Adaptive Dynamic Voltage Support Scheme for Multiple Grid-Forming Converters in Distributed Networks

Abstract

Grid faults are among the most severe disturbances in power systems, compromising grid reliability and increasing the risk of power outages. To address this issue, distributed generation units are expected to provide dynamic voltage support (DVS) during the period of low voltage ride-through (LVRT). This paper proposes an adaptive dynamic voltage support (ADVS) scheme to achieve distributed and communication-free cooperation among multiple grid-forming (GFM) distributed generation units to boost system voltage magnitude in distribution networks. This ADVS scheme contains two part: the optimal dynamic voltage support (ODVS) methodology and the online external system parameters estimation method for distributed generation units. The ODVS derives the output current characteristics of distributed generation unit to achieve the most efficient dynamic voltage support at the point of common coupling (PCC), which comprehensively considering varied grid conditions and the coordination among multiple units. The external system parameters required for the proposed ODVS derivations are obtained through real-time, local estimation by distributed generation unit through the online external system parameters estimation method. Lastly, a modified Grid-Forming (GFM) control strategy is developed to enable the implement the proposed ADVS scheme. The control-hardware-in-loop experiments conducted on the IEEE-33 bus system under different R/X ratio conditions have validated that the proposed scheme is applicable to varied grid conditions. Additionally, the external system parameter estimation errors under different R/X ratios were analyzed.