Internal Control Stability Assessment Method of a VSC-based transmission grid

The multiplication of interfaced generation units connected to the utility grid might form VSC-based transmission grids in a near future. To support the utility grid autonomously, the converters must provide grid-forming capabilities and be connected in parallel. As the structure of a transmission grid is changing and unknown, these requirements presume a robust local voltage control for each high-power VSC, to face various network topologies. Indeed, the stability is challenged when voltage-controlled VSCs are close to each other, namely, when the tie-impedance is low. The present contribution describes an impedance-based criterion method as a convenient and effective tool for assessing the stability of the voltage control of converters in a VSC-based transmission grid. The method is successfully applied to a typical two-VSC system to anticipate unstable situations.