Analytical prediction of optimal split ratio of consequent-pole permanent magnet machines

For consequent-pole permanent magnet (CPM) machines, the permanent magnet (PM)-arc ratio and split ratio have great influence on the output torque. This study establishes general relationship of the output torque/torque density with PM-arc ratio and split ratio considering the effects of slot/pole number combinations and the tooth-tips. In addition, both the optimal PM-arc ratio and split ratio for maximising the torque density are analytically derived and confirmed by finite-element analysis. It is found that the optimal PM-arc ratio is determined by the ratio of the airgap length to the PM thickness. It is demonstrated that the optimal split ratio depends on the ratio of average airgap flux density below one slot to maximum flux density in the stator iron which depends on the PM thickness and PM-arc ratio, and it is reduced when the effect of the stator tooth-tips is taken into consideration. The experimental results on the 12-slot/10-pole CPM machine are given to verify these analyses.