Modeling and Design of Capacitive Power Coupling as a Practical Candidate for Wireless Power Transfer
- Chi Kong TSE (Principal Investigator / Project Coordinator)Department of Electrical Engineering
- Ron Shu-yuen HUI (Co-Investigator)
DescriptionExisting mature wireless power transfer (WPT) technology is based on near-field inductive power transfer (IPT) that uses magnetic coupling for power transfer. There are known drawbacks of IPT, however, such as the use of ferrite material for coupling enhancement which increases cost and reduces power density. IPT also necessitates detecting metal objects that compromise safety and incur losses. The current technology is awaiting breakthrough that raises the power capacity and efficiency substantially, and we hope to be the key driver of this important technological transition. Capacitive power transfer (CPT), which utilizes high-frequency alternating electric fields, does not cause significant temperature rise in nearby metal objects. The directed nature of electric fields permits CPT to work without using supplementary material for flux guidance. Coupling capacitors are just metal plates, leading to low complexity and cost. Moreover, without cores, the operating frequency is limited essentially by the drive circuits as air-gap loss is negligible, thus permitting high-frequency operation and high power density. Furthermore, CPT has comparable or higher efficiency than IPT for applications of small gaps and similar power levels. The lower coupler-to-gap-volume ratio makes CPT an attractive solution for space-limited applications. There are some critical challenges of CPT that need to be overcome. First, existing models of CPT systems are unsatisfactory for various practical scenarios because parasitic capacitances can be comparable in magnitude to the coupling capacitance, leading to unrealistic estimation of power transfer capability and efficiency. Another key problem is the weak coupling of the capacitor pairs, limiting the power level and mandating a very short transfer distance. Existing solutions addressing the limited coupling voltage and increasing the operating frequency have resorted to specific compensation circuits, but there is no effective general design framework. Our first objective is therefore to establish a unified circuit model that includes parasitic capacitances formed with the surroundings and facilitates calculation of operating conditions for stable and parameter-insensitive power transfer. The model should be accurate in terms of power transfer characteristics, patterns of load variation, and parasitic capacitances of surroundings. The second objective is a performance evaluation framework based on the model developed above. This task involves extensive analysis of design assessment criteria. The third objective is to produce a complete circuit synthesis and design methodology for capacitive coupler structures and compensation circuits that cover key performance aspects including power level, transfer distance, tolerance to misalignments, and practical constraints such as size, weight and cost.
|Effective start/end date||1/01/23 → …|