo Shim, S.J. Han, I.S. Jeong, Y.H. Huh, C.C. Chung, S.W. Nam, and Jin Heon Seo

    In International Conference on Control, Automation and Systems (ICCAS), 2003
11. conference

    Design of Output Regulator for Rejecting Periodic Eccentricity Disturbance in Optical Disc Drive

    Hyungbo Shim, H. J. Kim, and C. C. Chung

    In International Conference on Control, Automation and Systems (ICCAS), 2003
12. conference

    A New Vision-Sensorless Anti-Sway Control System for Container Cranes

    Y. S. Kim, Hyungbo Shim, H. Yoshihara, N. Fujioka, H. Kasahara, and S. K. Sul

    In IEEE Industry Applications Society Annual Meeting, 2003
13. conference

    Multirate Output Feedback Control and Its Application to Galvanometer Servo Systems

    C. C. Chung, S. H. Lee, D. S. Jeong, and Hyungbo Shim

    In American Control Conference (ACC), 2003
14. conference

    An Approach to Robust Observer Construction Without Output Derivative Measurements

    Young I. Son, Hyungbo Shim, Juhoon Back, and Nam H. Jo

    In International Conference on Mechatronics and Information Technology (ICMIT), 2003
15. conference

    Remarks on Equivalence Between Full Order and Reduced Order Nonlinear Observers

    Hyungbo Shim and L. Praly

    In IEEE Conference on Decision and Control (CDC), 2003

    DOI
16. conference

    Enlarging the Class of Linear Systems Admitting Adaptive Observers Without Persistent Excitation

    Hyungbo Shim, Young I. Son, Juhoon Back, and Nam H. Jo

    In European Control Conference (ECC), 2003

2002

1. journal

   Passification of Non-Square Linear Systems Using an Input-Dimensional Dynamic Feedforward Compensator

   Y.I. Son, H. Shim, K. Park, and J.H. Seo

   IEICE Transactions on Fundamentals of Electronics, Communications and Computer Sciences, 2002

   DOI
2. journal

   Set-Point Control of Elastic Joint Robots Using Only Position Measurements

   Young-Ik Son, Hyungbo Shim, and Jin-Heon Seo

   KSME International Journal, 2002

   DOI
3. conference

   Adaptive Output Feedback Controllers for Feedback Passive Nonlinear Systems

   Young I. Son, Hyungbo Shim, Nam H. Jo, and Jin Heon Seo

   In International Conference on Control, Automation and Systems (ICCAS), 2002
4. conference

   Output Feedback Stabilization of Non-Minimum Phase Nonlinear Systems

   Nam H. Jo, Young I. Son, and Hyungbo Shim

   In International Conference on Control, Automation and Systems (ICCAS), 2002
5. conference

   Robustness of Discontinuous Feedback via Sample and Hold Control

   C.M. Kellett, Hyungbo Shim, and A.R. Teel

   In American Control Conference (ACC), 2002

   DOI

2001

1. journal

   Semi-Global Observer for Multi-Output Nonlinear Systems

   Hyungbo Shim, Young I. Son, and Jin H. Seo

   Systems & Control Letters, 2001

   DOI
2. conference

   Semiglobal Robust Stabilization of Nonlinear Systems Without Vanishing Condition

   N. Bok, Hyungbo Shim, Young I. Son, and Jin Heon Seo

   In IFAC Symposium on Nonlinear Control Systems (NOLCOS), 2001
3. conference

   On Performance Improvement of an Output Feedback Control Scheme for Non-Uniformly Observable Nonlinear Systems

   Hyungbo Shim and A.R. Teel

   In IEEE Conference on Decision and Control (CDC), 2001

   DOI
4. conference

   Further Results on the Nonlinear Separation Principle: The General ’Asymptotically Controllable’ Case

   Hyungbo Shim and A.R. Teel

   In IFAC Symposium on Nonlinear Control Systems (NOLCOS), 2001

   PDF
5. conference

   A Systematic Nonlinear Observer Design for a Class of Euler-Lagrange Systems

   R. Skjetne and Hyungbo Shim

   In Mediterranean Conference on Control and Automation (MED), 2001

2000

1. journal

   Nonlinear Output Feedback Stabilization on a Bounded Region of Attraction

   Hyungbo Shim and Jin Heon Seo

   International Journal of Control, 2000

   DOI
2. conference

   Output Feedback Passification of Nonlinear Systems

   J. Byun, Hyungbo Shim, and Jin Heon Seo

   In American Control Conference (ACC), 2000

   DOI
3. conference

   Passivity Framework for Nonlinear State Observer

   Hyungbo Shim and Jin Heon Seo

   In American Control Conference (ACC), 2000

   DOI
4. conference

   A Simple Observer for Nonlinear Systems in x-Coordinate Using Lipschitz Extension Technique

