Investigations on Rotary Transformer Configurations for Brushless Operation of Electrically-Excited Synchronous Machines

Permanent magnet AC (PMAC) machines are popular in high-end applications due to their high power density and efficiency but rely on rare-earth materials, require complex and limited field weakening operations, and are prone to the risk of demagnetization of permanent magnets. On the other hand, the electrically/hybrid-excited synchronous machines (EESMs/HESMs) are immune to these problems but employ brush and slip ring-based field excitation mechanism, which poses a challenge for high-performance applications. In this regard, rotary transformer-based technology offers a promising brushless field excitation mechanism. Therefore, in this paper, several configurations of rotary transformer reported in literature are studied and the five most promising ones are selected for further investigations. These five configurations are analytically modeled and simulated using finite element analysis (FEA), maintaining consistent nominal ratings. The results of analytical models and 3D FEA simulations show good agreement. Finally, the parameters and performance indices of the five configurations are compared, and based on the relative merits, the most suitable configuration is recommended for EESMs/HESMs.