Influence of rotor geometry of an interior PM motor on sensorless control feasibility

The sensorless control technique based on the superimposition of a high-frequency rotating voltage vector 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 E.M.F. is 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. The aim of this paper is 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.