ABSTRACT
High speed high power variable speed drives (rated at 750kW or higher) often use synchronous motors. For such high ratings the dc commutator motor becomes too expensive and induction motor drives require complicated, forced commutated inverters. The synchronous motor is capable of working at a leading power factor and thus can provide load commutation to the inverter. The current source inverter becomes rather simple and may use slow, less expensive, thyristors (ioff=200 to 300 s). To reduce torque pulsations at low speeds, pulse-width modulation of the otherwise rectangular stator currents may be used. Here, we present the basic scheme, steady-state equations and performance with load commutation and a high performance control system which provides constant leading power factor with load and speed response without overshoot.
