In this paper, interior permanent magnet synchronous motor (IPMSM) design for sensorless drive, considering cross coupling effect according to magnetic saturation, has been proposed. IPMSM is primarily driven by vector control,that requires precise position of the rotor. Thus, a position sensor such as encoder and resolver is attached to the axial direction to estimate the correct rotor position. Unfortunately, this leads to an increase in the cost of production and required motor size. And also, since the motor system applied to the vehicle is driven under extremely harsh environmental conditions, there is always a possibility of failure of the sensor. If the sensorless auxiliary control technology is developed against a sensor failure, the reliability of the vehicle power system can be greatly improved. In conclusion, in this paper, a study was conducted to improve the reliability of the motor applied to the EPS system of a vehicle.
Sensorless control was divided into a method based on inductance and a method based on back induced voltage. Because induced voltage is very small at zero or low speed, error in rotor initial position estimation may occur. Using the ratio of saliency addresses this problem. When using high-frequency injections at low speed, the rotor’s initial position is estimated at the smallest portion of the inductance. IPMSM has the minimum inductance at the d-axis. However, if magnetic saturation leads to magnetic neutral point variation, following the load current change, there is a change in the minimum point of inductance. In this case, it can lead to failure of initial rotor position estimation. As a result, it is essential that the blocking design has an inductance minimum point shift. In addition, since the local saturation of the electrical steel sheet occurs in actual operation, the magnetic independence of the d and q axes is not maintained. In addition, the cross-coupling inductance caused by magnetic saturation causes rotor position error in sensorless control. In conclusion, in this paper, Design method for sensorless control was proposed considering the inductance variation by armature reaction and Position error by cross coupling effect.
This phenomenon was analyzed based on the FEM analysis, and the validity of the proposed method is verified by conducting an optimization using an experimental design method.