Research on state vulnerability of power grid with large scale new energy sources based on short circuit capacity margin

Vulnerability of a power grid indicates its capability to resist cascading failures, and state vulnerability, which is an important part of vulnerability, of grid becomes a research hotspot in recent years. With the development of smart grid,large scale wind farms and photovoltaic plants are integrated into power grid, whose ability to provide short circuit capacity is weaker than synchronous machines, and are treated as PQ nodes in grid. This characteristic is more likely to cause or extend cascading failure. Therefore, research on state vulnerability of this kind of power supply nodes is worthy of careful study. In this paper, calculation method of short circuit capacity provided by large scale wind farms and photovoltaic plants is developed, and further, the concept of short-circuit capacity margin, which compares actual short circuit capacity demanded by the network with short circuit capacity provided by power supply nodes, is proposed to evaluate state vulnerability of power grid. It reveals the influence on the ability of power supply nodes to resist the cascading disturbances / failures of power grid in essence, meanwhile,it is also able to quantitative assessment abilities of different types of power supplies to support grid in the same output and then provide some guidance to adjust the balance of the short-circuit capacity margin of the power supply node by adjusting the grid operation mode or power control mode. The proposed method can be applied to offline or online state vulnerability assessment, to provide decision support for power system planning and dispatching. Finally, a case study based on IEEE39 node system proves the effectiveness and superiority of the proposed method.