Stability Analysis of General Takagi-Sugeno Fuzzy Two-Term Controllers

This paper deals with general fuzzy two-term controllers of Takagi-Sugeno (TS) type. Analytical structures and properties of general fuzzy PI/PD controllers are investigated with a modified rule base. The rule base contains three rules which effectively reduce the number of tuning parameters of the controllers. The fuzzy two-term controller uses at least three triangular or trapezoidal fuzzy sets on each input variable, algebraic product/minimum t-norm, bounded sum/maximum t-co-norm, and Centre of Gravity (CoG) defuzzification strategy. Four new models of TS type fuzzy controllers are proposed. The general fuzzy PI/PD controller with modified TS rule base is analogous to a variable gain (nonlinear) PI/PD controller. The gain either varies or remains constant in different regions of the input plane. The gain variations of the controller and the stability analysis of closed-loop control system with any one of the proposed models in the loop have been investigated. The applicability of the proposed controllers is shown with the help of examples.