A Harmonic Suppression Strategy Based on Adaptive Synchronous Rotating Frame Transformation for Improving the Estimation Accuracy of Sensorless Drivers With Small Capacitors

The small capacitor drivers use film capacitors instead of electrolytic capacitors in the dc-link, which will improve the life and reliability of the drivers. However, the dc-link voltage of the small capacitor drivers fluctuates seriously, and the ac component in it causes |(
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|th and |(
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|th harmonics in the extended back electromotive force. These harmonics will increase the estimated position error in the sensorless driver. A harmonic suppression method based on adaptive synchronous rotating frame transformation (ASRFT) is presented in this article to improve the control accuracy of sensorless drivers with small capacitors. First, the motor current harmonics caused by harmonics in the dc-link voltage are analyzed, and the relationship between these harmonics and the estimated sensorless position error was derived. Second, ASRFT and fixed synchronous rotation frame transformations can be used to extract current harmonics in corresponding harmonic coordinate systems. Then, the voltage compensation component generated by the harmonic compensation link will be injected into the driver to suppress the current harmonics extracted in the corresponding coordinate system. Finally, the controller parameters of the proposed method are designed. Using a 2 kW permanent magnet synchronous motor sensorless driver with a small capacitor, the proposed method is demonstrated to be effective.