Comparative Analysis of Wireless Power Transfer in EV Charging Systems

Thesis Abstract

The rapid electrification of transportation hinges on the efficiency, safety, and user acceptance of wireless power transfer (WPT) systems for electric vehicle (EV) charging, yet comparative evaluations across system configurations remain limited, creating gaps in design guidance and policy development. This study addresses the problem of inconsistent performance benchmarks across WPT in EV charging by providing a structured comparison of topologies, operating frequencies, coil geometries, and control strategies under realistic driving and environmental conditions. The aim is to quantify how variations in design choices influence efficiency, power transfer distance, thermal behavior, electromagnetic interference, and user-centric metrics such as perceived charging speed and safety margins. Specific objectives are (1) to compare resonant and non-resonant WPT topologies in both pad-to-vehicle and contactless charging configurations; (2) to evaluate the impact of operating frequencies (6.78 MHz, 13.56 MHz, and 85 kHz-like low-frequency alternatives) on efficiency and coil coupling under misalignment scenarios; (3) to analyze thermal performance and thermal runaway risk using coupled electro-thermal simulations; (4) to assess electromagnetic interference (EMI) and regulatory compliance across scenarios; and (5) to synthesize guidelines for design trade-offs that maximize overall system performance while minimizing user discomfort and safety concerns. The methodological approach adopts a multiphase, mixed-methods design. In the quantitative strand, a simulation-based experimental matrix comprising 12 WPT configurations and 5 misalignment levels is implemented using a high-fidelity finite element model (FEM) in COMSOL Multiphysics, validated against a physical 11 prototype consisting of a pad and a vehicle-side coil with 120 kW nominal power. Data collection involves automated extraction of efficiency, transferred power, coil temperature rise, linkage flux density, and EMI spectrum under standardized test cycles representing urban, highway, and mixed-use scenarios. A total sample equivalent to 60 simulation runs and 30 physical tests is employed to ensure statistical power for comparative analyses. Analytical techniques include multivariate regression to identify design factor effects on efficiency and thermal metrics, ANOVA to detect significant differences among WPT configurations, Tukey post hoc tests for pairwise comparisons, and response surface methodology to model interactions between misalignment, distance, and frequency. In the qualitative strand, semi-structured expert interviews (n=12) and workshop feedback from EV charging engineers and regulatory stakeholders are analyzed using thematic analysis to capture practical considerations, safety concerns, and implementation barriers, anchored by the Technology Acceptance Model and the Diffusion of Innovations theory to interpret user and industry adoption dynamics. The study hypothesizes that resonant, mid-to-high frequency WPT configurations with optimized coil geometries will yield superior system efficiency and reduced misalignment sensitivity, while still maintaining acceptable EMI and thermal profiles; non-resonant or very low-frequency approaches may exhibit broader tolerance to misalignment but suffer from efficiency penalties and larger coil footprints. Expected findings include (i) measurable efficiency gains (15–25% relative improvement) for optimized resonant configurations over non-resonant counterparts at 10 cm–15 cm lateral misalignment; (ii) thermal management advantages in designs with active cooling strategies and advanced materials, reducing peak coil temperature rise by 20–30°C under peak load; (iii) EMI levels within regulatory limits for high-frequency resonant systems but potential harmonic concerns requiring filtering in certain configurations; and (iv) divergent stakeholder perspectives on deployment readiness, with engineers prioritizing reliability and EMI compliance, and consumers demanding perceived charging speed and safety assurances. The study contributes to knowledge by providing a rigorous, cross-sectional framework for evaluating WPT designs in EV charging, establishing benchmark performance metrics, and delivering a decision-support toolkit for designers and policymakers. The main conclusion anticipates that comparative WPT analyses will reveal clear design trade-offs high-efficiency, compact resonant systems at mid-to-high frequencies offer the best performance under typical misalignment, whereas low-frequency, broad-tolerance systems are better suited for opportunistic charging contexts with lower efficiency penalties. Recommendations include standardized testing protocols, harmonized EMI guidelines, and guidelines for selecting WPT configurations aligned with vehicle class, parking infrastructure, and regulatory environments to accelerate safe and efficient adoption of wireless EV charging.