Ultralocal Model-Free Logarithmic Sliding-Mode Control for PMSM Angle Robust Tracking With Asymmetric Constraints

This paper primarily introduces a novel prescribed performance control method to achieve rapid and high-precision control in servo systems. Initially, an interesting asymmetric barrier function is proposed, so that the controlled plant with arbitrary initial values can be confined within an asymmetric boundary. To reduce the dependence of controller deployment on physical parameters, an ultralocal model (ULM) approach is adopted and the logarithmic sliding-mode manifold is synthesized to design the controller and observer, resulting in an order-reduced and transient-performance-improved error dynamics. Since there are no non-Lipschitz continuous elements in the logarithmic sliding-mode, the super-twisting algorithm can be used to weaken signal chattering while converging the equivalent error rapidly. The Lyapunov-based direct analysis proves the stability of the controlled servo system with unknown parameters. The superiority of the scheme is verified through a series of simulations and experiments on PMSM platform.