A Sensorless Control Strategy for IPMSM Based on Unified Model in Full Speed Range at Low Switching Frequency

In high-power applications such as rail transit, the switching frequency of inverter is relatively low, resulting in more and larger harmonics, which poses a significant challenge to sensorless control for interior permanent magnet synchronous motor (IPMSM) in full speed range. This paper proposes a unified rotor position estimation method suitable for low switching frequency, applicable across the full speed range. By injecting high-frequency voltage, a quadratic virtual back electromotive force (QVBEMF) model suitable for full speed range is established based on the active flux linkage. To ensure the frequency range of the injected voltage, square wave is chosen as the form of injected voltage. To suppress the influence of harmonics, QVBEMF is directly constructed from the observed virtual back electromotive force. Experimental results verify the effectiveness of the proposed sensorless control method at low switching frequency.