Experimental study on cogging-torque reduction of transverse-flux motor with skewed armature cores

Abstract

Transverse-flux motors are suitable for getting high torque density by increasing their number of poles owing to the independent coil design from the number of poles. However, these kinds of motors typically have a large amount of permanent magnets with increasing the number of poles. We have designed a transverse-flux motor with a consequent-pole rotor having almost half amount of magnets compared with conventional surface-mounted magnet rotors. Although this motor can generate comparably large average torque to the conventional motors, it has larger cogging torque. And, conventional skew structures, often applied to axially uniform motors, are generally effective for reducing the cogging torque by offsetting dominant harmonic components but cannot be applied to transverse-flux motors including our motor due to their axially non-uniform structure. This paper describes radially skewed armature cores, compatible to basic configuration of general transverse-flux motors, for the cogging torque reduction of our motor. Results of FEM magnetic analysis and its spectral analysis indicate that the most dominant harmonic component of the cogging torque reduces by 96%, and consequently, peak-to-peak value of the three-phase cogging torque reduces by 87%. These analysis results are almost agreed with experimental result, in which the most dominant harmonic component reduces by 86% and peak-to-peak value of the cogging torque can be approximately estimated to decrease by 82%. Therefore, the radial skew structure could be verified to effectively suppress the cogging torque of the transverse-flux motor.

Keywords

• cogging torque reduction
• radially skewed cores
• transverse flux motor
• consequent pole rotor
• experimental study
• fft spectral analysis
• fem magnetic analysis