| The shortage of energy and the deterioration of the environment have prompted people to look for renewable and clean energy.As an important part of renewable and clean energy,photovoltaic power generation has alleviated the problems of power consumption in remote mountainous areas and the high cost of line construction.However,photovoltaic power generation has intermittent characteristics Will affect the stable operation of distributed photovoltaic microgrid.In order to solve the problems caused by the continuous increase of distributed photovoltaic installed capacity in the microgrid,it has become an effective method to solve the power fluctuation of distributed photovoltaic microgrid by configuring the distributed hybrid energy storage system to smooth the difference between the photovoltaic output and the load demand.In this thesis,based on the analysis of microgrid structure,photovoltaic output characteristics,lithium ion battery and supercapacitor output characteristics,a layered control strategy for distributed hybrid energy storage system is proposed,and the effectiveness of the strategy is verified by simulation and experiment.The main work of this article is as follows:(1)This thesis firstly analyzes the structure of distributed photovoltaic microgrid;secondly,it analyzes the working principle of photovoltaic power generation system,lithium ion battery and super capacitor contained in distributed photovoltaic microgrid,and builds photovoltaic power generation model and lithium ion The second-order RC split battery model of the battery and the Thevenin equivalent circuit model of the supercapacitor;finally,the validity of the model built is verified by simulation,which lays the foundation for the simulation analysis of the output characteristics and experimental results of the hybrid energy storage system described later.(2)According to the characteristics of the distributed hybrid energy storage system,the overall architecture of the distributed hybrid energy storage system power allocation strategy is proposed;for the traditional allocation strategy,the difference in available capacity of different hybrid energy storage systems is not considered,resulting in the availability of some hybrid energy storage systems To solve the problem of running out of capacity,a power distribution method based on improved particle swarm optimization algorithm is proposed.This method aims at the largest proportion of the available energy storage capacity in the distributed hybrid energy storage system,considering the two factors of particle swarm algorithm search speed and convergence,and dynamically corrects the weight of the particle swarm algorithm to achieve the difference between the photovoltaic output and the load demand.The distribution of power among different hybrid energy storage systems lays the foundation for solving the power distribution problems of lithium ion batteries and supercapacitors in the hybrid energy storage system later.(3)Analyze the advantages and disadvantages of the four topological structures of lithium ion batteries and super capacitors in the hybrid energy storage system,combine the control characteristics of this paper to determine the structure of the hybrid energy storage system,and then aim at the power distribution of the lithium ion battery and super capacitor in the hybrid energy storage system Problem,based on the traditional first-order low-pass filter algorithm,this paper proposes a first-order low-pass filter algorithm that dynamically adjusts the filter time constant.This method can adjust the filter time constant according to the current energy storage state of the lithium-ion battery,thereby reducing the high adverse effects of high-frequency power components on lithium-ion batteries.Considering the characteristics of high power density and low energy density of supercapacitors,in view of the problem of insufficient remaining available capacity in the operation of supercapacitors,a transfer current is introduced,and a lithium ion battery is proposed to adjust the remaining available energy storage capacity of the supercapacitor by transferring current,and The method of solving the transfer current based on fuzzy control is given,so that the super capacitor always has a certain energy storage capacity during operation,and the continuous working ability of the super capacitor is improved.(4)In order to verify the effectiveness of the method proposed in this paper,simulation and system experiments are carried out in this paper.The results show that the method proposed in this paper can increase the remaining available capacity of each hybrid energy storage system in the distributed hybrid energy storage system;The current SOC of lithium-ion batteries and supercapacitors dynamically adjusts the low-pass filter time constant to reduce the impact of high-frequency fluctuating power on lithium-ion batteries;introducing a transfer current to modify the SOC of the supercapacitors to increase the remaining available capacity of the supercapacitors. |
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