Research on HVDC Model in Transient Voltage Stability Analysis of AC/DC Transmission Systems

Fast Simplified models of HVDC are widely used in large-scale AC/DC power system transient voltage stability analysis. An important concern of different models is that to what extent the analysis results are impacted by using simplified models. Under voltage reactive power characteristic of HVDC is analyzed based on CIGRE HVDC test benchmark. It is observed that reactive power absorbed by HVDC is proportional to 1.6-th power of AC bus voltage, while the reactive power supplied by fixed capacitors of converter station is proportional to square of AC bus voltage. The above feature makes HVDC harmful to transient voltage stability. Among different simplified models of HVDC, constant power and constant impedance model are quite inconsistent with actual HVDC model, while Quasi-Steady-State (QSS) model is fairly consistent with actual HVDC model. So QSS model is suitable for large-scale AC/DC power system transient voltage stability analysis. Main conclusions are validated through simulations on Chinese Southern Power Grid.