Relay feedback and wavelet based estimation of plant model parameters

The paper presents a relay feedback and wavelet based method for the estimation of completely unknown processes for autotune purposes. From a single symmetrical relay feedback analysis a set of general expressions are presented for on-line process identification. Using these expressions the exact parameters of open loop stable and unstable first order plus time delay (FOPDT) and second order plus time delay (SOPDT) transfer function models may be obtained from simple measurements made on the limit cycle. However, noise in limit cycle output results in inaccurate estimate of the process model parameters. This paper proposes an effective mother wavelet for tracking the critical points of a noisy output signal. Further, using the wavelets based noise reduction it has been shown how accurate measurements can be made on the noisy limit cycle signal. Simulation studies illustrate the value of the proposed identification method.