Novel Square-Wave Signal Injection Method Using Zero-Sequence Voltage for Sensorless Control of PMSM Drives

In this paper, a novel square-wave-type carrier signal injection method using zero-sequence voltage is proposed for sensorless control of permanent-magnet (PM) synchronous machine drives. Different from the conventional square-wave-type injection methods employed in the stationary reference frame and estimated synchronous reference frame, the proposed square-wave injection is performed on the estimated reference frame, which rotates anticlockwise at twice estimated rotor electrical angular speed. Compared to the conventional square-wave methods with carrier current sensing, the proposed strategy using zero-sequence voltage has two main advantages, 1) the amplitude of the resultant carrier response is not related to the injection frequency, and 2) the carrier response does not require differentiation calculation for rotor position estimation. Therefore, the proposed method is more robust and also much simpler for signal demodulation, which can combine the synergies of zero-sequence method and square-wave injection (i.e., increased accuracy, bandwidths, and stability, etc.). Finally, all the theoretical analyses are validated by experiments on a laboratory PM machine.