| Dynamic wireless charging (DWC) technology uninterruptedly charges the moving electric vehicle, making the power battery in shallow charge and discharge mode. It significantly reduces the required capacity of on-board battery, and highly extends the driving range. This technology is expected to be combined with currently developing internet of vehicles and smart grid big data, realizing flexible and intelligent wireless Wifi charging mode and convenient distributed charging network. This will greatly promote the development of electric vehicles, showing a good prospect of application. Dynamic wireless charging of electric vehicle requires the DWC system to achieve a stable transmission power over a wide misalignment range. In order to achieve the purpose of application, this thesis focuses on the sectional dynamic wireless charging system. The four key aspects, including the sectional power coils, compensation network with high misalignment tolerance, constant power control method and relay control strategy, are deeply studied.Firstly, the basic theory of wireless power transmission (WPT) used in DWC system is analyzed. Based on a variety of physical models, two kinds of controversial magnetic coupling WPT technologies are sufficiently studied and compared. The physical mechanism of archiving high efficient power transfer is explained. These two kinds of WPT technologies can be analyzed by the same theoretical model and the magnetic resonant WPT can be regarded as a special case of the SS type of magnetic inductive WPT. Based on the mutual model, the complex ratio transformer model is proposed, providing an intuitive physical picture of WPT in power transmission process, magnetic resonance and frequency splitting phenomenons.Secondly, from the actual size of electric vehicles, power consumption, the standards of driving road, the basic needs of DWC system for electric vehicle are analyzed, giving the feasible index on the sizes of transceiver coils, transmission power level, transmission distance and lateral misalignment. To smooth coupling of transceiver coils along driving direction and increase the lateral misalignment range, a sectional power coil design with asymmetric orthogonal rectangular structure is proposed. By the experimental test of the 5:1 physical scale-down power coil, the mutual coupling coefficient is kept in the range of 0.1-0.15 when the lateral misalignment becomes 40%, meeting the requirement of the DWC system.Then, from the perspective of smoothing the transmission power fluctuation, a general design method of primary compensation network is proposed. A generalized framework for describing transmission power of compensation network is established. The designed compensation network could smooth the transmission power by automatically adjusting the current in the transmitter coil according to the change of the coupling coefficient k and reflected impedance Zr. To further ensure the transmission efficiency and soft switching, the parameters of compensation network are optimized. Following the results of the optimization, a novel T type three-element compensation network with the higher degrees of freedom is stressed, companied with an inherent current limiting ability under no-load operation. A DWC prototype with fixed frequency control based on the T-type compensation network is built. The output power is kept almost stable even though magnetic coupling coefficient varies twice. The DC-DC transmission efficiency achieves about 90%.Based on the selected sectional track and T-Type compensation network maintaining high misalignment tolerance, a constant power control method in the secondary side without the real-time communication between primary and secondary sides is proposed. This method perturbs the rectified DC voltage and tracks transmission voltage gain point of extreme power according to the observation of output charging current. Thus the DWC system keeps the stable and almost constant transmission power regardless of the varied magnetic coupling coefficient. The secondary side receives rated power in the effective coupling range and automatically ceases transmission when out of the effective coupling area, which is suitable for high misalignment DWC application. An experimental validation on a physical scale-down DWC demonstration platform is carried out. The experimental result shows that the moving vehicle receives a constant power even though the driving line is 40% offset, which means that the constant power can be hold in the whole driving lane.Finally, to realize the sectional excitation and power supply of primary coils chain, a relay control strategy based on distributed control logic and the secondary active excitation detection method is proposed. The basic principle of relay control and its architecture of dynamic wireless charging system are described. By using the mutual coupling model, the theoretical model of the secondary active excitation detection circuit and the method of parameter selection are given. At the same time, a reasonable control flowchart is designed to avoid the simultaneously excitation conflict between primary and secondary sides. At last, a 5:1 physical scale-down DWC demonstration platform is built. The effective relay control of powered roadway with 8 primary coil chains is completed on this platform. The moving vehicle receives stable power smoothly at the above of the transmission coil. The experimental results verify the feasibility of the proposed method, providing a solution for primary power supply management of the sectional dynamic wireless charging system. |
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