Study On Control Strategy Of Voltage And Reactive Power For Large-Scale Wind Farm Cluster

The wind power is obviously random, intermittent and uncontrollable and is easily affected by wind speed. In our country, it is of the characteristics of large scale development, centralized grid connection and long-distance transmission. Many challenges are brought to the stable operation and economic dispatch of power system because of the integration of large scale wind power, in which reactive power and voltage control is one of the major concerns. Based on the analysis of current status of reactive power and voltage control of wind power farm, in this paper, the two stage voltage control strategy of the wind power farm PCC (point of common coupling) and the control strategy of the central point voltage of the wind power farm cluster are studied.In the two stage voltage control strategy of the wind power farm PCC, by coordinating the reactive power output of parallel capacitor group, static reactive power compensator, doubly-fed wind power generator, the PCC voltage can track the reference value. Firstly, according to the wind power prediction information, the power curve can be divided into several segments by using a hierarchical clustering method, and the hierarchical clustering method can ensure that the wind power fluctuation is small in each segment. After determining the number of segments, particle swarm optimization algorithm is used to optimize the number of capacitor groups in each segment. Under the actual wind speed, the capacitor group is pre-switched according to the optimization results, and the reactive power output of DFIG and SVC is coordinated to reduce the impact of wind power fluctuation on PCC voltage. In the reactive power distribution, give priority to the reactive power output of the DFIG. If the reactive power can’t meet the demand of the system, the surplus reactive power demand is assumed by the SVC. Through simulation analysis, it is verified that the reasonable capacitor group switching can effectively improve the voltage level of the PCC, and the coordinated control strategy can meet the demand of system reactive power regulation. At the same time, it can preserve the precious SVC adjustment capacity.In the coordinated control strategy of central point voltage of the wind power farm cluster, by regulating the reactive power outputs of wind power farm sub-station and collection sub-station, the central point voltage can track the reference value. When the central point voltage is beyond the limit of operation, according to the reactive power and voltage sensitivity of collection sub-station, it is necessary to determine the reactive power regulation of the collection sub-station. If the voltage is still beyond the limit, regulates the wind power farm sub-station reactive power outputs according to the sensitivity until the central point voltage is in the normal operating range. Using an actual wind power farm cluster topology, it is verified that the sensitivity method can effectively control the voltage of the central point in the specified operating range.