2016 |
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. |
Hyuntae Kim / Gyunghoon Park / Hyungbo Shim / Nam Hoon Jo Arbitrarily Large Gain/phase Margin can be Achieved by DOB-based Controller Proceedings Article In: Proc. of 2016 16th International Conference on Control, Automation and Systems, pp. 447-450, IEEE, Gyeongju, South Korea, 2016. Abstract | Links | BibTeX | Tags: Control system synthesis, Uncertain systems @inproceedings{KimParkShimJo16, In this paper, we prove that the DOB-based feedback controller can guarantee arbitrarily large but bounded gain margin and phase margin. This fact reminds that the DOB-based controller plays the role of robust controller even in the classical sense. We present a design procedure that ensures desired gain/phase margin even for the plants that have parametric uncertainty. |
Hyeonjun Yun / Gyunghoon Park / Hyungbo Shim / H. J. Chang State-Space Analysis of Discrete-Time Disturbance Observer for Sampled-Data Control Systems Proceedings Article In: Proc. of The 2016 American Control Conference, pp. 4233-4238, IEEE, Boston, MA, USA, 2016. Abstract | Links | BibTeX | Tags: Discrete-time system, Uncertain systems @inproceedings{YunParkShimChang16, We present a state-space analysis of discrete-time disturbance observer (DOB) for a class of sampled-data control systems. Unlike the continuous-time case, it is well-known that sampling process may yield non-minimum phase zeros (called sampling zeros). Motivated by the truncated Taylor series (TTS) model which well describes the behavior of sampling zeros in the state-space, we present a condition for robust stability of the uncertain sampled-data control system with the discrete-time DOB. In particular, using the discrete-time singular perturbation theory, we show that the uncertain plant with disturbance behaves like a disturbance-free nominal model with the help of the discrete-time DOB. |
2014 |
Youngjun Joo / Gyunghoon Park Reduced Order Type-k Disturbance Observer Based on a Generalized Q-filter Design Scheme Proceedings Article In: Proc. of 2014 14th International Conference on Control, Automation and Systems (ICCAS), pp. 1211-1216, IEEE, Seoul, South Korea, 2014. Abstract | Links | BibTeX | Tags: Uncertain systems @inproceedings{JooPark14, As a robust control scheme, a disturbance observer (DOB) has been widely employed in industrial applications to reject the effect of disturbances and plant uncertainties. The disturbance rejection performance of DOB is mainly determined by the design of two Q-filters, which are the core components of DOB structure. Despite the different roles of each Q-filter, they have been typically designed to have the same structure. In this paper, we generalize Q-filters' structures based on the observation about each Q-filter's objective and derive a robust stability condition for the proposed DOB based control system. In addition, following the generalized Q-filter design scheme, a reduced order type-k DOB is proposed to enhance the disturbance rejection performance and reduce the order of type-k DOB compared with the conventional one. Finally, a constructive Q-filter design procedure for guaranteeing robust stability of the closed-loop system is proposed under parametric uncertainties of plant which belong to an arbitrarily large compact set. |
2012 |
Nam Hoon Jo / Youngjun Joo / Hyungbo Shim / Young Ik Son A Note on Disturbance Observer with Unknown Relative Degree of the Plant Proceedings Article In: Proc. of 2012 IEEE 51st Annual Conference on Decision and Control (CDC), pp. 943-948, IEEE, Maui, HI, USA, 2012. Abstract | Links | BibTeX | Tags: Filtering theory, Uncertain systems @inproceedings{JoJooShimSon12, The disturbance observer (DOB)-based controller has been widely applied to real applications since it is able to recover, in spite of plant uncertainties and input disturbances, the performance of the nominal system. In this paper, we study robust stability of the DOB control system when the relative degree of the plant P is greater than or equal to that of nominal model Pn. Based on the standing assumption that the bandwidth of the Q-filter is sufficiently large, our study reveals the following: (1) If the relative degree difference is equal to one, then robust stabilization can be achieved by careful selection of the Q-filter and Pn. (2) If the relative degree difference is greater than one, then robust stabilization is not possible no matter how Q-filter and Pn are chosen. |
List of English Publication
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. |
Arbitrarily Large Gain/phase Margin can be Achieved by DOB-based Controller Proceedings Article In: Proc. of 2016 16th International Conference on Control, Automation and Systems, pp. 447-450, IEEE, Gyeongju, South Korea, 2016. |
State-Space Analysis of Discrete-Time Disturbance Observer for Sampled-Data Control Systems Proceedings Article In: Proc. of The 2016 American Control Conference, pp. 4233-4238, IEEE, Boston, MA, USA, 2016. |
2014 |
Reduced Order Type-k Disturbance Observer Based on a Generalized Q-filter Design Scheme Proceedings Article In: Proc. of 2014 14th International Conference on Control, Automation and Systems (ICCAS), pp. 1211-1216, IEEE, Seoul, South Korea, 2014. |
2012 |
A Note on Disturbance Observer with Unknown Relative Degree of the Plant Proceedings Article In: Proc. of 2012 IEEE 51st Annual Conference on Decision and Control (CDC), pp. 943-948, IEEE, Maui, HI, USA, 2012. |