Seguchi, M., "Self-Excited Wound-Field Synchronous Motors for xEV," SAE Int. J. Alt. Power. 6(2):2017, doi:10.4271/2017-01-1249.
Compact, high efficiency and high reliability are required for an xEV motor generator. IPM rotors with neodymium magnets are widely applied for xEV motors to achieve these requirements. However, neodymium magnet material has a big impact on motor cost and there is supply chain risk due to increased usage of these rare earth materials for future automotive xEV’s. On the other hand, a wound-field rotor does not need magnets and can achieve equivalent performance to an IPM rotor. However, brushes are required in order to supply current to the winding coil of the rotor. This may cause insulation issues on xEV motors which utilize high voltage and high currents. Therefore, it is suggested to develop a system which supplies electric energy to the rotor field winding coil from the stator without brushes by applying a transformer between stator coil and rotor field winding. Specifically, add auxiliary magnetic poles between each field winding pole and wind sub-coils to these poles. The magnetic flux generated from the stator induces a field current in the sub-coils. Rectifying the induced current by a diode enables applying direct current to the field windings of the rotor. This paper confirms the equivalent performance between an IPM rotor and wound-field rotor by FEM simulation.