Fuzzy Controller Design: A Sliding Mode Approach

Abstract

A fuzzy-sliding mode controller, which is designed by the techniques of the fuzzy logic controller and the sliding mode controller (or called variable structure control), is proposed in this work. Like the sliding mode of the sliding mode control system, the fuzzy-sliding mode control system has a fuzzy-sliding mode. The reason for calling “fuzzy-sliding mode” is that the sliding surface in the proposed scheme is a fuzzy set rather than a crisp set found in the conventional sliding mode control system. In the design of the fuzzy-sliding mode controller, one can easily determine the membership function, observe the fuzzy rules and predict the controlled system behavior. Furthermore, the number of inference rules, which is an exponential function of the number of system state variables in a conventional fuzzy logic controller, is reduced to a linear function of the number of system state variables in the fuzzy-sliding mode control system. Simulation results show that the proposed scheme has the following advantages: 1. The dynamics behavior of the controlled system can be approximately dominated by a fuzzified sliding surface. 2. Fuzzification of the sliding surface will not only increase the robustness to the system nonidealities but also decrease the chattering. 3. The fuzzy-sliding mode controller can control most of the complex ill-defined systems without knowing their mathematical models.