Adaptive failure compensation of hysteretic actuators for a class of nonlinear systems via output feedback

In this paper, an adaptive output feedback control scheme is proposed for a class of nonlinear systems with possible actuator failures. The system not only involves unknown parameters but also takes nonlinear terms linear in the unmeasured states into account and is preceded by hysteretic actuators whose nonlinearities are characterized by the saturated Prandtl-Ishlinskii model. By developing a high-gain observer with one dynamic gain, the closed-loop stability and arbitrarily small tracking error can be guaranteed. Furthermore, by estimating the upper bound of the unknown time-varying (piecewise constant) parameters caused by the actuator failures, together with an initialization technique, it is proved that the L-infinity tracking performance is achievable, which is fundamentally different from the commonly accepted concept that with actuator failures, it is impossible to improve the L-infinity tracking performance by using initialization technique. Copyright (C) 2015 John Wiley & Sons, Ltd.