Research On Voltage Sag Propagation Characteristics Of Power System With Large-scale Wind Farm

With the national energy structure adjustment accelerating the development of the scale of large grid-connected wind farm, large-scale and high degree of concentration grid-connected wind farm has a great impact on power adjustment control, power quality, and grid stability. The research on voltage sag propagation characteristics and evolution mechanism of power system with large-scale and high concentration wind farm is of great significance to reveal the laws that voltage has a great impact on LVRT, power system transient stability and power system relay protection. The detection accuracy of voltage sag duration is of great significance to suppress voltage sag and clear short-circuit fault because it is the premise and guarantee for DVR and other compensation devices working.Firstly, according to voltage sag evaluation index and propagation characteristics, three typical large-scale wind farm models are built in this paper based on the IEEE39bus standard test system. The thesis has studied effects of different short-circuit faults on the voltage sag area and the voltage sag propagation characteristics when wind farm incorporate the grid. The connection of wind power can change the existing network topology, operation mode and the three sequence impedance matrix, and then lead to the change of the voltage sag amplitude of each node. In addition, the system transient stability is simulated and analyzed on wind power, fault location and duration. The rule of the effects on power system transient stability is concluded. A series of improved measures are put forward to solve the above problems, such as choosing dynamic reactive power compensation device, speeding the pitch angle control, improving the protection strategy and increasing the wind power prediction accuracy. This study provides the basis and reference for the realization of large-scale new energy power safety and efficient utilization.Secondly, given that the drawback of the threshold value of duration of voltage sag detection method based on the information-entropy, detection accuracy can not meet the requirement. The starting and ending time of voltage sag are detected by using heuristic Stein unbiased risk soft-threshold in the base of information-entropy theory. Adaptability of the method is analyzed in conditions of different dropping amplitudes, harmonic waves and noise. The simulation results show that the algorithm can improve the adaptability and accuracy of the voltage sag detection.