Optimal Configuration Of Hybrid Energy Storage Capacity For Independent DC Microgrid

For remote regions or islands with abundant distributed energy,the introduction of independent DC microgrid with hybrid energy storage system can not only realize local energy consumption,but also solve problems such as system operation fluctuation and source-load power mismatch caused by difficult connection with large power grids.The capacity design of independent DC microgrid has always been the study focus and challenge in the field of microgrid since it would include a number of system indicators when configuring hybrid energy storage capacity.The solution to this issue is crucial to the efficient and dependable functioning of the system as well as the full exploitation of distributed energy.As a result,this study conducts the following research activities based on the present research status on the best allocation of hybrid energy storage capacity in DC microgrid:Analysis is done on power generating characteristics,wind and solar model structure,and DC microgrid models.In a hybrid energy storage system,the performance characteristics of a super-capacitor,a lead-acid battery,and various load types are compared.This research investigates the technique of power distribution to be carried by the super-capacitor in conjunction with the varied properties of the super-capacitor and lead-acid battery.The principle of low-pass filtering,empirical mode decomposition(EMD)and variational mode decomposition(VMD)and their respective allocation strategies are mainly described.The VMD decomposition method which uses center frequency and Pearson correlation coefficient to determine the layered number K is emphatically studied and put forward.Aiming at the two groups of components obtained by EMD and VMD decomposition,the time-frequency analysis is carried out by short-time Fourier transform(STFT),so as to obtain the basis of component reconstruction,and also reflect the optimization effect of VMD on the mode aliasing and incomplete decomposition.Based on the research of power allocation strategy,the reliable calculation method and evaluation index of hybrid energy storage capacity allocation are proposed.By calculating the change of state of charge(SOC)of the energy storage device at each sampling time,the power shortage and wind and light abandonment rate of the system during the whole sampling cycle were judged,and the life-cycle cost of the energy storage system was calculated.Finally,simulation experiments were conducted based on the one-week measured data of an independent DC microgrid.It is verified that the VMD power allocation strategy and capacity allocation method used in this paper can ensure the reliable power supply during the full sampling period,reduce the energy abandonment rate to 0.59%,and save about 20% of the configuration cost,which reflects the advantages of the strategy in the aspects of power supply reliability,energy consumption level and economy.In order to realize the bidirectional interaction between source and load in microgrid,a load transfer model based on peak cutting and grain filling was established to consider the participation of transferable loads in demand response.The optimization effect of the model was verified by calculating the mean square error of generation output and load power,and the energy storage configuration cost was reduced by about 1/3 compared with the original configuration scheme before and after the response.It is proved that taking demand response into account can further improve the power fluctuation of microgrid system and reduce the investment cost.