New Design Method for Pulse-Width Modulation Control Systems via Digital Redesign

Abstract

A design method is proposed for pulse-width modulation (PWM) control systems, where magnitude of control input is e xed but pulse width is adjustable. In the proposed method, e rst a discrete-time (DT) control system of the amplitude modulation type is designed, and then it is converted into a PWM control system. Pulse width and delay time for PWM input are determined at each sampling time so that the state error between the DT and PWM control systems can be small. The DT controller is determined by digital redesign of a given continuous-time (CT) controller. The digital redesign method previously proposed by the authors is based on the principle of equivalent area. Thus, in spiteof theinherent nonlinearity of PWM input, inasmuch as linear control theory can be employed in design of the baseline DT or CT controller, the PWM control system is obtained without using nonlinear control theory. In addition, because the proposed methods are described in state-space representation, they are applicable to multi-input/multi-output systems. The effectiveness of the methods is illustrated through computer simulation using a e exible spacecraft model.