An L-Index Based Static Voltage Stability Support Capability Evaluation Method for Wind Farms

The increasing intake of wind farms in power grids calls for the accurately evaluation of their voltage stability support capability to guide the operation and scheduling of power grids. This paper proposes a method for assessing the static voltage stability support ability of wind farms based on the L-index, accounting for their operational constraints. The proposed method is implemented through a two-layer optimization process. At the system level, an optimization problem is formulated to maximize the margin of voltage stability by adjusting the reactive power of all the sources and send the reactive power command to the wind station. At second level, another optimization problem is formulated to minimize the real power loss inside the wind station while satisfying the reactive power command from the upper level and keeping the operational safety of the wind farm. The solvability of the second level optimization problem remarks whether the wind station can support the required reactive power while meeting operational constraints. If not, the maximum reactive power limit of the wind station is fed back to the upper level until the wind farm-level optimization problem is solvable. The L-index at this point is used as the system's voltage stability index to evaluate the support effect of the wind farm. The simulations performed on a modified IEEE 14-bus system demonstrate the effectiveness of the proposed method.