Toshikatsu Akiba

Fundamental Design of a Consequent-Pole Transverse-Flux Motor for Direct-Drive Systems

Transverse-flux motors are suitable for large-torque generation because multipole devices are easy to be designed. However, these motors employ a surface permanent magnet rotor that consists of many magnets and mainly depend not on reluctance torque, but on magnetic torque, which is generated by the interaction between the magnetic fluxes produced by the magnets and stator-winding excitation. This paper proposes a consequent-pole transverse-flux motor that generates almost the same torque as conventional transverse-flux motors but uses half the number of magnets by generating both magnetic torque and reluctance torque.

Cogging-Torque Reduction of Transverse-Flux Motor by Skewing Stator Poles

Transverse-flux motors basically have coils wound in the rotational direction and armature cores surrounding them. This configuration allows the motors to be designed for multipole structures with the simple coil geometry independent of the pole number. Therefore, they have an advantage on high-torque generation over most motors having windings wound around teeth and put in slots. However, transverse-flux motors still have a production problem for their multipole rotor due to the assembly of the small and numerous permanent magnets. Thus, we have designed a consequent-pole transverse-flux motor, having a half amount of magnets on the rotor compared with the conventional surface-mounted magnet rotors, and capable of generating almost the same torque under the same size and excitation conditions. However, this motor also has large cogging torque due to the consequent poles, having deformed magnetomotive-force distribution. Thus, we propose a new skewed core structure for reducing the cogging torque, compatible to axially non-uniform structure of this motor. The Finite Element Method analysis result indicates the peak-to-peak value of the cogging torque that can reduce by 82% with this proposed skewed structure.

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.