A Restart Method of Permanent Magnet Synchronous Machine Sensorless Drives With a Single DC-Bus Current Sensor

When restarting a permanent magnet synchronous machine (PMSM) sensorless drive at an unknown initial speed, the initial position and speed must be estimated before applying pulsewidth modulation (PWM) signals to the inverter. Then, a proper initial voltage vector with the right direction and magnitude can be generated to avoid an inrush current that may impair power switches. Nevertheless, a PMSM sensorless drive with a single dc-bus current sensor is a challenging work and has not been solved thoroughly. Because the conventional zero-voltage injection method cannot work due to the unmeasured phase current in a single dc-bus current sensor drive. This article proposes a novel restart method by applying three pairs of active-voltage vectors during the flying state. Six dc-bus currents are sampled sequentially, and phase currents can be reconstructed. Then, the initial position and speed can be estimated continuously using a phase-locked loop (PLL) based on the phase current angle. Furthermore, the estimation errors due to the sequential samplings and inductance saliency are analyzed and compensated. The effectiveness of the proposed method is verified in two PMSM sensorless drives. A smooth and fast transition from the flying state to sensorless closed-loop control can be implemented by avoiding inrush currents, which improves the reliability of PMSM sensorless drives.