Precisely Controlled 3-Phase Squirrel Cage Induction Motor Drives for Aerospace Applications

The long sought means whereby complete control can be simply exercised over the speed and torque of a 3-phase squirrel cage induction motor has recently been reduced to practice and is currently in operation in full scale hardware. By means of an all solid-state cycloconverter type frequency changer power is supplied to the motor at a controlled frequency and voltage such that the motor is operated at controlled slip in a closed feedback system. In this loop the torque (and therefore, speed) can be instantaneously controlled. A low power level signal which varies the motor slip frequency is the controlling variable. The application of this concept to aerospace drives is discussed with particular attention given to servo-controlled antenna drive systems.