Analytical modeling and mitigation of unbalanced magnetic forces in dual-stator 6/5 variable flux reluctance machines

Purpose This study aims to analytically model and mitigate unbalanced magnetic forces (UMF) in a 6/5 variable flux reluctance machine (VFRM) by proposing a dual-stator topology. The objective is to reduce radial-force imbalance and mechanical deformation while maintaining comparable electromagnetic performance. Design/methodology/approach A permeance-based analytical model is developed using armature winding, field winding and air-gap permeance functions to calculate the air-gap flux density and radial magnetic stress. The proposed dual-stator structure employs an outer stator with AC armature windings and an inner stator with DC field excitation windings. Analytical radial-force results are compared with finite element analysis (FEA), and the electromagnetic forces obtained from ANSYS/Maxwell are transferred to ANSYS/Structural for deformation analysis. Findings The results show that the proposed dual-stator 6/5 VFRM provides a more balanced radial-force distribution than the conventional single-stator 6/5 VFRM. The maximum deformation is reduced from 33.6 to 25.5 µm, corresponding to a reduction of 33.04%. In addition, the deformation at the central rotor tooth region decreases from 30.1 to 19.4 µm, corresponding to a reduction of 35.5%. The quantitative comparison also shows that the dual-stator topology maintains comparable electromagnetic performance in terms of average torque, torque ripple, power factor and efficiency. Originality/value This study presents a dual-stator 6/5 VFRM topology and explains its UMF mitigation mechanism through analytical radial-force modelling and FEA-based structural verification. The proposed topology offers a rare-earth-free solution for low-pole VFRM configurations, in which electromagnetic advantages such as favourable back-EMF and torque characteristics may be accompanied by mechanical drawbacks such as unbalanced magnetic forces. By addressing the UMF problem of the 6/5 VFRM, the proposed structure contributes to the development of mechanically more balanced low-pole VFRM topologies.