Noboru Sebe

A NEW DILATED LMI CHARACTERIZATION AND ITERATIVE CONTROL SYSTEM SYNTHESIS

Abstract This paper presents a new iterative design procedure for multiobjective and structurally constrained feedback control. The proposed design procedure is based on new dilated LMI characterizations for the system properties, such as H2, H∞ norms and D-stability. The key idea of the new dilated LMI characterizations is divisions of A and B matrices in descriptor representation of systems. This paper also proposed to linearize the products of controller parameter K and auxiliary variable G by assigning the auxiliary variables instead of the change of variables technique. This linearization technique is effective from the viewpoints of computational complexity and accuracy.

A design method for fault-tolerant control systems based on H/sub /spl infin// optimization

We are concerned with new partial integrity. Partial integrity is essentially the property that the system remains stable in the presence of arbitrary failures of the specified sensors or actuators; our partial integrity generalizes this usual partial integrity so that the maximum number of possible failures can be specified. We derive a sufficient condition for new partial integrity based on H/sub /spl infin// optimization, and develop a design method using bilinear matrix inequalities.

Reliable Stabilization based on a Multi-compensator Configuration

Abstract This paper proposes a new multi-compensator configuration for reliable stabilization problem. In the proposed configuration, each compensator observes the outputs of the other compensators. This configuration provides reliable stabilization against actuator failures. A sufficient condition for the stability with this configuration is given in this paper. The transfer function of the closed-loop system is given explicitly.

Probabilistic safety management of control laws against deviations from normal operating-range

This paper proposes a probabilistic safety management framework for control laws to reduce the frequency of events that a physical value in a control system deviates from its normal operating-range. This safety function is realized mainly by the safety ability to suppress the fluctuations of transient responses after a device failure in order to prevent the deviations from the normal operating-range on the basis of dependability function to maintain the stability and the control performance even if the system is not in the normal operation. The proposed safety function in control laws can supplement ordinary safety-related systems in risk reduction according to international safety standards such as IEC 61508. This is the first study based on the distinction between safety and dependability in fault-tolerant control.

A design of controllers for simultaneous H infinity control problem

This paper is concerned with the design of a controller that attains the H infinity performance specifications with multiple given plants simultaneously. A numerical design method is presented in this paper. The proposed method consists of two stages, the modelling of a nominal plant with uncertainties and the synthesis of the robust stabilizing controller. The proposed method orders these two stages one after the other. In the modelling stage, a new modelling procedure, which is based on a parametrization of all the plants, is proposed.

Diagonal dominance and integrity

The diagonal dominance is the property of matrices that the diagonal elements are relatively larger than the off-diagonal elements. It is an important property for multivariable feedback systems, especially with diagonal controllers. In this paper, a new diagonal dominance defined by 2-norm is proposed. This diagonal dominance is less conservative (i.e. more relaxed) condition than the other dominance. This paper also clarifies the relation between the diagonal dominance and strictly positive realness. Integrity is the property that closed-loop systems remain stable in the presence of failures of sensors and/or actuators. This property is also important for multivariable control systems. The conventional integrity conditions are the diagonal dominance and the positive realness of the return difference transfer function of closed-loop systems. This paper clarifies that the essential condition is the positive realness. This paper also shows that the direct Nyquist array method is still a good design method from the viewpoint of integrity.

Fault-Tolerant Servo Systems against Actuator Failures

Abstract This paper concerns with a design of fault-tolerant servo systems against actuator failures. A controller structure consists of diagonal servocompensator and full matrix stabilizing controller is proposed for the fault-tolerant servo systems. Also, some remarks on constructing generalized plants are provided in this paper. A numerical example demonstrates the effectiveness of the proposed controller structure.

Design of Decentralized Stabilizing Controller Based on a Coprime Factorization

Abstract This paper presents a method for designing decentralized controllers based on coprime factorizations. The proposed method consists of two steps. The first step is to approximate the given plant to a block-diagonal system, which consists from decoupled subsystems. The approximation of the plant can be obtained by reducing the rank of the partial transfer function matrix of the right coprime factorization. And an iterative algorithm for the approximation is proposed here. The second step is to find a decentralized controller which stabilizes the plant, that is, its approximation with the coprime factor perturbation.

Controllability of autonomous decentralized systems

This paper proposes a new definition of controllability for autonomous decentralized systems (ADSs). This controllability is defined as controllability of the entire system in spite of failures in some subsystems. The degree of fault-tolerance is measured with the number of its allowed faulty subsystems. A necessary and sufficient condition for the controllability and its basic properties are shown. To satisfy the requirement for expansibility for ADSs, the homogeneity and symmetry are favorable. However, this paper clarifies that symmetric systems are uncontrollable. Certain failures in some subsystems cause the system to be symmetric and uncontrollable. Therefore it should be noted the tight relationships between the symmetry of systems and the autonomous controllability. The homogeneity and symmetry originated from the expansibility have some aspects that do not consist fault-tolerance.<<ETX>>

Decentralized H ∞ controller design

This paper deals with the design of decentralized controllers which attain the H/sub /spl infin// performance specifications. In most designs of decentralized controllers, controllers are designed for diagonal approximation of plants, but few discussions have been made on the approximation. In this paper, the approximation problem which takes into account of the general H/sub /spl infin// performance specifications is considered. The metric is defined by the parametrization of all the plants and is used in the approximation problem. A numerical design method is also presented.