Study On The Stability Of Grid-connected Voltage In Hybrid Wind Farms

As Chinese economic strength gradually increases,the consumption of non-renewable energy continues to increase,the remaining reserves of fossil fuels continue to decrease,and the pollution of the natural environment is becoming more serious.The cleanliness of wind energy,large reserves,and no pollution to the environment make large-scale development and utilization of wind energy an irreversible trend in China;Chinese energy structure has also been adjusted accordingly,as an inexhaustible new energy source,wind energy has attracted widespread attention.Research on various wind power generation technologies has gradually become the main research topic.Predictably,the hybrid wind farm composed of different wind turbines will gradually become the main direction of wind farm construction in the future due to the different advantages highlighted by the different operating characteristics.In this thesis,based on a hybrid wind farm consisting of a doubly-fed induction wind turbine and a permanent magnet synchronous wind turbine,based on the analysis of the transient stability of the hybrid wind farm when a three-phase ground fault occurs in the power grid,the control strategy to optimize the transient stability of the power grid.Firstly,the mathematical model and control model of doubly-fed induction wind power system and permanent magnet direct-drive wind power system are established.The concentrated equivalent of a hybrid wind farm consisting of doubly-fed induction wind farm and permanent magnet direct-drive wind farm,The model analyzes the operating characteristics of the hybrid wind farm,verifies the correctness of the equivalent model of the hybrid wind farm,and verifies the decoupling control ability of the converter to active and reactive power.The power and voltage characteristics of wind farm are analyzed and summar ized.The operating characteristics and reactive power output capabilities of hybrid wind farms based on doubly-fed induction wind farm and permanent magnet direct-drive farm when three-phase ground faults occur are analyzed and summarized.The controllable operating ranges of doubly-fed induction wind farms and permanent magnet direct-drive wind farms that meet the minimum requirements of reactive current for low-voltage crossing of wind farms are obtained,their respective optimized control strategies and current distribution methods are proposed,and their effectiveness is verified.Finally,considering the operating characteristics of the two most promising types of wind turbines and the widely distributed characteristics of the currently constructed wind farms,an optimized control strategy for hybrid wind farms when a three-phase ground fault occurs in the power grid is proposed,and The effectiveness was verified through simulation.Finally,it shows that the proposed control strategy can significantly improve the transient voltage and fault ride-through capability of the grid-connected hybrid wind farm,and has practical significance for improving the grid-connected stability of the hybrid wind farm.The research work in this thesis provides a theoretical basis for improving the transient voltage stability and fault ride-through capability of hybrid wind farms by utilizing the reactive power of the wind farm itself,and laying a theoretical foundation for the sustainable development of wind power.