Relay-based estimation of multiple points on process frequency response

Abstract

In this paper, a new technique for process frequency-response identification is proposed, which can identify multiple points on a process frequency response from a single relay feedback test. A modified relay is proposed and it can effectively excite a process not only at the process critical frequency ωc but also at 0.5ωc and 1.5ωc. As a result, the process frequency responses at multiple frequencies around ωc can be accurately estimated from one relay test using the FFT algorithm. The technique has been tested on various processes in real-time. The results show that the method is insensitive to noise and step-like load disturbance. The technique can also be easily extended to identify other frequency-response points of interest. © 1997 Elsevier Science Ltd.