Development of efficient electromagnetic-thermal coupled model of electric machines based on finite element analysis

Multi-physics optimization of an electrical machine design requires that its electromagnetic (EM) and thermal performance must be analyzed and optimized simultaneously since electric machines are heavily constrained by thermal limits. This paper presents the development of coupled models for the EM and thermal finite element (FE) analysis of electrical machines. Temperature-dependent material properties are used so that temperatures inside the machine can be predicted simultaneously with the EM performance. Three 30 kW fractional-slot concentrated winding surface PM machines optimized for maximum torque density, minimum cost, and maximum efficiency have been investigated in order to demonstrate this approach. The results show that the coupled EM/thermal models provide an efficient means of determining the maximum steady-state current density for electric machines that will meet predefined thermal constraints and avoid demagnetization of the rotor magnets. A procedure for efficiently identifying the maximum allowable current density using numerical methods is presented.