On the Efficiency Limits and Electric Field Stresses of Wireless Charging for Electric Buses
A 50-kW Experimental Study Based on Opportunity Charging
Calvin Riekerk (TU Delft - Electrical Engineering, Mathematics and Computer Science)
Wenli Shi (TU Delft - Electrical Engineering, Mathematics and Computer Science)
Gangwei Zhu (TU Delft - Electrical Engineering, Mathematics and Computer Science, City University of Hong Kong)
Jianning Dong (TU Delft - Electrical Engineering, Mathematics and Computer Science)
Thiago Batista Soeiro (TU Delft - Electrical Engineering, Mathematics and Computer Science, University of Twente)
Pavol Bauer (TU Delft - Electrical Engineering, Mathematics and Computer Science)
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Abstract
Inductive power transfer (IPT) presents a promising solution for opportunity charging of electric buses. However, achieving an optimal balance between pad area, power transfer efficiency, and misalignment tolerance remains a significant challenge. This article explores the tradeoffs between power transfer efficiency and area-related power density and investigates the electric field distribution in the charging pads of wireless charging systems. The design requirements are first established. Based on these, a multiobjective optimization (MOO) framework is developed to address insulation constraints and current density limitations within the windings. The resulting Pareto front reveals that lower area-related power densities correspond to reduced efficiency, highlighting a fundamental design tradeoff. Furthermore, the study identifies critical regions within the charging pads that are the most susceptible to insulation failure. A 50-kW prototype was implemented and tested, with experimental results showing a dc-dc power efficiency ranging from 97.165% to 96.824% under 100-mm X and Y misalignment, and a stray field of 13.86μ T.