Analysis and Optimization of High-Power MCR Bidirectional WPT System With High Distance- Diameter Ratio

High-power magnetically coupled resonant (MCR) bidirectional wireless power transfer (BWPT) within long distance can be potentially used in various applications. However, the coupling between transmission coils will drastically decrease with the rise of distance to diameter (d-D) ratio, and voltage/current stresses on resonant components tend to increase apparently, which further deteriorate the system efficiency and stability. In this paper, the relationship between the coupling coefficient and the d-D ratio in high-power BWPT systems is analyzed by mathematics methods. The correlations of transferred power and system efficiency with d-D ratio are presented consequently. The scheme of coils magnetic concentration and double-layer coils in parallel is adopted to improve the system performance. The theoretical analysis is demonstrated by the experimental results of a 2kW prototype, and the system efficiency is improved from 70.7% to 77.47% under the d-D ratio of 1 (300mm-300mm).