Analysis And Design Of Flux-Concentrating Consequent-Pole Fault-Tolerant Permanent-Magnet Vernier Machine

Due to the simple structure,large power density,and high efficiency,permanent magnet(PM)machines have been widely used in direct drive applications.However,regular PM machines cannot meet the requirements of low speed and large torque.According to the flux-modulation principle,PM vernier machine has a better prospect in the low speed and large torque application.However,two opposite polarity of PMs are mounted on the rotor of regular PM machine(which called as N-S PM machine)and the PM consumption is large.Due to the expensive rare earth PM,the price of machine is high.Hence,in order to improve the torque and fault-tolerant capability of PM machine,and reduce the cost,in this paper,a flux-concentrating consequent-pole fault-tolerant permanent-magnet vernier(FC-CP-FT-PMV)machine is designed.The main contents are including:(1)The relationship between airgap flux density,leakage flux and CP structure of CP PM machine is investigated,and the optimum pole-arc coefficient is found,where the effective flux is maximum and the leakage flux is minimum.Hence,a theoretical foundation for the choice of CP parameters is built.(2)Based on CP PMV machine and the uneven distribution of modulation poles,the increasing mechanism of flux density harmonics is analyzed.Moreover,combined with the magnetomotive force(MMF)of armature winding,the generation condition of working harmonics is studied,and contributions to back-EMF and electromagnetic torque are also investigated.(3)Based on the optimum pole-arc coefficient,the flux-modulation effect,and electromagnetic performance between the N-S and CP PMV machine with different pole pairs are analyzed and compared.(4)It can be found that there is a serious saturation problem in CP PMV machine through analyzing the flux density of salient core between CP PMs.Adopting the CP-Halbach array to generate the flux diffluence effect to weaken the saturation of salient cores.Furthermore,relationship between the magnetization angle,pole-arc coefficient,the PM thickness,the saturation of salient pole,and effective airgap flux density are investigated to find out the optimal range of size and magnetization angle.(5)The end leakage flux between the N-S and CP PMV machine are compared,which reveals that there is serious axial unipolar leakage flux on the end of CP PM machine.The step-staggered rotors with magnetic barriers are proposed to reduce end leakage flux and the interpole leakage flux between staggered rotors.(6)Finally,a prototype is manufactured and the test rig is built.The back-EMF,torque capability,and end leakage flux are measured,which is compared with the simulated results to verify the theoretical analysis.