Small Cogging-Torque Transverse-Flux Motor With Magnetic Short Circuit Under Unloaded Condition

Transverse-flux motors are easy to design for multipole structures without complicated winding geometry, and therefore, are suitable for high-torque generation. However, most of them employ surface-mounted or flux-concentrated permanent-magnet rotors, the magnets of which are placed on flux paths resulting from the coil excitation. This results in low permeance for the coil-excited magnetomotive force and many magnets on the rotor. To solve the problems, we designed a consequent-pole motor capable of generating almost the same torque with high permeance and half the amount of the magnets compared with conventional motors, so far. However, the motor also has a large cogging torque. This paper presents the fundamental design of a novel transverse-flux motor with small cogging torque by short circuit of the rotor-magnet flux inside the rotor only under unloaded condition and numerical-analysis verification of the drive principle. The analysis results indicate that the proposed motor can generate larger torque for the same current condition and 32× less cogging torque than the previously designed consequent-pole transverse-flux motor.