Research On Mobile And Efficient Wireless Power Transfer System Applied To Modern Trams

Modern trams have the characteristics of large passenger capacity,low pollution and energy consumption,short construction period and low cost.They have developed rapidly in China in recent years.As a new type of power supply,the wireless power transfer(WPT)system has the advantages of no exposed wires,no wear,safety,and good urban landscape when powering the tram.In this paper,the WPT technology applied to the modern tram is taken as the research object,and the coupling mechanism arrangement method and control strategy to improve the system efficiency of the WPT system suitable for dynamic power supply are mainly studied.Firstly,this paper studies the arrangement of the coupling mechanism of the mobile WPT system.For the operation characteristics of modern trams,a multi-stage segmented wireless power supply system is configured for the system and the LCC compensation topology is adopted.According to the mutual inductance calculation formula between the two line segments,the formula for calculating the mutual inductance between rectangular coils considering the wire diameter and the number of turns is derived.The mutual inductance calculation formula is used to configure the size and number of turns of the coupled coil for the system.On this basis,the reason why the output voltage of WPT system fluctuates with the movement of the secondary coil in the moving process is analyzed.From the perspective of optimizing the design and operation control strategy of the primary electromagnetic coupling mechanism,a power supply strategy is proposed that when the secondary coil is located at the middle of the primary coil,one primary coil is powered,and when the secondary coil is located at the edge of the primary coil,two adjacent primary coils are used to supply the secondary sidesimultaneously.According to the mutual inductance calculation formula,the arrangement spacing between two adjacent primary coils is obtained,so as to ensure a small volatility of the secondary output voltage.Theoretical analysis shows that the transfer efficiency of the WPT system is always maintained at a high level when the proposed strategy is adopted.Secondly,the efficiency optimization method of the wireless power transfer system based on the traction characteristics of the tram is studied.Based on the expression of transfer efficiency of LCC compensation circuit,the factors affecting transfer efficiency during system operation are analyzed.The results show that the system's transfer efficiency can be maintained at a high level by adjusting the equivalent load of the system as the optimal load.Combined with the characteristics of the traction inverter,a real-time efficiency optimization strategy with the maximum efficiency as the target and the input DC voltage of the traction inverter as the controlled quantity is proposed.Simulation analysis verifies the effectiveness of the proposed optimization method.Finally,the laboratory 50kW wireless power transfer system experimental platform is used for experimental verification.Experiments on the power supply and arrangement method of the coupling mechanism and the transfer efficiency optimization method of the motor load are carried out based on the experimental platform.The experimental results verify the effectiveness of the proposed schemes.