Research On Wind Farm Reactive Power Control Strategy With Involvement Of DFIG

Global climate change and energy supply security, are two major challenges whichthe world are facing nowadays. It is the important way to develop renewable energyvigorously for the challenges. Wind power is the main renewable energy that can be inlarge-scale commercial application, and Chinese installed capacity and equipmentmanufacturing scale of wind power ranks highest on the world, but on wind powertechnological level, whether the manufacturing of wind power equipment and theoperation of wind farm access system, there is still a significant gap between our countryand the world advanced level. Chinese wind power industry has always been greatlytroubled by “offline” and "abandoning wind power" and other problems, as the scale ofwind farm continues to expand, the randomness, indirectness and uncontrollability ofwind power also bring more problems, such as voltage fluctuation, reactive powerdissonance, harmonic content high, etc. Large-scale wind farms grid results in voltageinstability of power grid, among which voltage fluctuation problem in “grid-connectingpoint” is remarkable especially. This issue will influence not only the grid power quality,may even the security and stable operation of the grid connected system.Doubly-fed wind power induction generator (DFIG) is a kind of wind powergenerator run at variable speed and output constant frequency, whose huge advantage isthat it can realize decoupling control of active and reactive power, moreover get certainreactive power generating capacity.This paper tries to utilize the agile reactive power generating capacity of doubly-fedwind power generator on stabilizing voltage fluctuations in wind farms grid-connectingpoint.The control strategy will real-time calculate each doubly-fed turbines reactivegenerating potential, then reasonable call part of doubly-fed generator for the sending orabsorption of the reactive power, and take part in voltage control of grid-connectingpoint.The above-mentioned strategy is proposed correspondingly for the wind turbinegenerator volatility at non-fault state, yet in fault state, doubly-fed generator will providethe Crowbar to limit rotor current in the rotor side, in order to run through the faults.While the exit time of Crowbar also influences voltage recovery during the faultrecovery.This article, using EMTDC/PSCAD on multi-scene simulation analysis of wind farms consists of doubly-fed type wind power generators which take active Crowbar,researches in reactive power characteristics when the wind generator exit Crowbar atdifferent time before or after fault clearing, moreover analyses the influence on thevoltage recovery process of the grid-connecting points. Through the simulation analysis,it proves that the reactive power performs better when exiting from the Crowbar beforethe fault clearing.