2018 |
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. |
2016 |
Youngjun Joo / Gyunghoon Park / Juhoon Back / Hyungbo Shim Embedding Internal Model in Disturbance Observer with Robust Stability Journal Article In: IEEE Transactions on Automatic Control, vol. 61, no. 10, pp. 3128-3133, 2016. Abstract | Links | BibTeX | Tags: Control system synthesis, Observer, Robustness @article{JooParkBackShim16, Abstract: The disturbance observer has been widely employed in applications due to its powerful ability for disturbance rejection and robustness under plant uncertainties. However, it rejects the disturbance approximately rather than exactly since it is usually designed without considering structural properties of disturbance. In order to improve the disturbance rejection performance, we propose a design method to embed the internal model of disturbance into the disturbance observer structure. Furthermore, a systematic design procedure is proposed so that one can always design the disturbance observer to guarantee robust stability of the closed-loop system even though uncertain parameters of the plant belong to an arbitrarily large (but bounded) set. |
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. |
2014 |
Jung-Su Kim / Juhoon Back / Gyunghoon Park Design of Q-filters for Disturbance Observers via BMI Approach Journal Article In: Proc. of 2014 14th International Conference on Control, Automation and Systems (ICCAS), pp. 1197-1200, 2014. Abstract | Links | BibTeX | Tags: Robustness @article{KimBackPark14, The type-k disturbance observer, also known as high order disturbance observer, is a robust output feedback controller which can reject polynomial-in-time disturbances exactly and at the same time unmodeled disturbances approximately. To ensure the robust stability of the closed-loop system, the key component of the controller called Q-filter should be designed appropriately. In this paper, we formulate the design problem in terms of a set of bilinear matrix inequalities so that the coefficients of Q-filters are chosen simultaneously. The solution from the proposed method can be less conservative compared to the recursive design procedure developed recently. |
2010 |
Jae Sung Bang / Hyungbo Shim / Sang Kyun Park / Jin H. Seo Robust Tracking and Vibration Suppression for a Two-Inertia System by Combining Backstepping Approach With Disturbance Observer Journal Article In: IEEE Transactions on Industrial Electronics, vol. 57, no. 9, pp. 3197-3206, 2010, ISSN: 0278-0046. Abstract | Links | BibTeX | Tags: Robustness @article{BangShimParkSeo10, In this paper, we consider the problem of designing a robust controller for a two-inertia system which contains arbitrarily large (but bounded) model uncertainties and disturbances. The research is motivated by the fact that a two-inertia system represents most of an industrial robot arm system that has a flexible joint, for which vibration suppression and robust control against model uncertainties and external disturbances are very important. The proposed controller consists of two parts: the outer-loop controller designed by the backstepping approach and the inner-loop controller by the new partial disturbance observer (DOB). The DOB is responsible for compensating the input-matched uncertainties and disturbances, while the backstepping controller is designed for dealing with the rest. The proposed controller makes tracking error and vibration of the system suppressed within an arbitrarily small bound during operation time when full states are measured. The results are verified by simulations and experiments with a Luenberger observer. |
List of English Publication
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. |
2016 |
Embedding Internal Model in Disturbance Observer with Robust Stability Journal Article In: IEEE Transactions on Automatic Control, vol. 61, no. 10, pp. 3128-3133, 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. |
2014 |
Design of Q-filters for Disturbance Observers via BMI Approach Journal Article In: Proc. of 2014 14th International Conference on Control, Automation and Systems (ICCAS), pp. 1197-1200, 2014. |
2010 |
Robust Tracking and Vibration Suppression for a Two-Inertia System by Combining Backstepping Approach With Disturbance Observer Journal Article In: IEEE Transactions on Industrial Electronics, vol. 57, no. 9, pp. 3197-3206, 2010, ISSN: 0278-0046. |