Secondary Control of Hybrid Microgrids Interfaced with the Distribution Grid by Multiport Grid Forming Smart Transformers

Smart Transformers (ST) have become one of the most promising solutions for the integration of hybrid microgrids (MGs) into the medium voltage distribution grid. However, in most of the control approaches presented for ST based MGs, the frequency and voltage control of each ST port are decoupled. In addition, integration of ST based MGs in the primary and secondary frequency and voltage regulation of the medium voltage distribution grid has not been deeply explored. This paper presents a multidelay compensator based secondary control strategy for ST based AC/DC hybrid distribution grids operated under previously proposed primary and inertial control with multiport Grid Forming capabilities. The presented strategies cover both the MG and the MV distribution grid secondary control for the integration of ST based MGs, and takes into account the effect of the multiple delays present in the centralized secondary control.