MRFT based identification of process dynamics

The Modified relay feedback test (MRFT) was recently proposed for non-parametric tuning of PID controllers. In the present research, the use of the MRFT for identification of process dynamics is investigated. It is shown that the use of the MRFT allows one to ensure identification in the frequency domain, with frequencies generated automatically in the frequency range most important for a considered process. In fact, the range of generated frequencies can always be produced in such a way as to include and be in vicinity of the gain and phase cross-over frequencies. It is proposed that identification is done through minimization of a specific cost function that characterizes matching of the Nyquist plot of the model to the experimentally obtained points of the process Nyquist plot. The proposed methodology is illustrated by an example of identification of dynamics of an experimental level control setup.