   Hyungbo Shim, Young I. Son, Juhoon Back, and Jin Heon Seo

   In Joint Conference on Control, Instrumentation, Automation, and Robotics, 2000

1999

1. journal

   Comments on Observers for Nonlinear Systems in Steady State

   H. Shim, J. Byun, and J.H. Seo

   IEEE Transactions on Automatic Control, 1999

   DOI
2. conference

   Saturation Technique for Constructing Observer of Multi-Output Nonlinear Systems

   Hyungbo Shim, Young I. Son, and Jin Heon Seo

   In American Control Conference (ACC), 1999

   DOI

1998

1. conference

   Robust Control of Nonlinear Systems with Nonvanishing Nonlinear Parametrization

   Hyungbo Shim, K. T. Yu, Young I. Son, and Jin Heon Seo

   In IFAC Symposium on Nonlinear Control Systems (NOLCOS), 1998
2. conference

   Robust Tracking Control of Nonlinear Systems with Pure Feedback Uncertainties

   J. Byun, Nam H. Jo, Hyungbo Shim, and Jin Heon Seo

   In IFAC Conference on System Structure and Control, 1998
3. conference

   Backstepping Design for Disturbed Virtual Controls

   Hyungbo Shim, J. Byun, Nam H. Jo, and Jin Heon Seo

   In American Control Conference (ACC), 1998

   DOI
4. conference

   Robust Stabilization of Nonminimum Phase Nonlinear Systems

   Nam H. Jo, J. Byun, Hyungbo Shim, and Jin Heon Seo

   In American Control Conference (ACC), 1998

   DOI
5. conference

   Robust Stabilization of a Class of MIMO Nonlinear Systems: Sliding Mode Control & Passification Approach

   J. S. Lee, Hyungbo Shim, J. Byun, and Jin Heon Seo

   In American Control Conference (ACC), 1998

   DOI
6. conference

   Output Feedback Stabilization for Completely Uniformly Observable Nonlinear Systems

   Hyungbo Shim, J. Jin, J.S. Lee, and Jin Heon Seo

   In IFAC Conference on System Structure and Control, 1998

   PDF
7. conference

   Common Lyapunov Function for Exponentially Stable Nonlinear Systems

   Hyungbo Shim, D.J. Noh, and Jin Heon Seo

   In SIAM Conference on Control and Its Applications, 1998
8. conference

   Passivity Under Unmodeled Dynamics

   Hyungbo Shim, J. Byun, J.S. Lee, and Jin Heon Seo

   In IFAC Conference on System Structure and Control, 1998

1994

1. conference

   Design and Analysis of the Nonlinear Feedback Linearizing Controller for an Electro-Magnetic Suspension System

   S. J. Joo, J. Byun, Hyungbo Shim, and Jin Heon Seo

   In IEEE Conference on Control Applications (CCA), 1994

   DOI

[A] Disturbance Observer

[B] Multi-agent System

[C] Nonlinear Observer

[D] Output Feedback Stabilization

[E] Stability Analysis

[F] Control Method

[G] Security of Control System

[H] Switched/Hybrid System

[I] Parallel Feedforward Compensator

[J] Biological Dynamics and Control

[K] Data-Driven/Learning

[L] Others

Tutorial style articles

Disturbance observer

“Disturbance Observers”
H. Shim
in Encyclopedia of Systems and Control, Springer, 2020
doi:10.1007/978-1-4471-5102-9_100068-1
also available at arxiv:2101.02859

“Yet another tutorial of disturbance observer: Robust stabilization and recovery of nominal performance”
H. Shim, G. Park, Y. Joo, J. Back, and N.H. Jo
Special Issue on Disturbance Rejection: A Snapshot, A Necessity, and A Beginning
Control Theory and Technology, vol. 14, issue 3, pp. 237-249, Aug 2016
doi:10.1007/s11768-016-6006-9
also available at arxiv:1601.02075

