| This paper presents a wireless charging system for electric vehicle called Magnetically Coupled Resonant Wireless Power Transfer(MCR-WPT).MCR-WPT uses magnetic resonance to transfer electrical energy from the power supply to the secondary side,where it can be used to charge the power battery.Compared with the traditional wired charging method,this technology effectively overcomes the disadvantages of interface design and site limitation,and improves the security of charging process.In wireless charging system for electric vehicle(EV),the factors such as topology structure,working frequency and load have different effects on the transmission characteristics of the system.In order to realize the system’s constant voltage mode and constant current mode,this paper carries out the variable topology design,and completes the analysis on the transmission characteristics such as the energy efficiency of the system and constant voltage and constant current by means of simulation and experiment based on the system design.The main work is as follows:Firstly,the research background and the significance of the topic selected are expounded.The research status of wireless charging system,topological structure and control strategy are introduced.The main contents of this paper include the design and energy efficiency analysis of the variable topology resonance structure,the overall design and key module design of the system and the performance analysis,the simulation analysis and experimental verification of the system output characteristics and energy efficiency.Secondly,the characteristics of the resonant compensation structures with natural constant current and constant voltage are compared and analyzed.The variable topological resonant structure based on the improved double LCL compensation network is designed.The system model is established by using the equivalent circuit theory and the transmission characteristic formula is derived.Theoretical model by Matlab is used to analyze the influence of coupling coefficient,frequency and load on system energy efficiency.What is more,by use of the variable topology resonant structure model by Simulink,the characteristics of constant current and constant voltage are analyzed.The rationality of the above design is proved.Thirdly,based on the existing wireless charging system platform,the overall system and key modules of the wireless charging system with variable topology resonance structure are designed,including the compensation switch switching module,the improved rectifier module,the DC/DC module and the coupling module.At the same time,the realization method of each key module is described.In addition,the characteristics of other modules including soft switch circuit,frequency tracking circuit and communication module are analyzed.Finally,the corresponding simulation and experimental platform for the wireless charging system of EV with variable topology are designed.The constant current and constant voltage output function,frequency tracking function,soft switch function and output power are simulated and tested,and the transmission characteristics including system energy efficiency.The measured results show that in the constant current mode,the output power of the system increases rapidly and the battery can be quickly charged.In the constant voltage mode,the output power of the system decreases to make the charging current decrease,which can prolong the battery life.In conclusion,this MCR-WPT system can realize the switch between constant current mode and constant voltage mode,which not only avoids the overcharge caused by single constant current mode,but also avoids the undercharge caused by single constant voltage mode.The design can improve the battery efficiency and prolong the battery life. |
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