Modeling and Stability Analysis for Meshed AC-Connected HVDC System Considering Cable Ageing

Large-scale wind energy integration will lead to increasing interconnection of high-voltage direct current (HVDC) power transmission systems. However, the influence of AC power cables on the stability of HVDC systems remains to be studied. Therefore, modeling and stability analysis for meshed AC-connected HVDC system has been developed in this paper. Firstly, a representative meshed HVDC system composed of grid-forming (GEM) MMCs, grid-following (GFL) wind power plants (WPPs) and an interconnected AC cable has been modeled and analyzed. A novel modeling procedure for power cables based on per-unit-length parameter is also established to simplify system stability analysis under different cable lengths and ageing severities. Stability evaluation has then been conducted, proving that larger cable length and deeper cable insulation ageing severity may lead to unstable system operation. Finally, sensitivity-based controller parameter tuning has been proposed to enhance system stability more efficiently. Simulations prove the effectiveness of the theoretical analysis.