Importance

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Abstract

First and second input currents to a three-phase AC induction motor of either delta or wye winding configuration are directly regulated by a pair of phase-triggered, gate-controlled, semiconductor switches series-inserted between the motor and two phases of its three-phase AC power source, the third input current being the Kirchoff resultant of the two regulated input currents. The half-cycle firing points or firing angles of the gate-controlled switches are varied together to apply more or less power to the motor as a function of mechanical load to optimize the power factor of the motor. Voltage imbalances in the motor windings caused by directly regulating only two of three input currents are tolerable due to the current limiting effect of the gate-controlled switches when the induction motor is at less than full mechanical load, such current limiting minimizing heat losses (I.sup.2 R) caused by the voltage imbalance condition.

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First Claim