Asymmetric Space Vector Modulation for PMSM Sensorless Drives Based on Square-Wave Voltage-Injection Method

Square-wave voltage injection is an effective sensorless control method for permanent magnet synchronous motor drives to achieve zero- or low-speed operation. However, it faces great challenge in the case of rail transit application where the switching frequency is less than or equal to 500 Hz, which results in rich low-order harmonics. In order to improve the performance of high-frequency square-wave voltage-injection method over low switching frequency application, an asymmetric space vector modulation (ASVM) method is proposed, and it makes comparisons between carrier and modulation wave in the 1/4 and 3/4 point of each switching cycle. Compared with space vector modulation, ASVM can significantly reduce the low-order sideband and baseband harmonics in the bandpass filter bandwidth. As a result, the position estimation, which is calculated by the filtered current signal, is improved. Moreover, the inverter dead-time effect has been compensated as well. With these improvements, the rotor position can be estimated without using low-pass filters and its dynamic performance can be enhanced. The experimental results proved the effectiveness of the analysis.