2016 |
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. |
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. |
Gyunghoon Park / Hyungbo Shim / Kyungchul Kong Can Continuous-time Disturbance be Represented by Sampled Input Disturbance? Proceedings Article In: Proc. of 2016 16th International Conference on Control, Automation and Systems, pp. 1261-1266, IEEE, Gyeongju, Korea, 2016. Abstract | Links | BibTeX | Tags: Continuous-time system, Sampled data system, Stability @inproceedings{ParkShimKong16, Abstract: In this paper, we study whether any continuous-time disturbance to a continuous-time plant can be equivalently represented by a sampled input disturbance to a sampled-data model. With the help of the sampled-data system theory, we show that such equivalent sampled disturbance exists for almost sampling period and even for mismatched continous-time disturbances. Moreover, it is also discussed that whether the equivalent sampled disturbance is bounded significantly depends on the zeros of the sampled-data system. Simulation results verify the validity of the stability analysis. |
2015 |
Gyunghoon Park / Youngjun Joo / Chanhwa Lee / Hyungbo Shim On Robust Stability of Disturbance Observer for Sampled-data Systems under Fast Sampling: An Almost Necessary and Sufficient Condition Proceedings Article In: Proc. of 2015 IEEE 54th Conference on Decision and Control, pp. 7536-7541, IEEE, Osaka, Japan, 2015. Abstract | Links | BibTeX | Tags: Continuous-time system, Robustness @inproceedings{ParkJooLeeShim15, Despite increased interest on discrete-time disturbance observer (DOB) in both theory and application, study of robust stabilization via the DOB does not seem to be mature. This is because most of the existing studies on robust stability are based on the small-gain theorem, so that the results are just sufficient conditions and the amount of uncertainty that the DOB-based control system can tolerate is conservative. In this paper, motivated by a recent work on the continuous-time case, we present an almost necessary and sufficient condition for robust stability of the sampled-data system controlled by a discrete-time DOB under fast sampling. In particular, our study clarifies the phenomenon that the sampling process can hamper stability of the DOB-controlled systems by generating additional (and possibly nonminimum-phase) zeros, and explains why the blind discretization of the continuous-time DOB controller using fast sampling may fail. For the robust stabilization against both these extra zeros and plant uncertainty, we also propose a new design methodology for the nominal model and the Q-filter. It turns out that arbitrarily large uncertainty can be compensated by appropriately designing the Q-filters and by fast sampling. A benchmark problem is revisited to illustrate the validity of the proposed analysis and design method. |
Chanhwa Lee / Hyungbo Shim / Yongsoon Eun Secure and Robust State Estimation under Sensor Attacks, Measurement Noises, and Process Disturbances: Observer-Based Combinatorial Approach Proceedings Article In: Proc. of 2015 European Control Conference (ECC), pp. 1866-1871, IEEE, Linz, Austria, 2015. Abstract | Links | BibTeX | Tags: Continuous-time system, Security @inproceedings{LeeShimEun15, This paper presents a secure and robust state estimation scheme for continuous-time linear dynamical systems. The method is secure in that it correctly estimates the states under sensor attacks by exploiting sensing redundancy, and it is robust in that it guarantees a bounded estimation error despite measurement noises and process disturbances. In this method, an individual Luenberger observer (of possibly smaller size) is designed from each sensor. Then, the state estimates from each of the observers are combined through a scheme motivated by error correction techniques, which results in estimation resiliency against sensor attacks under a mild condition on the system observability. Moreover, in the state estimates combining stage, our method reduces the search space of a minimization problem to a finite set, which substantially reduces the required computational effort. |
2012 |
Chanhwa Lee / Youngjun Joo / Hyungbo Shim Analysis of Discrete-time Disturbance Observer and a New Q-filter Design Using Delay Function Proceedings Article In: Proc. of 2012 12th International Conference on Control, Automation and Systems (ICCAS), pp. 556-561, IEEE, JeJu Island, South Korea, 2012. Abstract | BibTeX | Tags: Continuous-time system, Stability @inproceedings{LeeJooShim12, 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. |
List of English Publication
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. |
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. |
Can Continuous-time Disturbance be Represented by Sampled Input Disturbance? Proceedings Article In: Proc. of 2016 16th International Conference on Control, Automation and Systems, pp. 1261-1266, IEEE, Gyeongju, Korea, 2016. |
2015 |
On Robust Stability of Disturbance Observer for Sampled-data Systems under Fast Sampling: An Almost Necessary and Sufficient Condition Proceedings Article In: Proc. of 2015 IEEE 54th Conference on Decision and Control, pp. 7536-7541, IEEE, Osaka, Japan, 2015. |
Secure and Robust State Estimation under Sensor Attacks, Measurement Noises, and Process Disturbances: Observer-Based Combinatorial Approach Proceedings Article In: Proc. of 2015 European Control Conference (ECC), pp. 1866-1871, IEEE, Linz, Austria, 2015. |
2012 |
Analysis of Discrete-time Disturbance Observer and a New Q-filter Design Using Delay Function Proceedings Article In: Proc. of 2012 12th International Conference on Control, Automation and Systems (ICCAS), pp. 556-561, IEEE, JeJu Island, South Korea, 2012. |