Research On Wind Farm PCC Voltage Stability And Coordination Control Strategy

As a new form of wind energy utilization, wind connected-grid technology has a rapid development in recent years. For local power grid comprising wind farm integration, the PCC voltage of wind farm is more susceptible to fluctuate within the network load or wind power fluctuation caused by the blowing wind speed, leading to grid voltage instability under the increasing wind power grid capacity. In order to solve the drawbacks effectively, people often configure reactive compensation devices in the system, the devices can not only improve the quality of the grid voltage, but also inhibit voltage drop in case of failure. However, due to the common-used reactive power compensation device has some shortcomings, such as the dynamic response time is relatively slow, control strategy is imperfect, leading to the device is difficult to achieve the basic requirements of PCC voltage stability.Firstly, this paper analyzes the characteristics of voltage and reactive power about double-fed wind turbines and squirrel cage wind turbines, and then by dynamic equivalence method, establish the mathematical model for the wind farm connected to grid and analyze the PCC voltage and reactive power characteristics based on this model. Based on bifurcation theory, impedance mode index, the ratio of mixing capacity, analyze wind farm voltage dynamic characteristics.Secondly, through the comparison analysis of comprehensive performance under wind farm reactive power compensation devices SVC and SVG, a combined reactive power compensation system is proposed by the SVC+SVG parallel connection, make a slope adjustment control strategy of the combined reactive power compensation system, analyze the PCC voltage and reactive power compensation effect under load variations and short-circuit faults and wind disturbance. The results show that compared to SVC or SVG functions alone, the combined reactive power compensation system has advantages of fast response, good compensation effect, it can provide reactive support for the system quickly, and the amount of reactive power compensation is just right, recover the PCC rated voltage fast and maintain a stable tendency.Finally, making a wind farm PCC voltage layered coordinated control strategy, aiming at a real wind farm connected power grid, and under load and wind fluctuation, make PCC voltage and active power grid loss as the control target, compare and analyze the simulations under the layered control strategy and without optimal control. The results show that the layered coordinated control strategy can be more efficient to smooth and stable the PCC voltage, and reduce the active power grid loss greatly.