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Park, Gyunghoon,Kim, Hyungjong Institute of Electrical and Electronics Engineers 2018 IEEE transactions on industrial electronics Vol.65 No.2
<P>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.</P>
Can Continuous-time Disturbance be Represented by Sampled Input Disturbance?
Gyunghoon Park,Hyungbo Shim,Kyungchul Kong 제어로봇시스템학회 2016 제어로봇시스템학회 국제학술대회 논문집 Vol.2016 No.10
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 continoustime 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.
Recovering Nominal Tracking Performance in an Asymptotic Sense for Uncertain Linear Systems
Park, Gyunghoon,Shim, Hyungbo,Joo, Youngjun Society for Industrial and Applied Mathematics 2018 SIAM journal on control and optimization Vol.56 No.2
<P>In this paper, we consider the problem of recovering a (predefined) nominal output trajectory in the presenceof 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 anasymptotic sense from the perspective of the internal model principle: that is, as long as the disturbanceand reference signals are generated by an exogenous system, the actual output not only is kept close to thenominal 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.</P>
Gyunghoon Park,Hyungbo Shim 제어로봇시스템학회 2015 제어로봇시스템학회 국제학술대회 논문집 Vol.2015 No.10
As a robust controller to compensate both model uncertainty and external disturbances, the disturbance observer (DOB) has been widely employed in a number of industrial applications, typically implemented in a discretetime fashion for sampled-data systems. Substantial research effort has gone into the study on how to design the discretetime DOB over the past decades, yet there is still no unified approach to robust stability analysis for the various types of DOBs. In this paper, by representing these variations into a general structure, we present a generalized framework for stability analysis that is available in whichever way the discrete-time DOB is designed and regardless of how large the model uncertainty is. As a consequence of the generalization, an almost necessary and sufficient stability condition under fast sampling is presented. Motivated by this new stability condition, a systematic design guideline for the discrete-time DOB is proposed in order to guarantee the robust stabilization against arbitrarily large (but bounded) model uncertainty. The validity of the presented analysis and design procedure is verified by an illustrative example.
Arbitrarily large gain/phase margin can be achieved by DOB-based controller
Hyuntae Kim,Gyunghoon Park,Hyungbo Shim,Nam Hoon Jo 제어로봇시스템학회 2016 제어로봇시스템학회 국제학술대회 논문집 Vol.2016 No.10
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.