Closed loop identification of systems within cascade connected control strategies

A brief review of the background to the Phase-Locked Loop (PLL) method of non-parametric system identification is presented. This introduces the idea of performing the non-parametric identification for any point on the frequency response curve of a process. The PLL identification method is then extended to perform the non-parametric identification of the component parts of a cascade connected control system. An advantage of the method is that the non-parametric identification is performed with the cascade control system connected in closed loop. An example demonstrating the identification method is given.