Optimized Rotary Transformer Design for Self-Excited Synchronous Traction Motors in EVs

Abstract

This paper presents the design, modeling, and optimization of a high-frequency axial rotary transformer for wireless power transmission in self-excited synchronous traction motors for electric vehicles. Traditional self-excited synchronous motors suffer from significant reliability issues due to mechanical brushes and slip rings used for rotor excitation. To overcome this limitation, a rotary transformer-based contactless excitation system operating at 33.8 kHz is proposed. Ferrite core material is chosen due to its low eddy current losses, thermal stability, and high permeability at high frequencies. Analytical modeling was performed to calculate leakage and mutual inductance forming the basis for the equivalent circuit models. The design was further validated using finite element analysis in ANSYS Maxwell. A Screening-Based optimization algorithm was employed to minimize copper losses while ensuring adequate voltage and current levels. The optimal design achieved with 10 primary and 15 secondary turns demonstrated effective power transmission and thermal robustness. © 2025 IEEE.