Relay-Based Identification of a Class of Nonminimum Phase SISO Processes

A set of general expressions is derived from a single symmetrical relay feedback test for identification of a class of process transfer functions. Using these expressions the parameters of open loop stable nonminimum phase transfer function models may be obtained from simple measurements made on the limit cycle. For comparison, the conventional describing function based identification formulae are presented. Fourier series based curve fitting with the options of nonlinear least squares method and trust-region algorithm is used to measure limit cycle parameters in the presence of measurement noise. Examples are given to illustrate the value of the proposed method