Design of Novel Fixed-time Disturbance Observer and Improved Sliding Mode Controller for PMSM

Abstract

This paper presents a novel fixed-time disturbance observer (FTDOB) and an improved sliding mode controller (IPSMC) with saturation function of adaptive variable fractional power times for the permanent magnet synchronous motor (PMSM) to solve the problems that PMSM are susceptible to parameter uncertainties and disturbances of external loads. The proposed FTDOB utilizes the uniform convergent part to drive the error trajectories into a compact set and then switches to the finite time convergent part to achieve exact convergence. It can achieve exact disturbance estimation within finite time independent of initial estimation error. In addition, the improved sliding mode control law for speed controller is developed through combining the rotate speed and q-axis stator current’s second-order model. A saturation function of adaptive variable fractional power times is designed to realize the coordinated control between chattering and tracking accuracy. Numerical simulations are provided to demonstrate that IPSMC+FTDOB is robust to the parameter perturbation, model errors and external disturbances, and it can effectively weaken the chattering and ensure the steady speed precision of PMSM.