The realization of a novel speed-sensorless induction motor drive

A simple low-cost controller for an induction motor has been implemented using a DC current sensor only. The fault current sensor is normally present in the DC link of an inverter for protection purposes, and in this case it is used as the compensation signal source. Derived on such way, feedback signal has some amount of switching noise, which is successfully removed by a simple filter. After filtration, feedback current signal is converted into a digital value by means of an 8-bit A/D converter. The proposed controller uses a simple estimation procedure to maintain a constant rotor flux under steady state load conditions. Implemented algorithm is partially successful even during transient conditions. The speed torque characteristics obtained with proposed controller are tested on standard 7.5 kW motors, with different number of poles. Results are promising.