Comparison of Torque Production and Design of Switched Reluctance and Variable Flux Reluctance Machines

In this paper, the discrepancies in torque production and design parameters (particularly rotor pole arc) for switched reluctance machines (SRMs) and variable flux reluctance machines (VFRMs) are analyzed. The analytical torque equations are derived for both machines. From this, the average torque production is found to be proportional to the fundamental self-inductance component, which is maximized via variance in rotor pole arc during optimization. Firstly, the analysis is performed under linear conditions, then taking into account saturation with the aid of the frozen permeability method. When the core is non-linear and both machines are operated under the same copper loss conditions with a fixed stator pole arc, the VFRM suffers from more saturation than the SRM. Consequently, the optimal rotor pole arc of VFRM for maximizing the fundamental inductance and average torque are always smaller than those of the SRM under all load conditions.