Analysis On Impact Of Dynamic Reactive Power Control On Voltage Stability In Wind Farms Integration Area

As the distribution feature of China's wind energy resources,wind farms are generally located in the end of the grid, which leads to small short circuit capacity at the access point. So local disturbances could seriously affect the voltage stability of wind farms integration area. Therefore, it's necessary to analyze the voltage stability in wind farms integration area, which can be the basis of optimizing voltage operation level. But the analysis presently often ignores the impact of dynamic reactive power compensation device control. As a result, this paper analyze the Impact of dynamic reactive power control strategy on voltage stability in wind farms integration area, which is from the view of reactive control strategy and based on typical model of wind farms integration area.This paper looks back actual active of reactive power sources in wind farms during the “5.14” high-voltage cascading trip-off accident of Zhangbei. So reactive power-voltage sensitivity is derived based on sensitivity method when DFIG and SVG adopt constant reactive power control mode,then its internal factors are analyzed in detail. According to the derivation,this paper concludes that constant reactive power of DFIG and SVG control mode in wind farms can also lead to increase in reactive power-voltage sensitivity,and the growth rate depends on three factors,which are wind farms initial inductive reactive power, capacitive reactive power and equivalent impedance. In the case of wind farms in different control mode and initial state, a simulation is carried out in PSS/E combined with a simple system and 5.14 accident. The results verify the consistency of the conclusion.Presently, abnormal oscillation occurred in Xinjiang Hami wind power integration area, under the condition that the wind farms sending line had not installed series compensated devices. According to this problem, this paper establishes linear model and PSS/E simulation model of equivalent system based on reactive power and voltage control situation in typical large scale wind power integration area. With the respect that wind farms dynamic reactive power compensation device regulator of different control mode has different influence in the voltage stability in wind power integration area, it adopts eigenvalues modal analysis method to analyze mechanism of abnormal voltage oscillation. The simulation results show that there is a strong interaction between thedynamic reactive power compensation device if they adopt constant system side voltage control; and when the system becomes weaker, or the number of wind farms under this control mode increases, or electrical distance between voltage control point and PCC bus becomes larger, the system small signal stability will get worse and oscillation frequency will increase. In addition, the study also finds that when dynamic reactive power compensation devices adopt constant reactive power control mode, the interaction becomes weaker between them and system small signal stability is better.Considering the analysis above, this paper designs AVC system of wind farm based on the Python language. It can achieve constant reactive power / constant voltage mode conversion of dynamic reactive power compensation device after the system is disturbed in the steady state. Through simulation testing on PSS / E platform, the results show that the design of AVC system in the steady state can achieve coordinated control of reactive power source, quick voltage adjustment, and to inhibit secondary synchronous oscillation phenomenon; when the system is disturbed by the capacitance, it can switch control mode, preventing PCC bus overvoltage.