A study of digital filter for rotor speed detection with slot harmonic current for induction motor

In rotor speed detection with slot harmonic component of the motor current of induction motors, the cutoff frequencies of filters for extracting slot harmonic component should be changed in accordance with the rotor speed. In this paper, we introduce DSP based band pass filter (infinite impulse response filter) to change the cutoff frequencies of the filter and investigate the static and dynamic characteristics of the filter. Moreover, we investigate the range of the cutoff frequencies which can estimate speed correctly. Finally, we demonstrate speed sensorless operation with the introduced band pass filter.