Multi-agent Systems

“Design of heterogeneous multi-agent system for distributed computation”
Jin Gyu Lee, Hyungbo Shim
In: Jiang ZP., Prieur C., Astolfi A. (eds) Trends in Nonlinear and Adaptive Control. Lecture Notes in Control and Information Sciences, Springer, 2022
doi:10.1007/978-3-030-74628-5_4
also available at arxiv:2101.00161

Security of Control Systems

“Zero-dynamics Attack, Variations, and Countermeasures”
Hyungbo Shim, Juhoon Back, Yongsoon Eun, Gyunghoon Park, Jihan Kim
In: Ishii H., Zhu Q. (eds) Security and Resilience of Control Systems. Lecture Notes in Control and Information Sciences, Springer, 2022
doi:10.1007/978-3-030-83236-0_2
also available at arxiv:2101.00556

Control based on homomorphic encryption

“Comprehensive Introduction to Fully Homomorphic Encryption for Dynamic Feedback Controller via LWE-Based Cryptosystem”
Junsoo Kim, Hyungbo Shim and Kyoohyung Han
Privacy in Dynamical Systems, Springer, 2020
doi:10.1007/978-981-15-0493-8
draft version available at arxiv:1904.08025

“Comparison of encrypted control approaches and tutorial on dynamic systems using Learning With Errors-based homomorphic encryption”
Junsoo Kim, Dongwoo Kim, Yongsoo Song, Hyungbo Shim, Henrik Sandberg, and Karl H. Johansson
Annual Reviews in Control, Volume 54, pp. 200-218, 2022
doi:10.1016/j.arcontrol.2022.10.002

Selected Publications

Disturbance Observer

1. conference

   On Robust Stability of Disturbance Observer for Sampled-Data Systems Under Fast Sampling: An Almost Necessary and Sufficient Condition

   Gyunghoon Park, Youngjun Joo, Chanhwa Lee, and Hyungbo Shim

   In IEEE Conference on Decision and Control (CDC), 2015

   DOI
2. journal

   An Almost Necessary and Sufficient Condition for Robust Stability of Closed-Loop Systems with Disturbance Observer

   Hyungbo Shim and Nam H. Jo

   Automatica, 2009

   DOI
3. journal

   Adding Robustness to Nominal Output Feedback Controllers for Uncertain Nonlinear Systems: A Nonlinear Version of Disturbance Observer

   Juhoon Back and Hyungbo Shim

   Automatica, 2008

   DOI

Multi-agent System

1. journal

   Singularly Perturbed Hybrid Systems for Analysis of Networks with Frequently Switching Graphs

   Aneel Tanwani, Hyungbo Shim, and Andrew R. Teel

   IEEE Transactions on Automatic Control, 2025

   Abs DOI

   For a class of hybrid systems, where jumps occur frequently, we analyze the stability of system trajectories in view of singularly perturbed dynamics. The specific model we consider comprises an interconnection of two hybrid subsystems, a timer which triggers the jumps, and some discrete variables to determine the index of the jump maps. The flow equations of these variables are singularly perturbed differential equations and, in particular, a smaller value of the singular perturbation parameter leads to an increase in the frequency of the jump instants. For the limiting value of this parameter, we consider a decomposition that comprises a quasi-steady-state system modeled by a differential equation without any jumps and a boundary-layer system described by purely discrete dynamics. Under appropriate assumptions on the quasi-steady-state system and the boundary-layer system, we derive results showing practical stability of a compact attractor when the jumps occur sufficiently often. As an application of our results, we discuss the control design problem in a network of second-order continuous-time coupled oscillators, where each agent communicates the information about its position to some of its neighbors at discrete times. Using the results developed in this article, we show that if the union of the communication graphs being used for information exchange between agents is connected, then the oscillators achieve practical consensus.

2. conference

   Adaptation of Parameters in Heterogeneous Multi-Agent Systems

   Hyungbo Shim, Jin Gyu Lee, and Brian D. O. Anderson

   In IEEE Conference on Decision and Control (CDC), 2025

   Abs DOI arXiv

   This paper proposes an adaptation mechanism for heterogeneous multi-agent systems to align the agents’ internal parameters, based on enforced consensus through strong couplings. Unlike homogeneous systems, where exact consensus is attainable, the heterogeneity in node dynamics precludes perfect synchronization. Nonetheless, previous work has demonstrated that strong coupling can induce approximate consensus, whereby the agents exhibit emergent collective behavior governed by the so-called blended dynamics. Building on this observation, we introduce an adaptation law that gradually aligns the internal parameters of agents without requiring direct parameter communication. The proposed method reuses the same coupling signal employed for state synchronization, which may result in a biologically or sociologically plausible adaptation process. Under a persistent excitation condition, we prove that the linearly parametrized vector fields of the agents converge to each other, thereby making the dynamics asymptotically homogeneous, and leading to exact consensus of the state variables.

