High frequency exciter of electrically excited synchronous motors for vehicle applications

Future electric vehicles requires electric motors with excellent torque-speed characteristics, high efficiency, and low costs. Equipped with controllable rotor flux, electrically excited synchronous motors are able to provide high torque at low speed and high efficiency at high speed. However, brushes and slip rings for field windings need maintenance and may influence reliability. In this paper a brushless power transferring approach through a high frequency rotating exciter is presented. Compared with conventional rotating exciters, the high frequency exciter is much more compact and energy efficient due to high energy conversion frequency. This enables the exciter to be integrated in the rotor and provides opportunities for electrically excited synchronous motors to compete with other motors in vehicle applications. A prototype of the rotating exciters with SiC based converter, Litz wire, and shaft-end mounting structure has been built and measured in standalone tests and combined tests with a synchronous machine.