Reactive Power Compensation Technology Of Grid-Connected Wind Farms And Analysis On The Cascading Trip-off Events

With the increasingly serious problem of energy shortage and environmental pollution,as a renewable clean energy,the development and utilization of wind energy has very important value.The proportion of large-scale wind power generation in Chinese power generation structure is higher and higher.The integration of large-scale wind farm need the reactive power compensation devices to provide reactive power.There is more reactive power when the protection operates,which will make cascading trip-off events happen.Therefore,the research of reactive power compensation technology of wind farm integrated into power grid and cascading trip-off events is very important.In this paper,the basic principle of DFIG variable speed constant frequency operation,equivalent circuit and power transmission relations are studied.The mathematical model of the doubly fed generator under the stationary coordinate system and under the synchronous rotating coordinate system is described.On this basis,the limit of reactive power of stator and grid side converter are researched deeply,which lays a foundation for the research of reactive power compensation for wind farm integrated into power grid.According to the domestic and overseas research on reactive power compensation devices,the basic principle of reactive power compensation devices used in wind farm is introduced.This paper focuses on the research of the basic principle and control strategies of SVG.The decoupling control method of current loop can realize the decoupling control of active power and reactive power of SVG.A simulation model based on this control method is built on the MATLAB/SIMULINK platform.The evolution process of the chain off grid accidents in the wind farm is analyzed.The voltage changes at each bus is derived when short-circuit fault occurs in transmission line.The simulation model of wind farm is built according to the actual topology structure and parameters of a certain wind farm in our country.The effects of SVG on the voltage regulation are verified in the system voltage fluctuation and the transmission line fault.At the same time,the voltage characteristic of each bus is simulated and analyzed when the high voltage transmission lines of wind farm are in fault condition.The simulation results show that: the reactive power compensation devices will produce reactive power to regulate the voltage when the high voltage transmission lines of wind farm are in fault condition.But the reactive power is surplus when the fault is cleared,which will make the over-voltage protection of generators operate.The analysis of this paper has great importance to improve the operation reliability of wind farm.