| Modern trams have the advantages of low cost,large passenger capacity and short construction period,and have developed rapidly in the past ten years.Wireless power transfer(WPT)technology has the advantages of high safety,no mechanical wear,and good urban landscape,and has received extensive attention in recent years.In order to further improve the flexibility of power supply,realize real-time supply of electric energy during vehicle movement and reduce the volume of energy storage devices,dynamic wireless power transfer(DWPT)technology came into being.This paper takes the DWPT technology of modern trams as the research object,and focuses on the switching strategy and positioning method of the coil in the over-switching domain.Firstly,the paper introduces the principle of DWPT and the line and power supply structure of modern trams,discusses the laying method and control structure of the coil in the power supply line,and determines the DWPT application scheme of multi-stage continuous coil and double-layer control mode.The LCC-S compensation topology is selected for voltage gain and efficiency analysis.Due to the particularity of the coupling coil structure of the DWPT system,the influence of coil shape,size,spacing,turns and core distribution on electromagnetic parameters is analyzed by mutual inductance model from two ways: theory and simulation,and on this basis,a set of coil parameters is designed by parameter sweeping method for subsequent analysis and experimental platform construction.In order to design the coil switching strategy,the paper modeled the switching unit of the DWPT system mathematically,and derived the circuit parameter expressions from the steady-state and transient models.From the theoretical calculation and simulation analysis,it is found that the current impact of the system during switching and the safety hazard of excessive resonant current when the single primary side is powered.In order to solve the above problems,a coil switching control strategy based on inverter phase-shift control is designed,including constant-shift phase angle change rate start-stop control and phase-shift 0° control strategy.In order to improve the power supply stability of DWPT,the switching phase and switching position are analyzed,and the results show that switching in the same phase and optimal switching area can improve the power supply stability.The correctness of the model establishment is verified by simulation and theoretical calculation,and the used coil switching strategy has a good effect on the system operation safety and power supply stability.Since coil switching needs to provide switching instructions through coil positioning,this paper proposes a coil positioning method based on mutual inductance calculation.The mutual inductance calculation expression is deduced from the mathematical modeling results.Considering the high operating frequency of the system and the existence of low-frequency oscillation of three-phase input,a recursive average filtering algorithm is introduced,and the corresponding control flow is given.Considering the problems of high vehicle speed and system delay in practical applications,a coil position prediction method based on coil mutual inductance calculation is proposed to ensure the timeliness of power supply.The effectiveness of the proposed coil positioning method is verified by simulation.Finally,the DWPT experimental platform is built for experimental verification,and the experiments of the coil switching strategy and the coil positioning method are carried out. |
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