Optimal design of a 6.78-MHz wireless battery charging system based on average power loss

High frequency wireless power transfer (WPT) such as working at megahertz (MHz) is widely considered to be a promising candidate for charging the lithium-ion batteries of mobile electronic devices. However, in a real battery charging application, the varying battery voltage and charging current will significantly affect the system efficiency and lead to the high power loss in the whole charging process, especially at MHz due to the obvious rectifier input reactance. Moreover, it makes the optimization design of wireless battery charging system more complicated and difficult. In this case, a 6.78-MHz wireless battery charging system is proposed and an optimization design procedure is developed to minimize the average power loss in the whole charging process. By using the circuit model of the wireless battery charging system, the system efficiency is derived and services as the basis for the optimization design. Finally, the experimental results are provided for verification. It shows that the system using the proposed optimization design can achieve a 24.5% reduction of the average power loss compared to the conventional one.