Dc-dc converters for renewable energy integration with medium-voltage dc grids

Abstract

FB-ZCS dc-dc converters achieve soft-switching and smooth current commutation by utilizing quasi-resonant operation between the leakage inductance of transformer and a resonant capacitor shunt-connected across the transformer-secondary. In every switching half-cycle, the resonant capacitor is charged to its full-voltage irrespective of converter loading by nature of its shunt-connection. This requires a dedicated charging interval which results in duty-cycle loss. As the converter loading reduces, duty-cycle loss increases as the reduced input current takes longer time to charge the resonant capacitor to its full-voltage. To satisfy the resonant condition for a given leakage inductance, a larger resonant capacitor will be required for higher current ratings and the charging interval of this capacitor results in significant duty-cycle loss, restricting the operation range of converter.