Research On Grid-Connected Voltage Stability Of Doubly-Fed Wind Power Generation

With the continuous advancement and development of China's economy and society,the consumption of traditional fossil energy is becoming more and more serious,the reserves are decreasing,and the pollution caused by the environment is also getting worse.As a clean new energy source,wind energy has a very rich reserves on the earth and no pollution to the environment.So it is very important to develop wind energy.In recent years,with the strong support and call of the state,China's wind power industry has developed rapidly,the installed capacity of wind turbines has been increasing,and the grid-connected capacity of wind power has been expanding.Wind power has become an indispensable part of China's power source.However,most of China's wind resources exist at the end of the network,which is in the weak link of the power grid.Wind power generation has volatility and randomness.So wind power grid connection brings a heavy burden to the safe and stable operation of the power grid.Therefore,it is particularly important to study the voltage stability of wind power grid-connected systems.This paper introduces the main problems and research status of wind power grid connection at home and abroad,expounds the structure and working principle of different types of wind turbines,and establishes the mathematical model of variable speed constant frequency doubly-fed wind turbines.The characteristics and methods of grid-connected operation of doubly-fed wind farms are studied.According to the power and voltage characteristics of the wind farm,the active output and reactive power of the wind farm are analyzed,and the effects of active output and reactive power on the wind farm voltage are studied.The grid-connected characteristics of the doubly-fed wind power generation system are studied in detail,and the grid-connected transient voltage stability of the doubly-fed wind turbine is analyzed.The simulation model of DFIG grid-connected system is established in MATLAB/simulink simulation software to analyze the impact of DFIG grid-connected on the stable operation of system voltage.The voltage stability of the grid-connected point of the doubly-fed wind turbines under different wind speed fluctuations and short-circuit faults in the system is studied.The simulation results show that the voltage at the grid point will fluctuate when the wind speed exceeds the rated wind speed.In the event of a short-circuit fault in the system,the grid-connected point voltage and the fan outlet voltage will change drastically.The reactive power regulation capability of the wind farm itself is far from satisfying the voltage stability of the system and the wind farm.It must rely on reliable reactive power compensation measures to improve the stability of the wind power grid-connected system.By comparing and analyzing the compensation performance of different reactive power compensation devices,it is concluded that the static synchronous compensator has the advantages of small size,fast response speed,stable reactive output,low harmonic content and large operating range.In this case,the dynamic reactive power compensation of the system is quickly realized.The installation position of the reactive power compensation device and the calculation of the reactive power compensation capacity of the system by STATCOM are studied.The reactive power compensation optimization analysis is carried out in the 9MW dual-fed wind farm grid-connected system.The simulation results verify that the 3Mvar reactive power compensation device is installed at the wind power grid connection point to ensure that the power grid can operate safely and stably under the wind speed fluctuation and the system short circuit fault,and at the same time,the capacity of the reactive power compensation device will not be too large.The problem of excessive cost is to improve the economics of wind power grid-connected operation.