Initial start-up and magnet polarity estimation method for HF test current injection based sensorless control of PMSM

This paper presents an initial start-up and magnet polarity estimation method for PMSM using the alternating HF test current injection based sensorless control scheme for low speed range and evaluation of the saturation dependent HF d-axis inductance. The proposed magnet polarity estimation method consists of two steps: The first step is to activate the HF injection based sensorless current control scheme providing either the orientation of the d or -d-axis. To eliminate the ambiguity of the result from the first step, the magnet polarity information is obtained in the second step by exciting the estimated d-axis with a DC current. The magnet polarity can be detected by evaluation of whether the d-axis inductance increases or decreases due to saturation. Initial position estimation errors which can occur due to secondary saliencies can be compensated for easily by use of the flatness based test signal pre-control which is used for the test current injection based sensorless control anyway. Experimental results show proper functioning of the proposed method.