Optimisation of the torque quality of a combined phase transverse flux machine for traction applications

Transverse flux machines can be a torque dense solution for applications requiring a relatively low speed such as electrically assisted bicycles or scooters. Common drawbacks include a high torque ripple caused by a high cogging torque and high back electromotive force harmonics. Cogging torque is of particular importance as it can be felt even when the system is disengaged and the bicycle is being pushed. This paper uses an optimisation procedure to reduce the cogging torque and overall torque ripple of a recently introduced type of transverse flux machine. This machine topology has been shown to have a 10% increase in torque compared to more conventional TFM designs but at the cost of an increased cogging torque and therefore torque ripple. During the optimisation there is a trade-off between reductions in cogging torque and the overall torque production of the machine, this will be analysed and compared to a more conventional TFM design to ensure the benefits of the newer design continue.