Limit cycle analysis of uncertain control systems with multiple nonlinearities

The describing function method can be used to analyze control systems with separable nonlinearities. Here, the method is employed in conjunction with some of the robustness tools for linear systems to develop algorithms for predicting the existence of limit cycles in uncertain systems with multiple nonlinearities connected in series. Uncertainty is assumed to exist in terms of parameter variations in both the linear and the nonlinear elements. Examples are provided to illustrate the results which are, of course, subject to the usual errors and restrictions of the describing function method