Research On Power Quality Problem Of Large Scale Offshore Wind Power’s Grid Connection

With the advantages of environmental protection and high energy efficiency,offshore wind power will become the focus of development in the field of renewable energy in the future.Due to the variability of wind speed at sea and the existence of a large number of power electronic devices in the wind turbine,etc.,the power quality problems caused by the grid connection cannot be ignored.For far offshore wind farms,VSC-HVDC will become an indispensable transmission technology in the future due to its unique technical advantages.According to the principle of wind farm equivalence,the simulation software PSACD was used to build the VSC-HVDC grid connection model of large-scale offshore wind farm composed of DFIG.In MATLAB,LSSVM algorithm was used to establish a comprehensive rating evaluation model for offshore wind farm power quality.The power quality problems of flicker,harmonic voltage and current,and voltage deviation of the offshore wind farm under different wind speeds and different installed capacities were researched.And use the comprehensive rating evaluation model of power quality for evaluation.The results show that when the wind speed fluctuates and the installed capacity is large,the power quality problem is more serious.It can provide reference for the location and capacity determination of offshore wind farms.According to the situation that some harmonics exceed the national standard,APF is installed at the PCC of wind farm to control it.A three-phase three-wire parallel APF model was built using PSCAD simulation software,using the i_p-i_q harmonic detection algorithm;in terms of APF current control,design the ring width of hysteresis comparator as variable ring width.By evaluating the power quality grade of the PCC after the APF is installed at the PCC of offshore wind farm,it is confirmed that it has an improved effect on power quality.A quality pricing model of offshore wind power is constructed.According to the different power users’different power quality requirements,Wind farm can governance power quality to provide high-quality power for them.On the other hand,Charge power quality governance fees on users that have high quality power reqirement in the form of power quality service fees.For general users,the supplier only needs to take conventional measures.So,the power quality governance of wind farms can be promoted from economic perspective.Through the reasonable allocation and investment of funds,the offshore wind farm can achieve the best balance between governance costs and governance results,and achieve the purpose of high price and high quality of offshore wind power.