A new demodulation strategy for rotating HF signal injection based IPMSM position observer

A synchronous reference frame (SRF) based demodulation strategy for the rotating HF signal injection scheme estimating the rotor position of the interior permanent magnet synchronous motor (IPMSM) is proposed in this paper, allowing the delays introduced both by the digital controller and by the filters being compensated no matter at a standstill or in rotation. The rotating HF voltages, as standard practices, are injected still in the stationary reference frame, while the carrier currents are extracted in the estimated rotor position oriented reference frame, in which the positive and negative sequence components of the currents pulsates in the same frequency, independent of the rotor speed. As a result, the delaying effects would produce the same phase deviations to both sequence components, providing an ideal conditions to compensate the overall phase error in the negative-sequence component using the positive-sequence, otherwise, the compensation would be degraded as the rotor speed increases. Consequently, the accuracy of the estimated rotor position is enhanced comparing to the conventional demodulation strategies. The effectiveness of the scheme is confirmed through experiments.