Using oversampling techniques to extract ac machine saliency information

Controlling an ac machine without speed or position sensor at zero frequency requires the extraction of its inherent or engineered saliencies. This extraction is currently linked to injected high frequency or transient test signals that are superposed to the fundamental wave. These test signals also affect noise emission, maximum inverter output voltage, and switching frequency. Different methods for an integration of the test signal injection into the fundamental wave excitation have been made, however a full integration in all operating states is still not possible. In this paper a method to extract the necessary saliency information without applying test signals is proposed and analyzed. It is based on oversampling techniques and uses the information that appears in current sensor signals during the switching transients. Different realizations are presented and their performance compared with respect to changes in the operating parameters. It is shown by measurement results that applying the proposed techniques it is possible to obtain the saliency information necessary for speed sensorless control.