Parallel structure and tuning of a fuzzy PID controller

In this paper, a parallel structure of fuzzy PID control systems is propose d. It is associated with a new tuning method which, based on gain margin an d phase margin specifications, determines the parameters of the fuzzy PID c ontroller. In comparison with conventional PID controllers, the proposed fu zzy PID controller shows higher control gains when system states are away f rom equilibrium and, at the same time, retains a lower profile of control s ignals. Consequently, better control performance is achieved. With the prop osed formula, the weighting factors of a fuzzy logic controller can be syst ematically selected according to the plant under control. By virtue of usin g the simplest structure of fuzzy logic control, the stability of the nonli near control system can be analyzed and a sufficient BIBO stability conditi on is given. The superior performance of the proposed controller is demonst rated through an experimental example. (C) 2000 Elsevier Science Ltd. All r ights reserved.