Impact of Intermittent Wind Generation on Power System Small Signal Stability

In recent years, the increasing concerns to environmental issues demand the search for more sustainable electrical sources. Wind energy can be said to be one of the most prominent renewable energy sources in years to come (Ackermann, 2005). And wind power is increasingly considered as not only a means to reduce the CO2 emissions generated by traditional fossil fuel fired utilities but also a promising economic alternative in areas with appropriate wind speeds. Albeit wind energy currently supplies only a fraction of the total power demand relative to the fossil fuel fired based conventional energy source in most parts of the world, statistical data show that in Northern Germany, Denmark or on the Swedish Island of Gotland, wind energy supplies a significant amount of the total energy demand. Specially it should be pointed out that in the future, many countries around the world are likely to experience similar penetration levels. Naturally, in the technical point of view, power system engineers have to confront a series of challenges when wind power is integrated with the existing power system. One of important issues engineers have to face is the impact of wind power penetration on an existing interconnected large-scale power system dynamic behaviour, especially on the power system small signal stability. It is known that the dynamic behavior of a power system is determined mainly by the generators. So far, nearly all studies on the dynamic behavior of the grid-connected generator under various circumstances have been dominated by the conventional synchronous generators world, and much of what is to be known is known. Instead, the introduction of wind turbines equipped with different types of generators, such as doublyfed induction generator (DFIG), will affect the dynamic behaviour of the power system in a way that might be different from the dominated synchronous generators due to the intermittent and fluctuant characteristics of wind power in nature. Therefore, it is necessary and imperative to study the impact of intermittent wind generation on power system small signal stability. It should be noticed that most published literature are based on deterministic analysis which assumes that a specific operating situation is exactly known without considering and responding to the uncertainties of power system behavior. This significant drawback of deterministic stability analysis motivates the research of probabilistic stability analysis in which the uncertainty and randomness of power system can be fully understood. The