Analysis and Design of a Three-Coil Coplanar Couper WPT System with Automatic Seamless CC to CV for Charging Battery
摘要
Load-independence constant current (CC) and constant voltage (CV) charging are the two stages of the battery charging. To simplify the complexity of the control strategy during the switching process from the CC mode to the CV mode of the wireless charging system, a low-profile three-coil inductive power transfer (IPT) system based on a switchable hybrid structure is proposed, where all coils are placed coplanar to save space and low-profile ferrite plates are strategically placed on and beneath the junctions of adjacent coils to enhance primary couplings and suppress cross couplings. Two switches are set on the primary side to reconfigure the resonant circuit to choose CC mode or CV mode, while increasing the compactness of the receiver side. The current in the primary coil remains essentially unchanged, when the load is open-circuited, short-circuited, or removed, indicating a higher level of safety in the system. Throughout the charging process, zero phase angle (ZPA) and zero voltage switching (ZVS) are maintained. Thus, a higher power transmission efficiency (PTE) is obtained. An experimental platform is built to verify the theory. The experimental and theoretical results are in good agreement, and the maximum PTE was measured as 96.73%.