Synchronous machines with very high torque density for automotive traction applications

This paper presents the electromagnetic and thermal analysis of a salient-pole synchronous machine and a permanent magnet synchronous machine with very high torque density for a wheel hub traction drive in an electric vehicle. In order to find the best trade-off between a very high peak torque and a high efficiency throughout the whole operating range, four highly utilized machines with an outer rotor and different stator slots to pole pair combinations are modeled and analyzed by using the finite element method (FEM). The most suitable designs for automotive application of each machine type are compared with each other in terms of peak performance, driving cycle efficiency and dominant loss mechanisms. In addition to electromagnetic analysis, the thermal behavior of the two types of machines is investigated in the maximum overload operation and in a common driving cycle. As a result, the advantages and disadvantages of optimized and highly utilized salient-pole and permanent magnet synchronous machines are identified with regards to their suitability for wheel hub drives.