Rotary Transformer Design for Brushless Electrically Excited Synchronous Machines

In modern automotive drive applications, Electrically Excited Synchronous Machines (ESM) have become an alternative to PSMs. Until now, ESMs need slip-rings to supply the rotor winding. However, carbon brush slip-ring systems are sensitive to environmental influences and produce conductive carbon dust during operation. This paper discusses the construction of a contactless energy transfer system to replace the slip-ring system in an electrical machine. The focus is laid on the power transferring device, a rotary transformer. Basic loss modelling methods are discussed, and an analytical model for winding losses is created. The model´s range of validity is increased by scaling rules, and it is verified by FEM software and practical measurements. The results were used for the dimensioning of a contactless power transfer system.