Study On The Inductively Coupled Power Transfer System For Electric Vehicle

The environmentally-friendly electric vehicles have drawn public interests because of fossil fuel shortage and environmental pollution.Nevertheless,problems exist in this conduction charging mode,which is used widely by current electric vehicles,for example,affecting the beauty of environment,high charging current and heavy connector;Complicated operation,parking and connecting charger cable with electric vehicle cable are needed before charging;electric spark and poor contact will appear when using for a long time on account of mechanical friction between plug and socket;Leakage accident may be caused by bad weather,wire aging,pulling to cables carelessly or forgetting to remove connector.In addition,undeveloped battery technology has also limited the promotion and development of electric vehicles.It makes the electric vehicles exist some shortcomings,for example long charging time,large battery space and short mileage.Inductively coupled power transfer technology is a direction of wireless power transfer technology.Electrical energy can be transmitted contactlessly from underground equipments to the electric motor or vehicle-mounted battery pack,which is a real time power supply from road to electric vehicles.With the help of such system,the mileage will be extended,and the supply of power will be more convenient and security.The paper studies on the inductively coupled power transfer system for electric vehicle,the main research contents contain:First,The composition of the inductively coupled power transfer system for electric vehicles is analyzed,and the main circuit structure of the system is established.Considering the aspects of the circuit device performance,transmission power level and the economy,a characteristics of several kinds of high frequency inverter circuits are compared.Compared with the characteristics of the vehicle mounted terminal rectifier circuit,the secondary rectifier circuit of the electric vehicle induction coupling charging system is selected.And then the structure for the main circuit of the system is established.Secondly,The theoretical models of mutual inductance and leakage inductance are established,presents a calculation method of loosely coupled transformer coupling coefficient,self inductance,mutual inductance and leakage inductance parameters.The measurement method is given the self inductance and mutual inductance of loose coupling transformer.To establish a system without compensation model,the efficiency calculation method of loose coupling transformer is introduced.In order to reduce the reactive power of the system and increase the efficiency of the system,four kinds of compensation topologies are analyzed,and the compensation capacitor is normalized.The calculation method of system equivalent impedance is listed,and the calculation steps of system efficiency are derived.Thirdly,the development process of the loosely coupled transformer is presented,and the loosely coupled transformer device suitable for the wireless transmission of the electric vehicle is designed.The Maxwell finite element software is used to study the coupling structure.Parametric scanning analysis of the changes of self inductance and mutual inductance and coupling coefficient with the gap and offset by static field,the preliminary design of loosely coupled transformer,design of resonant network parameters.Finally,the system circuit diagram is established in the Simplorer software,and the field circuit coupling simulation analysis based on Simplorer software and Maxwell software is carried out.Get the primary side and secondary side voltage and current parameters of the circuit,and get the system transmission efficiency.Analysis and comparison of the existing loose coupling transformer structure and improved coupling structure transmission efficiency.Compared with different air gap and offset,the power level and efficiency of the system are changed.