Identification of design rules for interior PM motors with different cooling systems

The conventional scaling rules for the optimal design of electric machines are best suited for naturally cooled machines with stator winding current densities less than 4A/mm2. In this paper, through a comprehensive sensitivity analysis, first, it is demonstrated that the correlations between some geometric variables and the performance metrics of interior permanent magnet (IPM) motors vary significantly with respect to the stator winding current density. For this purpose, three current densities are selected so as to approximately account for naturally cooled, fan-cooled and liquid-cooled machines. Subsequently, a parameterized IPM motor is optimized at these current densities through a large-scale design optimization algorithm by evaluating a total of 20,000 design candidates. The 100 best designs from each group are then identified and extracted to investigate the scaling rules for the optimal design of such IPM motors with different cooling systems. The outcomes of the study are in correspondence with the conventional design principles for naturally cooled machines. Nevertheless, it is illustrated that these rules vary for fan-cooled and liquid-cooled machines owing to the increased ampere loading, and also heavy saturation of the magnetic core in such machines. A configuration of a 50 hp, 48-slot, 8-pole IPM motor with a single-layer v-type magnet is used as the benchmark of this study.