Constant Frequency CC–CV Operation of Isolated <i>LLC</i> Resonant DC-DC Converter Using Switched Capacitor Network for WCS

In this letter a new circuit structure based on <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> 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 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> resonant dc-dc converter can provide CC–CV at a constant switching frequency. This work is an alternative solution based on fixed isolated <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LLC</i> 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. In addition, the kVA/kW optimization method is employed to reduce reactive component sizing for achieving high power density. A 600 W 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.