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Isolated bidirectional DC-DC converter for interfacing local storage in two-phase DC grids

In contrast to ac grids, the participation of energy converter devices is more pronounced in dc microgrids. With the appropriate use of this devices, dc grid distribution technologies can be enabled, offering more flexibility and controllability to the system. One of the trends for low-voltage dc grid networks is the use of a “two-phase” dc lines in order to facilitate the adaptation to the present-time ac grids, and also to allow the use of diverse loads. Another feature of such dc grids is the distributed storage elements in houses and buildings, that have highly importance in the system, being responsible for storage of energy during low demand, provide energy during peak consume, and participate in the grid voltage stability if necessary. This storage system needs an isolated power converter for grid interfacing and a battery bank with the capability to independently control the energy flow in each phase. In this view, this paper aims to present and discuss the analysis, design and simulation of two 15 kW two-stage converters, connected to each phase of a ±380 Vdc microgrid and sharing the same battery voltage. The first stage, connected to a battery bank with voltage range of 315 V to 567 V, consists of a non-isolated synchronous Boost converter with current control. Whereas the second stage, connected to grid and to the output of the Boost converter, is an isolated bidirectional LLC-type converter that uses a symmetrical resonant network in order to provide identical characteristics in both ways of energy transport.