Design and application of magnetic resonant coupling wireless charging system for electric vehicles using adaptive impedance matching network

In the wireless power transmission (WPT) systems, Class-E inverters are preferred due to its low power losses and operating capabilities under high frequencies. The optimum operation point of the Class-E inverters can be achieved under fixed load value and optimal switching conditions. Since the load value of the transmitter and receiver coils is constant in the fixed distance operation, Class-E inverters can be considered as an ideal coil driver in fixed distance WPT applications. However, variations in the distance between transmitter and receiver or the load value adversely affect the switching conditions which causes high switching losses. This thesis presents a novel adaptive impedance matching algorithm for magnetic resonance coupled wireless power transmission (MRCWPT) system based on Class-E inverter used as coil driver. The required capacitance is determined by using the calculated mutual inductance and an adaptive capacity array is used on the transmitter side for dynamically matching the impedance in WPT. Thus, the optimum switching condition of the inverter and impedance matching are dynamically sustained. The best combination of the capacity array involving a series capacitor network is determined by the developed adaptive impedance matching algorithm. The proposed adaptive impedance matching algorithm is verified in both simulation and experimental studies. A 1 kW laboratory prototype of MRCWPT system based on Class-E inverter is designed. Simulation and experimental results demonstrate that optimal switching conditions of the Class-E inverter and the impedance matching of the WPT system are successfully provided at the same time under variations in the distance. In addition, the efficiencies of both MRCWPT and Class-E inverter are considered at the same time to determine the optimum operating condition. The determination method for such a high power level has not been reported in the literature yet. Consequently, the maximum efficiency of the power transfer is calculated to be 91.13%.