Variable Flux Reluctance Machines for Heavy-Duty Vehicle Applications

This paper presents an extended design methodology for variable flux reluctance machines to investigate their potential for heavy-duty vehicle applications. The proposed strategy considers both constant-torque and flux-weakening operations in the design stage to maximize the efficiency, torque density, and power factor and to minimize the torque ripple. The nonlinear magnetostatic finite element analysis is coupled with the singlevalued curve of the laminated soft-magnetic rotor and stator for the constant-torque region, while the nonlinear magnetodynamic model, including the classical eddy current and excess fields in the laminated steel, is utilized for the maximum speed operation. A 3-ton fully electric tractor is selected as the benchmark for the feasibility study, where the maximum continuous torque is 200 Nm at a nominal speed of 1600 rpm. It is demonstrated that the optimal high-torque variable flux reluctance machine achieves a torque density of 20Nm/L and a power factor above 0.7 in both constant-torque and flux-weakening regions. Torque ripple is 10% during continuous operation, with efficiency reaching 90% at the nominal speed and 95% in flux weakening due to reduced copper loss by adjusting the dc-field excitation. Additionally, the optimal design is capable of sustaining 400 Nm overload for up to 65 seconds before reaching the 100 °C winding temperature limit.