Performance-Guaranteed Switching Adaptive Control for Nonlinear Systems With Multiple Unknown Control Directions

In this paper, an adaptive control strategy with novel performance-guaranteed switching mechanism is proposed for a class of nonlinear parametric strict-feedback systems with unknown parameters and multiple unknown control directions. Firstly, adaptive controller is designed by combining tuning function design and barrier Lyapunov function (BLF) techniques, to handle parameter uncertainties and avoid over-parametrization phenomenon. The unknown control directions are estimated online with the proposed novel switching criterion composed of a BLF-type monitoring function and a threshold function. It is shown that the correct directions can be identified rapidly with only finite times of switching and mis-switching problem is avoided. At switching moments, a novel reset mechanism is triggered to adjust the value of integrator to avoid failure of BLF method. Consequently, tracking error of reference signal converges to zero asymptotically and all closed-loop signals are proved to be bounded. In addition, the tracking errors can be restricted into prescribed intervals without information of control directions. Numerical results demonstrate the effectiveness and performance of the proposed method.