Yuichi Chida

Two-delay robust digital control and its applications-avoiding the problem on unstable limiting zeros

In the design of linear control systems, the existence of unstable zeros makes it difficult to construct many control systems. When the usual digital control scheme is used, unstable zeros appear in the discrete-time model due to the existence of limiting zeros even though the continuous-time plant is minimal phase. To avoid this unstable zero problem, two new digital control schemes, called two-delay output control and two-delay input control, are proposed. These control systems are proved to have no finite zeros. Asymptotic inverse systems, pole assignable unknown input observers, and output feedback controllers having the LTR (loop transfer recovery) property are developed using the two-delay output control. Zero assignable control systems and model matching control systems are developed using the two-delay input control. >

A New Method of Discretization of the Continuous-Time Controllers Based on the Matching of Frequency Response

In the present paper, a digital redesign problem that converts continuous-time controllers into digital controllers is considered. A new discretization method based on matching of the frequency response of a continuous-time control system is proposed. The frequency response is matched using the least squares method based on data of discrete frequency points. The matching problem is described using an LMI, and the stability condition of the closed-loop system and the redesigned controller are also described additional conditions of LMIs. An optimizing problem described by some LMI conditions is solved by an iterative procedure. Examples are presented that prove the superior performance of the proposed method

On-orbit system identification experiments on Engineering Test Satellite-VI

Abstract On-orbit system identification experiments were performed using the Engineering Test Satellite-VI (ETS-VI), launched in 1994. The purpose of the experiments is to check the validity of a mathematical model for ETS-VI which was previously obtained by ground experiments. Two kinds of system identification schemes are utilized. One is a traditional scheme based on polynomial black-box models such as the prediction error method, and the other is a subspace method based on state-space models. The purpose of this paper is to compare these system identification schemes using experimental data. It will be shown that the subspace method proves to be promising for the system identification of large space structures typified by ETS-VI.

Pitch angle control of wind turbine generator using less conservative robust control

In this paper, the pitch angle control design problem of wind turbine generator is considered. Dynamic characteristics of wind turbine system vary according to the wind speed and also the generator speed. But it is required to maintain the generator speed at the optimal one in spite of such variations. For this purpose, the pitch angle control of wind turbine which includes the robust stability performance is used. However, the conventional standard ℌ∞ control provides conservative performance, so the control performance is inferior to conventional controllers such as gain scheduling PI controls. In this paper, we show a result of a pitch angle control of wind turbine generator by using the less conservative robust control. Obtained control performances are verified based on the dynamic simulator “Bladed” and we confirmed that the obtained controller provides acceptable control performances by a fixed parameter controller. The performances are almost the same as the results by the gain scheduling PI control, and some performances of the ℌ∞ controllers are superior to the PI control.

Two-delay digital robust control-avoiding the problem of unstable zeros

In the design of linear control systems, the existence of unstable zeros makes it difficult to construct many control systems. When the usual digital control scheme is used, unstable zeros appear in the discrete-time model even though the continuous-time plant is minimal-phase. To avoid this unstable zero problem, the authors propose two digital control schemes called two-delay controls, in which the control input is changed twice in one sampling interval, and apply them to the design of robust controllers.<<ETX>>

FDI filter design using sliding mode observer and its application to an active control system

This paper describes a new method for detecting sensor faults using sliding mode observers. In general, required capabilities of FDI(Fault Detection and Isolation) filters are sensitivity of occurring faults and robustness against disturbances. A FDI filter that proposed in this paper can estimate faults even if disturbances exist. Moreover, we discretize continuous-time FDI filters into discrete-time FDI filters using difference equations and apply the FDI filter to a vibration experimental system. An example demonstrates the effectiveness of the proposed method in comparison with conventional methods.

EXTENDED H∞ CONTROL WITH POLE PLACEMENT CONSTRAINTS VIA LMI APPROACH AND ITS APPLICATION

Abstract As well known, extended H ∞ control accepts unstable weighting functions which are included in a generalized plant, so it has wider availability than standard H ∞ control. On the other hand, the root-clustering problem for H ∞ control has been considered by Chilali and Gahinet and the solution is derived. But it is not so easy to apply the solution to extended H ∞ control, because the formulation of the root-clustering controllers is discordant with that of extended H ∞ controllers. Therefore, we can not simply combine the root-clustering conditions with extended H ∞ control. In this paper, we propose a LMI based design method for this control problem by using modified formulation of controllers of the root-clustering problem derived by Chilali and Gahinet. These types of control problems appear in design problems of a vibration isolation controller which attenuates vibrations forced by narrow-band frequency disturbances. A controller for a simple vibration isolation experimental system is designed by the proposed method and performance of a designed controller is verified by experimental results.

Unknown Disturbance Estimator Design for Non-Minimum Phase Plants Using Parallel Feed-Forward Model

A novel design method of an unknown disturbance observer for non-minimum phase plants is proposed in the present paper. In order to improve the estimation performance, we introduce the approach as a virtual augmented plant by adding a parallel model to the non-minimum phase real plant. The parallel model is designed so that the virtual augmented model becomes the minimum phase. Thus, it is possible to design the unknown disturbance estimator for the minimum phase plant but for the non-minimum phase plant. As the result, it is possible to improve the estimation performances. In this case, it is important to clarify the relationship between the unknown disturbance estimation signal for the real plant and the virtual augmented plant. In the present paper, the unknown disturbance estimation signal of the real plant is re-constructed by using the disturbance estimation of the virtual plant. And the parallel model design method is also proposed. The effectiveness of the proposed method is verified by numerical simulations for several mechanical vibration systems. The results show that the proposed method can improve estimation performances in comparison with conventional methods.Copyright

Multivariate Control Design Considering Quantization Error and Input Time-Delay for Pneumatic Isolation Table

An active control in a pneumatic isolation table which is driven by on-off air valves is considered in the present paper. A control method for the table with quantized input action caused by the on-off valves has been proposed for rapid vibration suppression. The proposed method determines the control input by using the Lyapunov function for avoiding instability against the quantization of the control input. The method exhibits vibration attenuation performances that are superior to the conventional methods in some experiments. However, this method suppresses vibrations in only the vertical direction. Therefore, improvement of the vibration suppression performance is required in not only the vertical direction but also the roll and pitch directions. In the present paper, a conventional method is extended to a multivariate control system. The effects of the extended method are verified by numerical simulations and experiments.Copyright

Robust stability analysis method for vibration systems by using virtual perturbations

In this paper, a robust stability analysis problem for mechanical vibration systems is considered. As well known, mu-analysis is a useful tool in order to guarantee stability robustness, but obtained results by conventional procedures are sometimes conservative. It is caused by weakness of valuation tools of perturbations. For example, a specified weighting function whose gain covers all of the gains of unstructured perturbations requires tolerating wider perturbations than realistic ones. On the other hand, to guarantee stability robustness of active control system is extremely important and tight evaluation methods are required. In this paper, a new robust stability analysis method for mechanical vibration systems by using virtual parametric perturbations is proposed. The effectiveness of the proposed method is verified by a mechanical vibration system example and the proposed method can guarantee the stability robustness with reducing conservativeness in comparison with conventional methods