An Efficiency-Optimized Control Strategy for Variable Flux Machines

Variable flux machines enable online adjustment of the permanent magnet flux linkage, introducing an additional degree of freedom for efficiency-oriented control. This capability requires a coordinated treatment of operational efficiency and the energetic cost of MS manipulation. A state-based control structure is proposed that switches between standard operation and an efficiency optimizing decision mode. MS adjustments are executed through online-generated current trajectories that maintain torque while respecting voltage constraints. The decision logic relies on an amortization-time criterion: an MS change is only carried out if its energetic benefit is expected to outweigh the associated manipulation losses within a predefined horizon.The proposed control strategy was evaluated on a WLTP driving segment, demonstrating that the method consistently selects locally advantageous MS levels and yields measurable efficiency improvements without compromising torque control.