Position Sensorless Estimation With TNPLL and Adaptive STA‐SMO for Medium‐ to High‐Speed Six‐Phase FTPM‐RDM

ABSTRACT Reducing chattering in sliding mode observer–based sensorless control of fault‐tolerant permanent magnet rim‐driven motors at medium–high speeds remains challenging, particularly under open‐circuit faults where chattering becomes more severe. This paper proposes a rotor position estimation scheme using an adaptive second‐order super‐twisting observer with speed‐dependent sliding gains to improve dynamic response and robustness. A digital gain controller with a weighted average filter is developed to smooth gain transitions and suppress chattering induced by discrete switching and load disturbances. To address steady‐state error and first‐order feedback delay in conventional phase‐locked loop (PLL) extraction, a third‐order normalized PLL is introduced to enhance estimation accuracy. In addition, a fault‐tolerant control strategy based on current redistribution is presented to ensure continuous operation under single‐phase open‐circuit faults while reducing torque ripple. Experimental results verify the effectiveness and practicality of the proposed sensorless control approach.