2020 |
Jihan Kim / Juhoon Back / Gyunghoon Park / Chanhwa Lee / Hyungbo Shim / Petros G. Voulgaris Neutralizing zero dynamics attack on sampled-data systems via generalized holds Journal Article In: Automatica, vol. 113, pp. 108778, 2020, ISSN: 0005-1098. Abstract | Links | BibTeX | Tags: Cyber-physical system, Sampled-data control system, Secure control system, System security, Zero-dynamics @article{Kim20, Zero dynamics attacks can be lethal to cyber–physical systems because they can be harmful to physical plants and impossible to detect. Fortunately, if the given continuous-time physical system is minimum phase, the attack is not so effective even if it cannot be detected. However, the situation can become unfavorable if one uses digital control by sampling the sensor measurement and using a zero-order hold for actuation because of the ‘sampling zeros.’ When the continuous-time system has a relative degree greater than two and the sampling period is small, the sampled-data system must have unstable zeros (even if the continuous-time system is minimum phase), so that the cyber–physical system becomes vulnerable to ‘sampling zero dynamics attack.’ In this paper, we present an idea to neutralize the zero dynamics attack for single-input and single-output sampled-data systems by shifting the unstable discrete-time zeros into stable ones. This idea is realized by employing the so-called ‘generalized hold’ which replaces a standard zero-order hold. It is shown that, under mild assumptions, a generalized hold exists which places the discrete-time zeros at desired positions. Furthermore, we formulate the design problem as an optimization problem whose performance index is related to the inter-sample behavior of the physical plant, and propose an optimal gain which alleviates the performance degradation caused by generalized hold as much as possible. |
Hyungbo Shim Disturbance Observers Book Chapter In: John Baillieul; Tariq Samad (Ed.): Encyclopedia of Systems and Control, pp. 1-8, Springer London, London, 2020, ISBN: 978-1-4471-5102-9. Abstract | Links | BibTeX | Tags: Disturbance observer @inbook{Shim20, 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. |
Jin Gyu Lee / Hyungbo Shim A distributed algorithm that finds almost best possible estimate under non-vanishing and time-varying measurement noise Journal Article In: IEEE Control Systems Letters, vol. 4, no. 1, pp. 229-234, 2020, ISSN: 2475-1456. Abstract | Links | BibTeX | Tags: Noise measurement @article{LeeShim20, In this letter, we review an existing distributed least-squares solver and share some new insights on it. Then, by the observation that an estimation of a constant vector under output noise can be translated into finding the least-squares solution, we present an algorithm for distributed estimation of the state of linear time-invariant systems under measurement noise. The proposed algorithm consists of a network of local observers, where each of them utilizes local measurements and information transmitted from the neighbors. It is proven that even under non-vanishing and time-varying measurement noise, we could obtain an almost best possible estimate with arbitrary precision. Some discussions regarding the plug-and-play operation are also given. |
2019 |
Junsoo Kim / Hyungbo Shim Encrypted State Estimation in Networked Control Systems Proceedings Article In: Proc. of 2019 IEEE 58th Conference on Decision and Control, pp. 7190-7195, IEEE, Nice, France, 2019. Abstract | Links | BibTeX | Tags: Controller encryption, Distributed state estimation @inproceedings{KimShim19b, In this paper, we propose a distributed state observer in which the data of measurements and state estimates are protected by homomorphic cryptosystem. The proposed observer network is composed of local observers, where each of them utilizes encrypted local measurement, encryption of plant input, and encrypted estimates transmitted from its neighbors. All the operations in the network are performed on encrypted data without decryption, and the full state is recovered in every local observer as an encrypted message. Assuming the characteristic polynomial and the minimal polynomial of the state matrix for the plant are the same, the parameters in the observers are chosen to be integers. This not only allows finitetime convergence for the state estimates, but also makes the encrypted dynamic observers operate for infinite time horizon. |
Jongsoo Ha / Hyungbo Shim Study on Realizable Generalized Hold Functions As a Countermeasure against Zero Dynamics Attack Proceedings Article In: Proc. of 2019 IEEE 58th Conference on Decision and Control, pp. 5362-5367, IEEE, Nice, France, 2019. Abstract | Links | BibTeX | Tags: Generalized hold, Zero-dynamics @inproceedings{HaShim19, Zero dynamics attacks are known to be lethal in the sense that they are stealthy in principle and are not detected from output measurements. Therefore, instead of detecting the zero dynamics attacks, an idea to mitigate the effect of the zero dynamics attack has been proposed recently, which is to enforce the zeros to become stable by changing the zero-order hold to a generalized hold in the sampled data framework. Once all the zeros become stable, then even if the zero dynamics attack is engaged, its effect on the plant is negligible. However, it was observed that the amplitude of the generalized hold becomes unrealistically large in some cases, which leads to a large input to the physical plant. This paper studies this phenomenon at a deeper level and figures out that changing the intrinsic zeros requires an excessively large amplitude of the generalized hold while changing the sampling zeros can be done with a reasonable amplitude. |
Jeong Woo Kim / Hyungbo Shim / Insoon Yang On Improving the Robustness of Reinforcement Learning-Based Controllers Using Disturbance Observer Proceedings Article In: Proc. of 2019 IEEE 58th Conference on Decision and Control, pp. 8487-852, IEEE, Nice, France, 2019. Abstract | Links | BibTeX | Tags: Disturbance observer, Reinforcement learning @inproceedings{KimShimYang19, Because reinforcement learning (RL) may cause issues in stability and safety when directly applied to physical systems, a simulator is often used to learn a control policy. However, the control performance may be easily deteriorated in a real plant due to the discrepancy between the simulator and the plant. In this paper, we propose an idea to enhance the robustness of such RL-based controllers by utilizing the disturbance observer (DOB). This method compensates for the mismatch between the plant and simulator, and rejects disturbance to maintain the nominal performance while guaranteeing robust stability. Furthermore, the proposed approach can be applied to partially observable systems. We also characterize conditions under which the learned controller has a provable performance bound when connected to the physical system. |
Junsoo Kim / Hyungbo Shim / Kyoohyung Han Comprehensive Introduction to Fully Homomorphic Encryption for Dynamic Feedback Controller via LWE-Based Cryptosystem Book Chapter In: Privacy in Dynamical Systems, Chapter 10, pp. 209-230, Springer, 2019, ISBN: 978-981-15-0492-1. Abstract | Links | BibTeX | Tags: Controller encryption, Homomorphic encryption @inbook{KimShimHan20b, The cryptosystem based on the Learning-with-Errors (LWE) problem is considered as a post-quantum cryptosystem, because it is not based on the factoring problem with large primes which is believed to be easily solved by a quantum computer. Moreover, the LWE-based cryptosystem allows fully homomorphic arithmetics so that two encrypted variables can be added and multiplied without decrypting them. This chapter provides a comprehensive introduction to the LWE-based cryptosystem with examples. A key to the security of the LWE-based cryptosystem is the injection of random errors in the ciphertexts, which however hinders unlimited recursive operation of homomorphic arithmetics on ciphertexts due to the growth of the error. We show how this limitation can be overcome for dynamic feedback controllers that guarantee stability of the closed-loop system when the system matrix of the controller consists of integers. Finally, we illustrate through MATLAB codes how the LWE-based cryptosystem can be customized to build a secure feedback control system. This chapter is written for the control engineers who do not have background on cryptosystems. |
Jihan Kim / Gyunghoon Park / Hyungbo Shim / Yongsoon Eun Masking attack for sampled-data systems via input redundancy Journal Article In: IET Control Theory & Applications , vol. 13, no. 14, pp. 2300-2308, 2019, ISSN: 1751-8644. Abstract | Links | BibTeX | Tags: Linear Systems @article{KimParkShimEun19, 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. |
