Observer-based adaptive fuzzy backstepping dynamic surface control for a class of non-linear systems with unknown time delays

An adaptive fuzzy backstepping control approach is considered for a class of non-linear systems with unknown time delays and immeasurable states. Fuzzy logic systems are used to approximate the unknown non-linear functions, and a fuzzy state observer is designed for estimating the immeasurable states. By combining the adaptive backstepping technique and dynamic surface control technique, an adaptive fuzzy output-feedback backstepping control approach is developed. The proposed control method not only overcomes the problem of 'explosion of complexity' inherent in typical backstepping design approaches but also overcomes the problem of unavailable state measurements. It is proved that all the signals of the closed-loop adaptive control system are semi-globally uniformly ultimately bounded, and the observer and tracking errors converge to a small neighbourhood of the origin with appropriate choice of design parameters. Simulation results are provided to show the effectiveness of the proposed approach.