Modular Triple-Active Bridge DC-DC Converters for Utility-Scale Photovoltaics-Plus-Battery Storage Systems Connected to MVDC Grids

This paper presents a family of modular multi-port dc-dc converters based on the triple-active bridge topology to integrate utility-scale photovoltaics (PV)-plus-battery storage systems into medium-voltage dc grids. The proposed topologies can effectively reduce the number of power conversion stages as well as associated costs and losses compared to solutions with separate battery converters. Different configurations of the modular triple-active bridge converters are analyzed and compared. The topology with independent PV and parallel battery connection turns out to be the most promising solution due to higher PV energy yield with local maximum-power-point-tracking (MPPT), better utilization of the mismatching power between PV strings, higher tolerance of short-circuit faults in PV stings, and possibly smaller size of battery energy storage systems. The control strategy of this converter topology is also presented, which realizes local MPPT of PV strings and power management of battery storage systems. The proposed concept has been validated by time-domain simulations.