Improvement of Magnetic Coupling by Simple Modification of Pot Core Rotary Transformers

Wound field synchronous motors are increasingly considered for automotive applications thanks to their operational flexibility and good power density. Nevertheless, the conventional solution for supplying the field winding using sliprings and brushes suffers of various issues. Rotary transformers may provide an interesting alternative, as they permit to transfer power between moving parts without physical contact. Anyway, to such aim a gap has to be introduced between stationary and rotary parts: this affects the magnetic coupling, turning into a larger magnetizing current. This paper investigates a simple modification of common hollow ferrite pot cores permitting to reduce the equivalent reluctance of the gap in axial flux rotary transformers. The solution is analyzed using both reluctance network and finite elements simulations, calculating the main parameters and comparing to the related conventional solution. The results confirm an appreciable increase of the magnetizing inductance while maintaining comparable leakage inductances, leading to a better operation with improved efficiency.