A Dynamic Wireless Charging System With High Spatial Freedom And Constant Energy Transfer Characteristics

As a prime guarantee for the green travel of electric vehicle users,the development of charging infrastructure contributes to the blossom of the new energy vehicle industry and the realization of carbon peaking and carbon neutrality goals.Compared with the conventional charging method,dynamic wireless power transfer technology can provide contactless charging for a moving electric vehicle through electromagnetic coupling,and has the merits of convenience,safety and high efficiency.In practical,the spatial position of the receiver is time-varying for the movement of electric vehicle,and making it difficult to maintain a stable mutual inductance of the magnetic coupler.Moreover,the equivalent resistance of the onboard battery increases significantly as the state of charge rises during the charging process,and constant current-constant voltage charging scheme is usually adopted for the battery charging.Thus,it is crucial for a dynamic wireless power transfer system to provide constant current-constant voltage charging for the electric vehicle with time-varying load and spatial position.In this thesis,a dynamic wireless power transfer magnetic coupler with relatively constant coupling in spatial,and a variable compensation topology with strong resistance to coupling and load variations are investigated.Combining the magnetic coupler and the variable compensation topology,the spatial freedom and output stability of the dynamic wireless power transfer system is improved.The specific work of this thesis is as follows:(1)A dynamic wireless power transfer magnetic coupler with large transmission distance and stable coupling when the receiver moves in the traveling and misalignment directions has been proposed.And the spatial magnetic field distributions of several typical long-track transmitter based magnetic couplers are analyzed.When the power supply rail provides a directional and stable effective magnetic field for the receiver in spatial,the magnetic coupler can maintain a relatively constant coupling during the traveling and misalignment process of the receiver.By winding the transmitter coil unidirectionally along the traveling direction on a flux pipe ferrite to eliminate the magnetic pole of the power supply rail in the traveling and misalignment directions,a directional and stable effective magnetic field is generated for the H-type receiver.Thus,a relatively constant coupling of the magnetic coupler in spatial is achieved.This method constructs the power supply rail and receiver in the form of a single-phase coil,and avoids the cross-coupling between multi-phase coils and extra compensation network,inverter or rectifier.Finally,by combining with an inductor-capacitor-capacitor/series compensation network,the high spatial freedom coupling of the magnetic coupler and the relatively stable outputs of the system are realized when the spatial position of the receiver changes.(2)A variable compensation topology for constant current-constant voltage charging during the coupling and load variations is proposed.And several typical compensation networks with natural constant output characteristics are discussed.By multiplexing the compensation components and switches,a variable compensation topology consists of a semi-bridgeless active rectifier controlled series-series compensation network and an AC switch controlled series/inductor-capacitor-capacitor compensation network is proposed and analyzed.Phase-shift modulation is used to regulate the output fluctuation caused by system parasitic parameters,mutual inductance variations and discontinuous conduction mode,further a constant current-constant voltage output of the dynamic wireless power transfer system is achieved when the spatial position of the receiver changes widely.Moreover,a switching strategy which realizes inductor zero current cutting without current sampling circuit is proposed for modes switching,thus,simplifying the system control and realizing quick mode switching.Finally,the feasibility of the variable compensation topology and switching strategy is verified through experiments.This thesis achieves constant current-constant voltage output with high spatial freedom in dynamic wireless power transfer systems by four aspects: magnetic coupler,variable compensation network,phase-shift modulation control,and switching strategy.The theoretical analysis and experimental results show that the proposed magnetic coupler and variable topology can reduce the cost and complexity of the dynamic wireless power transfer system while achieve stable output with high spatial freedom.