Torque Ripple Reduction for 6-Stator/4-Rotor-Pole Variable Flux Reluctance Machines by Using Harmonic Field Current Injection

In this paper, a harmonic field current injection method is proposed for torque ripple reduction in 6-stator/4-rotor-pole (6s/4r) variable flux reluctance machines (VFRMs). Initially, the torque production of VFRM is analyzed based on an analytical torque model and harmonic analysis. The torque ripple of 6s/4r VFRM is found to have multiples of third harmonics. Then, one finite-element analysis (FEA)-based and one analytical equation-based method are developed to calculate the magnitude of the injected harmonic current. Both methods are proved to be effective in torque ripple reduction. Finally, the influence of the inductance mismatch on the proposed method is investigated. It shows that the torque ripple reduction performance is not affected much unless the fundamental component of nominal inductance is underestimated. The feasibility and effectiveness of the proposed methods are validated by both 2-D FEA and experimental test.