Stator/Rotor Pole Combinations of Variable Flux Reluctance Machines with 2nd Harmonic Current Injection Method

The 2
^nd
harmonic current injection method is recently developed to enhance the torque density of the variable flux reluctance machines (VFRMs). This paper investigates the effectiveness of the 2
^nd
harmonic current injection method in VFRMs with different stator/rotor pole combinations. By using magnetic gearing effect, it is found that the 2nd harmonic injection method can only be applied to the 6j/(6i ± 2)j (i i = 0, 1, 2...) VFRMs for the torque density enhancement. For the other stator/rotor pole combinations, the 2
^nd
harmonic current has no contribution in average torque production and only leads to excessive torque ripple. Further, by using global optimization method and finite element analysis (FEA), 6/8 is proved to be the optimal stator/rotor pole combination for 6-stator-slots VFRMs with the 2
^nd
harmonic current injection method, being able to exceed the maximal torque density of conventional VFRMs by 12% at a fixed copper loss.