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 gw c but also at 0.5 ω c and 1.5 ω c . As a result, the process frequency responses at multiple frequencies around ω c 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.