PI Controller with Fuzzy Logic Based On-Line Variable Reset-Rate

In this study, we propose a fuzzy logic based enhanced auto-tuning PI controller. The widely practiced conventional Ziegler-Nichols tuned PI controller (ZNPIC) exhibits poor performance for integrating and high-order systems. To overcome this limitation, in our proposed tuning method, the integral time (Ti) or the reset-rate (1/Ti) of the ZNPIC is continuously updated by a real-time nonlinear updating factor a depending on the process trend. The value of a is found out through a fuzzy inference engine with either 49 or 25 if-then rules defined on the process error and change of error. The usefulness of the proposed fuzzy auto-tuning ZNPIC, termed as FZNPIC, is tested for a number of second-order integrating plus dead time processes under both set point change and load disturbance. Simulation results of the proposed controller demonstrate significantly improved transient responses compared to other controllers. FZNPIC is found to be robust when applied with considerable change in dead time.