Analysis and design for constant current/constant voltage multi-coil wireless power transfer system with high EMF reduction

The investigation on the constant current (CC)/constant voltage (CV) charging for the electric vehicle wireless power transfer (WPT) system has been widely conducted. However, the CC/CV performance under misalignment cases has been scarcely studied especially for the multi-coil WPT system. The resonant tank compensation methodology for the exciter-quadrature-repeaters (EQR) transmitter-based multi-coil WPT system is studied to achieve high power factor CC/CV charging with low leakage flux over +/- 150 mm lateral misalignment range. The EQR transmitter consists of one small exciter coil powered by a single full bridge inverter and two larger decoupled quadrature repeater coils which are magnetically coupled to the exciter coil. A variable switched capacitor is applied on the exciter side to maintain a high power factor in the CV mode. A 3-kW experimental setup with a 200 mm nominal vertical distance was built and a three-coil WPT system with a single large repeater coil is chosen as a comparison. Experimental results show that the EQR transmitter-based WPT system achieves 92% coil-to-coil efficiency and reduces the leakage flux density by 70% compared with the existing three-coil system in the CV mode at 150-mm lateral misalignment.