Absolute stability analysis of PWM systems

The absolute stability, of pulse-width modulated (PWM) feedback systems with higher order linear plants is treated. The system consists of a linear, continuous plant with a piecewise-constant input from a pulse-width modulator, whose input is an error signal obtained by comparison of the plant output with the desired output. The overall system is modeled as a discrete, nonlinear feedback system. An absolute stability criterion in [4] is then used to check the stability of the system. Two effective computer algorithms are developed to find the largest possible absolute stability sectors obtainable under the sufficiency constraint of the criterion and their application is illustrated by several examples. The methods described provide the capability, to analyze higher order PWM systems in which the pole locations of the linear portion of the nonlinear feedback system are located in the negative half-plane, except for possibly one pole at the origin.