D-axis polarity detection for IPM synchronous motor drives by high frequency voltage injection

The self-sensing techniques for the estimation of rotor position at standstill suffer from the problem of magnet polarity uncertainty. This leads to a possible error in the direction of the estimated direct axis that can cause serious problems during the motor starting. This paper addresses the problem of polarity detection for interior permanent magnet synchronous machine drives employed in locked rotor applications. A novel method for polarity detection based on the properties of the cross-saturation inductance is proposed. The main advantage of the suggested strategy is its full compatibility with the high frequency voltage injection technique for rotor position estimation. The two techniques are implemented together in an interior permanent magnet motor drive and the effectiveness of the proposed method for polarity detection is proved through experimental results.