A position and speed sensorless control scheme using the counter EMF of PM motors debases the control performance at low speed. Here, the authors propose a controllable system at full speed, including zero speed, using saliency. At low speed, sensorless control is performed by observing a current ripple at a time when an alternating voltage has been applied to the salient-pole motor. Also, for discriminating the S and N poles of the magnet, magnetic saturation is used. A device has been applied to the motor rotor to allow the magnetic saturation to be brought about easily. Further, at times of high speed, a full speed range drive has been accomplished by switching smoothly over to a sensorless driving system, making use of the counter EMF.
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