Adaptive Virtual Inertia for AC Grids Connected to MT‐HVDC Grid by Considering DC Voltage Stability

ABSTRACT The growing integration of power electronics converters (PECs) and multi‐terminal high voltage DC (MT‐HVDC) grids within the power system decreases the system's inertia. Conversely, maintaining the voltage level of the MT‐HVDC grid is crucial for preserving the overall system's stability. One of the primary challenges in generating virtual inertia for AC grids connected to MT‐HVDC grids is the further decline in DC voltage caused by the additional power absorption needed for virtual inertia provision. This indicates that the implementation of virtual inertia negatively impacts DC voltage levels. In order to elucidate this issue, the present study develops a small‐signal model of the Cigre‐DCS3, incorporating a virtual synchronous generator (VSG). This model aims to analyse the effects of VSG parameters on the stability characteristics of the system under consideration. This analysis reveals a conflicting interaction between the DC voltage droop control loop and the virtual inertia time constant in the VSGs, as the presence of virtual inertia tends to adversely affect the DC‐side voltage stability. In response to this challenge, this paper introduces an innovative approach that integrates DC voltage stability considerations into the virtual inertia control loop. This integration aims to improve the dynamic response of VSGs while enhancing overall system reliability. The proposed method incorporates the rate of change of frequency, variations in frequency, and deviations in DC voltage to provide adaptive virtual inertia (AVI). Additionally, the stability of the presented controller is validated through Lyapunov stability analysis. Lastly, the simulation results illustrate the efficiency of the proposed approach in enhancing overall system performance.