## 2 Structure of Flared-Shaped IPM and Proposed Flared-Type CP IPM Motor  
### Typical Flared IPM Motor with Conventional PM Rotor Structure (Baseline Design)  
Recently, ferrite magnets have been used due to their low cost and stable supply So, a number of studies have shown that a structure of ferrite magnets inserted into the rotor can be modified for high efficiency and power. Based on this background, a structure of flared-shaped IPM motor using a flared-shape arrangement of ferrite magnets has been proposed and compared to a conventional ferrite IPM motor, and it has been confirmed that the flared-shape arrangement of ferrite magnets is helpful to maximize the use of the magnetic flux.  
A flared rotor structure allows more ferrite magnets to be inserted within the limited rotor structure. The main feature is that the permanent magnets are arranged in a flared form inside the rotor in order to fit as many magnets as possible into a limited structure. So, the pole of a flared rotor structure comprises several ferrite PMs. Additionally, the flared rotor structure has the characteristic that the magnetic flux lines from several magnets converge at the center of the pole. This advantage has the effect of concentrating magnetic flux like a spoke rotor structure. Therefore, the flared IPM motor is suitable for applications requiring low cost and high output, particularly as the cost of magnet materials can be greatly reduced compared to the NdFeB IPM motor in our previous work [20]. The flared rotor structure arranges several magnets in a flared shape, so it is easy to adjust the angle of the magnetic pole. Therefore, if the flared structure is adjusted, the angle of the magnetic pole may change, causing a change in the waveform. By optimizing the flared structure through GA, the shape of the rotor and ferrite magnets is optimized. Therefore, the optimal design model can effectively utilize magnetic flux and reduce the torque ripple of the proposed flared motor. As a result, the improvement of torque ripple was effective in the suppression of noise and vibration. To verify the analysis results, the optimal model is manufactured and verified by experimental results in our previous work [21; 22]. Figure 1 shows the structure of the IPM model with a flared pole structure. Also, in Figure 1, A, B, and C indicate phases, and (+) and (\(-\)) indicate input and output of phases. Additionally, the N-pole consists of 4 red magnets, and the S-pole consists of 4 blue magnets. The yellow arrow indicates the direction of the magnetic field lines generated from one magnet.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **Item** & **Unit** & **Value** & **Notes** \\ \hline \multicolumn{3}{c}{Number of poles/slots} & - & 8 poles/12 slots & - \\  & outer diameter & mm & \(\Phi\) 95.0 & \\ Stator & inner diameter & mm & \(\Phi\) 53.5 & 35H270 \\  & stack (Height) & mm & 27.5 & \\  & outer diameter & mm & \(\Phi\) 52.5 & \\ Rotor & inner diameter & mm & \(\Phi\) 16.5 & 35H270 \\  & stack & mm & 27.5 & \\ Magnet & material & - & ferrite (9 BE) & Br 0.42[T] \\ \multicolumn{3}{c}{size} & mm \(\times\) deg. & 3.0 \(\times\) 26.5 & (thickness \(\times\) angle) \\ \multicolumn{3}{c}{} \\ \multirow{2}{*}{Winding} & material & - & copper & - \\  & wire diameter \(\times\) turns & - & \(\Phi\) 1.0 \(\times\) 30 turns & concentrated type \\ \hline \hline \end{tabular}
\end{table}
Table 1: Specifications of the standard flared-shaped IPM model.  
Figure 1: Typical structure of flared-shaped IPM motor (1/4 model).