Position sensorless control of SynRM at low speeds by estimating high-frequency extended EMF using disturbance observer

Synchronous reluctance motors (SynRMs) have attracted attention as the motor which complement IMs and IPMSMs, etc., because SynRMs have no winding and magnet in the rotor. Position sensorless control at low speeds of SynRMs is now desired, and several methods have been proposed. This paper proposes a new position sensorless control method of SynRMs at low speeds by estimating a high-frequency extended e.m.f.(EEMF) caused by injecting a high-frequency current, by a disturbance observer on the stator frame. In this method, the frequency of the injecting high-frequency current is set to 200 Hz which is quite lower than a mechanical resonance frequency of the motor, to consider reduction in noise of the motor. The superimposed signal of thus low frequency influences the current control system driving the motor. Therefore, this paper proposes a new method for eliminating the superimposed signal by subtracting a reference value of the high-frequency current from the current fed back to the current controller. Finally, it is experimentally shown that the position sensorless control is capable, at low speeds and under load conditions, using the proposed method.