Parallel AC-Link Connection of Current-Fed Dual Active Bridge Converters

Abstract

This paper proposes a current-fed dual active bridge (DAB) converter, connected in parallel on the secondary-side AC-link, as a DC–DC converter with a high boost ratio and high input current capacity. Compared to conventional converters, the proposed converter can reduce the number of components without complicating power control and increase input current capacity. However, the parallel connection on the secondary-side AC-link could cause a circulating current. Therefore, this paper develops an equivalent circuit model of the proposed converter and theoretically analyzes the characteristics of the circulating current. The analysis reveals the influences caused by the circulating current on the proposed converter and shows a guideline for reducing the circulating current. Furthermore, using a prototype rated at 2 kW, the validity of the theoretical analysis is demonstrated through experiments. In the experiments, the validity of the theoretical analysis was confirmed, and it was verified that the proportion of the circulating current relative to the secondary-side converter’s current was less than 8% at maximum. In addition, introducing a phase-shift control on the primary-side converters reduced the input current ripple by 38.6%. Furthermore, even under conditions where the circulating current is relatively large, the efficiency drop of the proposed converter was minimal. This indicates that the influence of the circulating current on the proposed converter is sufficiently small.

Keywords

• Circulating current
• dual active bridge
• fuel cell
• high efficiency
• high voltage ratio
• input current ripple