A position error reduced sensorless control method for PMSM based on an improved sliding mode observer and PLL

Abstract The conventional sliding mode observer (SMO)-based sensorless control method for permanent magnet synchronous motor (PMSM) usually requires a sigmoid function, and a low-pass filter (LPF) to reduce the sliding mode noise. However, the influences of the sigmoid function on the rotor position estimation are not clear, and the conventional rotor position compensation method has large errors. To solve these drawbacks, a position error reduced sensorless control method for PMSM based on an improved SMO and phase-locked loop (PLL) is proposed in this paper. First, the influences of the sigmoid function on the rotor position estimation are analyzed in detail. Then, to remove these influences, an improved SMO is proposed by introducing a cross-compensation term in the observer. Next, the drawbacks of the conventional rotor position compensation method are explained, and an improved PLL is further proposed, which not only can compensate the rotor position error generated by the LPF without using the estimated speed, but also can reduce the sliding mode chattering better. As a result, better sensorless control performance is achieved. Finally, experimental studies are carried out, which show that the rotor position estimation error is reduced from 0.2 rad to 0.0025 rad at 200 r/min, and it is reduced from 0.022 rad to 0.0025 rad at 1,000 r/min, indicating the effectiveness of the proposed method in this paper.