Three-coil structure-based WPT system design for electric bike CC and CV charging without communication

In comparison with the traditional plug-in charging systems for the electric bike (EB), wireless power transfer (WPT) systems have superior advantages of convenience and safety. Combining the application requirement range of the EB, this study proposes a three-coil structure-based WPT system in order to achieve ideal and reliable constant current (CC) output and constant voltage (CV) output without the need for a sophisticated control strategy and the real-time communication links between the transmitter and receiver sides. Two ac switches are utilised at the transmitter side to implement the change of charging mode from CC to CV. By correctly selecting the parameters of compensation components, the required load-independent CC and CV characteristics with zero phase angle in the CC and CV modes can be achieved. Besides this, a load identification method based on the active power calculation used to estimate the equivalent resistance of the battery in the whole charging process, is utilised to judge the switching point from CC to CV mode. Finally, the feasibility of the method is verified through the construction of a laboratory platform with a 3.3 A charging current and a 57 V charging voltage.