Research On Hybrid Energy Storage System Applied In Smoothing Fluctuant Power Of Wind Farm

The new and renewable energy is widely used in the world,especially the friendly wind power.However,because of the adverse influences of natural wind driven and environmental factors,the output power of wind turbine has the characteristics of intermittency,randomness and uncertainty.In short,the wind power is full of random fluctuation.The terrible fluctuation not only has negative effects on power quality,but also strikes the power system strongly.Furthermore,it will threaten the stability and security of the entire grid seriously.Therefore,how to smooth the wind power effectively and make it stable and controllable has become a critical question,which has an influence on the grid-connected operation of wind farm.This article has research on hybrid energy storage system applied in smoothing fluctuant power of wind farm.Firstly,based on analysis of fluctuant characteristics of wind power,allocation schemes of energy storage system are given.Aiming at the requirement for energy storage system during smoothing control,battery-supercapacitor hybrid energy storage system is chosen.Secondly,according to the principle of smoothing control,the article proposes a double-layer control model for the hybrid energy storage system.The first layer is system control layer,wthich is used to get the target of smoothing control.Based on wavelet packet theory,the smoothing stragety is utilized to acquire grid-connected target power of wind farm and reference output power of hybrid energy storage system.Due to the stragety of power allocation,a reasonable distribution of energy storage power between battery and super capacitor comes true.Then,on the second equipment control layer,the article pays attention to how to control the energy storage system.On the basis of structure and operation principle of bi-direction AC/DC and DC/DC converter,their mathematical model are derivated,and their control strategy are designed.Finally,a model of hybrid energy storage system is established in PSCAD/EMTDC.The process of smoothing fluctuant wind farm power is simulated.The results show that,the battery-supercapacitor hybrid energy storage system is able to restrain the fluctuation of wind power,which demonstrates the reasonability and availability of stragety in this article.And the hybrid energy storage system is superior to a single type energy storage system on smoothing performance.In combination with the double-layer control model,the hybrid energy storage system can smooth fluctuant power preferably,and both battery and super capacitor get reasonable distribution of energy storage power.In the condition of fault,the hybrid energy storage system can also provide a certain amount of reactive power support.All these results verify the correctness and validity of the strategy of restraining power and controling method of hybrid energy storage system in this article.