## 2 Proposed FP-AFPMG and Optimization Process  
### Proposed FP-AFPMG  
In order to upgrade the output power (\(P_{out}\)) of the three-phase AFPMG shown in Figure 1 for standalone wind turbine power generation in remote areas, some improvements were added without changing the number of the stator winding turns and the diameter of the conductor in each phase. The first improvement shown in Figure 2 is carried out by adding one stator core placed on the upper side and one stator core placed on the lower sides of the original  
Figure 1: Original shape of the most qualified axial flux permanent magnet generator in [10]. generator. The stator cores are added in order to upgrade the output power (\(P_{out}\)) and to limit the diameter of the generator. The number of stator slots and the dimension of the stator slot are equal with the original generator. The thickness of the stator yoke on the upper and lower side of the generator shown in Figure 2 is half the thickness of the stator yoke of the original generator. The second improvement is carried out by changing the winding type from core wound to tooth wound. Due to the addition of the stator core on the upper and lower sides of the original generator, the number of the flux lines flowing on the middle stator yoke is higher than the upper and lower stator yokes, as illustrated in Figure 3.  
When using the core wound winding type, the voltage (\(E_{f}\)) generated in each coil located in layer 2 is higher than the coil located in layer 1 and layer 3, as shown in Figure 4a. To generate equal \(E_{f}\), the winding type needs to be changed from core wound to tooth wound, as shown in Figure 4b. By generating equal \(E_{f}\) between each of the coils located in layer 1, layer 2, layer 3, and layer 4 of Figure 4b, the coil can be more easily connected in parallel or in series. The third improvement is carried out by modifying the permanent magnet shape, as shown in Figure 5. Figure 5a,c is the permanent magnet shapes of the original generator. To simplify the manufacturing process of the permanent magnet in Figure 5a, its shape is modified to the permanent magnet shape shown in Figure 5b. Furthermore, the arc-shaped permanent magnet (PM) with an arc height of 2 mm, as shown in Figure 5d, is employed in order to make the flux density in the air gap more sinusoidally distributed. By improving the flux density waveform close to a sinusoidal waveform, the THD of the on-load voltage waveform (\(V_{t}\)) can be improved. Figure 3: Flux lines in the magnetic circuit of the proposed generator. Figure 2: Modified shape of the original generator in Figure 1.  
Along with the rapid development of power electronic devices and efforts to improve generator performances, the last improvement is carried out by changing the phase system of the original generator into a five-phase system. As a five-phase system is categorized into a multiphase system, the power density (\(P_{density}\)) of the generator can be increased and the ripple torque produced by the generator can be decreased, as stated in Section 1. To restrict the flux density in the stator teeth at around 1.5 T to 2 T and in the stator yoke at around 1.1 T to 1.5 T, according to [11], the generator is firstly simulated in a magnetostatic solution type from the Ansys Maxwell software under a constant permanent magnet dimension and a constant air gap length. After the simulation is complete, the dimensions of the generator were tabulated in Table 1 and illustrated in a three-dimensional model in Figure 6. \begin{table}
\begin{tabular}{c c c} \hline
**No** & **Part** & **Dimension (mm)** \\ \hline
1 & Inner and outer diameters & 135 and 233 \\
2 & Air gap length & 1 \\
3 & Upper and lower sides stator yoke & 19 \\
4 & Middle side stator yoke & 38 \\
5 & Stator slot width & 12 \\
6 & Stator slot height & 20 \\
7 & Stator slot wedge height & 2 \\
8 & Stator slot opening height & 2 \\
9 & Stator slot opening width & 4.5 \\
10 & Edge thickness of the permanent magnet & 8 \\ \hline \end{tabular}
\end{table}