Influence of Slot Combination on Performance of Brushless Doubly Fed Generator with Hybrid Rotor

Brushless doubly fed generator (BDFG), a class of adjustable-speed machine with a special structure, shows great prospect in wind power generation. Since different rotor structures lead to great differences in the BDFG performance, the research of BDFG rotor structure has been a hotspot. However, only a few of the research studies have paid attention to the rotor and stator slot combination of the BDFG, especially for the BDFG with a novel hybrid rotor. Improper slot combination will lead to efficiency decrease, additional loss increase, and undesirable torque in an electrical machine. In order to study the principle of slot combination of the BDFG with the hybrid rotor, the combination approach of theoretical analysis and experiments is presented in this paper. Furthermore, a coupling factor which reflects the coupling ability of the BDFG with different slot combinations is proposed. Moreover, the best slot combination of the proposed BDFG is determined, and several parameters such as useful harmonic contents, total harmonic voltage distortion (THDu), core loss, and copper loss are considered as major criteria for judgment.