Power factor optimization with semi-definite programming relaxation in three-phase wireless power transfer systems for electric vehicles

In this paper, an excitation method for a three-phase wireless power transfer system for electric vehicle charging is proposed. The semi-definite programming relaxation current optimization model (SRCOM) is developed to derive transmitter coil currents for the multi-phase system that minimizes the coil loss through optimizing the current distribution among transmitter coils. The power factor constraints for each phase are developed to maintain high power factors in each phase and achieve soft switching for the high power phases. Semi-definite programming relaxation is adopted to convert the non-convex power factor constraint into convex form. Tightening constraints are introduced to compensate for the relaxation and ensure solution feasibility. Simulation has verified SRCOM can improve the power factor under different receiver misalignment scenarios thereby reducing inverter switching loss. This comes at the cost of a small increase in coil conduction loss.