Gain margins and phase margins for nonlinear control systems with adjustable parameters

Abstract

A method for finding the grain margins and phase margins of nonlinear control systems for asymptotic stability is presented. The effects of adjustable parameters are analyzed. The systems considered are first linearized by the describing function method and modified by adding a gain-phase margin tester. Then the characteristic equations are formulated and factored into stability equations, and the parameter-plane method is used to find the boundaries of constant gain margin and phase margin. From these boundaries useful information about the effects of adjustable parameters on gain margins and phase margins can be obtained. >