## 4 Influence of Magnetic Load and Current Density on Temperature
### Combined Effect of Magnetic Load and Current Density on Temperature  
Four schemes are proposed to explore the combined effects of magnetic load and current density on temperature under rated load. Among them, the current density of Case 1 and Case 2 remains unchanged, while the magnetic load is changed. The air-gap magnetic flux densities of Case 3 and Case 4 are unchanged, and the current densities are changed. In addition, the back-EMF, stator outer diameter, and slot fill rate of the four schemes also remain unchanged. The parameters of the four schemes are shown in Table 2. As shown, the permanent magnet thickness and pole embrace of Case 1 are increased to achieve higher magnetic load, while the pole embrace of Case 2 is decreased to reduce the magnetic load. Furthermore, to maintain the same back-EMF, the core length of Case 1 is shortened, while the core length of Case 2 is increased. For Case 3 and Case 4, in order to achieve higher current density, the parallel winding number is reduced in Case 3, and in Case 4, the parallel winding number is increased to reduce the current density. To guarantee the same slot fill rate of 75%, the slot area of Case 3 is reduced and the slot area of Case 4 is increased. Figure 12: Temperature distributions under 2 A/mm\({}^{2}\) and 6 A/mm\({}^{2}\): (**a**) whole temperature distribution under 2 A/mm\({}^{2}\); (**b**) partial temperature distribution under 2 A/mm\({}^{2}\); (**c**) whole temperature distribution under 6 A/mm\({}^{2}\); (**d**) partial temperature distribution under 6 A/mm\({}^{2}\). Figure 13: Temperature comparisons under different current densities: (**a**) temperature comparisons of rotor yoke, stator yoke, and PM; (**b**) temperature comparisons of stator teeth and winding. After 2D-FEA simulation using Ansys Maxwell software, the stator core loss, rotor core loss, eddy current loss of the PM, and copper loss under rated load are obtained, as shown in Figure 15. It can be seen that Case 4 has the largest stator core loss, which is 4548 W. This is because, among the four schemes, Case 4 has the same maximum stator teeth magnetic flux density as Case 1, and the core length of Case 4 is longer than that of Case 1. The stator core loss of Case 3 is the smallest, which is 2978 W, because although the stator magnetic flux density of Case 3 is larger than that of Case 2 (which has the smallest stator magnetic flux density), the core length of Case 3 is shorter than that of Case 2. In addition, the stator core losses for Case 1 and Case 2 are 3923 W and 3284 W, respectively. The stator core loss of Case 1 is larger than that of Case 2; this is because although the core length of Case 1 is shorter than Case 2, the magnetic load is larger. For the rotor core loss, the maximum value is 58 W in Case 2. For eddy current loss of the PM, Case 3 has the largest eddy current loss at 700 W. The smallest eddy current loss of the PM is 527 W, which occurs in Case 2. In addition, the maximum copper loss is 16,005 W, which appears in Case 3; this is because Case 3 has the highest current density. The copper loss of Case 4 is the smallest, at 9407 W, because the current density of Case 4 is the smallest. For Case 1 and Case 2, since the core length of Case 2 is longer than that of Case 1, and the current densities of the two cases are the same, the copper loss of Case 2 is larger. Figures 16 and 17 show the temperature distribution and comparison under the four schemes. From the figure, the temperature of each part of Case 3 is the highest: temperature of the stator winding is 150 \({}^{\circ}\)C, and the temperature of PM is 75.6 \({}^{\circ}\)C. In contrast, Case 4 has the lowest temperature: the stator winding temperature is 102.2 \({}^{\circ}\)C, and the PM temperature is 66 \({}^{\circ}\)C. For Case 1 and Case 2, Case 1 (with the higher magnetic load) has the lower temperature.