Accurate detection of secondary current in shaft hole of induction motors for reliable controls

Accurate controls for the speed and the torque of induction motors (IM) are realized using the detected secondary current (I/sub 2/) signal with the inverter having a constant ratio of the primary voltage over the driving frequency (V/sub 1//f). A new method for detecting I/sub 2/ is presented setting a MI sensor head inside a drilled hole through a shaft of an actuator type IM, in which an almost pure I/sub 2/ signal having the slip frequency is stably detected, An accurate and reliable control system for the IM is constructed using the I/sub 2/ feedback loop with the inverter.