Optimal synthesis of fuzzy sliding mode controllers [for induction motors]

When using fuzzy logic to enhance the functionality of another control algorithm, the optimal design of the fuzzy parameters is a question which requires special consideration. This paper proposes an optimal synthesis of a sliding mode controller using fuzzy logic which outperforms the traditional sliding mode controller. A description of a variable structure control with sliding mode is presented. The problems associated with this control technique are then addressed. Fuzzy logic as one solution to these problems is explained. The concept of a fuzzy switching surface is introduced to solve the chattering problem in the switching mode. The optimal membership function for this fuzzy surface is then found using a genetic algorithm. In the reaching mode, another variable structure is introduced by fuzzy partitioning the state space which is different from the variable structure at the switching surface in the sense of having a control action with variable amplitude but constant sign. The optimal structure of each side of the fuzzy switching surface is found by optimal input membership functions and output singletons using the proposed approach. This approach is applied to the indirect field oriented control of an induction motor. The simulation results verify the efficiency of the proposed approach.