Robust stability of fuzzy control systems is studied through the Popov-Lyapunov approach. First, we transform a fuzzy control system into a Lur'e system with uncertainties or nonlinearities. Second, the Lyapunov's direct method is used to guarantee the stability of the perturbed Lur'e system, and then a robustness measurement which gives the bound on allowable uncertainties or nonlinearities is derived. Also, if the bound of the uncertainties/nonlinearities of the system is known, we can find an estimated region of asymptotic stability in phase space. A nonlinear numerical example and a magnetic bearing experiment demonstrating the feasibility of the method are illustrated. (C) 1997 Elsevier Science B.V.
