Design Of The Wireless Charging System For Electric Vehicles Using Loosely Coupled Transformer

Urban transportation is one of the main consumers of fossil fuel.To deal with the problems arising from the exhaust emission from petrol cars and optimize the energy structure,electric vehicles(EVs)have attracted more and more attention as a cleaner alternative.Though conductive charging is currently the most widely used charging method for EVs,wireless charging has also been under development for the past few decades since it is safer,applicable to unmanned operation and the charging process can be uninterrupted even in harsh environments,such as underwater and dusty environment.Loosely coupled transformer is the core component in a magnetic coupled wireless charging system.Its loss of all kinds will have significant influence on system performance like efficiency and temperature rise,especially when there exists lateral offset and angular offset.Firstly,this dissertation introduces some common modeling methods of loosely coupled transformers.For each model,the key issues,applicable conditions and how it is equivalent to the real product are summarized.Additionally,this dissertation also conducts thorough analysis of the magnetic-field pattern of several typical structures of loosely coupled transformers.Secondly,this dissertation proposes a design procedure of loosely coupled transformers working at fixed frequency,based on which the parameter calculation and the implementation of the prototype is finished.With regard to the key issues like the loss and temperature rise of loosely coupled transformers,the electromagnetic field and thermal linked simulation is conducted by Ansoft Maxwell and the steadystate thermal module of Ansys workbench.Thirdly,a wireless charging system for EVs which is in line with the industry standards from the perspective of operating frequency,air gap and system efficiency is produced and tested.This system can transfer 6.6 kW rated power reaching up to the efficiency by 95% when the primary side and the secondary side is perfectly aligned.This dissertation also conducts temperature rise test on this system and the results show good agreement with the simulation results.Finally,this dissertation lists several newest industry standards of wireless charging technology for EVs at home and abroad and finds their similarity and differences of the performance index and technical route.On the basis of the standards evolution,this dissertation envisions the future of wireless charging technology.