Design of a Wound Rotor Brushless Doubly-Fed Machine With 1/5 Pole-Pair Combination

The brushless doubly-fed machine (BDFM) can be used in the variable speed constant frequency field. For BDFM, the choice of the pole-pair combination and the design of the rotor are significant. The output factor of the BDFM with 1/5 pole-pair combination is higher than that of the 2/4 pole-pair counterpart. However, the rotor of the BDFM with 1/5 pole-pair combination is hard to design for its wide pole-pair ratio. This article presents a 1/5 pole-pair combination BDFM used in hydropower with a three-phase symmetrical wound rotor to solve the design challenge. First, the magnetic field modulation theory of the BDFM and the optimal output power in terms of different pole-pair combinations are introduced. Then, the slot-number phase diagram and the ampere-conductor wave method are applied to design windings of a BDFM with 1/5 pole-pair combination. Finally, the finite element (FE) models of the 1/5 and the 2/4 pole-pair combination BDFMs are established for comparison. A prototype of the 1/5 pole-pair combination is manufactured based on the proposed design scheme. Simulated and experimental results verified the feasibility of the design scheme.