Research On Low Volatge Ride-through Of Wind Turbines With Doubly-fed Induction Generator

With the advancement of science and technology and the continuous development of the economy,China is vigorously developing new energy sources to reduce the consumption of existing energy.In the new energy,wind power generation has the advantages of saving energy,clean and environmental protection,and huge development potential.It has developed rapidly at home and abroad and has become a hot spot for researchers in various countries.The advancement of wind power technology has made wind power account for a growing proportion of power supply,and the failure rate of wind power has also received the attention of researchers.China’s wind farms are located in relatively remote places,so wind farms are connected to the grid away from the load center.The transmission system in this case is weak and unstable.It has a great impact on the stability of the fan.When the grid voltage fluctuates,whether the unit continues to be connected to the grid has a significant impact on the stability of the power system.When the power grid fails,it causes a voltage drop,which may cause large-scale off-grid of the unit,causing another impact on the power grid and even causing the system to collapse.Therefore,improving the low-voltage ride-through capability of the unit is very important for the safe operation of the power system.In this paper,the double-fed wind turbine,which is a large part of wind power generation,is taken as the research object,and the low-voltage ride-through capability of the wind turbine is analyzed.Firstly,the operation principle and internal power relationship of the doubly-fed electric machine are introduced in detail.The coordinate transformation is carried out according to the characteristics of the doubly-fed machine.The mathematical model of the doubly-fed machine is constructed based on the suitable synchronous coordinate system.The stator flux vector control is introduced.The method decouples rotor side voltage,active power and reactive power.Secondly,the variation of the doubly-fed motor in the case of grid voltage drop is studied.The space vector method is introduced to help analyze its characteristics and the related electromagnetic relationship is obtained.Then,the causes of the overvoltage and overcurrent generated by the doubly-fed motor during the drop and the change of the DC bus are analyzed,which provides a theoretical method to find the ability to improve the low-voltage ride-through capability of the doubly-fed machine.In the case of considering stator excitation,the selection of a suitable mathematical model requires accurate reflection of changes in the doubly-fed machine.The control strategy combining software and hardware is adopted,and a protection circuit is added on the DC bus side on the hardware,and the method of controlling the orientation vector of the stator flux linkage through software.The proposed control strategy is verified by Matlab/Simulink simulation software.Experiments show that the proposed control strategy is more effective than the traditional control strategy.In the case of considering stator excitation,the selection of a suitable mathematical model requires accurate reflection of changes in the doubly-fed machine.A combination of hardware and software is used to add a protection circuit on the DC bus side of the hardware,and the software uses a stator flux linkage orientation vector control method.The proposed control strategy is verified by Matlab/Simulink simulation software.Experiments show that the proposed control strategy is more effective than the traditional control strategy.