Study On Balancing Control Strategies Of Distributed Energy Storage System In Microgrid

The intermittency of solar and wind power generation output power and randomness of loads power may affect the microgrid voltage,frequency and the reliability of power supply,which is an important technical problem that needs to be settled at present.Because of the characteristics of simple control,small transmission losses,wide geographical distribution and flexibility,the DESS can effectively weaken the negative effect of the intermittency and randomness of the solar and wind power generation,improve the penetration rate of the renewable energy,and can meet the requirements of users in demand side at the same time.Reasonable and effective energy storage control strategy can not only improve the efficiency and stability of the grid operation,and can also improve the efficiency of energy storage system operation and prolong the service life of the energy storage system.Therefore,it has important practical significance for the large-scale utilization of renewable energy to research the DESS operation control strategy.In the microgrid with DESS,the battery characteristics,hardware configuration and the initial operation states of each distributed energy storage unit are different,and their features such as the available capacity,the charging/discharging efficiency and the cost function are also inconsistent in the charging/discharging process,which will reduce the accuracy of power dispatch of the whole DESS,increase system power losses and affect the service life of the DESS.Therefore,around this problem,the control frame structure of the microgid with intermittent DG and DESS is built in this paper based on distributed control method and a control strategy for each unit respectively is proposed.The main research contents of this paper are shown as follows:(1)This paper firstly makes an introduction about the role of the energy storage devices in microgrid,analyzes the advantages and disadvantages of two kinds of access to the MG of the energy storage devices,and takes distributed access mode as the breakthrough point of this paper.Based on the battery energy storage,this paper establishes the corresponding equivalent circuit model,analyzes and designs charging/discharging control strategy of bi-directional DC/DC converter of the battery energy storage system.Meanwhile,the system control frame structure of the microgid based on DBESU is built and the system control strategy based on the distributed control method and hierarchical control method is proposed.(2)As the traditional droop control strategy doesn't take measures in active power balancing problem based on the SOC of each energy storage,therefore,in this paper a strategy to improve the accuracy of power dispatch and prolong the life span of the DESS is proposed,in which SOC and charging/discharging efficiency of multiple parallel DBESU are considered.In this method,which adopts the distributed control strategy,the SOC and charging/discharging efficiency of each DBESU are employed in the controller to adjust its output power in real-time,thus realizing the equal power dispatch and implementing SOC and efficiency error balancing of parallel DBESU.At the same time,a balancing factor is projected to optimize the SOC balancing control effect and achieve better performance,which adopts two-step optimizing way based on the SOC of each DBESU.Finally,a Matlab/Simulink model is built to test the balancing effect of the proposed control strategy.(3)To make the microgrid operate in an economic way,reduce the system power losses and avoid the behavior of over-charging and over-discharging of the DBESU in taming the power fluctuations by the DG,minimizing power losses and optimal power scheduling,in this paper a control strategy is proposed,in which the SOC and equal incremental cost criterion of multiple parallel DBESU are considered.Based on the equal incremental cost criterion,the objective function of system power losses is transformed and solved.And in this method,which only needs the local information,the SOC and incremental cost of each DBESU are employed in the controller to adjust its output power in real-time,thus realizing dynamic balance between supply and demand,and eliminating SOC error of parallel DBESU.Meanwhile,an automatic power limitation supervisor based on SOC to avoid the charging/discharging power too high and SOC out of the scope is proposed,which can caused the over-charging and over-discharging of the DBESU.Finally,a Matlab/Simulink model is built to test the effectiveness and balancing effects of the proposed control strategy.