Low-speed position sensorless drive for highly efficient permanent magnet synchronous motor without rare-earth metals

In this paper, we discuss a position sensorless drive for an axial structure motor without rare-earth metals in a low-speed region. Since this motor has no saliency, a conventional position sensorless drive using harmonic injection cannot be applied. Therefore, we apply a position sensorless drive based on Induced Voltage caused by Magnetic Saturation (IVMS) to this motor. As IVMS becomes very small for motors without saliency, we introduce a differential amplifier and adjust its gain appropriately. We implemented this method by using a microcomputer and an analog circuit. As a result, excellent drive performance in a low-speed region was obtained in experiments for the motor (200V/11kW).