Wind Fram Equivalent Modeling And Validation Studies

More and more wind farms are incorporated into power system, which causessome impacts to an extent on the voltage stability of area grid where wind farms areconnected. Generally, there are hundreds of wind turbines installed in wind farm, so itis hard to build detailed model. It needs to research equivalent method of wind farmthat is suitable for needs of engineering and that can raise working efficiency withkeeping computational accuracy. The main research contents and conclusions of thispaper are as follows:1. The aerodynamic model, shaft model and collecting-electric systemmathematical model are built based on introducing the mechanism of wind powergeneration. The equivalent circuit and voltage equations of fixed speed wind turbinesand variable speed wind turbines are introduced.2. Some common equivalent methods of wind farm are introduced, such ascapacity-weighted stand-alone equivalent method, improved capacity-weightedstand-alone equivalent method, parameters transform stand-alone equivalent method,variable-scale reduced-order multi-machine equivalent method and multi-machinerepresentation method based on units clustering algorithm. The scopes of applicationof different equivalent methods are stated. The equivalent line loss model is used tomodel collecting-electric lines in wind farms.3. The equivalent models of wind farms including squirrel-cage asynchronousmotor and doubly-fed induction motor are modeled equivalently when the parametersof wind turbines are the same and when they are different, considering effects causedby collecting-electric lines of wind farm on the equivalent models. The static voltagestability margin of different models of wind farms with squirrel-cage motors anddoubly-fed motors is analyzed and the approximation quality of kinds of models tothe actual voltage collapse point is studied by using P-V analytical method. Fromsimulation results, when wind farm consists of wind turbines with the same type, thevariable-scale reduced-order equivalent method is more accurate than stand-aloneequivalent method so it can express the operation states of wind farm better; whenwind farm consists of wind turbines with different types, wind turbines operate indifferent sates at the same condition due to different types so the variable-scalereduced-order multi-machine model is not suitable while the parameters transformstand-alone equivalent model can display operation states of wind farm better. The simulation results also indicate that wind farm composed of squirrel-cage motorsneeds to absorb reactive power from the grid while wind farm with doubly-fed motorsabsorbs little reactive power even zero. So wind farm composed of doubly-fed motorsperformances better voltage stability which is good for voltage stability of area gridand makes power system be able to accept more capacities of wind power.4. The dynamic models of squirrel-cage motors and doubly-fed motors are builtwith capacity-weighted equivalent method and multi-machine representation methodbased on units clustering algorithm. The simulation results show that multi-machinerepresentation method based on units clustering algorithm is more closer to detailedmodel so that it can reflect the actual dynamic performance of wind farm better due tothat motors with approximate dynamic response are divided into the same team indynamic model with multi-machine representation method based on units clusteringalgorithm.5. The equivalent software for wind farm is designed using capacity-weightedstand-alone equivalent method and multi-machine representation method based onunits clustering algorithm with VC++platform. The calculation results are applied tosimulation software and simulation results show that the software has engineeringvalue.