Research On Dynamic Wireless Charging System For Electric Vehicles And Several Control Strategies For Power Stabilization

In recent years,the energy crisis and environmental problems have aroused wide attention.The development of electric vehicles is still affected by the methods of supplement and storage for electric energy.The current wired charging mode faces the problems of inflexible charging,complex operation and potential safety hazards.In order to meet the demand of driving range for electric vehicles,electric energy storage relies on huge batteries.The development of wireless power transfer technology provides a new method to solve the charging problems for electric vehicles,especially the technology of dynamic wireless charging for electric vehicles(EV-DWC).This technology can not only solve the above problems about charging,but also effectively reduce the usage of energy storage equipments and vehicle cost,and promote the driving range of electric vehicles.The EV-DWC system based on short-segmented transmitting coils adopts many short coils at the transmitting side.The system controls and switches the coil array according to the real-time position of electric vehicles.Only a small number of short-segmented coils related to the position of electric vehicles are at the energized state.Hence the power loss in the transmitting side is small.Due to the movement of the receiving side and the switching control of the transmitting coils,the receiving power fluctuates when the mode of single transmitting coil and single receiving coil is applied.To deal with the power fluctuation,this dissertation studies the generation mechanism of power fluctuation in short-segmented EV-DWC system.Several power stabilization control strategies are put forward from different points.This dissertation provides technical reference for promoting the practicability and the engineering practice of dynamic wireless charging technology for electric vehicles.The research contents and results of this dissertation mainly include the following aspects:1)The characteristics of EV-DWC and the power fluctuation mechanism under single transmitting coil and single receiving coil symmetrical topology are analyzed.The overall structure of two-stage hierarchical and sectional EV-DWC is introduced in this dissertation.The characteristics of receiving power varying with the position changing of receiving side are investigated for EV-DWC with short-segmented transmitting coils.The generation mechanism of power fluctuation in EV-DWC with short-segmented transmitting coils under single transmitting coil and single receiving coil symmetrical topology is analyzed and explored in detail.Finally,the basic ideas of passive and active control strategies of power fluctuation are put forward.2)The flexible control strategy of receiving power for wireless power transmission system with non-fixed receiving position is studied.The circuit model of multi-phase Class-D parallel inverters is developed.The calculation method based on the construction of iterative summation for trigonometric function is designed.The output voltage control method of the inverters based on the adjustment of maximum phase difference is investigated.The power flexible control strategy for wireless power transmission system with non-fixed receiving position is proposed,which realizes identification of load access and exit as well as the power stability control after access.Finally,the characteristics of passive power fluctuation suppression scheme for EV-DWC systems are analyzed according to the proposed flexible control strategy of receiving power for the wireless power transmission system with non-fixed position.3)The power enhancement strategy based on decentralized energy pickup mode for the EV-DWC system is studied.An EV-DWC system based on decentralized energy pick-up mode is designed.According to decentralized energy pickup device and positioning detection coil,the positioning scheme based on imitative relaying coil structure is proposed.The positioning detection and switching control strategy for EV-DWC with short-segment transmitting coils is presented.4)The power fluctuation suppression strategy based on the excitation topology design of the transmitting side for EV-DWC system is studied.The power stabilization control strategy based on constant mode with multiple transmitting coils is studied.The optimization strategy for switching control of segmented transmitting coils based on the moving searching window with variable width is proposed.Considering the mutual inductance between two transmitting coils in double transmitting coil topology,the power stabilization control strategy based on topology alternating and frequency alternating is proposed.On the other hand,the power stabilization control strategy based on topology alternation and compensation alternation is also presented.5)The switching control of the segmented transmitting coils and power stability control strategy for the hybrid dynamic-static wireless charging system with multi-load at intersection are investigated.Firstly,the topology and principle of hybrid dynamic-static wireless charging system for multiple electric vehicles based on short-segmented transmitting coil structure at intersection are introduced.The general circuit model for the dynamic wireless charging system with the complex cross-coupling between multiple transmitting coils and multiple receiving coils is developed.The characteristics of the system varying with the number of loads and the change of each load positions are analyzed.The power stability control strategy is proposed by the control scheme of multi-stage compensation capacitor and the control scheme of mode alternating for decentralized topology at the transmitting side based on the detection of the number and locations of loads.