The potential of brushless doubly-fed machines for adjustable speed drives

The more widespread adoption of adjustable-speed drives to promote process efficiency through energy conservation is currently hampered by the high cost of power electronic conversion units for use with AC motors. The examination of alternative methods of obtaining speed control in both synchronous and induction machines leads to the conclusion that a self-cascaded machine has considerable promise. The motor has six input terminals to the same stator windings: one three-phase set presenting a different pole number to the other three-phase set. The rotor is a specialized form of a robust cage construction without slip rings. When operated in a doubly-fed mode, this machine requires only a fraction of its input power to be processed by a power electronic converter. The resulting system has the potential to provide a low cost, robust, fault-tolerant, precise speed, and adjustable speed drive