Planar multi-coil wireless charging is an advanced power transfer technology that utilizes multiple coils arranged in a flat configuration to enable efficient energy transfer via electromagnetic induction. This system enhances the charging process by providing a larger and more flexible charging area, allowing for improved alignment tolerance and faster power delivery. By incorporating multiple coils, it supports the simultaneous charging of multiple devices and reduces charging times compared to traditional single-coil systems. This flexibility is achieved using multiple transmitter coils or relay coils (resonator coils), which consist of an inductor coil paired with capacitors. These relay coils help utilize the leakage magnetic field and tune the system to a resonant frequency for efficient energy transfer. Typically, in a planar multi-coil wireless charging system, when a transmitter coil is active, its magnetic field can influence nearby inactive coils, causing leakage that can be compensated for with relay coils. However, such a system does not provide dynamic control of the main transmitter coil and relay coils due to the lack of circuits supporting dual-mode operation at high frequencies.
We propose a novel dual-mode transmitter-relay multi-coil system for an efficient planar multi-coil wireless charging system for battery-free devices. This will be explored through a novel high-frequency H-bridge inverter design, incorporating a resonant topology to support dual-mode operation and accommodate dynamic loads influenced by supercapacitor storage. This study will also consider frequency splitting, which refers to multiple resonant frequencies caused by over-coupling between nearby or multiple active coils, reducing power transfer efficiency. To avoid frequency splitting, an appropriate study of resonance topology, as well as activation strategy, will be considered.
Resonance topologies have been widely investigated for wireless charging systems with only transmitter coils but have not been modelled or investigated for relay coils. During this project, the resonance topology for dual-mode operation, considering both transmitter and relay coils, will be explored. Additionally, to avoid over-coupling, a smart activation strategy was developed based on the load impedance and receiver position. The activation strategy aims to detect the receiver coil's position and activate the valid sending coils, as well as the nearby relay coils. This activation is based on modelling the coupling factor between the sending side and receiving side coils to avoid frequency splitting and over-coupling issues.
The proposed novel charging approach is particularly beneficial for applications in consumer electronics, electric vehicles, and other devices requiring efficient wireless power transfer. Despite the high demand for such multi-coil systems, supply approaches remain a challenge. This proposed approach will be tested on a 10-watt battery-free system with applications in large-area charging setups. The approach seeks to balance efficiency, adaptability, and computational demands, showing potential for wireless charging in various applications, including but not limited to industrial tools, sensors, and consumer electronics.