Research On Wind Farm Power Fluctuation Smoothing Strategy With Hybrid Energy Storage System

With the global consensus on the utilization of clean renewable energy,wind power installed capacity has grown rapidly.However,the wind power output has strong randomness.If being directly connected to the grid,it will adversely have negative impacts on the safe and stable operation of the power system,and may even result in the grid collapse problem.The installation of the hybrid energy storage system with certain capacity in the wind farm with frequent fluctuations is an effective means to solve the above problems,which helps to improve the safety of the wind power generation under grid-connected mode.In this paper,the wind power fluctuation smoothing strategy with hybrid energy storage system is studied.A wavelet packet-fuzzy coordinated control strategy is proposed.This strategy can not only stabilize the wind power fluctuation,but also improve the service life of the battery.The key research contents of this paper are below:Firstly,operating principles of wind power generation system and the working principles of the energy storage components are analyzed in detail.On the basis of comparing the current equivalent model,the battery and super capacitor selected are PNGV,series RC equivalent models respectively.In Matlab,the energy storage component equivalent models are built,the battery equivalent model is PNGV and the supercapacitor equivalent model is RC.The charge and discharge characteristics of the battery and the supercapacitor are studied,which lays the foundation for the formulation of the hybrid energy storage high-frequency component and low-frequency component power allocation strategy.Secondly,based on the typical wind power data of a wind farm,the spectrum analysis is carried out according to the Fourier transform,and the distribution of wind power fluctuation frequency is obtained,the influence mechanism of power fluctuations in different frequency bands on the grid connection of wind power is described,which provide the reference for smoothing high component and low component power fluctuations.Combined with the grid-connected requirements of wind power fluctuation indicators and the cost of supercapacitor and battery capacity allocation,the wavelet packet decomposition of the selected wind farm output power curve is performed in Matlab to obtain the optimal wavelet packet decomposition layer under the actual power demand.According to the wind power characteristics of different frequency bands and the characteristics of different energy storage types under the optimal decomposition layer,the capacity configuration of the battery and supercapacitor of the hybrid energy storage system in the wind farm is determined.Thirdly,combining with the characteristics of energy storage unit and capacity allocation,a hybrid energy storage system based on wavelet packet-fuzzy coordinated control strategy is designed to stabilize wind power fluctuation.Firstly,according to the low-frequency power fluctuation component and the state of charge(SOC).The fuzzy control method is used to obtain sharing coefficient of the low-frequency component of the supercapacitor;Then part of the low-frequency component and the high-frequency component which the supercapacitor bears are overlaid to achieve HESS power optimal allocation;At last,the traditional low-pass filter control strategy,wavelet packet control strategy and wavelet packet-fuzzy coordinated control strategy are analyzed experimentally.The results show that compared with the traditional low-pass control strategy,the wavelet packet control strategy has less grid-connected power curve fluctuation under the requirement of wind power grid-connected fluctuation.Moreover,compared with wavelet packet control strategy,the wavelet packet-fuzzy coordinated control strategy can make full use of the supercapacitor capacity and reduce the number of times of battery charge and discharge.Fourthly,the control structure of the hybrid energy storage system is studied.The main hardware circuit and software control flow chart of the system are designed in detail,and using wind storage experiment platform to verify the practicability of the wavelet packet-fuzzy coordinated control strategy for stabilizing the wind power fluctuations.The experimental results show that compared with the wavelet packet control strategy,the wavelet packet-fuzzy coordinated control strategy can not only effectively smooth the wind power fluctuation,but also reduce the battery charge and discharge times by 26.67%,and the supercapacitor charge and discharge times increase by 29.17%,thus extending the service life of the battery in the hybrid energy storage system.