A Wide-Range Static Inverter Suitable for AC Induction Motor Drives

A dc to ac, variable voltage, variable frequency, three-phase, external impulse commutated inverter, rated at 200 kVA, is described that controls the speed of an induction motor that is suitable for traction applications. The inverter is supplied from a variable voltage dc source for the load circuit and a fixed voltage dc source for the commutation circuit. Isolation between the two sources is provided by a high-frequency pulse transformer. The output ac voltage is controlled from 0 to 250 volts; the output frequency is controlled from 4 to 400 Hz. The load is a low-slip, 12 000 r/min induction motor with a continuous rating of 15 hp over a 10:1 speed range, and 60 hp over a 2:1 speed range. The theory of operation and design equations for the inverter power circuit, the design and construction of the motor, and the test results of the inverter-motor combination are presented.