Indirect Input-Series DC Transformer With Wide Input Voltage Range

To avoid fault hazards of the centralized capacitor on the high-voltage side, an indirect input-series dc transformer ((IS)-S-2 DCT) with a wide input voltage range is proposed in this article, where the input filter capacitors of adjacent cells are not directly connected in series. The high-voltage input side includes a boost inductor and N full-bridge cells and transformer primary windings. The transformer secondary windings of adjacent cells are connected in series directly to share the same LC resonant tank and rectifier diodes. The proposed converter can be thought of as a boost converter cascaded a fixed voltage gain LC resonant DCT. Owing to the fixed voltage-second product of transformer primary voltage, the maximum magnetic flux density of the high-frequency transformer is fixed and is related to the resonant frequency over a wide switching frequency range, simplifying the transformer design. The capacitor voltage double sequencing method is used to ensure input voltage sharing of each full-bridge cell. Soft switching of all secondary diodes and most primary switches is realized through the resonant tank. The operating characteristics of the proposed (IS)-S-2 DCT are analyzed. A three-full-bridge-cell-based (IS)-S-2 DCT prototype was built, and the proposed solution is well verified by the experimental results.