Capacitive Power Transfer Through a Conformal Bumper for Electric Vehicle Charging

Wireless power transfer (WPT) is emerging as a practical means for electric vehicle (EV) charging. Of the most common approaches to WPT, inductive coupling, and capacitive coupling, capacitive power transfer (CPT) is proposed to charge an EV at a kilowatt scale power level. CPT implementation replaces copper coils and permeable focusing/shielding materials of inductive approaches with foil surfaces, making CPT a cost effective and structurally simple system to implement while maintaining efficient power transfer capability. This paper addresses the primary technical hurdles to kilowatt scale CPT system development, namely, safe field confinement by achieving high coupling capacitance between the vehicle and the charging station. High capacitive coupling is achieved through a conformal (flexible and compressive) transmitter bumper that molds and contours itself to the vehicle. This minimizes the air gap and confines the field during charging. Here, a conformal surface demonstrates 3-5 times more coupling capacitance than its rigid counterpart of equal area. The associated power electronics are also discussed in detail, utilizing a Class E-2 amplifier/rectifier. An experimental docking station was built to charge the 156 V battery pack of a Corbin Sparrow EV and measured throughput power is demonstrated at >1 kW at similar to 90% efficiency via a coupling capacitance of 10 nF operating at 530 kHz.