Sensorless torque control of induction machine in low speed and low torque region

This paper proposes a control strategy for a sensorless torque control when an induction machine is driven with the adaptive full-order observer. In low speed and low torque reference region, the magnitudes of stator voltage and current which are the inputs of the adaptive full-order observer for the sensorless control are too small. And, the frequency is too low to obtain the high performance sensorless torque control. In order to enhance the control performance of the sensorless torque control, the proposed strategy modifies the d- and q-axis current references in the synchronous reference frame considering the current limit, voltage limit, the rated slip frequency and the magnetizing current conditions. Even though the current reference is modified for the better performance, the generated torque is kept as a constant value. Based on the proposed strategy, the performance of sensorless torque mode control can be improved remarkably even in the low speed and low torque operation. Validation of the proposed strategy is evaluated at 7.5kW experimental setup.