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.