Adaptive fuzzy logic controller with rule-based changeable universe of discourse for a nonlinear MIMO system

The accurate input-output universe of discourse (UOD) on which membership functions are defined is hard to acquire, especially for nonlinear multi-input and multi-output (MIMO) systems, and control accuracy will reduce greatly in the steady state due to limited fuzzy control rules. This paper presents a design scheme for the adaptive fuzzy logic controllers to control a MIMO system with online changeable input-output UOD of the controller, which could solve two problems mentioned above to a great extent. We obtain fuzzy inference rules that are defined by the error and change of error to describe the variation law of the input-output UOD according to the current trend of the controlled process, so the proper widths of the UOD can be derived from the fuzzy inference rules dynamically in real-time. Simulation results for the nonlinear MIMO system show the effectiveness of the proposed fuzzy logic controller.