A Time-Delay Compensation Method for PMSM Sensorless Control System under Low Switching Frequency

In rail transit application, the performance of the permanent magnet synchronous motor (PMSM) sensorless control system is limited by the low switching frequency. In this case, the time-delay of system is becoming more significant and degrades the control performance. To solve the problem, a time-delay compensation method based on high frequency (HF) square-wave voltage injection strategy is proposed in this paper. Firstly, a series time-delay filter is used to extract the HF response current, which can improve the signal-to-noise ratio. Then, a zero-order holder is used to obtain the HF current envelope containing rotor position information. The rotor speed and position are estimated by a Luenberger observer. For the time-delay compensation, the feedback current in a-β coordinates is utilized to calculate the estimated delay angle error. It serves as the input of a PI controller, through which the estimated delay angle can be acquired. And then, the estimated delay angle is compensated to the actual system. Simulations verified the effectiveness of the proposed method.