Pre-Charge Strategy and Light-Load Voltage Balance Enhancement for DC/AC Flying Capacitor Converter

This paper introduces a control strategy that utilizes common mode current (CMC) for two objectives: 1) pre-charging a flying capacitor converter (FCC) with DC source, and 2) enhancing voltage balancing of flying capacitors under light load conditions. The methodology presented herein is applicable to existing PV, batter storage, and motor drive inverter systems that integrated with L-C filter. The proposed pre-charging process minimally impacts both load current and leakage current, which is a critical consideration for applications that sensitive to AC power quality. Two methods are proposed for CMC control: 1) common mode voltage (CMV) injection, and 2) switching frequency variation. These proposed methods are verified through computer simulations and experimental verification via laboratory testing using a prototype.