Analysis and Optimization of Polarity Detection Methods for Electric Vehicle Traction IPMSM

Interior permanent magnet synchronous motors are used in the traction drive of most modern vehicles. These machines are designed to have a high power density, and they are likely to operate under heavy saturation. Therefore, they exhibit strong magnetic nonlinearity, which poses challenges to sensorless control. For the startup of a sensorless electric drive, polarity detection is crucial, since an unstable control action could be induced if the 180 degree angle estimation error is not corrected. This work revisits the polarity detection fundamentals and their decision logic, applied to a real 157 kW IPMSM drive for electric vehicle applications. As proved, this kind of motor may have locally inverse saturation characteristics, so the polarity detection decision logic should be refined accordingly. Analysis and experimental validation are put together along the paper in order to stress wrong assumptions (from state-of-the-art) and implementation solutions that fit with the motor.