## 3 Electromagnetic Characteristic Analysis
### Loss Analysis
The stator winding loss of the motor is about 33.31 W.  
The motor rotor includes a rotor core and permanent magnet. The axial flux permanent magnet motor will produce induced electromotive force during operation. The periodic change of induced electromotive force will cause eddy current loss in both the rotor core and permanent magnet. Maxwell software is used to analyze the eddy current loss of the rotor core and the permanent magnet, respectively. The simulation conditions are consistent with those used for simulating the average torque values. The rotor core is modeled as a solid in the simulation process. The eddy current vector distribution of the rotor core is shown in Figure 21, and the eddy current vector distribution of the permanent magnet is shown in Figure 22.  
During the solution process, rational mesh division will significantly enhance the solution accuracy. For the axial flux permanent magnet motor, the stator components are stationary parts with relatively low precision requirements; hence, larger-sized elements are used for meshing. The permanent magnets and rotor core are moving parts that require higher computational accuracy; thus, smaller-sized elements are selected. The air gap, being the core component where energy conversion takes place in the motor, demands extremely high computational accuracy. Very-small-sized mesh elements are chosen for the air gap, but the size should not be excessively small, otherwise the computational simulation process would become excessively lengthy. The remaining parts of the solution domain have lower accuracy requirements and can be meshed with relatively larger-sized elements. \[P_{\text{h}}=k_{\text{h}}\cdot f\cdot B_{\text{m}}^{\alpha} \tag{8}\]0 Eddy current vector distribution in the rotor core. Therefore, in the simulation mesh division, the stator uses a meshing unit with a length of 2 mm, the rotor and permanent magnet use a meshing unit with a length of 1 mm, the air gap uses a meshing unit with a length of 0.5 mm, and the rest of the solution domain uses a meshing unit with a length of 4 mm. The meshing result is shown in \[P_{\text{h}}=k_{\text{h}}\cdot f\cdot B_{\text{m}}^{\alpha} \tag{8}\]1  
The core material of the rotor is stainless steel 304, and its conductivity is 1.4 \(\times\) 10\({}^{6}\) S/m. The conductivity of the rotor core is specified in the Maxwell transient solver to simulate the eddy current loss. The eddy current loss of the rotor core is shown in Figure 24, and it is about 113 mW. The permanent magnet material is N45 SH, and its conductivity is 10\({}^{-6}\) S/m. The conductivity of the permanent magnet is specified in the Maxwell transient solver to simulate the eddy current loss. The eddy current loss of the permanent magnet is shown in Figure 25, and it is about 421 mW. \[P_{\text{h}}=k_{\text{h}}\cdot f\cdot B_{\text{m}}^{\alpha} \tag{8}\]2 Manual meshing result of axial flux permanent magnet motor: (**a**) full model; (**b**) quarter model. \[P_{\text{h}}=k_{\text{h}}\cdot f\cdot B_{\text{m}}^{\alpha} \tag{8}\]3 Eddy current vector distribution in permanent magnet. There are two kinds of mechanical losses of axial flux permanent magnet motor. Bearing friction loss is related to the bearing speed, bearing type, and lubricant characteristics. Rotor wind friction loss is related to parameters such as coolant density and dynamic viscosity. It is difficult to accurately calculate the mechanical losses. According to the relevant research, the empirical formula of mechanical loss is as follows:  
\[P_{\text{h}}=k_{\text{h}}\cdot f\cdot B_{\text{m}}^{\alpha} \tag{8}\]4  
where \(P_{\text{f}}\) is the mechanical loss of the motor, \(P_{\text{Bf}}\) is the friction loss of the bearing, \(P_{\text{Wf}}\) is the wind friction loss of the rotor, and \(P_{\text{out}}\) is the rated output power of the motor.