Consideration of magnet materials in the design of PMSMs for HEVs application

This paper discusses two vital issues regarding design and performance of high power Permanent Magnet Synchronous Machines (PMSMs) using different magnet materials; high temperature applications and machine design without using rare earth permanent magnets. In the first part, designs were developed using NdFeB and SmCo magnets for hybrid bus application. They were evaluated at different temperatures taking into account the fact that remanent flux density of NdFeB magnets reduces with increase in temperature at faster rate than that of SmCo magnets. Based upon the torque-speed and efficiency plots of the machines, feasibility of the designs are suggested for specific temperature range. Ferrite magnets can also work at higher temperature than NdFeB but they provide significantly less flux density. Four variants of PMSMs using ferrite magnets are designed and discussed here. Comparison of their torque speed and efficiency characteristics is made with that of the NdFeB machine having the same volume. The results lead to design consequences of PMSMs in the absence of rare earth magnet materials.