Kojiro Hagino

Robust control with adaptation mechanism for improving transient behaviour

This paper deals with the problem of designing a robust controller with adaptation mechanisms for the purpose of improving transient performance in time-response. The controlled object is a linear system with unknown parameters which vary within certain prescribed bounds. In the proposed method, a target model with adjustable parameters is constructed in order to obtain on-line information on parameter uncertainty and to improve transient time-response. A robust controller is established in a parameter-dependent form, in which parameters are adjusted on-line on the boundary surface of the possible parameter space according to the error between the state trajectory of the plant and that of the target model.

Trajectory-based design of robust non-fragile controllers for a class of uncertain linear continuous-time systems

This paper deals with a design problem of robust non-fragile stabilizing controllers for a class of uncertain linear continuous-time systems. The proposed design approach of robust non-fragile controllers is based on computation of the trajectory for the uncertain linear system and differs from the existing methods based on quadratic stabilization via Lyapunov criterion. In this paper, we show that sufficient conditions for asymptotical stability of the linear system with uncertainties and controller gain variations, and a LMI-based design algorithm of a robust non-fragile controller. Furthermore, we extend the result to the design problem of decentralized robust non-fragile controllers for a class of uncertain large-scale interconnected systems. Finally, the effectiveness of the proposed design scheme of robust non-fragile controllers is shown through illustrative examples.

A stability guaranteed active fault-tolerant control system against actuator failures

A strategy is proposed for fault-tolerant control system (FTCS) design using multiple controllers. The design of such multiple controllers is shown to be unique in the sense that the resulting control system does neither have the problem of conservativeness of conventional passive fault-tolerant control (FTC) nor the risk of instability associated with active FTCS in case of an incorrect fault detection and isolation (FDI) decision. In other words, the stability of the closed-loop system is always ensured regardless the FDI decisions. The correct FDI decision will further lead to optimal performance of the system. The paper presents an interesting way to deal with the conflicting requirements among stability, redundancy, and graceful degradation in performance for fault-tolerant control systems. Detailed design procedure has been presented with consideration of possible parameter uncertainties.

Observer-based guaranteed cost control scheme for polytopic uncertain systems with state delays

This paper deals with a design problem of an observer-based guaranteed cost controller for polytopic uncertain systems with state delays. In this approach, firstly a full order observer is designed and next a feedback controller ensuring an upper bound on a given quadratic cost function is derived. In this paper, we show that sufficient conditions for the existence of the observer-based guaranteed cost controller are given in terms of linear matrix inequalities (LMIs). Additionally, we deal with a design problem of a suboptimal observer-based guaranteed cost controller. Finally, a numerical example is included.

Observer-Based Robust Tracking Control with Preview Action for Uncertain Discrete-Time Systems

This paper deals with a design problem of an observer-based robust preview control system for uncertain discrete-time systems. In this approach, we adopt 2-stage design scheme and we derive an observer-based robust controller with integral and preview actions such that a disturbance attenuation level is satisfactorily small for allowable uncertainties.

Robust non-fragile controllers for uncertain linear continuous-time systems

This paper deals with a design problem of robust non-fragile controllers for linear continuous-time systems with uncertainties which are included in both the system matrix and the input one. In this paper, we deal with two classes of control gain perturbations and show that sufficient conditions for the existence of the robust non-fragile controller are given in terms of linear matrix inequalities (LMIs). Finally, illustrative examples are presented.

Adaptive Robust Stabilizing Controllers for a Class of Uncertain Switched Linear Systems

This paper discusses a design problem of an adaptive robust stabilizing controller for a class of uncertain switched linear systems. The uncertainties under consideration are supposed to satisfy the matching condition, and switchings among subsystems are determined by using the nominal system. The proposed adaptive robust stabilizing controller consists of the switching rule, the state feedback law with constant gain matrix and the state feedback law with the variable gain matrix tuned by adjustable parameters. In this paper, we show that the switching rule, the feedback gain matrices and the adjustment law of the adjustable parameter

Synthesis of adaptive robust output feedback controllers for a class of uncertain linear systems

This paper discusses a design problem of an adaptive robust output feedback controller for a class of uncertain linear systems. The uncertainties under consideration satisfy the matching condition and are bounded, but their upper bounds are unknown. The proposed adaptive robust output feedback controller consists of a fixed gain controller, an adjustable parameter and a variable gain controller. In this paper, we present a design method of an adaptive robust output feedback control system. Finally, illustrative examples are presented to show the efficiency of the proposed adaptive robust controller.

Observer-based robust control giving consideration to transient behaviour for linear systems with

In this paper, we present an observer-based controller design method which achieves performance robustness together with robust stability for linear multivariable systems with structured uncertainties. The performance robustness means that the deterioration of control performance is suppressed when we compare the transient behaviour for the uncertain system with a desired one generated by using the nominal system directly and at the same time excessive control input is avoided. In this approach, we adopt a similar way to the model-following technique and assume that the control law consists of a state feedback law for the nominal system and a compensation input for the purpose of preventing the error between the transient behaviour for the uncertain system and the desired one. The compensation input is additional modification term given by feedback form of an estimated error signal and is determined so that an upper bound of a quadratic cost function for the error system between the real trajectory for the plant and the desired one is minimized. We show that a condition for the existence of the compensation input which minimizes an upper bound of the quadratic cost function for the error system is given in terms of linear matrix inequalities (LMIs). Finally, numerical examples are presented.

Synthesis of variable gain robust output feedback controllers for a class of uncertain Lipschitz nonlinear systems

This paper proposes a variable gain robust output feedback controller for a class of uncertain Lipschitz nonlinear systems. The variable gain robust output feedback controller is designed so as to reduce the effect of uncertainties and Lipschitz nonlinearities. In this paper, we show sufficient conditions for the existence of the proposed variable gain robust output feedback controller for uncertain Lipschitz nonlinear systems. Finally, numerical examples are presented.