Optimized indirect adaptive robust control for a class of uncertain nonlinear systems with time-varying parameters

This paper concerns high-accuracy tracking control and parameter estimation for semi-strict feedback systems with unknown time-varying parameters. The unsmooth and discontinuous parameters and matrix parameters are all taken into consideration. An optimized indirect adaptive controller based on Z-swapping and improved least-square algorithm is developed to handle parametric and unmolded uncertainties simultaneously. Each design index of this adaptive law can be adjusted freely according to the order of the magnitude of unknown parameters and state variables so that the coupling of the estimating process can be avoided. The Lyapunov-based stability analysis illustrates that the proposed method can obtain a prescribed estimating result as well as transient and final tracking performance. Simulations based on two common systems verify the outstanding performance of the proposed method.