A graphical method for finding the frequency response of nonlinear closed-loop systems

SEVERAL methods1¿7 have been developed for finding the steady-state sinusoidal response of closed-loop systems containing nonlinear elements. Most of these methods require either unnecessarily severe assumptions or long iterative procedures. This paper presents a graphical procedure for finding the frequency response of a large class of systems for which the describing function provides an adequate representation for the nonlinear elements. Attention is restricted to frequency-insensitive zero-memory nonlinear elements. The method is direct, requiring only an understanding of the point of view, and it can be extended to cover systems containing more than one nonlinear element.