Limit cycles in control systems with multiple nonlinearities and parameter uncertainties

The describing function method can be used to analyze control systems with separable nonlinearities. In the paper, together with some well established robustness tools for linear systems, the method is used in the prediction 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. The software tools developed for this purpose are discussed and utilized to provide illustrative examples. The results are, of course, subject to the usual errors and restrictions of the describing function method