Research On Energy Management Control Of Battery Energy Storage System Based On Modular Multilevel Converter

In recent years,as the state has increased its support for the new energy industry,in order to achieve the goal of "carbon neutrality",large-scale grid-connected applications of renewable energy have gradually become a trend.In order to reduce the impact of the instability and intermittentness of renewable energy on the grid,renewable energy systems supporting battery energy storage have been widely used in engineering.Modular Multilevel Converter(MMC)with AC and DC transmission characteristics is applied to the distributed configuration of energy storage battery due to its modularity and easy expansion,and has been extensively studied.But at present,the energy management research of modular multi-level battery energy storage system is not enough,and further research is needed on the system energy management strategy and the power transmission control of each battery energy storage side.Therefore,this article is based on a modular multi-level battery energy storage system to study its energy management control.This article first analyzes the working principle,mathematical model and capacitor voltage of the modular multi-level battery energy storage system(MMC-BESS).The three-port energy transmission formula is deduced.Under the condition of maintaining energy conservation,the three-port energy transmission mode is listed,and the battery charging and discharging control method is further analyzed.By comparing multiple modulation strategies,the carrier phase shift modulation strategy is selected.Secondly,given that the State of Charge(SOC)of the battery in the energy storage system is a key factor in the energy transfer of the energy storage battery,this paper analyzes the battery characteristics and extracts the second-order battery through experiments and data processing.Based on the basic parameters of the equivalent circuit model,an estimation method of SOC is proposed.Then,based on the analysis of the control objectives of the energy storage system,a cooperative control scheme of energy storage SOC is designed,which is composed of energy layer,MMC layer and energy storage battery layer.Among them,the energy layer mainly completes the issuance of the entire system energy scheduling instructions,and combines the energy storage SOC to determine the energy conservation conditions,and adopts the method of eliminating non-critical loads to maintain the energy conservation of the entire system.The MMC layer realizes AC-side power decoupling control.The capacitor voltage balance control solves the problem of capacitor voltage imbalance affected by SOC cooperative control.At the same time,based on this balance control scheme,the sub-module unbalanced power tolerance is analyzed;the energy storage battery layer is based on The SOC discretization feature completes the distribution of active power to each battery pack,and improves the traditional power distribution method.At the same time,in order to ensure the SOC coordinated control rate,constraint conditions are added and the time constraint relationship of SOC coordinated control is established.Finally,this article uses MATLAB simulation software to verify the proposed MMC-BESS control strategy.At the same time an MMC battery energy storage system was built using RTDS hardware-in-the-loop and experimental tests were carried out.The results of simulation and experiment show the feasibility of the control strategy in this paper.