Modeling Of Offshore Wind Farms Considering Wake Effect And Analysis Of Reactive Power Voltage Distribution

As a kind of renewable green energy, the wind power has an important meaning in utilization. Amongst, the offshore wind energy holds enormous amount and has been becoming the focused development direction of wind power in China. Whereas, the previous conclusions about the onshore wind power can not be directly applied to offshore wind power, due to different surroundings for the offshore and onshore wind powers. The natural wind has inherent properties of random and intermittent, and the wake effect between wind turbines and the utilization of submarine cable will inevitably influence the distribution of active and reactive power flows and the voltage characteristics, when the generated offshore wind power is connected with the grid. Moreover, the installation capacity of offshore wind energy is generally larger, and thus shows the form of large capacity wind power farm, which may further lead to increasing impact on the grid. As a result, it is necessary to deeply investigate the voltage distribution feature of the offshore wind power.Firstly, the composition and structure of DFIG (doubly-fed induction generator) is introduced in this paper, and the maximum wind energy tracking principle is then expounded, from the view of coordinated control of wind turbine, generator and variable pitch system. Furthermore, the variable-speed constant-frequency generating theory of DFIG is analyzed, and the active and reactive power decoupling control policy of DFIG is studied.Secondly, the software of DIgSILENT/PowerFactory is employed to build up the model of a wind turbine group and to verify validity of the model. On basis of above model, a simple wind farm model is established, and a wind speed model is also established upon the offshore wake effect. Furthermore, both theoretical analysis and simulation methods are utilized to conduct the research on the impact of upward turbine to downward turbine in the mainstream direction, and the model validity and the wake effect impact on active power output of wind farm are verified by simulations.Finally, the power frequency overvoltage impact on the line voltage is studied, which is caused by the charging power of submarine cable, and influence of inner voltage characteristics of offshore wind farm is also studied by comparing the different collector systems. Herein, a planning offshore wind farm in Jiangsu is used as an example, the distribution characteristics of reactive power voltage and the influences caused by the offshore wind farm connection in the grid are investigated by simulation.