Speed and current sensorless field oriented induction motor drive operating at low stator frequencies

The paper aims to demonstrate that, by exploiting the sensorless zero sequence voltage (SZSV) airgap flux estimation technique, it is possible to realize field oriented induction motor drives without speed and current sensors, able to operate down to zero speed. According to the SZSV technique, a zero sequence stator voltage component is generated as a result of the injection of a suitable high frequency signal on the stator voltage. By manipulation of such a zero voltage component, that is unaffected by speed and load changes, it is possible to detect both the amplitude and the angular position of the airgap flux. In the present paper, it is shown that such a technique allows also to estimate the motor speed and the phase currents, enabling implementation of a field oriented control as well as speed and current closed control loops using a simple hardware that, with minor modifications, resembles that of an inexpensive constant Volt/Hertz drive. Experimental tests are shown in order to practically confirm the expected features of the proposed approach.