CAPACITIVE WIRELESS POWER TRANSFER SYSTEMS FOR ELECTRIC VEHICLE CHARGING
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This work presents a capacitive wireless power transfer (WPT) system for electric vehicle charging that achieves high efficiency and record-breaking power transfer density. This high performance is enabled by multi-MHz operation, innovatively designed matching networks, enhancements in the design of the capacitive coupling plates, and use of new interleaved-foil air-core coupled inductors. A multi-module system is shown to reduce fringing-fields, and the impact of foreign objects is also investigated. The capacitive WPT system utilizes two pairs of metal plates separated by an air-gap as the capacitive coupler, and incorporates L-section matching networks to provide gain and reactive compensation. High efficiency and simplicity is achieved by eliminating the need for high-voltage capacitors, and instead the parasitic capacitances formed between the coupling plates and the vehicle chassis and roadway are utilized as part of the matching networks. A comprehensive design methodology for a capacitive WPT system is presented that guarantees high performance by ensuring zero-voltage switching of the inverter transistors, and by selecting matching network component values to maximize efficiency. Coupling plate enhancements include the use of circular plates enveloped in a high-breakdown-strength dielectric material to alleviate arcing, allowing kilowatt-scale power transfer across a large air-gap. New toroidal interleaved-foil (TIF) inductors provide a better tradeoff between quality factor, size and self-resonant frequency compared to conventional solenoidal inductors, making them suitable for compactly and efficiently processing kilowatt-scale power at multi-MHz frequencies. A 13.56-MHz, 12-cm air-gap prototype capacitive WPT system utilizing TIF inductors with a quality factor of 2055 in its matching networks is designed, built and tested. This system achieves record-breaking performance for a capacitive EV charging system, transferring 3.75 kW with an efficiency of 94.7%, corresponding to a power transfer density of 49.4 kW/m2. A multi-module capacitive WPT system is built, wherein the adjacent modules are out-phased with respect to one another, achieving a fringing field reduction of 50% compared to its individual modules. A study of the impact of foreign objects is performed (including metal, wood, plastic, and water) and the system’s performance is found to be significantly impacted only when water is in very close proximity (< 3 cm) of the coupling plates. However, even in this case the system performance can be recovered to a large extent by operating at the modified resonant frequency.
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94 pages
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2020-12
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capacitive wireless charging; capacitive wireless power; interleaved foil; matching network; wireless charging; wireless power
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Afridi, Khurram Khan
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Monticone, Francesco
Lal, Amit
Lal, Amit
Degree Discipline
Electrical and Computer Engineering
Degree Name
Ph. D., Electrical and Computer Engineering
Degree Level
Doctor of Philosophy
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dissertation or thesis