A fuzzy logic supervisor for PID control of unknown systems

The design of a fuzzy logic supervisor for proportional plus integral plus derivative control of unknown systems is carried out in this paper. The PID controllers are designed using Ziegler-Nichols tuning rules. Since the Ziegler-Nichols method provides nominal parameter values for the PID controller, the desired system response is not realized without additional tuning. A fuzzy supervisor is proposed to reduce the amount of additional tuning. The objective of the fuzzy supervisor is to gradually increase the derivative gain of the controller as the system error approaches zero. When the error and change in error are in the zero membership regions, the proportional gain is increased to improve the settling time of the system and an integral gain, if required, is added to eliminate steady-state error. Simulation results, demonstrating improvements in the response of the systems with fuzzy supervisor, are presented