| The wind power has features as randomness and volatility. Running a largeproportion of wind power makes the voltage stability problem more difficult to solve.Taking into account of the importance of voltage stability control, maximizing the voltagestability margin is one of its target. The part of grid not analyzed is always equivalentlysimplified to improve the computing speed and mitigate the difficulty in getting thewhole network information. Therefore, It is practically meaningful to calculate theaccurate voltage stability margin based on the external network equivalent.This paper derivates steady models of doubly-fed and Squirrel cage wind farm, andelaborate the P-V calculation method for voltage stability margin. Four kinds of windfarm external grid equivalent models are established for contrasting the applicability ofdifferent models by calculating the voltage stability margins. A partition correlation indexwith different loads increasing ways and grid kinds is proposed for evaluating theaccuracy of voltage stability margin calculation, combining the network topologies ofdifferent external gird partition ways, and this index could guide the result errorcorrection and area dividing of voltage stability margin calculating.The correction method of the network parameters was based on the changingdirections of samples in each step of time by the PMU measuring of voltage vectors andcurrent vectors. Reducing the error between equivalent parameter and actual value wasensured for parameter identification of the Ward voltage source equivalent model.Parameters of the external grid equivalent model, for a local power system grid innortheast, are calculated by borderline data collections. The voltage stability margins ofweak nodes are obtained when the output powers of wind farms increase with heavyloads. The result is corrected by the partition correlation index, and contrasted with theactual entire network calculation for verifying the accuracy of the equivalent method. |
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