High Power Capacitive Power Transfer for Electric Vehicle Charging Application

Capacitive power transfer (CPT) technology is an effective way to charge electric vehicles, in which electric fields between metal plates are used to transfer power. Compared to the conventional inductive power transfer (IPT) system, a CPT system has three advantages: it does not generate eddy-current loss in nearby metal objects; it can reduce the system weight and cost; it has better misalignment performance. However, the coupling capacitance in a CPT system is usually in the pF range, which limits the CPT system power and efficiency.;Through overcoming the limitation of small capacitance in a CPT system, this dissertation has achieved three breakthroughs in CPT technology: the system power is increased from several tens of watts to several kW; the transfer distance is increased from less than 1 mm to hundreds of mm; the transfer efficiency is increased from about 30% to over 90%.;A double-sided LCLC compensation circuit has been proposed to realize high-power and long-distance capacitive power transfer. The compensation circuit provides resonances with the coupling capacitance, and increases the voltages on metal plates to kV level to achieve kW power transfer. A prototype has been constructed and validates the proposed circuit. Experimental results show that the prototype realizes 2.4 kW power transfer across an air-gap distance of 150 mm with a dc-dc efficiency of 90.8%. The experiments also show that the CPT system has better misalignment performance than the conventional IPT system.;An IPT-CPT combined system has also been proposed to integrate the IPT and CPT technology together. The combination can increase the efficiency of the CPT system, and improve the misalignment performance of the IPT system. A prototype has been constructed to validate the combined idea. Experimental results show that the prototype realizes 2.84 kW power transfer across an air-gap distance of 150 mm with a dc-dc efficiency of 94.4%.;Using the designed LCLC compensation circuit, a dynamic CPT system has been proposed to realize power transfer to receivers in moving status. A long-track coupler structure is used to reduce the pulsation of received power. A prototype has been constructed to validate dynamic charging. Experimental results show that the prototype realizes 154W power transfer across an air-gap distance of 50 mm with a dc-dc efficiency of 85.4%.;Considering practical applications, the safety issues and foreign object influence have been studied in this dissertation. The high voltage issue can be solved by reliable insulation, and the electric field emissions can be reduced through capacitive coupler structure design. The foreign object, either metallic or dielectric, can influence the coupling capacitances in a CPT system depends on the position and size. The CPT system can also influence the voltage and power loss in the foreign object.;To sum up, this dissertation has demonstrated that the CPT technology is a good solution to realize the charging of electric vehicles. In future work, the power density and efficiency of the CPT system will be further improved to make it more competitive with the inductive and conductive charging technology.