Magnetic Circuit Feature Investigation of a Radial-Axial Brushless Hybrid Excitation Machine for Electric Vehicles

The magnetic circuit feature of a radial-axial brushless hybrid excitation machine (RA-BHEM) is studied in this article. An axial stator is placed on one side of the rotor, which is wound with ac excitation winding to adjust the air-gap flux flexibly to make it have good flux regulation capability. The flux distribution of the RA-BHEM is a radial-axial 3-D mixed magnetic circuit, which is difficult to be analyzed by the 2-D finite-element analysis (FEA). Therefore, a radial-axial equivalent magnetic circuit (RAEMC) model is established to obtain the air-gap flux density with different excitation magnetomotive forces (MMFs), which simplifies the design process and reduces the amount of calculation. The flux density distribution in different MMFs is analyzed by 3-D finite FEA and the results are consistent with the RAEMC model results. The torque characteristics in the low-speed region and the flux-weakening capability in the high-speed region are analyzed to verify the possibility of the proposed machine in the field of electric vehicles (EVs). Finally, a 2-kW prototype is manufactured to verify the correctness of the above analysis.