Research On Control Strategy Of Large-scale Wind Farm Outgoing By DC Transmission

In recent years, with the depletion of fossil energy and the severe environmental problems, more and more new energy resources are needed to replace fossil energy such as coal, oil and so on. On this background, the new energy resources generation becomes the current development hot spots, especially wind power. In the development of wind power, wind farm of which wind power reaches million kilowatts of large-scale becomes the first choice due to its stable wind speed. This kind of wind farm is always far away from the load center and the transmission power is large, so it is suitable to use direct current transmission mode. Thus, this paper focuses on the control strategy of power transmission of large scale wind farm through direct current transmission mode.According to the wind farm output characteristics, three problems are studied in this paper, including wind-fire capacity ratio of sending terminal wind far, transmission of wind power by variable current control strategy and control strategy of hybrid multi-terminal wind power transmission.(1) The annual output characteristics of the wind farm are obtained according to the annual wind speed data of wind farm, and then the output probability density of wind farm is obtained. Wind-fire capacity ratio selection scheme is proposed on the basis of probability density of wind farm. The best wind-fire capacity ratio scheme is selected under the given probability in this scheme.(2) For the large wind farms far away from coal, water and other energy base, if the wind-fire capacity ratio is selected as the above scheme, it will undoubtedly increase the investment. Especially for the offshore wind farm, it may not be feasible to build conventional power plants like thermal power plant at the sending terminal. So the variable current control strategy of the DC isolated island transmission is proposed. Controllable and variable wind power can be transmitted according to the power fluctuation of wind farm.(3) The wind field is affected by the wind speed fluctuation, and it has effect s on the power quality of the receiving terminal. This paper presents the topology of hybrid multi-terminal DC transmission. The sending terminal uses the conventional DC, and the receiving terminal adopts multi-terminal VSC parallel structure. The sending terminal VSC is defined as the voltage channel and power channel. Power channel uses constant power control mode and voltage channel uses constant voltage control mode. The placement of voltage channel is usually near conventional energy plant of the sending terminal to stabilize power fluctuation. The feasibility of the proposed hybrid multi-terminal DC transmission scheme is verified through simulation of the example.In short, whether it is to configure thermal power in sending terminal or to use the hybrid multi-terminal DC transmission mode, certain thermal power plant is needed to stabilize fluctuations in wind power. The scheme proposed in this paper can effectively convey the power of large wind farm, which has a certain reference value for the construction of large scale wind power plant in China.