Research on a Strategy of Suppressing Grid Flicker Caused by Wind Turbine Based on Independent Pitch Control

Wind power is a kind of green energy, renewable, pollution-free, inexhaustible, so wind power has a broad market prospects, its technology is also in continuous progress, wind turbine assembly unit capacity is higher and higher, the scale of wind farm is also towards large-scale development. As the capacity of wind turbine assembly increases, the blade diameter of the matching wind turbine needs to be increased correspondingly to obtain more wind energy. Taking offshore wind turbine as a representative, the blade diameter of some wind turbines has reached more than 100 meters. When the blade diameter becomes larger, it will bring a series of problems. The main performance is that the elasticity and flexibility of wind turbine tower, transmission shaft, blades and other main components will increase correspondingly, while the damping value of power electronic components will be smaller. These problems make the fatigue load variable of large wind turbine more complex, which will lead to the low frequency mode of the unit The more complex the modes are, the more complex they are. When the diameter of the wind turbine increases, the pitch angle increases due to tower shadow effect, wind shear and turbulence time-varying factors, which causes the blade to swing and shimmy more significantly, and then causes the fatigue load condition of the wind turbine to be more obvious, which seriously affects the mechanical stress intensity change between various transmission mechanisms of the wind turbine, thus reducing the service life of the wind turbine Limit. With the increase of blade diameter, the frequency of grid flicker will also be caused, which will cause voltage instability and reduce the power quality of grid after the wind turbine is connected to the grid. With the increase of impeller diameter and fan capacity, in recent years, independent variable pitch control technology came into being.Independent pitch control technology not only has the characteristics of centralized pitch control, but also can balance the unbalanced load on variable speed wind turbine, so as to reduce the fatigue load of wind turbine. Therefore, it has been paid attention to in the field of wind power research in the world. There are many research results in this area, but the research on the relationship between independent pitch control strategy and grid flicker is relatively less. The factors causing voltage fluctuation include air density, impeller speed, pitch angle, wind field distribution and power grid condition. This paper analyzes the wind shear and tower shadow effect which cause the vibration of wind turbine, studies the relationship between independent pitch strategy and wind turbine voltage change, proposes a control strategy of independent pitch and designs a controller to control the power of wind turbine during operation The method of voltage variation to make it stable, and then reduce the flicker of power grid, and carry out simulation experiments to verify its effectiveness. The control strategy can reduce the grid flicker at the common point of wind turbine outlet and grid connection, improve the stability of wind turbine grid connection, and improve the overall power quality of the grid.