Cooperative Primary Control of a Hybrid AC/DC Microgrid Based on AC/DC Virtual Generators

This article presents a dynamic control strategy for a hybrid AC/DC Microgrid (MG). To allow a high penetration of renewable energies, provide an increased system reliability during islanding and reduce the dependency on the mains, Energy Storage Systems (ESSs) are included in both the DC and AC grids. The MG is composed by DC grid, with connection to the mains and a central battery ESS, and a flexible number of AC subgrids coupled to the DC bus through AC/DC 3-phase Interlinking Converters. The paper presents three main contributions: 1) A DC bus regulation scheme is proposed based on DC virtual generators and P/V DC droop that allows to adapt the participation in the power sharing for DC bus regulation and provides with an automatic transition between grid-connected and islanding modes; 2) In order to provide a cooperative operation between the different AC subgrids, allowing the automatic power sharing between them through the DC bus, a Hybrid AC/DC Virtual Generator control scheme is proposed based on the Virtual Synchronous Generator concept, for its implementation in the interlinking converters; 3) an AC voltage and frequency compensator suitable for systems with high resistive line impedance. The discussion is supported with small signal analysis, simulations and Hardware-in-the-loop.