Probabilistic assessment of oscillatory stability margin of power systems incorporating wind farms

Keywords: Oscillatory stability margin Monte Carlo simulation Nataf transformation Statistical indices Wind power a b s t r a c t With the increase in penetration of wind power which is essentially intermittent and random, the dynamic performance of the power system will change significantly, and so will the characteristics of the oscillations and their stability margins. This paper provides an attempt to include probabilistic character of wind power into the power system oscillatory stability margin (OSM) analysis. Nataf transformation approach is applied to generate the wind speed samples, which models the correlation between the various wind farms. The mathematical model of OSM for wind farm integrated power system is formulated and is calculated by the integration-based eigenvalue tracing approach. Considering the uncertainties of the wind power, several statistical indices are presented to evaluate OSM. Monte Carlo simulation (MCS) is used to calculate these statistics. The impact of wind power uncertainty on OSM restricted by inter-area mode is investigated in four-machine two-area test system and 16-machine five-area test system , respectively, for different wind farm locations, wind power penetration levels and wind speed correlation (WSC) degrees. Appropriate conclusions are finally drawn. Stability considerations have long been recognized as an essential part of power system planning, design, operation and control. Oscillatory instability which is inherent in interconnected power system is one of the major constraints affecting power system operation security. The rapid growth of Chinese installed wind power capacity—which has approximately doubled annually during the past 5 years—has further increased the risk of oscillatory instability and, consequently, the importance of this problem. Generally , wind power sources are located far from the load centers while conventional generators are typically closer to the major loads. An example is the Jiuquan Wind Power Base in western Gan-su province in China, with abundant wind resources, low electricity consumption and relatively weak grid network. The wind power must be delivered to metropolitan load centers through long-distance transmission lines, which could lead to a maximum use of the existing network, cause inter-area oscillations to be ever more lightly damped and result in smaller stability margins. Consequently , the prediction and identification of oscillatory stability margin (OSM), is among the major concerns for electric power engineers for the purpose of keeping adequate OSM on system operation and planning. Oscillatory stability is related to Hopf bifurcations (HBs) which can be detected by using small signal stability (SSS) analysis. …