MOTORSTEUERGERÄT

Let the rotating axis whose direction coincides with the direction of the current vector that achieves maximum torque control be called the qm-axis, and the rotating axis perpendicular to the qm-axis be called the dm-axis. A motor control device switches its operation between low-speed sensorless control and high-speed sensorless control according to the rotation speed of the rotor. In low-speed sensorless control, the magnetic salient pole of the motor is exploited, and the d-q axes are estimated by, for example, injection of a highfrequency rotating voltage. In high-speed sensorless control, the dm-qm axes are estimated based on, for example, the induction voltage produced by the rotation of the rotor. During high-speed sensorless control, the ³(dm)-axis current is kept at zero irrespective of the ´(qm)-axis current.