Design Optimization of a Rotary Transformer Converter for the Excitation of Electric Machines

The rotary transformer (RT) converter transfers power from a stationary winding to a rotary winding via power electronics converter, and it is a promising solution to achieve brushless excitation for wound-rotor synchronous machines (WRSM). As the RT is a loosely coupled transformer, it usually has large leakage inductance and small magnetizing inductance. In this paper, the phase-shift full-bridge (PSFB) converter is incorporated to utilize the leakage inductance of the RT for soft-switching of the main switches. Moreover, the output filter capacitor can be saved as the field winding of the WRSM is highly inductive and can be directly connected to the output rectifier of the PSFB converter. The design optimization for the PSFB converter in this application is developed by deriving the optimal turns ratio and calculating the optimal turns number of the RT to achieve the lowest total power losses. A RT converter prototype is built, and the experimental results are provided.