Power loss analysis and thermal assessment on wireless electric vehicle charging technology: The over-temperature risk of ground assembly needs attention

Abstract

To support e-mobility, wireless electric vehicle charging (WEVC) emerges as a promising technology by virtue of convenience characteristics and the mitigation of range anxiety. Recently, the safety issues on WEVC systems have drawn considerable attention. In light of thermal safety, the most critical part of WEVC systems is the surface of ground assembly (GA). During the charging process, its temperature increases due to the power losses, possibly resulting in cutaneous injury to living bodies and the ignition of foreign objects. Especially when there are evitable misalignments between the GA and vehicle assembly, its temperature rise will be higher as a penalty of efficiency deterioration of WEVC systems. Unfortunately, it has rarely been deemed as a safety hazard yet. Taking a commercialized WEVC system rated at 6.6 kW as an example, this paper focuses on the safety assessment of GA surface. The overtemperature-related losses, including core loss, ohm loss and eddy-current loss, are calculated. The thermal analysis is conducted based on the heat transfer theory. The temperature distribution of GA surface is obtained using transient-state FEM simulations. Based on IEC standards, four hazard levels are proposed as evaluation criteria. Finally, the calculated accuracy is validated experimentally. The results reveal direct influence of misalignments on the temperature rise. The sensitivity of different misalignments to the temperature rise is also analyzed. When the horizontal displacement exceeds 98.86 mm or the angular offset (type II) exceeds 9.91 deg., the highest hazard level could be reached, which highlights severe over-temperature risks of GA surface.