Jihan Kim / Hyungbo Shim A Countermeasure against Zero-dynamics Sensor Attack via Generalized Hold Feedback Proceedings Article In: Proc. of the SICE Annual Conference 2019, pp. 663-668, SICE, Hiroshima, Japan, 2019. Abstract | Links | BibTeX | Tags: Cyber-physical system, Generalized hold, Resilient control system, Sampled-data control system @inproceedings{KimShim19, The zero-dynamics attack is well-known for its lethality and stealthiness. This infamous attack has usually been studied as a type of actuator attack. In this paper, however, we focus on the zero-dynamics attack having a form of a sensor attack. In particular, when the system monitors abnormal behavior of the plant using the anomaly detector, an undetectable sensor attack can be generated, which deceives the anomaly detector. It is noticed that this sensor attack is not so effective when the plant is stable even if the attack is still undetectable. In view of this point, we propose to reexamine the so-called ‘generalized hold’ as a countermeasure against the undetectable sensor attack. Specifically, using the fact that the output feedback composed of the ‘generalized hold’ can stabilize the unstable systems by selecting an appropriate hold function, we show that the plant can be safe from the undetectable sensor attack. |
Jin Gyu Lee / Hyungbo Shim Behavior of a network of heterogeneous Li´enard systems under strong output coupling Proceedings Article In: Proc. of 8th IFAC Symposium on Mechatronic Systems & 11th IFAC Symposium on Nonlinear Control Systems, pp. 256-261, IFAC, Vienna, Austria, 2019. Abstract | Links | BibTeX | Tags: Approximate synchronization, Blended dynamics, Heterogeneous multi-agents, Internal model principle, Lienard system, Oscillations, Singular perturbation, Strong coupling @inproceedings{LeeShim19b, In this paper, to participate in the understanding of a biological system, we analyze the synchronous and oscillatory behavior of coupled Liénard systems. In particular, we will consider a network of heterogeneous Liénard systems under output diffusive coupling to take into account two fundamental characteristics of a biological system. The key idea in this work is to emphasize the role of a network, which introduces an emergent behavior that each individual element approximately follows, hence making elements approximately synchronize. The intuition comes from a series of developments recently made in the name of ‘blended dynamics,’ and thus, the common philosophy of ‘blended dynamics’ approach enables us to illustrate a biological phenomenon that collective behavior is preserved even when there are some malfunctioning elements. |
Gyunghoon Park / Chanhwa Lee / Hyungbo Shim / Yongsoon Eun / Karl H. Johansson Stealthy adversaries against uncertain cyber-physical systems: Threat of robust zero-dynamics attack Journal Article In: IEEE Transactions on Automatic Control , vol. 64, iss. 12, pp. 4907 - 4919, 2019, ISSN: 0018-9286. Abstract | Links | BibTeX | Tags: Actuators @article{ParkLeeShimEunJohansson19, In this paper, we address the problem of constructing a robust stealthy attack that compromises uncertain cyberphysical systems having unstable zeros. We first interpret the (non-robust) conventional zero-dynamics attack based on Byrnes- Isidori normal form, and then present a new robust zero-dynamics attack for uncertain plants. Different from the conventional strategy, our key idea is to isolate the real zero-dynamics from the plant's input-output relation and to replace it with an auxiliary nominal zero-dynamics. As a result, this alternative attack does not require the exact model knowledge anymore. The price to pay for the robustness is to utilize the input and output signals of the system (i.e., disclosure resources). It is shown that a disturbance observer can be employed to realize the new attack philosophy when there is a lack of model knowledge. Simulation results with a hydro-turbine power system are presented to verify the attack performance and robustness. |
Seyed Hamze Moosapour / Mohammad Ataei / Hyungbo Shim / Mohsen Ekramian Asymptotic stabilization of a class of nonlinear systems with long input delay in the presence of disturbance Journal Article In: ISA Transactions, vol. 91, pp. 125-134, 2019, ISSN: 0019-0578. Abstract | Links | BibTeX | Tags: nonlinear systems @article{MoosapourAtaeiShimEkramian19b, Asymptotic stabilization of a class of nonlinear systems with known constant long input delay is addressed in the presence of external disturbance by applying sliding mode control method. Modified prediction variable scheme is employed to compensate long delays in the input, where conventional prediction variable approaches cannot be employed. This is mainly due to the fact that the external disturbance appears in the prediction variable, which renders the controller dependent on the external disturbance. In order to tackle this problem, the nonlinear disturbance observer based predictor is used. A suitable disturbance observer is designed to estimate the external disturbance that appears in the prediction variable. Respected to some existing results, the prediction-based control for more general class of the nonlinear systems in the presence of external disturbance is the main contribution of this paper. Actuator and sensor delays exist in the most common dynamic systems. So, the proposed control scheme can be employed in many conventional systems. The simulation results indicate the robustness and efficiency of the proposed controller. |
Jisu Kim / Hyungbo Shim / Jin Heon Seo State Estimation and Tracking Control for Hybrid Systems by Gluing the Domains Journal Article In: IEEE Transactions on Automatic Control, 2019. Abstract | Links | BibTeX | Tags: Hybrid system, Observer, Tracking @article{KimShimSeo19, We study the design problems of state observers and tracking controllers for a class of hybrid systems whose state jumps. The idea is to utilize the well-known method of gluing the jump set (a part of domain where the jumps take place) onto its image, which converts the hybrid system into a continuous-time system whose state does not jump. Sufficient conditions for this idea to be implemented are listed and discussed with a few concrete examples. In particular, we present a structural condition for an observer design, and, for tracking control, we introduce a feedback to compensate residual discontinuity in the vector field after gluing. The benefits of the proposed approach include that the observer design does not require detection of the state jumps, and that the tracking control does not require the plant state jumps when the reference jumps. |
Seungjoon Lee / Hyungbo Shim Distributed Algorithm for Economic Dispatch Problem With Separable Losses Journal Article In: IEEE Control Systems Letters, vol. 3, no. 3, pp. 685-690, 2019. Links | BibTeX | Tags: Blended dynamics, Distributed optimization @article{LeeShim19, |
Kiran Kumari / Bijnan Bandyopadhyay / Kyung-Soo Kim / Hyungbo Shim Output Feedback based Event-Triggered Sliding Mode Control for Delta Operator Systems Journal Article In: Automatica, vol. 103, 2019. Abstract | Links | BibTeX | Tags: Sliding mode control @article{KumariBandKimShim19, In this paper, we present an output feedback based design of event-triggered sliding mode control for delta operator systems. For discrete time systems, multi-rate output sampling based state estimation technique is very useful if the output information is available. But at high sampling rates, the discrete-time representation of the system using shift operator becomes numerically ill-conditioned and as a result the observability matrix becomes singular as the sampling period tends to zero. Here, a new formulation of multi-rate state estimation (MRSE) for a small sampling period is presented. We first propose a new observability matrix, and then discuss its relationship with the observability matrix defined in the conventional sense. For the delta operator system with matched uncertainty, we have presented the design of MRSE based sliding mode control (SMC). Additionally, to make the control efficient in terms of resource utilization, MRSE based event-triggered SMC is proposed. The absence of Zeno phenomenon is guaranteed as the control input is inherently discrete in nature. Finally, the effectiveness of the proposed method is illustrated through numerical simulations, considering a ball and beam system, and a general linear system as a numerical example. |
Hyeonjun Yun / Hyungbo Shim / Hyo-Sung Ahn Initialization-free Privacy-guaranteed Distributed Algorithm for Economic Dispatch Problem Journal Article In: Automatica, vol. 102, pp. 86-93, 2019. Abstract | Links | BibTeX | Tags: Blended dynamics, Synchronization @article{YunShimAhn19, This paper considers the economic dispatch problem for a network of power generators and customers. In particular, our aim is to minimize the total generation cost under the power supply-demand balance and the individual generation capacity constraints. This problem is solved in a distributed manner, i.e., a dual gradient-based continuous-time distributed algorithm is proposed in which only a single dual variable is communicated with the neighbors and no private information of the node is disclosed. The proposed algorithm is simple and no specific initialization is necessary, and this in turn allows on-line change of network structure, demand, generation constraints, and even the participating nodes. The algorithm also exhibits a special behavior when the problem becomes infeasible so that each node can detect over-demand or under-demand situation of the power network. Simulation results on IEEE 118 bus system confirm robustness against variations in power grids. |
