The spatial freedom of wireless power transfer (WPT) systems can be improved using a high operating frequency such as several megahertz (MHz). In the conventional compensations the load of the coupling coils is usually assumed to be pure resistive. However, in MHz WPT systems this assumption is not accurate anymore due to the nonneglectable rectifier input reactance. This paper discusses the impedance characteristics of the full-bridge rectifier at MHz and their influence under the series–series, parallel–series, series–parallel, and parallel–parallel compensation topologies. An undesirable nonzero phase (i.e., none unity power factor) is shown to exist at the primary input port, which leads to decreased power transfer capability. In order to minimize this negative effect, the compensation capacitors are optimally designed, and the series–series topology is found to have the smallest phase under load and coupling variations. Finally, an experimental 6.78 MHz system is built up to verify the optimized design of the compensation capacitors. The results show that the average nonzero phase is effectively reduced together with the improved power factor from 0.916 to 0.982.

中文翻译：

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使用全桥整流器的兆赫兹WPT系统补偿电容器的分析和优化设计

使用诸如几兆赫兹（MHz）的高工作频率，可以改善无线功率传输（WPT）系统的空间自由度。在常规补偿中，耦合线圈的负载通常被假定为纯电阻性的。但是，在MHz WPT系统中，由于整流器输入电抗不可忽略，因此该假设不再准确。本文讨论了全桥整流器在MHz时的阻抗特性及其在串联，串联，并联，串联和并联补偿拓扑下的影响。初级输入端口处存在不期望的非零相位（即，无单位功率因数），这导致功率传输能力降低。为了最大程度地减少这种负面影响，对补偿电容器进行了优化设计，发现串联和串联拓扑在负载和耦合变化下具有最小的相位。最后，建立了一个实验性的6.78 MHz系统，以验证补偿电容器的优化设计。结果表明，平均非零相位有效地降低了，功率因数也从0.916降低到0.982。