Phase-Shifting Square-Wave Voltage Injection for Third Position Harmonic Suppression in IPMSM Sensorless Drive

This study examines the pulsating square-wave voltage injection (SWVI) sensorless drive for interior permanent magnet synchronous motors (IPMSMs) at zero or low speed. It is well-known that increasing the injection frequency to half of the PWM switching frequency can simplify the demodulation process and improve dynamic performances. However, existing literature reports that the position estimation error appears as the third harmonics at high injection frequencies. The cause of this estimation error has not been consistently and conclusively addressed. This article proposes a phase-shifting SWVI to reduce the third harmonics without additional digital filters. The third harmonics component in the estimation error can be canceled out under two injection angles with equal magnitudes and opposite signs. The optimal magnitude of the injection angle is analyzed using both mathematical expressions and graphical approaches. Signal processing is refined to reduce the oscillation in position and speed. Finally, the effectiveness of this sensorless drive is verified through experiments conducted on an IPMSM platform.