Analysis of the Voltage Stability Margin of the Sending-end Grid for the Large-scale PV Cluster Transmission by VSC-HVDC

In the large-scale photovoltaic cluster transmission by voltage source converter based high voltage direct current transmission (VSC-HVDC), the replacement of synchronous generators by VSC-HVDC as the stable voltage sources will result in different voltage characteristics from those of conventional grids. This paper focuses on the static voltage stability characteristics, especially the stability margin of the sending-end grid in the system. At first, dual port model of sending-end grid is introduced as the base of the static voltage stability analysis. Then, P-V curves are drawn by solving the quadratic complex equation of the system. After that, according to the simulation results, the threshold voltage is chosen to represent the voltage stability boundary and the static voltage stability margin index is defined as the gap between the real voltage and the threshold voltage. The index is applied into analyzing the impact of reactive power compensation capacities on improving voltage stability of the system. Finally, the simulation results verified the feasibility and effectiveness of the proposed static voltage stability margin index.