LAUSR

Both rotating and anticlockwise pulsating signal injection methods based on zero-sequence voltage sensing have been reported to have large signal-to-noise ratio and bandwidths, and great stability for the sensorless control of permanent-magnet synchronous machines. However, the initial rotor position estimation and magnetic polarity identification using zero-sequence voltage have not been investigated. Therefore, this paper presents two types of magnetic polarity identification methods, based on the amplitude variation of zero-sequence voltage due to saturation changing, and based on the secondary harmonics of zero-sequence voltage, for the two carrier injection methods, respectively. It is found that the amplitude variation based method using zero-sequence voltage has higher detection sensitivity for the real magnetic polarity compared to the conventional method using the carrier current. In contrast, the secondary harmonic based identification method using zero-sequence voltage for rotating signal injection has the advantage of fast response, and moreover has large signal amplitude and less distortion compared to the conventional secondary carrier current harmonics. However, the secondary harmonic method loses the capability for polarity detection for the anticlockwise pulsating injection method. Experiments are carried out on a laboratory permanent-magnet machine to verify the theoretical analyses.