Chanhwa Lee / Hyungbo Shim / Yongsoon Eun On Redundant Observability: From Security Index to Attack Detection and Resilient State Estimation Journal Article In: IEEE Transactions on Automatic Control, vol. 64, no. 2, pp. 775-782, 2019. Abstract | Links | BibTeX | Tags: Attack detection, Cyber-physical system, Resilient state estimation @article{LeeShimEun19, The security of control systems under sensor attacks is investigated. Redundant observability is introduced, explaining existing security notions including the security index, attack detectability, and observability under attacks. Equivalent conditions between redundant observability and existing notions are presented. Based on a bank of partial observers utilizing Kalman decomposition and a decoder exploiting redundancy, an estimator design algorithm is proposed enhancing the resilience of control systems. This scheme substantially improves computational efficiency utilizing far less memory. |
Junsoo Kim / Chanhwa Lee / Hyungbo Shim / Yongsoon Eun / Jin Heon Seo Detection of Sensor Attack and Resilient State Estimation for Uniformly Observable Nonlinear Systems having Redundant Sensors Journal Article In: IEEE Transactions on Automatic Control, vol. 64, no. 3, pp. 1162-1169, 2019, ISBN: 0018-9286. Abstract | Links | BibTeX | Tags: Attack detection, Cyber-physical system, Resilient state estimation @article{KimLeeShimEunSeo19, This paper presents a detection algorithm for sensor attacks and a resilient state estimation scheme for a class of uniformly observable nonlinear systems. An adversary is supposed to corrupt a subset of sensors with the possibly unbounded signals, while the system has sensor redundancy. We design an individual high-gain observer for each measurement output so that only the observable portion of the system state is obtained. Then, a nonlinear error correcting problem is solved by collecting all the information from those partial observers and exploiting redundancy. A computationally efficient, on-line monitoring scheme is presented for attack detection. Based on the attack detection scheme, an algorithm for resilient state estimation is provided. The simulation results demonstrate the effectiveness of the proposed algorithm. |
2018 |
Hiroshi Ito / Hyungbo Shim Adaptable iISS Small-Gain Formulation and Its Application to Observer-Based Output Feedback Design Proceedings Article In: Proc. of 2018 IEEE 57th Conference on Decision and Control, pp. 5616-5621, IEEE, Miami, USA, 2018. Abstract | Links | BibTeX | Tags: iISS @inproceedings{ItoShim18, For a popular class of nonlinear systems, an observer can be constructed by rendering estimation error dynamics linear in unmeasured state variables. However, measurement disturbance violates the structure of the error dynamics and brings in undesirable terms in which the estimation error and the plant state are often coupled and multiplied by the measurement disturbance. This is why local analysis and semi-global design have been performed in many cases. This paper introduces new flexibility into the iISS small-gain framework to accommodate such terms. It is demonstrated how the flexible framework enables global analysis of observer-based output feedback control systems to achieve convergence and boundedness in the presence of measurement disturbance. |
Donggil Lee / Seungjoon Lee / Taekyoo Kim / Hyungbo Shim Distributed Algorithm for the Network Size Estimation: Blended Dynamics Approach Proceedings Article In: Proc. of 2018 IEEE 57th Conference on Decision and Control, pp. 4577-4582, IEEE, Miami, USA, 2018. Abstract | Links | BibTeX | Tags: Blended Dynamics Approach @inproceedings{LeeLeeKimShim18, This paper presents a distributed algorithm for the network size estimation problem. The problem is to find the total number of nodes in the network. The proposed algorithm utilizes the continuous-time dynamics for achieving synchronization,whichprovidesawaytoassigneachelementof the equilibrium point of the dynamics close to the network size. The algorithm guarantees that each node directly estimates the total number of nodes in the network. Moreover, the network size can be estimated regardless of initial condition. We also derive the stopping criteria of the algorithm and extend the result to the case where the network varies intermittently with time. |
Junsoo Kim / Jin Gyu Lee / Chanhwa Lee / Hyungbo Shim / Jin H. Seo Local Identification of Sensor Attack and Distributed Resilient State Estimation for Linear System Proceedings Article In: Proc. of 2018 IEEE 57th Conference on Decision and Control, pp. 2056-2061, IEEE, Miami, USA, 2018. Abstract | Links | BibTeX | Tags: Linear Systems @inproceedings{KimLeeLeeShimSeo18, This paper presents a distributed attack-resilient state estimation scheme for continuous-time linear systems having redundant sensors when some of them are corrupted by adversaries. We first design a distributed state observer so that individual observers from each of output measurements communicate with their neighbors and cooperate to recover the full state of the system. Then, the observers are partitioned into disjoint groups and local monitoring systems are designed for each of them. Even though the system is not observable from measurements in each group, every influential attack is detected and identified by local monitors using only local information and local observer estimates within the local group, with the help of sensing redundancy. In process of local attack identification, a notion of sensor attack identifiability is introduced which does not require observability. Finally, all corrupted output measurements are removed from the observer communication and the distributed resilient state estimation is achieved |
Jin Gyu Lee / Hyungbo Shim Heterogeneous Van der Pol Oscillators under Strong Coupling Proceedings Article In: Proc. of 2018 IEEE 57th Conference on Decision and Control, pp. 3666-3673, IEEE, Miami, USA, 2018. Abstract | Links | BibTeX | Tags: Heterogeneous @inproceedings{LeeShim18, The behavior of a network of heterogeneous Van derPoloscillatorsunderoutputdiffusivecouplingisstudied.By the intuition on strong coupling given by the series of ‘blended dynamics’ research, we first show that under sufficiently strong coupling gain the network achieves practical synchronization among heterogeneous oscillators even when there is no common internal model. Then, a further analysis finds a necessary and sufficient condition for the network to achieve synchronous and oscillatory behavior. It should be noted that the condition is the existence of a stable limit cycle for an emergent Van der Pol oscillator we introduce in this paper. Since the stability of each oscillator is not asked, the individual can be any system having the same structure with the Van der Pol oscillator, for instance, double integrator, linear oscillator, and a Van der Pol oscillator with an unstable limit cycle. Finally, by applying a modified singular perturbation theory, we show that the individual agent oscillates near the stable limit cycle of the emergent Van der Pol oscillator. |
Jung Hee Cheon / Kyoohyung Han / Hyuntae Kim / Junsoo Kim / Hyungbo Shim Need for Controllers having Integer Coefficients in Homomorphically Encrypted Dynamic Syste Proceedings Article In: Proc. of 2018 IEEE 57th Conference on Decision and Control, pp. 5020-5025, IEEE, Miami, USA, 2018. Abstract | Links | BibTeX | Tags: Dynamic System @inproceedings{CheonHanKimKimShim18, Encryption of feedback controller based on homomorphic encryption techniques allows control operation on encrypted sensor measurements, to protect data secrecy of networked control systems. In this paper, we first revisit the fact that an encrypted dynamic controller based on partially homomorphic cryptosystems cannot operate for infinite time horizon in general due to the problem of the size of encrypted controller state. Then, it is highlighted that an encrypted LTI controller can operate for infinite time horizon when the denominator of its transfer function is a monic polynomial with integercoefficients.Inthiscase,itdoesnotutilizebootstrapping techniques from fully homomorphic encryption for resizing the controller state, and it does not assume the decryption of controller state from time to time. In this respect, we discuss potentialbenefitsofusingPIDcontrollersandFIRfilters.Then, we introduce a way how to approximately convert controllers having non-integer coefficients to have integer coefficients without losing stability. |
