Research On Low Voltage Ride Through Technology For Wind Power And Photovoltaic Power Generation System Based On STATCOM

Due to the problems of environmental pollution and resource shortage caused by the use of primary energy power generation,as well as the characteristics of the wind and solar energy,which have a large total amount,are easy to access and non-polluting,the world’s power generation methods shift from traditional energy generation to new energy generation such as wind and solar energy.As the installed capacity of wind power and the scale of PV industry gradually increases,the connection between wind farms and PV stations and power grids is getting closer and closer.The drop in grid voltage will affect the stable operation of wind power and photovoltaic power generation,and may even lead to off-grid wind power and photovoltaic power generation power systems,causing grid fluctuations again.The stable operation of the power grid has put forward higher requirements for the grid connection of wind power and photovoltaic power generation.Among them,one of the basic requirements is that the wind power and photovoltaic power systems have certain Low Voltage Ride Through(LVRT)capability.The current research around LVRT capability only takes wind power or photovoltaic power generation system as the research object,this paper focuses on the system that connects to wind power and photovoltaic power generation at the same time in the following three areas:(1)Based on the mathematical model and the grid-connected control strategy of wind power system with Doubly Fed Induction Generator(DFIG)and photovoltaic power system,an IEEE 3-machine 9-node Simulink simulation model of 220 kV with wind power system and photovoltaic power system is built.The characteristics of the grid-connected wind power generation system and photovoltaic power generation system during the grid voltage drop are analyzed from the perspective of electromagnetic balance and power balance.The rationality of the theoretical analysis is verified by simulation.(2)Comparison and analysis of Static Synchronous Compensator(STATCOM)and Static Var Compensator(SVC)illustrate the superiority of selecting STATCOM.Based on the voltage type STATCOM,the mathematical model and working principle were analyzed.An improved i_d-i_q detection method is used for the reactive current in the mathematical model to compensate for the error in the traditional detection method i_d-i_q for unbalance faults.The coupling relationship between active and reactive currents in the mathematical model is decoupled by Proportional Integral Control(PI)strategy and Linear Active Disturbance Rejection Control(LADRC)strategy,respectively to improve the LVRT capability under different strategies.(3)The STATCOM is connected to the grid connection point of wind power system and PV power system with 3 machines and 9 nodes.The case that the voltage of wind power and PV grid connection point drops to 0.8 p.u.and 0.2 p.u.is simulated by short circuit fault.The changes of voltage at the connection point and STATCOM output power under PI strategy and LADRC strategy are observed.An IEEE14-node Simulink simulation model of 10kV including wind power system,PV power system,and STATCOM is built,and the voltage drop magnitude of 14 nodes before STATCOM compensation is first derived with a three-phase short-circuit fault,and then reactive power compensation is applied to the system.The comparative relationship between the voltage magnitude of 14 nodes under PI strategy and LADRC strategy is observed.It is finally concluded that STATCOM can release reactive power to the grid when the grid voltage dips,increase the grid-connected voltage of wind power and PV power systems,maintain wind and PV systems above 0.2 p.u.for 0.625s of grid voltage dips to avoid off-grid wind turbines and PV systems,and thus achieve low-voltage ride-through of wind power and PV power systems,and the LADRC strategy has a faster response and better compensation effect.