Disturbance Observer-Based Improved Non-Singular Fast Terminal Sliding Mode Control for the PMSM with Matched and Mismatched Disturbances

The permanent magnet synchronous motor (PMSM) has been widely applied in electric drives. However, parameter perturbations and external disturbances can significantly affect the performance of the PMSM system. This is particularly true when these disturbances do not satisfy the disturbance matching condition, which can greatly increase the difficulty of motor speed control. To solve this problem, a composite control method utilizing an improved non-singular fast terminal sliding mode controller (NFTSMC) and a disturbance observer is proposed. Firstly, a nonlinear disturbance observer (NDO) based on the principle of higher-order sliding mode differentiator is proposed to estimate the matched and unmatched disturbances of the system. Secondly, to address the issue of conventional NFTSMC struggling to balance fast convergence and chattering inhibition, a new sliding mode reaching law (NSMRL) is proposed. This NSMRL can adapt to changes in the sliding mode surface and system state, while also providing further chattering inhibition. And an improved NFTSMC based on NSMRL is further designed. Finally, the NDO observations are incorporated into the improved NFTSMC through feed-forward compensation. The simulation results suggest that the proposed control strategy exhibits superior chattering inhibition ability, fast dynamic response, and disturbance inhibition effect.