Hybrid Grid Control using Smart Transformer with Multiport Grid Forming Capabilities and Interlinked Primary Control

One of the most promising solutions for interfacing distribution networks relies on the concept of Smart Transformer (ST). However, in most of the control approaches presented for the ST operation, there is a decoupling between the grid inertia and the ports of the ST. In addition, the strategies does not consider the integration of ST interlinked network in the primary frequency and voltage regulation of the Medium Voltage grid. This paper presents an alternative primary and inertia control strategy for AC/DC hybrid distribution grids interfaced with the grid by means of a ST, taking into account the concern of grid operators about the integration of Distributed Energy Resources (DERs) with Grid Forming (GF) capabilities based on Virtual Synchronous Generators. The proposed control provides GF operation in all the ports of the ST and interlinked frequency and DC voltage primary control between the AC and DC subgrids for hybrid grid power sharing. The proposal is supported by simulations in Matlab/Simulink
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and small signal analysis.