3. journal

   A Design Method of Distributed Algorithms via Discrete-Time Blended Dynamics

   Jeong Woo Kim, Jin Gyu Lee, Donggil Lee, and Hyungbo Shim

   Automatica, 2024

   Abs DOI

   We develop a discrete-time version of the blended dynamics theorem for the use of designing distributed computation algorithms. The blended dynamics theorem enables to predict the behavior of heterogeneous multi-agent systems. Therefore, once we get a blended dynamics for a particular computational task, design idea of node dynamics for individual heterogeneous agents can easily occur. In the continuous-time case, prediction by blended dynamics was enabled by high coupling gain among neighboring agents. In the discrete-time case, we propose an equivalent action, which we call multi-step coupling in this paper. Compared to the continuous-time case, the blended dynamics can have more variety depending on the coupling matrix. This benefit is demonstrated with three applications; distributed estimation of network size, distributed computation of the PageRank, and distributed computation of the degree sequence of a graph, which correspond to the coupling by doubly-stochastic, column-stochastic, and row-stochastic matrices, respectively.

4. journal

   Decentralized Design and Plug-and-Play Distributed Control for Linear Multi-Channel Systems

   Taekyoo Kim, Donggil Lee, and Hyungbo Shim

   IEEE Transactions on Automatic Control, 2023

   DOI
5. journal

   Blended Dynamics Approach to Distributed Optimization: Sum Convexity and Convergence Rate

   Seungjoon Lee and Hyungbo Shim

   Automatica, 2022

   DOI
6. journal

   Completely Decentralized Design of Distributed Observer for Linear Systems

   Taekyoo Kim, Chanhwa Lee, and Hyungbo Shim

   IEEE Transactions on Automatic Control, 2020

   DOI
7. journal

   Fully Distributed Resilient State Estimation Based on Distributed Median Solver

   Jin Gyu Lee, Junsoo Kim, and Hyungbo Shim

   IEEE Transactions on Automatic Control, 2020

   DOI
8. journal

   A Tool for Analysis and Synthesis of Heterogeneous Multi-Agent Systems Under Rank-Deficient Coupling

   Jin Gyu Lee and Hyungbo Shim

   Automatica, 2020

   DOI
9. conference

   Behavior of a Network of Heterogeneous Lienard Systems Under Output Coupling

   Jin Gyu Lee and Hyungbo Shim

   In IFAC Symposium on Nonlinear Control Systems (NOLCOS), 2019

   DOI
10. journal

    Initialization-Free Privacy-Guaranteed Distributed Algorithm for Economic Dispatch Problem

    Hyeonjun Yun, Hyungbo Shim, and Hyo-Sung Ahn

    Automatica, 2019

    DOI
11. conference

    Heterogeneous Van Der Pol Oscillators Under Strong Coupling

    Jin Gyu Lee and Hyungbo Shim

    In IEEE Conference on Decision and Control (CDC), 2018

    DOI
12. conference

    Distributed Algorithm for the Network Size Estimation: Blended Dynamics Approach

    Donggil Lee, Seungjoon Lee, Taekyoo Kim, and Hyungbo Shim

    In IEEE Conference on Decision and Control (CDC), 2018

    DOI
13. journal

    Robustness of Synchronization of Heterogeneous Agents by Strong Coupling and a Large Number of Agents

    Jaeyong Kim, Jongwook Yang, Hyungbo Shim, Jung-Su Kim, and Jin Heon Seo

    IEEE Transactions on Automatic Control, 2016

    DOI

Nonlinear Observer

1. journal

   A Toolkit for Globally Robust Observer-Based Feedback with Relaxed Characterization of iISS/ISS

