Slip frequency estimation for sensorless low speed control of induction motor

This paper proposes a novel slip frequency estimation algorithm without using a speed or position sensor, especially aimed at the very low rotor speed estimation. The stator flux is obtained by the simple digital integration from the compensated stator voltage and the high-pass filtered stator currents. And the rotor speed is estimated from the proposed slip frequency estimation algorithm, which has advantages of more accuracy and stability in the very low speed range. It is reported in the paper that a rotor speed estimation as low as 5 rpm is verified through the experiments combined with the voltage command type vector control and the proposed slip frequency estimation algorithm.