Hayato Dan, Takeshi Hatanaka, Hyungbo Shim A Modularized Design for Output Synchronization of LTI Dynamical Networks with Communication Delays Journal Article In: SICE Journal of Control, Measurement, and System Integration, vol. 11, no. 6, 2018. Abstract | BibTeX | Tags: output synchronization @article{DanHatanakaShim18b, In this paper, we address output synchronization for a network of heterogeneous agents with linear time invariant single-input-single-output dynamics in the presence of communication delays. To this end, we present a three-stage modularized design procedure: (i) a parallel feedforward compensator is designed to convert the dynamics to a minimum-phase system with relative degree one, (ii) the resulting system is then transformed into a feedback equivalent to a passive system, and (iii) the agents are interconnected based on a passivity-based output synchronization law. The benefit of the present control scheme is that not only implementation but also the design stage of the controller is distributed, namely the agents do not need to know the entire network structure. The present solution is then shown to achieve output synchronization. We finally demonstrate the present controller through simulation. |
Hayato Dan / Takeshi Hatanaka / Hyungbo Shim A Parallel Feedforward Compensator Approach to Output Synchronization for a Network with Non-passive Dynamics and Communication Delays Proceedings Article In: Proc. of the SICE Annual Conference 2018, SICE SICE, Nara, Japan, 2018. Abstract | BibTeX | Tags: output synchronization @inproceedings{DanHatanakaShim18, In this paper, we address output synchronization for a network of homogeneous agents with linear time invariant SISO dynamics in the presence of communication delays. To this end, we present a three-stage design procedure: (i) a parallel feedforward compensator is designed to convert the dynamics to a minimum-phase system with relative degree one, (ii) the resulting system is then transformed into a feedback equivalent to passive system, and (iii) the agents are interconnected based on a passivity-based output synchronization law. The benefit of the present control scheme is that not only implementation but also the design stage of the controller is distributed, namely the agents do not need to know the entire network structure. The present solution is then shown to achieve output synchronization. |
Hamin Chang / Hyuntae Kim / Gyunghoon Park / Hyungbo Shim DO-DAT: A MATLAB Toolbox for Design & Analysis of Disturbance Observer Proceedings Article In: Proc. of 9th IFAC Symposium on Robust Control Design & 2nd IFAC Workshop on Linear Parameter Varying Systems, IFAC Brasil, 2018. Abstract | Links | BibTeX | Tags: Disturbance observer @inproceedings{ChangKimParShim18, Although the disturbance observer (DOB)-based controller has been extensively applied and various theoretical results on the DOB have been presented, the exclusive, user-friendly, and unified tool for the computer-aided design of DOB has not been developed yet. In this paper, the MATLAB toolbox DO-DAT (Disturbance Observer - Design & Analysis Toolbox) is introduced. Particularly, we explain the way of using the toolbox and present the applications of main functions in terms of the stabilization of the system and the time-domain performance analysis. |
Jiyeon Nam / Gyunghoon Park / Taekyoo Kim / Hyungbo Shim A Posteriori Detection of Moment of Attack on Cyber-physical Systems: A Back-and-forth Observer Approach Proceedings Article In: Proc. of 7th IFAC Workshop on Distributed Estimation and Control in Networked System, pp. 188-193, IFAC IFAC, Netherlands, 2018. Abstract | Links | BibTeX | Tags: Cyber-physical systems @inproceedings{NamParkKimShim18, In this paper, we address the problem of finding the moment at which an attack to a cyber-physical system initiates, which we call the “moment of attack.” The proposed algorithm is not a real-time method, but the search is performed a posteriori. Nevertheless, the problem becomes of particular interest for forensic evidence, or for high-cost manufacturing processes. In fact, when a production system is attacked, the manufactured output before the attack does not have to be discarded if exact time of the attack is found. To tackle the problem for “temporarily stealthy” sensor attack of polynomial types (with which the conventional real-time anomaly detectors hardly estimate the moment of attack), we propose a batch-type detection algorithm for the moment of attack via the back-and-forth observer approach. |
Seungjoon Lee / Hyeonjun Yun / Hyungbo Shim Practical Synchronization of Heterogeneous Multi-agent System Using Adaptive Law for Coupling Gains Proceedings Article In: Proc. of 2018 Annual American Control Conference (ACC), IEEE, Milwaukee, WI, USA, 2018. Abstract | Links | BibTeX | Tags: Synchronization @inproceedings{LeeYunShim18, Practical synchronization of the heterogeneous multi-agent system is studied in this paper. In particular, we propose an adaptive law to adjust the coupling gains to achieve practical synchronization in a fully distributed manner without the need of any global information such as the total number of agents in the network or the algebraic connectivity of the communication topology. In addition, a distributed protocol is proposed such that the performance of practical synchronization becomes independent of any global information as well as the addition of new agent. |
Suseong Kim / Seungwon Choi / Hyeonggeun Kim / Jongho Shin / Hyungbo Shim / H. Jin Kim Robust Control of an Equipment-added Multirotor Using Disturbance Observer Journal Article In: IEEE Transactions on Control Systems Technology, vol. 26, no. 4, pp. 1524-1531, 2018. Abstract | Links | BibTeX | Tags: Aerodynamics, Disturbance observer, Mathematical modeling, Vehicle dynamics @article{KimChoiKimShinShimKim17, Modifications of multirotor unmanned aerial vehicles are increasingly popular by integrating tools, sensors, or a robotic arm depending on types of applications. In these circumstances, precise motion control against model uncertainty and disturbance is essential. This brief presents an inner-loop control structure to recover the dynamics of a multirotor combined with additional objects similar to the bare multirotor using disturbance observer (DOB)-based approach. In addition, in the process of the inner-loop controller design and the associated stability proof, it is revealed that the safe operation bounds of the modified multirotor in accordance with the amount of inertia added to the multirotor. The proposed control design is validated with flight experiments using a multirotor integrated with a four-DOF robotic arm, where the multirotor is commanded to follow a desired trajectory while the robotic arm is in motion. The results show superior tracking performance of the proposed structure in comparison with backstepping control without DOB. |
Gyunghoon Park / Hyungbo Shim Guaranteeing Almost Fault-free Tracking Performance from Transient to Steady-state: a Disturbance Observer Approach Journal Article In: Science China Information Sciences, vol. 61, no. 7, 2018. Abstract | Links | BibTeX | Tags: Disturbance observer, Fault-tolerant @article{ParkShim18, ** Invited Paper for the Special Issue on Advances in Disturbance/Unvertainty Estimation and Attenuation Technique With Applications ** In this paper, we propose an output-feedback fault-tolerant controller (FTC) for a class of uncertain multi-input single-output systems under float and lock-in-place actuator faults. Of particular interest is to recover a fault-free tracking performance of a (pre-defined) nominal closed-loop system, during the entire time period including the transients due to abrupt actuator faults. As a key component, a high-gain disturbance observer (DOB) is employed to rapidly compensate the lumped disturbance, a compressed expression of all the effect of actuator faults (as well as model uncertainty and disturbance) on the system. To implement this high-gain approach, a fixed control allocation (CA) law is presented in order to keep an extended system with a virtual scalar input to remain of minimum phase under any patterns of faults. It is shown via the singular perturbation theory that the proposed FTC, consisting of the high-gain DOB and the CA law, resolves the problem in an approximate but arbitrarily accurate sense. Simulation results with the linearized lateral model of Boeing 747 are performed to verify the validity of the proposed FTC scheme. |
