Improved Fast Terminal Sliding Mode Control With Disturbance Observer for Five-Phase Fault-Tolerant IPM Motor Drives

This paper presents a composite control strategy for five-phase fault-tolerant fractional-slot concentrated winding interior permanent magnet (FTFSCW-IPM) motor drives, aiming to alleviate the long-standing trade-off between fast dynamic response, chattering suppression, and disturbance rejection in sliding mode control. A variable exponential fast terminal reaching law with a continuous switching function is developed to explicitly shape the reaching dynamics, enabling rapid convergence when the system state is far from the sliding surface while ensuring smooth behavior near the surface. To further enhance robustness against load torque disturbances, a Luenberger torque disturbance observer (LTDO) with a slightly enhanced correction structure is incorporated as a feedforward compensation channel, thereby decoupling disturbance rejection from the sliding-mode switching gain design. In addition, a systematic comparative study involving four representative control schemes is conducted to clearly distinguish the individual and combined effects of the fast terminal sliding mode structure and the disturbance observer. Both simulation and experimental results demonstrate that the proposed strategy achieves excellent speed tracking performance and improved disturbance rejection under sudden load torque variations.