STABILITY ANALYSIS OF CONTROL-SYSTEM HAVING PD TYPE OF FUZZY CONTROLLER

Stability of a control system having PD type of fuzzy controller (a two-input and single-output controller) is analyzed in this paper using Yakubovich's method. In this analysis, the controller is treated as a two-input and two-output controller, and the nonlinearity of the controller is characterized as the sector condition. Absolute stability conditions are derived for the control system as three conditions; two are conditions for either one of control modes, P or D, is independently operating; the third is the condition for two modes are simultaneously active. The former two conditions are nothing but Popov's conditions for two SISO systems. A new graphical method is proposed to solve the latter condition. This method is explained illustratively using an example, and the results obtained are compared numerically with those by other graphical methods as well as simulation results.