An enhanced phase-locked loop for dynamic performance enhancement of sensorless IPMSM drives in low-speed range

Sensorless drives for interior permanent magnet synchronous motors (IPMSMs) are used in a wide variety of applications because of their size, efficiency and reliability benefits. In electric propulsion systems, due to the continuous heavy-duty operation of the system, dynamic performance and stability of the sensorless control would be seriously influenced by rapidly changing load, inverter loss and magnetic oversaturation, etc. Without substantial compensation, conventional phase-locked loops (PLLs) and estimators might suffer a loss of synchronization with the rotor position. This paper presents an enhanced PLL (EPLL) for sensorless IPMSMs operated in low-speed range. The proposed scheme couples the online estimation of the inductance ratio with the current changes and estimated rotor position to accurately estimate rotor position and speed, even under conditions of overly magnetic saturation. The work emphasizes the development of a robust and effective control framework that mitigates the challenges associated with low-speed stability and motor saturation, thereby enhancing the dynamic performance and reliability of sensorless IPMSM drives. In addition, the proposed EPLL is robust to the uncertainty of motor parameters. It eliminates the double frequency ripples without additional compensation. Experimental results demonstrate the proposed method produces high precision for IPMSM rotor position estimation at low speeds and the dynamic performance of the system is enhanced.