Research On The Power Adjustment Of Wind Power Generation System

With the fast development of the worldwide economy, the human are facing more and more severe energy problem and environment problem. The burning of fossil fuels since the industrial revolution has increased the levels of greenhouse gas in the atmosphere, such as carbon dioxide, nitrous oxide. Because of the greenhouse effect, our planet is becoming warmer and warmer. In the meantime, the development of industry has increased the consumption of energy resource, such as coal, oil and natural gas, but these energy resources are not renewable. Facing these severe problems, the human are turning their eyes to clean, renewable energy resources. Comparing to the conventional energy sources, uses of clean,renewable energy resources neither emit greenhouse gas to the atmosphere, nor consume fossil fuels.As a kind of energy sources, wind power is clean and renewable which has been used for long time. Nowadays, the human are starting a new round of development of wind power. By reason of that electricity is the most important power source in modern society, the main way of developing wind power is transforming wind power to electricity. In our country, there are abundant wind power resource. According to the preliminary investigation, the wind power resource is about 2.53×108 KW on the land, adding the offshore wind power resource, the total wind power resource that can be used is about 10×108 KW.But due to that the wind speed is stochastic,wind power is unstable, especially with that large-scale wind power is being connected to the power grid, the power system stability is under great pressure. How to ensure that the whole power system operation is stable and reliable is becoming an important issue for power system researchers today.There are two kinds of wind power generation system, the fixed-speed constant-frequency(FSCF) wind power generation system and variant-speed constant-frequency(VSCF) wind power geneartion system.The FSCF wind power generation system can't adjust active power and reactive power,its utilization rate of wind power is very low.The VSCF wind power generation system could implement active power and reactive power control and adjustment,its utilization rate of wind power is high. There are two main types of generator of VSCF wind power generation system, directly driven wind turbine with permanent magnet synchronous generators(D-PMSG) and doubly fed induction generators(DFIG), both of them can implement the control of active and reactive power, maximum power point tracking(MPPT) and maximum utilization rate of wind power. In this paper, the analysis and simulation study of DFIG characteristics are implemented.Low voltage ride through(LVRT) capability is very important for wind power system. The regulations require that the wind turbine-generator keep connected with the power grid even in the situation of grid voltage drop. So,it is required that the wind power generation system must output reactive power to the power grid in the situation of grid voltage drop. But, due to the capacity of wind turbine-generator and corresponding converter is limited, they can't output large amount of reactive power to restrain the grid voltage drop. In this paper, that interconnecting the static synchronous compensator(STATCOM) with the wind power generation system is studied. The reactive power is outputed by the STATCOM to compensate the grid voltage drop. This method decreases the complexity of controlling the wind turbine-generator, also improves the response time of reactive power compensation and remedy the defects that the capacity of wind turbine-generator and corresponding converter is limited.The other problem for wind power system is that the active power output is unstable, owing to the stochastic characteristics of wind speed. In this paper, it is researched preliminarily to adjust the power output of wind power system by means of energy storage system(ESS), and the Battery Energy Storage System (BESS) is selected as a research object. The simplified model of BESS is established preliminarily, and the corresponding simulation model of wind power system interconnected with BESS is established, too. The characteristics of the whole system is analysed, and corresponding control theory is designed. By simulation and analysis, it is proved that BESS can compensate the output power fluctuation of wind power system, and also improve the stability of the power system operation.At last, according to the mathematical model of BESS, the sliding mode variable structure control theory is applied in the BESS control. The corresponding sliding mode hyperface and variable structure control strategy is designed. The simulation results prove that the sliding mode variable structure control possesses better dynamic performance and robustness performance.