Research On Coordination Control Strategy Of Hybrid Energy Storage System To Suppress The Wind Farm Power Fluctuations

The use of new and renewable energy has become the effective way to solve theenergy crisis and global warming, as a new type of friendly renewable energy windpower has been widely used. But wind power is affected by weather and environmentseriously, has the characteristics of intermittency, randomness and uncertainty，thischaracteristics are reflected in the power fluctuation. With the expansion of windpower application’s scale, the challenge for power grid security is becoming biggerand bigger. It will impacts power quality, seriously will threaten stability andsecurity of the entire power network. How to suppress the power fluctuation of windfarm is the most important thing for electric power department. According tochargeable and dischargeable characteristics of storage equipment, we allocate acertain capacity of energy storage equipment at the wind farm and make full use ofthe power-type energy storage equipment and energy-type energy storage equipment’sadvantages to smooth the wind power fluctuations after analyzing the historical dataof power sufficiently. The method above is one of the effective ways to reduce theimpact to the grid caused by active power fluctuations of wind power.Firstly, this paper uses the Fourier transform to analyze the frequency spectrumcharacteristics of wind power, and then proposes a new kind of real-time discretewavelet transform frequency division method to allocate the fluctuation powerbetween the hybrid energy storage system. With the typical historical power data ofthe wind farm as the research object, we use power-type energy storage device tosuppress short-term wind power fluctuations, energy-type energy storage device tosmooth longer-term power fluctuations based on the distribution principle of windpower fluctuations frequency’ value, implement a real-time analysis of wind powerand allocation of energy storage power. Then take the power values and the servicetime into account，through analysis of the statistics, we get a reasonable capacity andpower configuration scheme.Secondly, this paper builds a reasonable evaluation index of energy storagesystem. Based on this, puts forward a coordination control method of hybrid energystorage system using two levels’ fuzzy control method to suppress the wind powerfluctuations which has the function of SOC adjustment and smooth output effectimprovement. It can realize a real-time adjustment of the energy storage devices’ charging and discharging power., prevent the charged state out of limit, and increasereliability of energy storage system, it also can decrease the single fuzzy control’sinfluence to smooth effect. The simulation results show that the control strategyadopted by this paper can inhibition fluctuations of wind power effectively, it alsoverify that the two levels’ fuzzy control method has a great advantage compared withsignal level control method.Finally，the paper has a detailed discussion on the bidirectional DC/DC andDC/AC inverter’s control method and establishes their mathematical models. Thenbuild a simulation model including hybrid energy storage system to test the rationalityand effectiveness of the system’s structure and it’s control method. At last connectwind generator to the model, a wind-energy storage system is composed to applysimulation and test based on the method of wind fluctuation power’s allocation andhybrid energy storage system’s coordination control using wavelet transform and twolevels’ fuzzy control theory, at last it achieves a good result.