Gyunghoon Park / Chanhwa Lee / Hyungbo Shim On Stealthiness of Zero-dynamics Attacks against Uncertain Nonlinear Systems: A Case Study with Quadruple-tank Process Proceedings Article In: Proc. of 23rd International Symposium on Mathematical Theory of Networks and Systems, pp. 10-17, Hong Kong, 2018. Abstract | Links | BibTeX | Tags: Zero-dynamics @inproceedings{ParkLeeShim18, This paper studies the problem of constructing a zero-dynamics attack on “nonlinear and uncertain” cyberphysical systems being of non-minimum phase, particularly for the case of the quadruple-tank rocess. In most of the previous works, the zero-dynamics attack is usually designed by linearizing the nonlinear system at an operating point. As a consequence, the stealthiness of the attack may be easily violated whenever the plant has even small model uncertainty or the state trajectory under the attack moves too far from the operating point (so that the linearization is not accurate enough). Without relying on the linearization of the plant at all, in this paper we propose a nonlinear zero-dynamics attack based on the Byrnes-Isidori normal form representation. In particular, it is shown via the Lyapunov analysis that the proposed attack for the quadruple-tank process always remains stealthy until some of the tanks become empty or overflow even in the presence of small parametric uncertainty, which cannot be ensured by the existing methods. Simulation results are presented to verify the performance of the proposed attack. |
Jung Hee Cheon / Kyoohyung Han / Seong-Min Hong / H. Jin Kim / Junsoo Kim / Suseong Kim / Hoseong Seo / Hyungbo Shim / Yongsoo Song Toward a Secure Drone System: Flying with Real-time Homomorphic Authenticated Encryption Journal Article In: IEEE Access, vol. 6, pp. 24325-24339, 2018. Abstract | Links | BibTeX | Tags: Homomorphic encryption @article{CheonHanHongKimKimKimSeoShimSong18, Controlling or accessing remotely has become a prevalent form of operating numerous types of platforms and infrastructure. An exploding number of vehicles such as drones or cars, in particular, are being controlled wirelessly or connected through networks. This has brought unanimous concern that today’s networked vehicle systems are vulnerable to attacks and the results could be fatal. Unfortunately, in contrast to active investigation on the security of the vehicles themselves, sensors, or communication channels, existing approaches for these real-time, safety-critical systems do not take controllers into enough consideration. In order to protect the controller that performs the arithmetic operations using sensor measurements and generates command signals, we adopt homomorphic cryptography for the controller. It removes risks associated with the management of the secret key inside the controller, by eliminating the need to encrypt and decrypt the data for the mathematical operation within the controller. Specifically, we propose an efficient linearly homomorphic authenticated encryption (LinHAE) scheme for the ground control center of a multi-rotor drone, in a manner that enables real-time operation for safe autonomous flight. To facilitate the linear scheme, we design the ground controller targeted to allow state update using additions and multiplications by a system-specific constant. The proposed LinHAE guarantees the security against eavesdropping and forgery attacks, unlike homomorphic encryption alone that does not provide means to check whether the received signal at the drone side is authentic or compromised. We introduce a LinHAE with security and computational tractability, and describe how it can fit into the standard architecture for drone systems and how the specific controller is implemented. Building on these ingredients, we report the first successful operation of a multi-rotor flying robot that autonomously flies under the ground controller with real-time homomorphic authenticated encryption. |
Gyunghoon Park / Hyungbo Shim / Youngjun Joo Recovering Nominal Tracking Performance in an Asymptotic Sense for Uncertain Linear Systems Journal Article In: SIAM Journal on Control and Optimization, vol. 56, no. 2, pp. 700-722, 2018. Abstract | Links | BibTeX | Tags: Disturbance observer, Internal model principle, Nominal performance recovery, Robustness @article{ParkShimJoo18, In this paper, we consider the problem of recovering a (predefined) nominal output trajectory in the presence of model uncertainty and external disturbance. In particular, whereas the nominal performance recovery (NPR) has been studied in an approximate fashion in the literature, we extend the notion of the NPR in an asymptotic sense from the perspective of the internal model principle: that is, as long as the disturbance and reference signals are generated by an exogenous system, the actual output not only is kept close to the nominal trajectory as much as desired but also asymptotically converges to the nominal one as time elapses. It is shown via the singular perturbation theory that the asymptotic NPR can be achieved for uncertain minimum-phase systems under arbitrarily large (but bounded) model uncertainty. A disturbance observer (DOB) approach is employed in the controller design, with the internal model embedded into the so-called Q-filter, which is a key component of the DOB. Simulation results for mechanical positioning systems illustrate that the asymptotic NPR can enhance robust performance of control systems. |
Gyunghoon Park / Hyungjong Kim Adaptive Regulation to Nominal Response for Uncertain Mechanical Systems and Its Application to Optical Disk Drive Journal Article In: IEEE Transactions on Industrial Electronics, vol. 65, no. 2, pp. 1450-1458, 2018. Abstract | Links | BibTeX | Tags: Frequency estimation, Mechanical system, Nominal performance recovery, Robustness @article{ParkKim18, In this paper, we present an add-on type robust controller for uncertain mechanical systems with a sinusoidal disturbance of an unknown frequency. The main purpose is to recover (predefined) nominal tracking performance in an “asymptotic” sense, that is, the actual output asymptotically converges to the nominal trajectory, as well as the maximum difference between them is maintained small enough during the operation. As a key component of the proposed controller, a disturbance observer that contains an internal model is proposed. Especially, the parameters of the internal model are updated in an “adaptive” fashion in order to cope with the unknown frequency of the disturbance, for which a frequency identifier is employed in the controller design. The nominal performance recovery of the proposed controller is analyzed in the sense of Lyapunov and singular perturbation theory. Both simulation and experimental results point out that the proposed control scheme can serve as a robust track following controller for uncertain optical disk drive systems where eccentricity of disk causes a sinusoidal disturbance. |
2017 |
Juhoon Back / Jihan Kim / Chanhwa Lee / Gyunghoon Park / Hyungbo Shim Enhancement of Security against Zero Dynamics Attack via Generalized Hold Proceedings Article In: Proc. of IEEE Conf. on Decision and Control, pp. 1350-1355, Melbourne, Australia, 2017. Abstract | Links | BibTeX | Tags: Generalized hold @inproceedings{BackKimLeeParkShim17, Zero dynamics attack is lethal to cyber-physical systems in the sense that it is stealthy and there is no way to detect it. Fortunately, if the given continuous-time physical system is of minimum phase, the effect of the attack is negligible even if it is not detected. However, the situation becomes unfavorable again if one uses digital control by sampling the sensor measurement and using the zero-order-hold for actuation because of the `sampling zeros.' When the continuous-time system has relative degree greater than two and the sampling period is small, the sampled-data system must have unstable zeros (even if the continuous-time system is of minimum phase), so that the cyber-physical system becomes vulnerable to `sampling zero dynamics attack.' In this paper, we begin with its demonstration by a few examples. Then, we present an idea to protect the system by allocating those discrete-time zeros into stable ones. This idea is realized by employing the so-called `generalized hold' which replaces the zero-order-hold. |
Jin Gyu Lee / Hyungbo Shim Synchronized Behavior of Heterogeneous Multi-agent Systems Under Funnel Coupling Proceedings Article In: Proc. of SWARM 2017: The 2nd International Symposium on Swarm Behavior and Bio-Inspired Robotics, pp. 266-269, Kyoto, Japan, 2017. Abstract | Links | BibTeX | Tags: Funnel control, Practical synchronization @inproceedings{LeeShim17b, First,generalizationofthefunnelcontrolbasedcouplinglawisprovidedtoachieveapracticalsynchronization. In addition to this, we detail the discussion on the synchronized behavior of heterogeneous agents under funnel coupling. In particular, emergent dynamics has been conjectured, which can predict the synchronized behavior by its solution trajectory. Discussion and comparison associated with the similar concept named blended dynamics in strong coupling technique have been given, and also the effectiveness of our conjecture is illustrated by simulations. |
