Effect Of Jiuhu UHVDC System Fault On Sending Wind Turbines

With the rapid development of society and economy,demand of energy is growing in China.China has a inverse distribution of primary energy and load demand,objectively requires a wide range of energy to optimize the allocation.In recent years,in order to solve the contradiction between supply and demand of energy load in China,a large scale wind power plants will be built in the inland regions where wind energy resources are concentrated.Because most of the wind power areas show the typical characteristics of low load and weak power grid,it is imperative that the wind power will be sent out by UHVDC.Jiuquan-Hunan ±800k V UHVDC is the planning of a start in 2014,plans to transmit wind power and photovoltaic power of Jiuquan region to Hunan,to achieve the use of large-scale clean energy.However,there are still many unstable factors in the initial operation of the Jiu-Hu UHVDC project.When alternating current grid occurs over-voltage caused by commutation failure of the Jiu-Hu UHVDC system that normal and stable operation of the wind turbine is easily damaged due to the poor anti-interference ability of the wind farm compared to the conventional thermal power plant.It may lead to large-scale wind turbine separated from the power grid in high voltage and directly threats system security.In view of the above problems,the study on the effect of Jiu-Hu UHVDC commutation failure on Jiuquan wind power will become a hot spot.At present,the research work on the Jiu-Hu UHVDC commutation failure is mainly modeling,simulation and the study on restraining strategy of transient over-voltage caused by commutation failure.Depending on the actual engineering data of Jiuhu UHVDC,this thesis builds a simplified model based on PSCAD/ EMTDC simulation platform.Firstly,this thesis describes how to construct the basic model of generator,transformer,large-capacity DFIG,and the problems needing attention in the construction process and the setting of the relevant parameters are introduced in detail.Secondly,based on the simulation model,the mechanism of over-voltage caused by DC commutation failure is analyzed,and the over-voltage level of the grid bus in Jiuquan wind farm is verified by the commutation failure of Jiuhu UHVDC.At the same time,several influencing factors of transient overvoltage of wind power grid bus are analyzed by simulation test.At last,according to the basic norms of the high-voltage through of the wind farm grid bus in foreign countries,this thesis puts forward some preliminary suggestions on the high-voltage through standard ofJiuquan wind farm.Based on the high-voltage through standard of Jiuquan wind farm,this thesis puts forward the strategy of restraining the transient overvoltage by installing the static var compensator(SVC)in the Jiuquan wind farm.The simulation results show that the proposed scheme can avoid the occurrence of over-voltage to a certain extent.