Comparison between a novel claw-pole electrically magnetized synchronous machine without slip-rings and a permanent magnet machine

Electrical machines used in EV/HEV traction applications are usually driven at speeds where field weakening operation is required. In this region, electrically magnetized machines are more easily operated than permanent magnet machines. This paper discusses the performance of an electrically magnetized synchronous machine where the field coils are placed in magnetically conducting end-plates attached to the stator, eliminating the need of slip-rings. The performance is compared to a radial permanent magnet synchronous machine of similar size, using simplified thermal models and electromagnetic finite element simulations. The machines are intended to be incorporated in a novel HEV application, where the electrical machine is used to adjust the acceleration of the piston in the combustion engine in order to improve the combustion process. Results indicate that at steady state operation the permanent magnet machine is able to deliver more torque per total mass (1.74 Nm/kg) than the electrically magnetized machine (1.06 Nm/kg). This is mainly due to the increased weight or the arrangement used for the electrical magnetization.