Influence of Inner/Outer Stator Pole Ratio and Relative Position on Electromagnetic Performance of Partitioned Stator Switched Flux Permanent Magnet Machines

Based on the 6-pole outer stator(armature winding-stator),the influence of inner(permanent magnet-stator)/outer stator pole ratio n(n=NIS/NOS),stator relative positions and rotor pole number combinations on electromagnetic performance of partitioned stator switched flux permanent magnet(PM)machines(PS-SFPMMs)is investigated in this paper.Since the armature windings and PMs are located in two separated stators and PMs are stationary,PS-SFPMMs have high fault tolerance capabilities.To maximize the torque performance,the PM of inner stator pole should be aligned with outer stator pole when n is odd while the iron rib of inner stator pole should be aligned with outer stator pole when n is even.No matter what n is selected,the rotor pole number NR can be any integers except the phase number and its multiples.The analysis results indicate that the optimal NR is closed to(NIS+NOS)/2 and it is odd when n is odd while it is even when n is even.Meanwhile,symmetrical phase back-EMF waveform will be obtained when the ratio of Min(NOS,NIS)to the greatest common divisor of Min(NOS,NIS)and NR is even.Based on the optimal rotor pole numbers for 6-pole outer stator with different n and corresponding optimal relative position together with same rated copper loss,the average torque is improved by 18.4%,25.1%and 25.7%respectively in PS-SFPMMs with n equal to 2,3 and 4 when compared with PS-SFPMM with n equal to 1.The analyses are validated by experiment results of the prototype machine.

Enhancement of Torque Density in Wound Field Switched Flux Machines with Partitioned Stators Using Assisted Ferrites

In this paper,ferrites are applied in a partitioned stator wound field switched flux(PS-WFSF)machine to increase the air-gap flux density,and hence,the average electromagnetic torque and overload capability.Introducing short-circuited ferrites in the inner stator in the PS-WFSF machine can increase the open-circuit phase fundamental back-EMF and average electromagnetic torque at a 60 W copper loss by 2.33%and 3.77%,respectively.Moreover,the proposed PS-WFSF machine with ferrites can exhibit a better overload capability than conventional PS-WFSF machines without ferrites,e.g.,a 7.36%torque increment can be achieved when the copper loss is 120 W.The torque increment mechanism is analyzed and verified using finite element(FE)analysis.Moreover,the demagnetization of the ferrites in the proposed machine under rated on-load and overload conditions is investigated.Both prototypes of the proposed PS-WFSF machine with ferrites and a conventional one without ferrite are built and tested to validate the analytical and FE analyses.

Influence of Rotor Iron Bridge Position on DC-winding-induced Voltage in Wound Field Switched Flux Machine Having Partitioned Stators

In this study,the influence of the position of the rotor iron bridge on the DC-winding-induced voltage pulsation in a partitioned stator wound field switched flux machine is investigated.Analytical and finite element(FE)analyses show that both the open-circuit and on-load DC-winding-induced voltages can be minimized by positioning the rotor iron bridge adjacent to the inner air gap closer to the DC winding.This is due to a smoother inner air-gap magnetic reluctance while maintaining the average electromagnetic torque at 92.59%of the maximum value.The analyzed machine with the rotor iron bridge adjacent to the inner air gap is prototyped,and the experimental results validate the analytical and FE results.