Restart strategy for sensorless PMSM drive system based on zero‐voltage vector

The zero-voltage vector (ZVV) method is widely employed to restart a free-running permanent magnet synchronous machine (PMSM) stably in a sensorless drive system due to its simple implementation. However, in the conventional method, it is hard to determine the action time and interval time of ZVV pulses, which may result in overcurrent. Moreover, the estimation accuracy is susceptible to current measurement noise. To cope with these problems, an enhanced ZVV method based on two feedback loops is proposed. With the proposed strategy, an inner closed loop is constructed to regulate the action time of the ZVV pulse by keeping the current amplitude at the reference value, which prevents the overcurrent. Meanwhile, the reference value of the current amplitude is adjusted automatically based on the outer loop to determine a suitable interval time of the ZVV pulse. Furthermore, the phase-locked loop technique is exploited to extract rotor speed and position. The feasibility of the proposed method is verified under simulation and experimental results with a 5.5 kW sensorless PMSM drive system.