Sensorless position control and initial position estimation of an interior permanent magnet motor

This paper describes a torque, speed or position control method at the stand still and low speed in the interior permanent magnet (IPM) motor drive system without any rotational transducer. While IPM motors originally have magnetic saliency, it varies according to the load conditions and the control performance can be easily degraded. In this paper the saliency or impedance difference is used as the conventional methods and, nevertheless, in order to amplify the difference containing the information of the rotor angle and to maintain a reasonable performance under any load condition, a high frequency injection scheme is proposed. A speed and position estimation scheme based on the characteristics of the high frequency impedance is proposed. The scheme extracts the high frequency impedance components related to the rotor position. An initial angle estimation scheme for the starting from an arbitrary rotor position is also proposed. It can distinguish the north magnetic pole position from the south one in several tens of milliseconds. The proposed scheme enables position control of a transducerless or position-sensorless IPM motor. The experimental results clarify the satisfactory operation of the proposed position control algorithm under any load condition.