Investigation of appropriate pole number combinations for brushless doubly fed machines applied to pump drives

Three alternative brushless doubly-fed induction machine (BDFM) pump drive configurations are investigated as a replacement for a 60 hp wound rotor induction machine drive. The BDFM, utilizing a bidirectional power converter to realize precise (synchronous) speed control, is shown to require a power electronic converter of substantially reduced rating which can result in significant system cost savings. In addition, the BDFM system offers controlled, unity power factor operation. A procedure for analyzing BDFM designs is presented (with examples) and steady state performance results are predicted for the BDFM pump drives. This paper explains the design decisions that are made in regards to power converter rating and pole-pair selection.