Coupled electromagnetic-thermal analysis of electric machines including transient operation based on finite element techniques

Since the mass and volume of electric machines are heavily dependent on their thermal constraints, it is important to find ways to analyze and simultaneously optimize their electromagnetic (EM) and thermal performances. This paper presents an approach for coupling the finite element EM and thermal analyses of electrical machines using temperature-dependent material properties so that temperatures inside a candidate machine can be predicted simultaneously with its electromagnetic performance. In addition to steady-state conditions, the coupled analysis has been extended in this paper to transient operation for machines that are required to deliver high torque/power for short intervals. Three 30 kW 10-pole 12-slot surface PM machines optimized for maximum torque density, minimum cost, and maximum efficiency, respectively, have been investigated. This coupled EM-thermal analysis makes it easier for designers to maximize the winding current density to achieve the highest possible torque/power ratings within thermal limits set by the winding insulation or demagnetization limits.