A Novel NPC Dual-Active-Bridge Converter With Blocking Capacitor for Energy Storage System

In recent years, dc microgrids have been widely concerned for natural interface with renewable energy sources, dc loads, and energy storage systems (ESS). A novel neutral point clamped (NPC) dual-active-bridge (DAB) converter with a blocking capacitor is proposed for ESS in dc microgrids. By inserting a blocking capacitor in primary loop of the traditional NPC DAB converter, the voltage amplitudes across the primary and the secondary windings of the transformer can be matched when the voltage ratio is equal to 0.25, 0.5, 0.75, and 1. Therefore, the proposed topology can adapt to a wide range of energy storage battery voltage variations. Asymmetric pulsewidth modulation plus phase shift modulation are applied to improve the dynamic performance of the proposed converter. The phase-shift ratio between the two bridges and the asymmetric duty ratio are regulated to control the power flow of the proposed NPC DAB converter. Compared with the traditional NPC DAB converter, the proposed topology has lower transformer rms current and wider soft-switching region. Finally, experimental results from a 500-W hardware prototype are presented to verify the feasibility and the advantage of the proposed converter. Compared with the traditional NPC DAB converter, the maximum promotion of efficiency is up to 3.8%.