A modular concept development for resonant soft-charging step-up switched-capacitor multilevel inverter for high-frequency AC distribution and applications

This article presents a step-up switched-capacitor (SC) multilevel inverter (MLI) with reduced ripple power loss by employing a soft-charging technique and modular cell. SCMLI possesses many attractive features for high-frequency ac (HFAC) applications. With a two-phase alternating structure, the voltage ratings of the components in the proposed SCMLI are substantially reduced compared with the unfolding H-bridge-based topologies while preserving the features of voltage step-up and self-voltage balancing offered by the series-parallel SC method. This structure also enables higher operating frequency by extending the maximum charging duration of capacitors. By inserting a small resonant inductor, soft-charging is achieved in all SC units in the inverter which mitigates the ripple loss and electromagnetic interference issues existing in many SCMLIs. The soft-charging operation of the proposed inverter under staircase modulation is elucidated based on the theory of underdamped SC circuit. The mathematical analysis is validated by the simulation and experimental outcomes showing a dramatic reduction in the ripple power loss by employing the soft-charging technique. The technique is highly suitable for high-frequency power distribution.