A Multiport Embedded DC Power Flow Controller for Meshed DC Distribution Grids

Ring and meshed dc distribution grids have attracted increasing interest lately. Their multipoint and multiterminal structure facilitates flexible operational control and reliable power supply across the network. However, the dc grids implemented with existing power converters lack sufficient control freedoms for proper power flow adjustment; therefore, it is necessary to develop additional dc power flow controllers (DCPFCs) to be added to these grids for improved power flow control capability. Specific to multiterminal dc networks built with modular multilevel converters (MMCs), this article proposes an embedded DCPFC (e-DCPFC) directly integrated in the MMC topology. Unlike previously proposed solutions, the e-DCPFC configuration is derived from the conventional MMC and does not need any isolation transformers or external power supply. Its other main features include modular construction, convenience for multiport extension and bidirectional power flow adjustment capability. In this article, the topology, working principle, and the coordinated control strategy for e-DCPFC and its host MMC are elaborated. Experimental results from a lab prototype verify the proposed topology and its performance under typical working conditions.