Research On Class-e High Frequency Inverter For WPT System

As a new,safe and reliable power transmission technology,wireless power transfer can solve the problems of safety,convenience and environmental adaptability by traditional transmission methods,and has broad application prospects in electric vehicles,power systems,aerospace,communication equipment and implantable medical equipment.This paper mainly focuses on the influence of nonlinear parasitic capacitance on the soft-switching characteristics of class-E inverters in high-frequency state and the research and design of wide-load class-E inverters in magnetically-coupled resonant wireless power transfer systems.For the nonlinear drain-source parasitic capacitance in the class-E inverter,the equivalent linear capacitance calculation formula of the parasitic capacitance is derived,which improves the accuracy of the high frequency class-E inverter design.Two different equivalent capacitance calculation formulas are derived by the charge charging principle and the capacitor charging principle,which are respectively brought into the circuit and simulated at three different resonant frequencies.The experimental simulation and prototype test results show that the parasitic capacitance can be well avoided at 1MHz operation.At high frequencies,the parasitic capacitance becomes a decisive factor for the soft switching of the inverter,and is derived based on the charge charging principle.Equivalent linear capacitance is better than the other.In the research and design of wide-load class-E inverters,this paper theoretically studies the load network design method of wide-load class-E inverters for the optimization design of wideload class-E inverters.The obtained design method of the class-E inverter load network can realize the soft switching of the inverter under a wide load condition.At the same time,the switching voltage peak of the inverter is reduced,and the stability of the switching voltage waveform under load variation is improved,thereby improving the transmission power,transmission efficiency and stability of the magnetically coupled resonant wireless power transfer system under wide load conditions.Finally,a 1MHz four-coil magnetically coupled resonant wireless power transfer system was built based on the limitation of capacitor withstand voltage.The prototype adopts the design method of the wide load class-E inverter load network proposed above,and considers the existence of parasitic capacitance.The feasibility and accuracy of the proposed design method are verified by experimental tests.The improved load network design method reduces the switching voltage peak of the Class-E inverter by 12.8%,while reducing the rate of voltage change over a wide load range.The system efficiency peak reached 83.5%,and the Class-E inverter efficiency was about 96.0%.