Seungjoon Lee / Hyungbo Shim Consensus of linear time-invariant multi-agent system over multilayer network Proceedings Article In: Proc. of 17th International Conference on Control, Automation and Systems (ICCAS) , IEEE, Jeju, South Korea, 2017. Abstract | Links | BibTeX | Tags: Nonhomogeneous media @inproceedings{LeeShim17d, Consensus of multi-agent system has been studied extensively for past decades. However, most literature considered a single communication network. In this paper, multilayer graph is introduced to allow individual agent to interact over multiple communication networks, each with different output information. Necessary conditions for achieving consensus under the usage of dynamic controller is proposed. Proposed conditions show the interplay between the system theoretical condition, such as detectability, with the graph theoretical condition, such as connectedness of the communication network. It is also shown that a dynamic controller can be designed for a given example when necessary conditions are satisfied. |
Hyeonjun Yun / Seungjoon Lee / Hyungbo Shim Consensus-based Distributed Coordination for Optimal Energy Generation of Hierarchical Systems Proceedings Article In: Proc. of 56th Annual Conference of the Society of Instrument and Control Engineers (SICE), pp. 871-876, Kanazawa, Japan, 2017. Abstract | Links | BibTeX | Tags: Distributed optimization, Multi-agent system, Power grids, Synchronization @inproceedings{YunLeeShim17, This paper considers the optimal energy generation problem for hierarchical system, which consists of multi-cluster power system. In particular, consensus-based distributed hierarchical coordination algorithm is proposed to meet the power generation/demand balance. By using Lagrangian-based approach, we show that the optimization problem for the hierarchical system can be separated into each layer's consensus problem with communication between each layer's leader agent. The convergence is proved in the sense of global practical stability by the singular perturbation theory. Simulation result shows that the solution obtained by the proposed algorithm converges to the optimal solution. |
Hyeonjun Yun / Hyungbo Shim / H. J. Chang Singular Perturbation for Sampled-Data Systems With Fast Subsystems Proceedings Article In: Proc. of the 20th World Congress, pp. 8475-8480, IFAC Toulouse, France, 2017. Abstract | Links | BibTeX | Tags: Singular perturbation @inproceedings{YunShimChang17, We present a sampled-data version of the well-known Tikhonov’s theorem on singular perturbation theory. In particular, we claim that the nonlinear sampled-data systems with fast subsystems can be treated as a singularly perturbed system in a discrete-time sense. In this case, we show that the sampling period can be considered as a singular perturbation parameter. Following the nomenclature of the singular perturbation theory, we define the degenerate (DG) system and the boundary-layer (BL) system and obtain the solution of the sampled-data system as an approximation of the solutions of the lower-order subsystems. Finally, a simple example, sampled-data implementation of disturbance observer, is included to validate the theory. |
Nam Hoon Jo / Chanyoung Jeon / Hyungbo Shim Noise Reduction Disturbance Observer for Disturbance Attenuation and Noise Suppression Journal Article In: IEEE Transactions on Industrial Electronics , vol. 64, no. 2, pp. 1381 - 1391, 2017. Abstract | Links | BibTeX | Tags: Motor drive, Observer @article{JoJeonShim17, In most research works on the disturbance observer (DOB)-based controller, stability conditions are only sufficient and not effective for handling large uncertainties. To deal with large uncertainties, a necessary and sufficient condition for robust stability has been recently provided by utilizing a novel design technique for the Q -filter. Although this design method can deal with large uncertainties, it is not capable of suppressing the effect of sensor noise. To achieve noise suppression as well as disturbance attenuation, this paper proposes a robust controller by utilizing a modified DOB structure. In contrast to the conventional DOB structure, noise suppression ability of the proposed controller can be adjusted by an appropriate choice of the Q-filter. Moreover, a necessary and sufficient condition for the modified DOB system to be robustly stable is newly presented. To show the effectiveness of the proposed controller, the performance is compared with other disturbance attenuation methods through simulation studies. Finally, in order to verify the validity of the proposed method, laboratory experiments are also conducted with brushless dc motor drives, which confirms that the proposed controller is quite useful for attenuating both input disturbance and sensor noise, while DOB controller is not capable of suppressing sensor noise. |
Zhaowu Ping / chanhwa Lee / Hyungbo Shim Robust Estimation Algorithm for Both Switching Signal and State of Switched Linear Systems Journal Article In: International Journal of Control, Automation and Systems, vol. 15, no. 1, pp. 95-103, 2017. Abstract | Links | BibTeX | Tags: Switched system, Switching signal estimation @article{PingLeeShim17, We present a hybrid-type observer for detecting the switching time and estimating both the active mode and the states of continuous-time switched linear systems. The systems under consideration have external inputs and are affected by unknown disturbances. In addition, noise corrupts the output measurements. In this setting the switching cannot be detected immediately, and thus, this paper presents a condition that relates the amount of delay to the sizes of the unknown disturbances/noises, the external inputs, and the states, and the strength of the observability. Once the condition is satisfied, the proposed observer and algorithm return the exact active mode and approximate state information of the switched system. A numerical example is also presented to show the performance of our algorithm.. |
2016 |
Taekyoo Kim / Hyungbo Shim / Dong-il “Dan” Cho Distributed Luenberger Observer Design Proceedings Article In: Proc. of 2016 IEEE 55th Conference on Decision and Control, pp. 6928-6933, IEEE, Las Vegas, NV, USA, 2016. Abstract | Links | BibTeX | Tags: Observer @inproceedings{KimShimCho16, This paper presents a distributed design scheme of the Luenberger-type state observer for continuous-time linear dynamical systems. The proposed observer consists of networked local observers, and each local observer computes the estimate by the local measurements, which may not be sufficient to recover the full state. Therefore, by communicating with the neighboring observers, the proposed observer compensates for the insufficient information. The novelty of the proposed method is the design of two observer gains; one for local measurements and the other for the information exchange. By exploring the structure of gain matrices, our design can assign the injection gain only to “detectable” part of the estimate for the local measurements, and for the “undetectable” portion of the estimate, the gain of the information from neighboring observers is set to be relatively higher than others. It turns out that this intuitive idea leads to a simple design of distributed Luenberger-type observers. |
Jaeyong Kim / Hyungbo Shim / Jingbo Wu On Distributed Optimal Kalman-Bucy Filtering by Averaging Dynamics of Heterogeneous Agents Proceedings Article In: Proc. of 2016 IEEE 55th Conference on Decision and Control, pp. 6309-6314, IEEE, Las Vegas, NV, USA, 2016. Abstract | Links | BibTeX | Tags: @inproceedings{KimShimWu16, This paper studies a design and analysis of distributed Kalman-Bucy filter in sensor networks. When observability of the target system from each sensor is lost, boundedness of the covariance matrices for the individual Riccati equations are not guaranteed. In order to overcome this difficulty and to recover the optimality of the centralized Kalman-Bucy filter, we introduce exchange of covariance matrices with other agents. Then, since those Riccati equations and estimators are heterogenous, achieving consensus among them becomes the question. We employ the recently introduced notion of averaged dynamics, which is the average of all distributed Kalman-Bucy filters' dynamics, and show that sufficiently strong coupling gains guarantee arbitrarily precise recovery of optimality and the estimation error converges to zero when there is no noise. Numerical simulations show the performance of the proposed scheme. |
