Computer-aided design of nonlinear H∞ controllers using describing functions

A computer-aided procedure for design of nonlinear H_infin controllers for nonlinear plants, whose dynamic and static behavior are highly sensitive to the amplitude level of excitation, is presented. The procedure is based on describing function concepts involving sinusoidal input describing function models of the nonlinear plant, and it includes an application of a newly developed inverse describing function technique to arrive at nonlinear gains of the H_infin controller. The procedure is applied to a servomechanism problem to demonstrate the typical results that may be achieved