Maximised torque and minimised magnet use in permanent magnet machines for automotive applications

Permanent magnet (PM) machines are a very promising design alternative in comparison with other types of electrical machines. However, the price of rare-earth magnets has become a serious concern. The goal of this study is to compare the torque capability and electromagnetic performance of PM machines of different sizes. Generally, smaller size is a profound advantage, but may constitute a deficiency from the thermal point of view by contributing to a higher loss density, which makes the cooling of the machine more problematic. Therefore, to overcome this problem, this paper also predicts the temperature and heat transfer exposure of PM machines by proposing a thermal modeling method using suitable coolant. This paper finally determines the most suitable size of a smaller PM machine in order to reduce the usage of rare-earth magnets and other materials but which still maintains the output performance of the reference PM machine.