## 2 Structure and Principle
### A New DHPM Vernier Motor Using Saddle Coil and Salient Pole  
A DHPM-type vernier motor (the predecessor) was prepared to reduce the PMs on the rotor by half. In addition, it reduces the use of PMs on the stator by half by adding a coil-based electromagnet. The result demonstrates that the DHPM-type vernier motor exhibits higher performance than the typical SPM-type counterpart. However, it requires a large number of PMs. Previously, motors employing electromagnet coils and PMs on the stator side--that is, predecessors of this work--have been proposed [12]. Recent studies suggest a design that mounts the magnet near the tooth's center for motors with PMs on \begin{table}
\begin{tabular}{c c} \hline Air gap length & 0.5 mm \\ Coil & 0.8 mm, 1.09 \(\Omega\) \\ Coil turn number & 150 \\ Magnetic thickness & 2 mm \\ Outside diameter & 84 mm \\ Thickness & 35 mm \\ \hline \end{tabular}
\end{table} 
Table 1: Major specifications. Figure 1: Conventional double half permanent magnet (DHPM)-type vernier motor (predecessor). the stator side. This method has the advantages of reducing the electromagnet inductance, increasing the torque integer, and reducing rotational speed. Due to the fixed polarity of the PM, the motor performance does not increase as expected by generating the short-circuit flux when a three-phase alternating current flows through the stator coils. This result is the case even when the PM has been added to the stator electromagnets. To solve this problem, in the proposed motor, we replaced the PMs in the stator with salient poles and designed them to be inclined to the shape of a stator, as depicted in Figures 2 and 3, respectively. Furthermore, the stator core and salient pole are graded. Therefore, the proposed DHPM vernier motor employs a new saddle-shaped winding coil. However, Figure 1 displays the shape of the rotor within the predecessor, replacing one of the PM magnetic poles installed in the rotor of the SPM-type vernier motor with a salient pole. The newly proposed model of the new DHPM vernier motor is also of the same construction, and the air gap between the stator and rotor is the same. Figure 3: Design of the new double half permanent magnet (DHPM) vernier motor; (**a**) New DHPM vernier motor, (**b**) The shape of slot cores and salient poles on the inclination. Figure 2: Newly presented double half permanent magnet (DHPM)-type vernier motor. The comparison model in Figure 1 (the predecessor) is the DHPM vernier motor with PMs placed on the stator. The proposed models in Figures 2 and 3 are structures arranged by replacing the PMs with salient poles. Furthermore, the salient poles and slot cores are trapezoidal. Compared to the predecessor model in Figure 1, the proposed model in Figure 2 has the same outer diameter size, and the cross-sectional area is reduced depending on the inclination angle. Thus, the proposed model with saddle coils and salient poles has the advantage that it has greater torque than the comparison model even though it uses the same number of coil windings. The coils of the predecessor and proposed models are wound using the same pattern, parallel to the axis. The turns of the windings are the same. Thus, the resistance on the coils is almost the same. Moreover, the proposed model reduces the volume and surface area, which proportionally decreases the magnetic resistance. When the coils are winding to the stator of a newly designed motor, the shape is different from that of a conventional cylindrical motor. If the direction of the coil winding within the slot is called the \(Z\)-axis, the stator of the motor newly designed between \(Z=0\) and \(Z=\mathsf{x}\) is inclined. The height of the coil wound around the slot by this angle increases linearly, resulting in the shape of the coil winding around the slot core of the teeth's part being the same as that of the saddle.