Noninvasive speed measurement of inverter driven induction motors

Abstract

A frequency component in the stator current of the induction motor which is caused by rotor dynamic eccentricity is used for a noninvasive speed measurement. The frequency of this component is related to the rotor speed, and its bandwidth is related to the supply frequency and the phase-lock-loop RC filter cutoff frequency. In the case of an inverter drive, the signal can be extracted from the phase current reconstructed from the DC link current. The use of switched-capacitor filters allows a frequency component related to the rotor speed to be extracted from the DC link of variable-frequency, inverter-driven induction motors.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>