   Hiroshi Ito and Hyungbo Shim

   IEEE Transactions on Automatic Control, 2023

   DOI
2. journal

   Nonlinear Observers Robust to Measurement Disturbances in an ISS Sense

   Hyungbo Shim and Daniel Liberzon

   IEEE Transactions on Automatic Control, 2016

   DOI
3. journal

   Recursive Observer Design Beyond the Uniform Observability

   Hyungbo Shim and J.H. Seo

   IEEE Transactions on Automatic Control, 2003

   DOI
4. journal

   Nonlinear Observer Design via Passivation of Error Dynamics

   H. Shim, J.H. Seo, and A.R. Teel

   Automatica, 2003

   DOI
5. conference

   Remarks on Equivalence Between Full Order and Reduced Order Nonlinear Observers

   Hyungbo Shim and L. Praly

   In IEEE Conference on Decision and Control (CDC), 2003

   DOI

Output Feedback Stabilization

1. journal

   Nonlinear Output Feedback Stabilization on a Bounded Region of Attraction

   Hyungbo Shim and Jin Heon Seo

   International Journal of Control, 2000

   DOI

Stability Analysis

1. journal

   Further Extensions on a Stability Property with Slowly Varying Inputs

   Hyungbo Shim and Nam H. Jo

   Dynamics of Continuous, Discrete and Impulsive Systems, 2010

   Special issue in honor of Prof. Hassan K. Khalil’s 60th birthday

   Abs PDF

   In this paper we present three extended results on the stability property with slowly varying inputs that has been studied in, e.g., Khalil and Kokotovic (1991). The stability property has played an important role in control methodologies such as gainscheduling controls or robust controls for systems having slowly varying parameters. We begin with a review of the first extension, which shows that the inputs may vary fastly, but once its ‘average’ is slowly varying, then the same stability property still holds. The second extension deals with the case when a (transcritical) bifurcation occurs so that the assumptions of the stability property are violated. We propose a Jump & Wait strategy which will still guarantee the stability property even under this case. Finally we prove that the Jump & Wait strategy can be employed not with the input itself but with the average of the input if the proposed structural condition is satisfied.

Control Method

Security of Control System

1. journal

   Fully Distributed Resilient State Estimation Based on Distributed Median Solver

   Jin Gyu Lee, Junsoo Kim, and Hyungbo Shim

   IEEE Transactions on Automatic Control, 2020

   DOI

Switched/Hybrid System

Parallel Feedforward Compensator

1. journal

   Design of Stable Parallel Feedforward Compensator and Its Application to Synchronization Problem

   Hongkeun Kim, Seongjun Kim, Juhoon Back, Hyungbo Shim, and Jin Heon Seo

   Automatica, 2015

   DOI

Biological Dynamics and Control

1. journal

   Further Extensions on a Stability Property with Slowly Varying Inputs

   Hyungbo Shim and Nam H. Jo

   Dynamics of Continuous, Discrete and Impulsive Systems, 2010

   Special issue in honor of Prof. Hassan K. Khalil’s 60th birthday

   Abs PDF

   In this paper we present three extended results on the stability property with slowly varying inputs that has been studied in, e.g., Khalil and Kokotovic (1991). The stability property has played an important role in control methodologies such as gainscheduling controls or robust controls for systems having slowly varying parameters. We begin with a review of the first extension, which shows that the inputs may vary fastly, but once its ‘average’ is slowly varying, then the same stability property still holds. The second extension deals with the case when a (transcritical) bifurcation occurs so that the assumptions of the stability property are violated. We propose a Jump & Wait strategy which will still guarantee the stability property even under this case. Finally we prove that the Jump & Wait strategy can be employed not with the input itself but with the average of the input if the proposed structural condition is satisfied.

2. journal

   A System Theoretic Study on a Treatment of AIDS Patient by Achieving Long-Term Non-Progressor

   Hyungbo Shim, Nam H. Jo, H. Chang, and Jin Heon Seo

   Automatica, 2009

   Abs DOI

   There has been much recent interest in the long-term non-progressor (LTNP), who has been infected with human immunodeficiency virus (HIV) but does not proceed to AIDS. Under the assumption that a mathematical model describing the HIV infection and drug effects is true for real systems, we claim that it is possible to steer the state of any patients to that of LTNP if the model parameters belong to the proposed parameter intervals. Once the state is transferred close to LTNP, CTL memory is established and the viral load remains very low level even after the medication is stopped. In order to justify the claim, we first analyze the stability and the bifurcation of the model and show that there exists an equilibria curve towards LTNP, which is stable for all fixed constant inputs except some singular points. Then, we propose a new treatment strategy based on a useful property of Non-vanishing Basin of Attraction (NvBA)-stability. An extensive simulation study is also included to validate the proposed treatment for various initial conditions and to show the robustness against the parameter uncertainty. From a practical perspective, it deserves further investigation whether the proposed treatment strategy could switch a patient into LTNP in the real world.