Maximum-Torque-per-Watt Control Framework for Variable Flux Reluctance Machines with Magnetic Saturation and Cross-Coupling

This paper suggests a maximum-torque-per-watt (MTPW) control approach for a variable flux reluctance machine (VFRM), considering factors like the machine's magnetic saturation and cross-coupling between field and armature windings, which are both located in the stator. The VFRM's torque production, which can be highly affected by saturation, relies on the cross-coupling between field and armature windings, and on the varying field and armature currents. The operating points on the torque-speed locus are determined by different combinations of these currents. The paper presents a strategy to obtain the optimum combination of reference field and armature currents based on a saturation-dependent VFRM model with a focus on minimizing the total copper loss, as it is the most dominant loss component for all operating regions of the VFRM. The proposed method is evaluated in both constant-torque and field-weakening operation regions, by employing both saturation-dependent and saturation-independent VFRM model. It is concluded that the adoption of the saturation-dependent model becomes highly critical in the constant-torque region, whereas the effect of saturation becomes insignificant in field-weakening operation.