Electromagnetic Performance Investigation of A Brushless Electrically-Excited Synchronous Machine for Long-Distance Heavy-Duty Electric Vehicles

Journal article, 2025

Long-distance heavy-duty electric vehicles, e.g., electric trucks, expect demanding requirements from the electric drive system, including high starting torque, high torque density, high power factor, high efficiency, etc. Permanent magnet synchronous machines (PMSMs) have been widely used for traction applications. However, the high cost and associated environmental issues due to the rare-earth permanent magnet material intensify researchers to explore new solutions. Accordingly, a brushless electrically-excited synchronous machine (EESM) is designed and investigated in this paper. The brushless EESM is also quantitatively compared with a PMSM candidate for the aforementioned application. Differing from conventional EESMs in which the brushes and slip rings are used for rotor field winding excitation, a contactless/brushless rotating transformer is adopted for the presented EESM to feed the rotor field winding. It is shown that the interior PMSM exhibits higher efficiency in low-speed region, but lower efficiency in high-speed region. By contrast, the brushless EESM exhibits lower efficiency in low-speed region, but much higher efficiency in high-speed region. Hence, the EESM is more suitable for long-distance heavy-duty electric vehicle applications where significant highspeed operations are required. Moreover, compared to the PMSM, the EESM is more cost-effective, sustainable, and environmentally friendly due to the absence of the rare-earth permanent magnet material. Both the PMSM and the EESM are prototyped and manufactured. Experimental results are provided to validate the effectiveness of the presented designs.