Capacitive coupling wireless power transfer is a method of transmitting high-frequency power through variations in the electric field. In this method, a high-frequency voltage is applied to transmitting electrode to generate an electric field. That field couples to receiving electrode and transfers energy in the form of displacement current. Unlike conduction current at low frequencies, displacement current can transfer energy through insulating materials such as air and asphalt. The system can be modeled as an equivalent circuit, where the electric-field coupling between electrodes is represented as a capacitor, allowing the circuit behavior to be understood analytically.
Since this method transmits power through the overlapping area of the transmitting and receiving electrodes, it can be implemented with a simple and flexible structure. This structure is well-suited for power supply over wide and long areas. For example, by installing a long transmitting electrode and mounting a short receiving electrode on the vehicle, it becomes possible to achieve parking-time with high tolerance to positional misalignment as well as low-cost in-motion charging. Furthermore, this method operates with low current and high voltage, which helps to reduce Joule heating and contributes to low-loss transfer. Additionally, since the magnetic field generated by the current is small, eddy-current heating is suppressed. Moreover, conductive materials can be used for shielding the electric field, making shielding comparatively easy to implement, and enabling thin, lightweight, and low-cost system configuration.
Since capacitive coupling uses high frequencies such as the MHz range, high-frequency circuit technology is critical. Furthermore, power electronics circuit technology is essential for supplying power to vehicles equipped with batteries and motors. By combining these technologies - including power conversion circuit designs that efficiently operate high-speed, high-power semiconductors and control circuit designs that adapt to load variations - PowerWave is working to commercialize the capacitive coupling transfer system and aiming to build the next-generation core infrastructure through high-power in-motion power supply.