Figure 1 shows the structure and winding pattern of the CSVFRM, which consists of a 10-pole rotor and a 12-slot stator. The coils consist of 6 phases (A, B, C, D, E, and F), which correspond to 2 sets of 3 phases alternating current. Therefore, the A and D, B and E, and C and F phases correspond to the U, V, and W phases, respectively. 3-phase AC voltages (*V*_{u}, *V*_{v}, and *V*_{w}) and DC voltages (+*V*_{dc} and -*V*_{dc}) are applied to each coil as shown in Figure 1. Therefore, the phase current consists of AC and DC components. The magnetomotive force due to the DC current is modulated by the salient poles of the rotor, and the rotating magnetic field due to the 3-phase AC current synchronizes with this modulated flux.

Figure 2 shows the control diagram of the CSVFRM operated under vector control and DC current control. The relationship between the phase current amplitude *I*_{ac}, d- and q- axes currents *i*_{d}, *i*_{q} are shown in (1).

$$\begin{array}{}{\displaystyle {I}_{ac}=\sqrt{\frac{2}{3}}\sqrt{{i}_{d}^{2}+{i}_{q}^{2}}}\end{array}$$(1)

Furthermore, in order to perform a unipolar drive, equation (2) must be satisfied.

$$\begin{array}{}{\displaystyle {I}_{ac}\le {I}_{dc}}\end{array}$$(2)

In this paper, we verify the characteristics by changing the current ratio *n* shown in (3).

$$\begin{array}{}{\displaystyle {I}_{dc}=n\sqrt{\frac{2}{3}}\sqrt{{i}_{d}^{2}+{i}_{q}^{2}}}\end{array}$$(3)

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