Direct adaptive fuzzy control for a class of nonlinear systems with unknown control gain sign

Abstract

This paper proposes a novel direct adaptive fuzzy control scheme for a class of uncertain SISO nonlinear systems with unknown control gain sign. Within this scheme, a fuzzy system is used to approximate an unknown ideal controller which can achieve the control objective. The adjustable parameters of the fuzzy system are updated online using the error between the unknown ideal controller and the fuzzy controller. Differently from most previous works, the Nussbaum function technique is not used to deal with the unknown control gain sign. In fact, in this paper, the unknown control gain sign is considered as an unknown constant parameter and it is identified online by an appropriate adaptation law. The stability of the closed-loop system is performed using a Lyapunov approach. Simulation results are provided to verify the effectiveness of the proposed design.