Comparative Study of Field Back EMF Ripple in Partitioned Stator Hybrid Excited Machines

Although the field winding can help to regulate the air-gap flux, the back electromotive force (back EMF) induced in the field winding significantly affects the overall performance of hybrid excited (HE) machine systems, including flux-regulation capability, torque–speed characteristics, losses, torque ripples, and safe/stable operation. This article focuses on comparative analysis and suppression of the field back EMF ripple in partitioned stator HE machines (PS-HEMs) having different inner stator configurations. The field back EMF ripples of different machines are comprehensively compared under ideal current source excitations and pulsewidth modulation (PWM)-controlled voltage source converter excitations. The results indicate that the low-order field back EMF harmonics can be effectively reduced by appropriate designs of inner stator topology, field winding configuration, and stator/rotor pole number combinations. Besides, a novel dual-shaping technique of cup rotor is proposed and proved to be effective for the low-order field back EMF harmonics suppression. Moreover, a field-circuit coupled model is built to reveal the influence of PWM harmonics on the overall performance of the machine system, with particular emphasis on their impacts on the field back EMF ripple. Finally, the finite-element (FE) analyses are verified by the experimental results of a partitioned stator (PS) prototype machine having a switched-flux type hybrid-excited inner stator.