Optimized Design Of Isolated Class E DC-DC Converter

Miniaturization and lightweight are the pursuits of the power converters.Increasing the switching frequency of the converters is an effective way to reduce the volume of passive components and improve the power density.Multi-MHz isolated Class E resonant converters featurs with zerovoltage-switching,simple topology and isolation,and they have been attracting much more attentions.ON-OFF control is adopted in Class E dc-dc converter in order to realize soft-switching under different loads to obtain high efficiency.This thesis is dedicated to the optimal design of the isolated Class E dc-dc converter.There are many resonant components in the isolated Class E dc-dc converter,which makes it operates complexly.This thesis analyses the operation principle of the converter.It is found that the resonant current is approximately sinusoidal if the resonant network has a good characteristic of frequency selection.Thus,the converter could be divided into two parts,namely,inverter network,rectifier network.In the rectifier network,the duty cycle of the synchronous rectifier(SR)is optimized for reducing the voltage and current stress of the SR,and the parameters of the resonant elements are designed for reducing the current in rectifier network.In the inverter network,the duty cycle of main power switch and parameters of the resonant elements are designed with the consideration of achieving soft-switching and improving the efficiengy.The parameters in resonant network are designed for ensuring the resonant current to be sinusoidal.Also,the design method of the air-core transformer based on PCB is introduced.The impact of the varaition of the input voltage on the operation of isolated Class E dc-dc converter is analyzed in this thesis.It is pointed out that the increase of the input voltage will result in reverse conduction or hard-switching of the SR and reverse reduction of the main power switch,which degrades the conversion efficiency.So,adaptive driving signals are proposed for the SR and main power switch to ensure soft-switching and avoid reverse conduction,and thus the conversion efficiency is improved.Finally,a prototype of the isolated Class E DC-DC converter with 20 MHz,36V~54V input,12V/24 W output,is fabricated and tested in the lab.The experimental results are provided to validate the effectiveness of the proposed design approach and the adaptive driving signals.