Dynamic Wireless Power Transfer for Electric Vehicles




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The transportation industry consumes 29% of energy, out of which Gasoline accounts for 56% of the transportation fuel. Extensive use of gasoline leads to the emission of harmful gases which are hazardous to the environment. To reduce the pressure on conventional fuels, the electric vehicle (EV) is an alternate solution. A major hurdle in implementation is the limited range of EVs. Mainly EVs need a large battery capacity to increase the range of the EV. One of the possible solutions is to charge the vehicle while moving referred to as “Dynamic Wireless Power Transfer (DWPT)”. Charging the vehicle while moving can significantly reduce the battery energy storage capacity on the vehicle. This dissertation identifies the challenges in the implementation of DWPT for EVs. DWPT can be implemented either with small segmented coils layed on the road or with long tracks on the road. Long tracks have problems of low coupling coefficient, complicated power electronics structure and overall lower efficiency. In comparison to long track DWPT, segmented DWPT has higher coupling coefficient, less complexity of power electronics and higher overall efficiency. However, to apply segmented coil structure to DWPT, some challenges have to be addressed. This dissertation evaluates different magnetic couplers by simulating and comparing for misalignment and coupling coefficient applications with and without shielding. Further, it compares different reactive compensation circuits suitable for misalignment tolerance, load independence, power factor, and efficiency. A major challenge in the implementation of dynamic wireless power transfer (DWPT) is automatic detection of EVs to avoid loss in efficiency and alleviate any safety concerns. This work proposes a novel coil detection method for segmented DWPT. Detection of the EV ahead of its arrival will initiate energizing of the transmitter buried inside the road to enable just-in-time transfer of power. At low speeds, communication can be a reliable method to power up the transmitter coil. However, at high speeds on highways, communication latency time for the detection of an EV is long and hence impractical. This work proposes a low cost and low power EV detection system based on a novel orthogonal coil arrangement to detect EVs traveling at high speeds. Lastly, this dissertation presents a maximum efficiency point tracking algorithm for Wireless Power Transfer (WPT). Conventionally, the load is considered only resistive in the literature. However, in most of the cases, the battery is the end load, and the equivalent circuit of battery consists of resistive and reactive elements. Therefore, to improve the overall efficiency of the system, load impedance has to be matched with source impedance. In this work, an algorithm is presented to maximize the efficiency of the system. The proposed algorithm varies both frequency and phase shift of the inverter output voltage to minimize the input power, whereas output power is kept constant by the output side dc-dc converter. Battery voltage and current regulation are maintained by the output side dc-dc converter.



Electric vehicles, Electric vehicles--Batteries, Wireless power transmission



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