Maximizing Efficiency while maintaining Voltage Regulation of Wireless Power Transfer Systems using a Buck-Boost Converter

This paper presents an analysis of a Wireless Power Transfer (WPT) System using a buck-boost converter for voltage regulation with the objective of maximizing efficiency by reducing conduction losses and achieving zero voltage switching (ZVS). Unlike conventional buck-boost converter gain characteristics, the buck-boost converter cascaded with the receiver of a WPT system does not have a monotonically increasing gain curve and instead shows a concave characteristic. Thus, a required output voltage can be obtained with two different values of duty ratio of the buck-boost converter if the voltage gain required is below the maximum attainable gain of the system. This novel work will investigate which duty ratio will yield a higher efficiency at various switching frequencies of the transmitter by considering conduction losses and the ability to obtain ZVS. Discussion on coupling strength between coils and its impact on ZVS capability is also shown. Experimental results on a 5W, 5V output system with the two possible duty ratios are used to verify the analysis.