| Wind energy is a kind of clean and renewable energy. Wind is also used by human beings like other renewable energy sources. But the inherent characteristics that wind is random, intermittent and uncontrollable would result in great volatility of wind output. Amount of wind integration into grid would endanger security and stability of power systems. To establish a micro-grid is an important means to solve the above problems, the micro-grid is composed of wind power as well as other sources, characteristics of which is complement to wind power. Not only are the power quality and reliability of power system improved, but also wind power utilization is maximized. The hot issue on optimal operation of micro-grid with wind-hydro power hybrid system has been studied.First of all, the structure of micro-grid with hybrid wind-hydro power system is designed. The micro-grid includes a small wind farm, a small hydro power station, an energy storage device and local loads. Based on wind power technology, hydropower technology, energy storage technologies, micro-grid and other related theories, the complementary characteristics of wind power and hydropower is analyzed. Considering that adjustable hydropower station can adjust its output swiftly, but it is not available to consume the excess output when there is power surplus in the micro-grid. In the case, energy storage device is introduced. This device is used to storage part of wind power at moment of power surplus and discharge the stored energy at moment of power shortage. For increasing the reliability of power supply, the micro-grid is designed to connect to the main grid.Secondly, mathematical model of micro-grid with wind-hydro hybrid power is established. Based on optimal operation theory of power systems, the necessity of optimal operation of micro-grid with wind-hydro hybrid power plus energy storage is discussed and mathematical model which makes micro-grid gain maximal profit is constructed. With help of the model, wind source in the micro-grid would be utilized fully and no wasted wind power produced. In addition, impacts on large power grid because of uncertainty of wind power would be decreased greatly. In this model, complicated constraints are considered, which include output limits of wind turbines, reservoir capacity limit of adjustable hydropower station, load variation, the power balance requirement of micro-grid and so on.Finally, numerical simulation of optimal operation of micro-grid with hybrid wind-hydro power has been done. Referred to the established mathematical model, CPSO is used in solving the specific example. Power allocation of all sources as well as profit of the micro-grid regarding the given calculation condition has been analyzed deeply. In addition, the scenario that wind farm and hydropower station operated independently has been simulated. The comparison demonstrated that micro-grid with hybrid wind-hydro power will operate with higher safety and reliability and get more profit. In order to illustrate that battery is necessary in micro-grid, simulation has been done in circumstance of time-of-use tariff when battery discharges.Based on the above studies, micro-grid with hybrid wind-hydro power plus energy storage will efficiently decrease its impact when wind power is injected into the main grid and provide users reliable electricity supply. Meanwhile, the value of wind and hydropower resources will be reflected maximally. |
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