PCB Winding-based High-frequency Three-winding Rotary Transformer Enabling Brushless Bipolar Field Control from Stator of EESM/HESM

Permanent magnet AC (PMAC) machines are popular in high-end applications due to their high power density and efficiency. They rely on rare-earth materials, provide limited field weakening and over-load operation, and are prone to the risk of demagnetization of the permanent magnets. On the other hand, electrically/hybrid-excited synchronous machines (EESMs/HESMs) can address all the above limitations but require brush and slip ring for field excitation. This poses a challenge for high-performance applications. The rotary transformer (RT) is a promising candidate for brushless/contactless field excitation of EESMs/HESMs. Therefore, in this paper, a three-winding RT utilizing PCB-printed windings is modeled in 3D finite element method (FEM) taking eddy current effects into account, which are prominent at high frequency. This study shows that interposed secondary winding configuration improves power equalization between the two secondaries. Three topologies with varying number of winding layers are modeled and compared. In addition, the PCB trace dimensions are optimized based on the required performance indices. Finally, the RT is modeled with three different core shapes. The core size is optimized with threelayer secondary winding topology. The L-L core configuration is recommended for the use in deriving brushless field excitation system for EESMs/HESMs.