An improved fixed time sliding mode control and disturbance observer for surface-mounted permanent magnet synchronous motor drive system

This paper proposes a novel fixed-time reaching law (FTRL)–based sliding mode control (SMC) with a disturbance observer (DOB) for surface-mounted permanent magnet synchronous motor (SPMSM) drives. Unlike conventional fixed-time SMC methods, the proposed reaching law accelerates convergence while ensuring fixed-time stability irrespective of the initial state. Based on this reaching law, a speed controller and a fixed-time disturbance observer are systematically designed within the field-oriented control framework to estimate the unwanted load torque and uncertainty of the system in fixed time. Lyapunov-based analysis confirms the fixed-time stability of the closed-loop system. Both simulation and experimental studies show enhanced dynamic performance with faster response, minimized overshoot, and improved disturbance rejection compared with traditional fixed-time SMC approaches, confirming its effectiveness for high-precision SPMSM control.