A Two-Stage Non-Isolated Hybrid Switched-Capacitor Microinverter Utilizing a Fixed-Ratio Resonant DC-DC Stage with Startup Functionality and Flying Capacitor Multilevel DC-AC Stage

This work demonstrates the feasibility of a two-stage photovoltaic microinverter that leverages efficient and power-dense hybrid switched-capacitor converters in both stages. The first stage is a dc-dc 1-to-10 cascaded series-parallel (CaSP) converter which showcases the usability of a fixed-ratio resonant switched-capacitor converter for a volumetrically-dense high step-up conversion-ratio in this type of application. Voltage regulation and inversion is provided by the second stage: a flying capacitor multilevel (FCML) converter, which converts the inter-mediate 350 V – 400 V dc bus voltage to a 240 V<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rms</inf> ac output. Experimental hardware results demonstrate full functionality of the architecture, and highlight the use of the CaSP converter to provide a successful startup sequence for the FCML inverter at full voltage. The converter achieves a peak efficiency of 94.3% and a combined converter power density of 9.67 kW/L.