Slip Power Recovery in an Induction Motor by the Use of a Thyristor Inverter

The low-speed efficiency of an induction motor is improved by rectifying slip-frequency power, inverting this to line frequency, and injecting it back into the supply directly (line feed-back) or through auxiliary stator windings (stator feedback). Torque-speed curves then have the nature of a variable-speed drive. The low power factor and nonsinusoidal supply current of the line feedback connection are improved by use of the stator feed-back method but the improvement of efficiency is then much less. Line feedback with a two-phase induction motor eliminates the need for a variable control voltage source.