A Negative Sequence Impedance Design and Regulation Strategy for Negative Sequence Current Sharing Among Grid-Forming Sources in Microgrids Considering Topology Impacts

The accurate control of negative sequence (NS) current distribution among multiple grid-forming (GFM) sources can lower the requirement on NS current capability of the sources. Existing control approaches mainly focus on microgrids (MGs) with fixed points of common couplings and on only the NS current distribution among inverter-based resources (IBRs). As MG configuration has been rapidly evolving to be more complicated, it is critical to take into consideration the impact of MG topologies on the NS current sharing. Moreover, synchronous generators (SGs) are still commonly applied as sources in MGs. The NS current distribution among IBRs and SGs also needs to be considered. In this paper, a novel NS impedance design and regulation approach is proposed to achieve accurate and flexible NS current sharing among different GFM sources (IBRs and SGs). The approach accounts for MG topology impacts by including MG's NS admittance matrix in the impedance design. The effectiveness of the proposed approach is evaluated through simulations and compared to existing solutions in a MG with four different source locations. Results show improved flexibility and accuracy in NS current sharing when MG topology impacts are considered. The proposed approach is also validated through experimental testing on a converter-based hardware testbed.