Constant Frequency CC-CV Operation of Isolated LLC Resonant DC-DC Converter Using Switched Capacitor Network for WCS

In this letter a new circuit structure based on LLC resonant isolated DC-DC converter is proposed to achieve constant current-constant voltage (CC-CV) characteristics for wireless charging system (WCS). Complex reconfigurable network-based LLC resonant DC-DC converter can provide CC-CV at a constant switching frequency. This work is an alternative solution based on fixed isolated LLC resonant DC-DC circuit where extra capacitor switch arrangement is used to achieve CC-CV characteristics at a constant switching frequency with seamless transition feature. All inverter switches are soft switched throughout CC-CV operation. Additionally, the kVA/kW optimization method is employed to reduce reactive component sizing for achieving high power density. A 600W prototype with an average kVA/kW ratio of 30 and a peak efficiency of 96% at a coupling coefficient of 0.2 has been designed to validate the proposed WCS.