Subtransmission System Planning Model And Algorithm Considering The Connection Of High Density Offshore And Onshore Wind Farm

China has the largest growth of installed capacity of wind power all over the world.In recent years,the focus of China’s wind power development has shifted to the onshore and offshore wind farm construction in the economically developed southeastern coastal areas.In central load area,the radial structure of power grid generally takes 500 kV substation as the center,while another characteristic is that it lacks local power supply.The integration of wind power in high-voltage distribution network poses great challenge in the aspects of planning and operation of power grid because of the fluctuation and uncertainty of wind power output.In this thesis,studies concentrate on the high-voltage distribution network with high-penetration wind power.The study includes the characteristic parameters and models of wind power fluctuation,principles of integration of offshore wind power,the impact on voltage of multi wind power integrated to the regional grid,and the planning and optimization of dynamic VAR compensation considering the high-penetration wind power.Detailed work is as follows:1)Four types of wind power models are analyzed based on the requirement of power grid planning.With the recorded wind power data and wind speed data in Southern China coastal area,the second and minute fluctuation characteristics of wind power and wind speed,the daily output curve of wind power are analyzed using clustering method and statistical tools.With the results,this thesis puts forward the short-time(second and minute)fluctuation models and their parameters of onshore and offshore wind power applicable for power grid planning,and proposes the extraction method for wind power daily output curve based on clustering method.2)The principles of selecting the transmission mode,voltage level and type of transmission line for offshore wind power integration are studied.The impact of power fluctuation on voltage of PCC is deduced in theory,based on which the selection of PCC considering short-circuit capacity is put forward.Then,approximate calculation method of the reactive power demand and the impact on frequency are proposed.The effectiveness of the proposed method is tested on the Zhuhai Guishan offshore wind farm.3)Evaluation function for assessing the impact of different reactive power control modes on regional grid voltage is derived.Then,the estimation formula to determine the maximum integrated capacity of offshore wind power is derived with voltage constraints,showing that the maximum integrated capacity is linear with the short-circuit capacity approximately.The study shows that the wind power fluctuation is the main restriction factor affecting the integrated capacity of offshore wind power and the degree of voltage fluctuation is relevant to the reactive power control mode.With constant power factor control mode of wind power,the closer to the wind farm the bus is,the greater its voltage fluctuates.While with constant terminal voltage control mode,the closer to the oscillation center the bus is,the greater its voltage fluctuates.Note that the location of oscillation center is relevant to the voltage level of wind power.4)Considering the voltage stability issue in regional grid caused by large amount of small-scale wind farms,the thesis proposes the disturbance index(DI)and fluctuation index(FI)to evaluate the impact of wind power fluctuation on grid voltage.Disturbance vector(DV)is formulated based on DI index to serve as the feature of wind power,based on which the Kendall correlation coefficient is introduced to evaluate the similarity between different wind farms in the aspect of their impact on the power grid.Then,Affinity Propagation clustering algorithm is used to group the wind farms and determine the disturbed area(DA)to reduce the searching space in selection of candidate location for dynamic VAR compensation.The proposed method is carried out on the IEEE 39-bus system with wind power integration to validate the effectiveness of the proposed indexes and algorithm,and the change rule of DA under multi-fluctuation scenario considering the simultaneous fluctuation of the wind power in the same/different group is also studied.5)A heuristic planning scheme for dynamic VAR compensation in regional power grid with high-penetration wind power is proposed.Supporting index(SI)is proposed to evaluate the voltage improvement with VAR compensation on specific bus when wind power fluctuation occurs.Based on the wind farms clusters and their DAs,the candidate location set is determined.Then,considering the probability of fluctuation scenarios,a sorting method to determined installed location is proposed and the capacity optimization is carried out with the severest wind power fluctuation scenario constraints.The planning scheme is applied both on IEEE 39-bus system and Zhanjiang Grid in 2020,to validate its effectiveness.The study results provide effective analysis tool and theoretical guide for assessing the impact of large-scale wind farms integration in the coastal area in China,and is of significance to the planning of the wind power integration and power grid with increasing development of onshore and offshore wind power.