Variable-structured robust controller by fuzzy logic for servomotors

A variable-structure robust controller whose structure is continuously changed by fuzzy logic so that the system responds quickly if the error or its rate is large and vice versa is proposed. Such a controller is insensitive to both the plant noise and the observation noise. It is applied to speed control for an induction servomotor. Experiments show that the controller is superior to both a sliding-mode controller and a proportional integral-derivative (PID) controller. The paper includes the stability analysis of the overall system and the design procedure by using Lyapunov's method. >