Generalized Design Method of the Three-Phase Y-Connected Wound Rotor for Both Additive Modulation and Differential Modulation Brushless Doubly Fed Machines

The brushless doubly fed machine (BDFM), which eliminates slip rings and brushes, shows great potential in application fields where reliability is a prime concern. This paper presents the generalized design methodology of the novel three-phase Y-connected wound rotor for both additive modulation BDFM and differential modulation BDFM with specific schemes. First, the above two types of BDFMs are explicated by magnetic field modulations of two main magnetic fields. Then, design principles are illustrated to further improve the conductor utilization ratio of the rotor winding (RW) and reduce harmonic contents of the magnetomotive force (MMF) with a three-phase AC winding. Design examples and specific procedures of the proposed novel three-phase Y-connected wound rotor are also presented for both additive and differential modulation BDFMs, respectively. Finally, finite element models of two types of the BDFM are established and a differential modulation prototype is manufactured. Proposed design schemes are verified by comparative simulation and experimental results at different speeds and load conditions.