Study On The Coordination Control Strategy Of Voltage And Reactive Power For Large Scale Wind Farm

Since2011, cascading trip-off of wind turbine generator has occurred frequentlyin China. During the accident, a large number of wind turbines trip off. The powersystem losses a lot of active power. The power system frequency is lower. These harmthe security and stability of power system and the power quality seriously. Byanalyzing the process of cascading trip-off of wind turbines, we find that not all ofwind turbines trip off in the cascading trip-off accident and whether the wind turbinestrip off is related to the wind turbines voltage. For this, a voltage and reactive powercontrol strategy which considers the wind turbines difference is proposed to preventand suppress the cascading trip-off of wind turbine generator.In this paper, the doubly-fed wind turbine is studied. Firstly the mathematicalmodel of double-fed wind turbine is established. Based on this, the reactive powercapability of DFIG is analyzed. The Gamesa G58-850kW double-fed wind turbine isanalyzed under different wind speed.The structure of wind farm collector system is discussed in this paper. Thecollector system voltage Characteristics and the effect that the wind power fluctuationhas on the wind turbines voltage are analyzed. By analyzing the spatial and temporaldistribution characteristic of the collector system voltage in a49.3MW wind farm ofJilin, we find the wind power fluctuation has fluctuation effect on the wind turbinesvoltage and there is great difference between different wind turbines voltage. Whenthe grid voltage disturb, the wind turbines may trip-off.By utilize the collector system topology characteristics, a voltage and reactivepower control strategy which is based on the network analysis is proposed in thepaper. The control strategy improves the dynamic reactive power reserves capacity bycontrolling the reactive power between wind turbines and compensation device. Andit reduces the difference of wind turbines voltage and improves the wind turbines voltage level by controlling the reactive power between wind turbines. In the processthe reactive power output of wind turbines is obtained by non-iterative calculationmethod which is based on the collector system topology characteristics. The methodhas advantages of simple and less time consuming.