Research On Reactive Power Characteristic Of Wind Farm And Coordination Control Of Dynamic Reactive Power Compensation Device

The integration of wind farms has lots of influences on the voltage stability of thetraditional power grid due to the intermittence and fluctuation of wind power. So far, oneof the main measures to improve the stability of the grid containing wind farms is usingthe reactive power compensation device. With the increase of the compensation device,the grid dynamic reactive power compensation needs can’t be achieved by the existingdispersed independent control strategy. Therefore, it’s very necessary to propose a newcoordination control strategy of the dynamic reactive power compensation for the gridcontaining wind farms.First, the voltage characteristics and reactive power properties of the double-fedwind generator unit, the direct drive wind generator unit and the squirrel cage windgenerator unit are analyzed, the mathematical models of one wind farm and wind farmsare deduced using the dynamic equivalence method of the wind farm, on theses bases, thevoltage characteristics and reactive properties of the wind farms are obtained.Second, the mathematical model of the system augmented state space taking thereactive characteristic equations of wind farms into account is established, the weaknodes of the system are determined by the Jacobian sensitivity matrix. The target functionis gained by the weigh of the voltage fluctuation LQ index and the voltage securitymargin L index of the weak nodes, thus the optimal coordinated control strategy of thereactive power compensation devices is achieved.Finally, the simulation model of a certain regional grid in the northeast China isestablished in the PSCAD platform. The proposed control strategy is used to achieve thedynamic regulation of the reactive power output of the reactive power compensationdevices at the merging point of the wind farms and the thermal power generating unitnearby under different conditions containing the sudden increases and dips of wind speedas well as the switching of the compensation devices. The results show that the problemsof insufficient reactive power compensation and low voltage are avoided during the load peak period, in the similar way, the problems of excess reactive power compensation andhigh voltage are avoided during the load valley period. The proposed strategy is able toreduce the influences of wind power fluctuation on the weak nodes to improve thesecurity margin of the grid.