Modular multilevel dual active bridge DC-DC converter with ZVS and fast DC fault recovery for battery energy storage systems

This paper proposes a novel modular multilevel dual-active-bridge (MMDAB) dc-dc converter for spilt-battery energy storage system (BESS) in medium-voltage dc (MVDC) grid application. The proposed converter can be derived from conventional DAB converter and therefore exhibits favorite characteristics of galvanic isolation, inherent zero-voltage-switching (ZVS) condition and small passive components. In addition, compared to cascaded DAB converter, the proposed converter has limited dc fault current rising and fast dc fault recovery due to the leakage inductance and the kept cell energy during the fault. A new modulation method with minimal passive components requirement and low dv/dt has been proposed, and the corresponding control system is also developed to realize the power flow control and balancing control. A case study of 500 kW, 20 kHz MMDAB-based BESS is performed in simulation to validate the performance.