| Owing to characteristics of randomicity, intermittence and uncontrollable of windpower, and along with growing capacity of installation, wind power influences more andmore significantly on safe and stable operating of the power grid. Theory and method fordynamic equivalent modeling of large scale wind farms has become an urgent research task.Equivalent result of wind farm relates with the type of wind turbine, strategy of control,wind speed, wind direction, wake effect, etc. A direct-drive wind farm equivalent methodwas studied in this paper. The main contributions of this paper are as follows:(1) Dynamic modeling and characteristic analysis of the direct-drive wind turbine, inwhich, the model of wind speed and wake effect was given, the dynamic models ofdirect-drive wind turbine was proposed and the control strategies of full-scale powerpulse-width modulation converter were studied. The transient characteristics, when windspeed changes and power system faults, were calculated. Simulation results show that: themodel and the control strategies are effective, the active power and reactive power of windturbine were changed and the DC voltage of convertor was few fluctuated with wind speedchanged, the direct-drive wind turbine can provide reactive power support to voltagerecovery, has not influence on short-circuit current of short-circuit node when power gridfaults, and ensures continuous operation of wind turbines and improves security andstability of the electric power system.(2) In order to study modeling approach of direct-drive wind turbine (DDWT) whilewind farm dynamic equivalence, DDWT model order was reduced. Firstly, a13-orderdetailed model of DDWT was established. And then by applying eigenvalue analysismethod, dominant eigenvalues were determined, the state variables associated with thedominant eigenvalues were retained and other state variables were eliminated, the systemstate equation of model was reduced to4-order. Finally, dynamic characteristics of thereduced-order model and the detailed model were compared by using time domainsimulation. The comparison result indicates that the reduced-order model has good consistency to the detailed model.(3) Study on stability equivalence of wind farm and uncertainty flow calculation. WithStudying the equivalence way on the collector system within wind farm, a simple andpracticable equivalence method-equivalent power loss method was proposed, and validityand accuracy of the equivalent power loss method was verified. Due to randomicity andfluctuation of wind speed, the uncertainty power flow quantity calculation method wasestablished, in which the randomness of wind speed, uncertainty of wind power generation,the effect of wake effect were considered. UP user function was achieved by usingdynamic link library on developing platform of power system analysis softwarepackage/user program interface (PSASP/UPI). Thus the randomization power flowcalculation considered the wind turbine was implemented.(4) Dynamic equivalence method of wind farm was studied and transient stability ofpower system with wind farm counted in was analyzed. Mode and coherency equivalentwas applied to acquire equivalent of wind farm. In order to keep mode being constant,reduced-order model was used for direct-drive wind turbine, and grouping rule of windfarm, according to grouping rule of wind turbine operating characteristics being similar,was investigated to ensure coherency of wind turbine. Based on actual operating data ofwind farm, equivalent parameters of wind turbine were identified by applying optimizationalgorithms. Equivalence model and parameter were verified. The transient stabilitycalculation of wind farm was implemented by programming with UPI(User ProgrammingInterface) of PSASP, and the transient stability characteristics of the equivalent wind farmunder wind speed disturbances and system fault were analyzed. Finally, the voltage andfrequency stability of the Dabancheng wind farms integrating to Urumqi grid wasanalyzed.
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