FB-ZCS DC–DC Converter With Dual-Capacitor Resonant Circuit for Renewable Energy Integration With MVDC Grids

Full-bridge zero-current-switching (FB-ZCS) dc-dc converters realize quasi-resonant soft-switching and smooth current commutation by utilizing the leakage inductance of high-frequency transformer and a resonant capacitor. The following two types of resonant capacitor configurations are proposed in the literature: First, shunt-connected across the transformer-secondary and, second, series-connected with the transformer-primary. Shunt-connected capacitor has the drawbacks of storing full-load-rated resonant energy irrespective of converter loading. This results in large duty-cycle loss and consequently regulation loss at light-loads. Series-connected capacitor addresses this issue but suffers from higher peak-voltage stress across components and insufficient voltage for resonance at light-loads. To address these limitations, a dual-capacitor resonant circuit is proposed in this article. Series-capacitor facilitates current-adaptive resonant energy storage and shunt-capacitor is designed only for a fraction of full-load-rated resonant energy, which lowers the duty-cycle loss and supports soft-switching at light-loads. This combination also reduces the series-capacitor voltage required for resonance, thereby reducing the peak-voltage stress. Steady-state analysis of converter operation is presented and the advantages over existing converters are demonstrated through simulations for medium-voltage dc application. Experimental results from a scaled-down prototype are presented to validate the proposed converter.