Limit cycle analysis of uncertain fuzzy vehicle control systems

In this paper, some useful frequency domain methods including describing function, parameter space and Kharitonov approach are applied to analyze the stability of a fuzzy vehicle control system for limit cycle prediction. A systematic procedure is proposed to solve this problem. In general, fuzzy control systems are nonlinear systems. The fuzzy controller can be linearized by the use of classical describing function firstly. By doing so, it is feasible to treat the stability problem of fuzzy control systems as linear one. In order to consider the robustness of the fuzzy vehicle control system, parameter space method and Kharitonov approach are then employed for plotting the stability boundaries. Furthermore, the effect of transport delay is also addressed. Much information of limit cycles can be obtained by this approach. Our work shows that the limit cycles caused by a fuzzy controller can be easily suppressed if the system parameters are chosen carefully.