High-speed sensorless control of a PMSM operating under periodic magnetic saturation conditions

A single-phase diode rectifier fed inverter with a small dc-link capacitor has found widespread use in permanent magnet synchronous motor (PMSM) drives for appliances because of its cost effectiveness in comparison with the conventional power factor correction (PFC) circuit-based inverter. In this application, the d-q axes currents supplied to the PMSM are controlled to have ripples with a frequency that is usually two times that of the ac mains voltage, and this results in periodic magnetic saturation at the stator of the PMSM. In this paper, a back electromotive-force (back-EMF) estimator for the high-speed sensorless control of a PMSM operating under periodic magnetic saturation conditions is proposed. The transfer function of the back-EMF estimator is analyzed to examine the effect of the stator inductance variations due to the periodic magnetic saturation on the accuracy of the estimated rotor position, and a simple compensation method for the estimated position errors caused by the periodic magnetic saturation is proposed on the basis of the analysis. The effectiveness of the proposed method is experimentally verified with a PMSM drive for a vacuum cleaner centrifugal fan, whose maximum operating speed reaches 30,000 r/min.