Sensorless control of AC machines at carrier frequency signal injection using analog filter circuit

In this paper, new saliency measurement method using analog filter circuit is proposed to reduce injection voltage level. In order to measure a rotor saliency at zero or low speed range, additional voltage signal is injected. Here, the higher frequency voltage signal is preferred for the rapid dynamic performance of the rotor angle estimation. In this high frequency injection, Signal-to-Noise Ratio (SNR) gain decreases because of the large machine reactance. To increase SNR gain, the analog filter circuit which amplifies injection frequency component of the current feedback signal is added before the Analog to Digital Converter (ADC). However, this introduction causes voltage distortions at carrier frequency injection. The signal distortion factor is analyzed and new sensorless method with angle distortion compensator is proposed. The experimental results verify the effectiveness of the recommended sensorless method using low level of injection voltage signal; therefore, the system noise can be diminished significantly.