Jihan Kim / Gyunghoon Park / Hyungbo Shim / Yongsoon Eun Zero-stealthy Attack for Sampled-data Control Systems: the Case of Faster Actuation than Sensing Proceedings Article In: Proc. of 2016 IEEE 55th Conference on Decision and Control, pp. 5956-5961, IEEE IEEE, Las Vegas, NV, USA, 2016. Abstract | Links | BibTeX | Tags: Continuous-time system @inproceedings{KimParkShimEun16, In this paper, we introduce a new vulnerability of cyber-physical systems to malicious attack. It arises when the physical system, that is modeled as a continuous-time LTI system, is controlled by a digital controller, i.e., the output is measured only at discrete sensing times. Since the anomaly detector monitors the output signal, nothing abnormal can be detected through the output if the output looks normal at sensing times. This implies that if an (actuator) attack drives the internal states passing through the kernel of the output matrix at each sensing time, then the attack compromises the system while it remains stealthy. We show that this type of attack is feasible when the control system uses multi-rate sampling, and the sampling rate for input signal is higher than that for output measurements. Simulation results for the X-38 vehicle illustrate this new attack strategy possibly brings disastrous consequences. |
Gyunghoon Park / Hyungbo Shim / Chanhwa Lee / Yongsoon Eun / Karl H. Johansson When Adversary Encounters Uncertain Cyber-physical Systems: Robust Zero-dynamics Attack with Disclosure Resources Proceedings Article In: Proc. of 2016 IEEE 55th Conference on Decision and Control, pp. 5085-5090, IEEE, Las Vegas, NV, USA, 2016. Abstract | Links | BibTeX | Tags: Cyber-physical system, Uncertain systems @inproceedings{ParkShimLeeEunJohansson16, In this paper we address the problem of designing a robust stealthy attack for adversaries to compromise an uncertain cyber-physical system without being detected. We first re-interpret the zero-dynamics attack based on the normal form representation. Then, a new alternative zero dynamics attack is presented for uncertain systems. This alternative employs a disturbance observer and does not require exact system knowledge in order to remain stealthy. The proposed robust zero-dynamics attack needs a nominal model of the system and, in addition, utilizes the input and output signals of the system. The proposed attack illustrates how the adversary is able to use disclosure resources instead of exact model knowledge. A simulation result with a hydro-turbine power system is presented to verify the attack performance. |
Jisu Kim / Hyungbo Shim / Jin Heon Seo Tracking Control for Hybrid Systems with State Jumps using Gluing Function Proceedings Article In: Proc. of 2016 IEEE 55th Conference on Decision and Control, pp. 3006-3011, IEEE, Las Vegas, NV, USA, 2016. Abstract | Links | BibTeX | Tags: Continuous-time system @inproceedings{KimShimSeo16, In this paper, we propose a novel controller design technique to track a reference trajectory for a class of hybrid systems having state-triggered jumps. The idea is, by gluing start and end points of jumps in the state space, to change the domain into another domain where the state jumps disappear. After gluing, the hybrid systems can be considered as continuous or piecewise continuous dynamical systems without any state jumps. Therefore, it would be possible to construct tracking controllers for the hybrid systems through conventional design methods. The proposed technique guarantees that the state converges to the reference except the region where jumps occur or arrive at. Simulation results for various examples illustrate the effectiveness of the proposed approach. |
Junsoo Kim / Chanhwa Lee / Hyungbo Shim / Yongsoon Eun / Jin Heon Seo Detection of Sensor Attack and Resilient State Estimation for Uniformly Observable Nonlinear Systems Proceedings Article In: Proc. of 2016 IEEE 55th Conference on Decision and Control, pp. 1297-1302, IEEE, Las Vegas, NV, USA, 2016. Abstract | Links | BibTeX | Tags: Control system synthesis @inproceedings{KimLeeShimEunSeo16, This paper presents an attack-resilient estimation scheme for uniformly observable nonlinear systems having redundant sensors when a subset of sensors is corrupted by adversaries. We first design an individual high-gain observer from each measurement output so that partial information of system state is obtained. Then, a nonlinear error correcting problem is formulated by collecting all the information from each partial observers and it can be solved by exploiting redundancy. For most of the time, a computationally efficient monitoring system is running and it detects every influential attacks. A simple switching logic explores another combination of output measurement to find a correct candidate only when a residual signal exceeds its threshold. |
Juhoon Back / Hyungbo Shim Discussion on: An Adaptive Gradient Law with Projection for Non-Smooth Convex Boundaries Journal Article In: European Journal of Control, vol. 12, no. 6, pp. 620-621, 2016, ISSN: 0947-3580. Abstract | Links | BibTeX | Tags: smoothness @article{BackShim06, The paper by K. Kuhnen and P. Krejci extends the parameter projection method, which requires smoothness of the boundary function u(x) associated to a given convex set, to the case of arbitrary convex domains. The basic idea is to transform the discontinuous projected differential equation into an operator-differential equation whose |
Osama Hassanein / Sreenatha G. Anavatti / Hyungbo Shim / Tapabrata Ray Model-based Adaptive Control System for Autonomous Underwater Vehicles Journal Article In: Ocean Engineering, vol. 127, no. 2016, pp. 58-69, 2016. Abstract | Links | BibTeX | Tags: @article{HassaneinAnavattiShimRay16, The paper deals with the development of indirect adaptive controllers based on Hybrid Neuro-Fuzzy Network (HNFN) approach for Autonomous Underwater Vehicles (AUVs). The non-linear, coupled and time-varying dynamics of AUVs necessitates the development of adaptive controllers. The on-line identification and adaptation of the controller is carried out using the HNFN approach. The methodology uses the input-output data to come up with a structure for the controller and optimal adaptation of the parameters to achieve the required accuracy. The Semi-Serial-Parallel-Model is employed both for identification and control. Initial validation of the identification results are carried out numerically using a mathematical model. Hardware-in-loop (HIL) simulations are presented to validate the controller before carrying out the experiments. Experimental results show that the proposed controller is capable of suitably controlling the AUV in real environment and demonstrate its robust characteristics. |
Caixia Li / Sreenatha G. Anavatti / Tapabrata Ray / Hyungbo Shim A Game-Theoretic Approach to the Analysis of Traffic Assignment Proceedings Article In: Proc. of The 20st Asia Pacific Symposium on Intelligent and Evolutionary Systems, pp. 17-30, Springer, Cham, Canberra, Australia, 2016. Abstract | Links | BibTeX | Tags: Traffic management @inproceedings{LiAnavattiRayShim16, In order to improve the cooperation between traffic management and travellers, traffic assignment is the key component. In terms of the traffic assignment, it can be classified into two models based on the behavior assumption governing route choices: the User Equilibrium (UE) and System Optimum (SO) traffic assignment. By the definition of UE and SO traffic assignment, traffic users usually competitively choose the least cost routes to minimize their own travel cost, while system optimum traffic assignment requires traffic users work cooperatively to minimize overall cost in road network. Thus, the paradox of benefits between UE and SO makes both of them are not practical. Thus, a solution technique needs to be proposed to balance between UE and SO models, which can compromise both sides and give more feasible traffic assignments. In this paper, Stackelberg game theory is introduced to the traffic assignment, which can achieve the trade-off process between traffic management and travellers. Since the traditional traffic assignments have low convergence rates, the gradient projection algorithm is proposed to improve the efficiency of the traffic assignment. |
List of English Publication
2020 |
Neutralizing zero dynamics attack on sampled-data systems via generalized holds Journal Article In: Automatica, vol. 113, pp. 108778, 2020, ISSN: 0005-1098. |
Disturbance Observers Book Chapter In: John Baillieul; Tariq Samad (Ed.): Encyclopedia of Systems and Control, pp. 1-8, Springer London, London, 2020, ISBN: 978-1-4471-5102-9. |
A distributed algorithm that finds almost best possible estimate under non-vanishing and time-varying measurement noise Journal Article In: IEEE Control Systems Letters, vol. 4, no. 1, pp. 229-234, 2020, ISSN: 2475-1456. |
2019 |
Encrypted State Estimation in Networked Control Systems Proceedings Article In: Proc. of 2019 IEEE 58th Conference on Decision and Control, pp. 7190-7195, IEEE, Nice, France, 2019. |
Study on Realizable Generalized Hold Functions As a Countermeasure against Zero Dynamics Attack Proceedings Article In: Proc. of 2019 IEEE 58th Conference on Decision and Control, pp. 5362-5367, IEEE, Nice, France, 2019. |
On Improving the Robustness of Reinforcement Learning-Based Controllers Using Disturbance Observer Proceedings Article In: Proc. of 2019 IEEE 58th Conference on Decision and Control, pp. 8487-852, IEEE, Nice, France, 2019. |
