Influence of rotor geometry of an IPM motor on sensorless control feasibility

The sensorless control technique based on the superimposition of a high-frequency stator voltage is commonly used to detect the rotor position of a synchronous interior-permanent-magnet (IPM) motor. This technique is effective at zero and low motor speed, where back electromotive force is null or extremely low. Then, the accuracy of the rotor-position detection depends strictly on the rotor saliency, that is, on the geometry of the IPM rotor. This paper aims to determine some IPM rotor-design criteria so as to improve the sensorless rotor-position detection. Since the design has to be effective in different operating conditions, both saturation and cross-coupling effects have to be taken into account. It is found that the effectiveness of the sensorless rotor-position detection can be improved by means of a proper design of the IPM motor geometry even under heavy operating conditions.