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

Brushless doubly-fed machines have the capability of precise (synchronous) speed control over a wide speed range through the use of a bi-directional power converter due to the magnetic coupling of two different pole numbered stator windings through a specifically configured rotor. The application of a brushless doubly-fed machine, with different pole-pair combinations is investigated for use as a limited speed range pump drive by using a steady state equivalent model developed in a companion paper. The proposed brushless doubly-fed machine designs when compared to an equivalent induction motor drive show the advantages of operation at close to unity power factor and reduced power converter rating. These results from the simulation demonstrate the substantial economic advantage of using the brushless doubly-fed machine in limited speed-range operations