Comprehensive Introduction to Fully Homomorphic Encryption for Dynamic Feedback Controller via LWE-Based Cryptosystem Book Chapter In: Privacy in Dynamical Systems, Chapter 10, pp. 209-230, Springer, 2019, ISBN: 978-981-15-0492-1. |
Masking attack for sampled-data systems via input redundancy Journal Article In: IET Control Theory & Applications , vol. 13, no. 14, pp. 2300-2308, 2019, ISSN: 1751-8644. |
A Countermeasure against Zero-dynamics Sensor Attack via Generalized Hold Feedback Proceedings Article In: Proc. of the SICE Annual Conference 2019, pp. 663-668, SICE, Hiroshima, Japan, 2019. |
Behavior of a network of heterogeneous Li´enard systems under strong output coupling Proceedings Article In: Proc. of 8th IFAC Symposium on Mechatronic Systems & 11th IFAC Symposium on Nonlinear Control Systems, pp. 256-261, IFAC, Vienna, Austria, 2019. |
Stealthy adversaries against uncertain cyber-physical systems: Threat of robust zero-dynamics attack Journal Article In: IEEE Transactions on Automatic Control , vol. 64, iss. 12, pp. 4907 - 4919, 2019, ISSN: 0018-9286. |
Asymptotic stabilization of a class of nonlinear systems with long input delay in the presence of disturbance Journal Article In: ISA Transactions, vol. 91, pp. 125-134, 2019, ISSN: 0019-0578. |
State Estimation and Tracking Control for Hybrid Systems by Gluing the Domains Journal Article In: IEEE Transactions on Automatic Control, 2019. |
Distributed Algorithm for Economic Dispatch Problem With Separable Losses Journal Article In: IEEE Control Systems Letters, vol. 3, no. 3, pp. 685-690, 2019. |
Output Feedback based Event-Triggered Sliding Mode Control for Delta Operator Systems Journal Article In: Automatica, vol. 103, 2019. |
Initialization-free Privacy-guaranteed Distributed Algorithm for Economic Dispatch Problem Journal Article In: Automatica, vol. 102, pp. 86-93, 2019. |
On Redundant Observability: From Security Index to Attack Detection and Resilient State Estimation Journal Article In: IEEE Transactions on Automatic Control, vol. 64, no. 2, pp. 775-782, 2019. |
Detection of Sensor Attack and Resilient State Estimation for Uniformly Observable Nonlinear Systems having Redundant Sensors Journal Article In: IEEE Transactions on Automatic Control, vol. 64, no. 3, pp. 1162-1169, 2019, ISBN: 0018-9286. |
2018 |
Adaptable iISS Small-Gain Formulation and Its Application to Observer-Based Output Feedback Design Proceedings Article In: Proc. of 2018 IEEE 57th Conference on Decision and Control, pp. 5616-5621, IEEE, Miami, USA, 2018. |
Distributed Algorithm for the Network Size Estimation: Blended Dynamics Approach Proceedings Article In: Proc. of 2018 IEEE 57th Conference on Decision and Control, pp. 4577-4582, IEEE, Miami, USA, 2018. |
Local Identification of Sensor Attack and Distributed Resilient State Estimation for Linear System Proceedings Article In: Proc. of 2018 IEEE 57th Conference on Decision and Control, pp. 2056-2061, IEEE, Miami, USA, 2018. |
Heterogeneous Van der Pol Oscillators under Strong Coupling Proceedings Article In: Proc. of 2018 IEEE 57th Conference on Decision and Control, pp. 3666-3673, IEEE, Miami, USA, 2018. |
Need for Controllers having Integer Coefficients in Homomorphically Encrypted Dynamic Syste Proceedings Article In: Proc. of 2018 IEEE 57th Conference on Decision and Control, pp. 5020-5025, IEEE, Miami, USA, 2018. |
A Modularized Design for Output Synchronization of LTI Dynamical Networks with Communication Delays Journal Article In: SICE Journal of Control, Measurement, and System Integration, vol. 11, no. 6, 2018. |
A Parallel Feedforward Compensator Approach to Output Synchronization for a Network with Non-passive Dynamics and Communication Delays Proceedings Article In: Proc. of the SICE Annual Conference 2018, SICE SICE, Nara, Japan, 2018. |
DO-DAT: A MATLAB Toolbox for Design & Analysis of Disturbance Observer Proceedings Article In: Proc. of 9th IFAC Symposium on Robust Control Design & 2nd IFAC Workshop on Linear Parameter Varying Systems, IFAC Brasil, 2018. |
A Posteriori Detection of Moment of Attack on Cyber-physical Systems: A Back-and-forth Observer Approach Proceedings Article In: Proc. of 7th IFAC Workshop on Distributed Estimation and Control in Networked System, pp. 188-193, IFAC IFAC, Netherlands, 2018. |
Practical Synchronization of Heterogeneous Multi-agent System Using Adaptive Law for Coupling Gains Proceedings Article In: Proc. of 2018 Annual American Control Conference (ACC), IEEE, Milwaukee, WI, USA, 2018. |
Robust Control of an Equipment-added Multirotor Using Disturbance Observer Journal Article In: IEEE Transactions on Control Systems Technology, vol. 26, no. 4, pp. 1524-1531, 2018. |
Guaranteeing Almost Fault-free Tracking Performance from Transient to Steady-state: a Disturbance Observer Approach Journal Article In: Science China Information Sciences, vol. 61, no. 7, 2018. |
On Stealthiness of Zero-dynamics Attacks against Uncertain Nonlinear Systems: A Case Study with Quadruple-tank Process Proceedings Article In: Proc. of 23rd International Symposium on Mathematical Theory of Networks and Systems, pp. 10-17, Hong Kong, 2018. |
Toward a Secure Drone System: Flying with Real-time Homomorphic Authenticated Encryption Journal Article In: IEEE Access, vol. 6, pp. 24325-24339, 2018. |
Recovering Nominal Tracking Performance in an Asymptotic Sense for Uncertain Linear Systems Journal Article In: SIAM Journal on Control and Optimization, vol. 56, no. 2, pp. 700-722, 2018. |
Adaptive Regulation to Nominal Response for Uncertain Mechanical Systems and Its Application to Optical Disk Drive Journal Article In: IEEE Transactions on Industrial Electronics, vol. 65, no. 2, pp. 1450-1458, 2018. |
2017 |
Enhancement of Security against Zero Dynamics Attack via Generalized Hold Proceedings Article In: Proc. of IEEE Conf. on Decision and Control, pp. 1350-1355, Melbourne, Australia, 2017. |
Synchronized Behavior of Heterogeneous Multi-agent Systems Under Funnel Coupling Proceedings Article In: Proc. of SWARM 2017: The 2nd International Symposium on Swarm Behavior and Bio-Inspired Robotics, pp. 266-269, Kyoto, Japan, 2017. |
Consensus of linear time-invariant multi-agent system over multilayer network Proceedings Article In: Proc. of 17th International Conference on Control, Automation and Systems (ICCAS) , IEEE, Jeju, South Korea, 2017. |
Consensus-based Distributed Coordination for Optimal Energy Generation of Hierarchical Systems Proceedings Article In: Proc. of 56th Annual Conference of the Society of Instrument and Control Engineers (SICE), pp. 871-876, Kanazawa, Japan, 2017. |
Singular Perturbation for Sampled-Data Systems With Fast Subsystems Proceedings Article In: Proc. of the 20th World Congress, pp. 8475-8480, IFAC Toulouse, France, 2017. |
Noise Reduction Disturbance Observer for Disturbance Attenuation and Noise Suppression Journal Article In: IEEE Transactions on Industrial Electronics , vol. 64, no. 2, pp. 1381 - 1391, 2017. |
Robust Estimation Algorithm for Both Switching Signal and State of Switched Linear Systems Journal Article In: International Journal of Control, Automation and Systems, vol. 15, no. 1, pp. 95-103, 2017. |
2016 |
Distributed Luenberger Observer Design Proceedings Article In: Proc. of 2016 IEEE 55th Conference on Decision and Control, pp. 6928-6933, IEEE, Las Vegas, NV, USA, 2016. |
On Distributed Optimal Kalman-Bucy Filtering by Averaging Dynamics of Heterogeneous Agents Proceedings Article In: Proc. of 2016 IEEE 55th Conference on Decision and Control, pp. 6309-6314, IEEE, Las Vegas, NV, USA, 2016. |
Zero-stealthy Attack for Sampled-data Control Systems: the Case of Faster Actuation than Sensing Proceedings Article In: Proc. of 2016 IEEE 55th Conference on Decision and Control, pp. 5956-5961, IEEE IEEE, Las Vegas, NV, USA, 2016. |
When Adversary Encounters Uncertain Cyber-physical Systems: Robust Zero-dynamics Attack with Disclosure Resources Proceedings Article In: Proc. of 2016 IEEE 55th Conference on Decision and Control, pp. 5085-5090, IEEE, Las Vegas, NV, USA, 2016. |
Tracking Control for Hybrid Systems with State Jumps using Gluing Function Proceedings Article In: Proc. of 2016 IEEE 55th Conference on Decision and Control, pp. 3006-3011, IEEE, Las Vegas, NV, USA, 2016. |
Detection of Sensor Attack and Resilient State Estimation for Uniformly Observable Nonlinear Systems Proceedings Article In: Proc. of 2016 IEEE 55th Conference on Decision and Control, pp. 1297-1302, IEEE, Las Vegas, NV, USA, 2016. |
Discussion on: An Adaptive Gradient Law with Projection for Non-Smooth Convex Boundaries Journal Article In: European Journal of Control, vol. 12, no. 6, pp. 620-621, 2016, ISSN: 0947-3580. |
Model-based Adaptive Control System for Autonomous Underwater Vehicles Journal Article In: Ocean Engineering, vol. 127, no. 2016, pp. 58-69, 2016. |
A Game-Theoretic Approach to the Analysis of Traffic Assignment Proceedings Article In: Proc. of The 20st Asia Pacific Symposium on Intelligent and Evolutionary Systems, pp. 17-30, Springer, Cham, Canberra, Australia, 2016. |