Research On Control Strategy Of VSC-HVDC Transmission System With Wind Power

With more attention paid to the issues such as energy security,ecological environment and climate change,it has become the general consensus and concerted action of the international community to promote energy transformation and deal with global warming to accelerate the development of renewable energy such as wind power.But because of the characteristics of renewable resources such as wind power fluctuation,randomness and regional development imbalance,consumptive problem has become increasingly serious.VSC-HVDC based on voltage source converter and full control device with the advantages of flexible power control,good power quality,and no commutation failure has become the most effective way for wind power,especially for offshore wind power grid.Not only that,the VSC-HVDC technology plays an irreplaceable advantage in weak grid power supply,expansion of urban power grid and the power market.VSC-HVDC has become an important link in the construction of smart grid in China.In this master thesis,it mainly aims at the study of VSC-HVDC control strategy.Firstly,the operating principle of VSC-HVDC transmission system is analyzed.At the same time,the double loop control strategy of the voltage outer loop and current inner loop is introduced,it have the characteristics of fast current response and the decoupling control of active power and reactive power.And then the control principle and characteristics of the master slave control,voltage margin control and DC voltage droop control of the VSC-HVDC transmission system are described in detail.On the basis of the mentioned above,a comprehensive coordinated control strategy of hierarchical control mode of the three coordinate converter is put forward,this strategy can adapt a wide range of unbalanced power to avoid the overload phenomenon of converters.After that,the control strategy of wind power integration is studied.The DC voltage droop control method suitable for power flow frequent fluctuation is adopted at received end converter and this can achieve continuous power control,but the DC voltage will produce a significant deviation.In order to improve this problem,an improved DC voltage droop control strategy which can realize no-deviation regulation DC voltage is presented.A compensation term is superimposed on the DC voltage reference value to offset DC voltage deviation caused by the variation of the power.Finally,a multi-terminal simulation model is built under the environment of Matlab/Simulink to verify the effectiveness of the proposed control strategies respectively.