Research On Control Strategy Of Hybrid Energy Storage System Based On Bipolar DC Microgrid

With the widespread application of distributed renewable energy,the network connection forms of microgrids are increasing.At the same time,the power control strategies of energy storage systems in the new network connection situation should be discussed synchronously.This paper mainly studies the power coordination control strategy of hybrid energy storage systems in bipolar DC microgrids in the form of three-bus grid connection.Aiming at the problem of fluctuating power and imbalance in the microgrid system using the three-bus network,a suitable solution is proposed.The main contents are as follows:This paper aims to stabilize the DC microgrid bus voltage and optimize the charging and discharging process of the hybrid energy storage system.The working characteristics of the DC microgrid architecture and related access units are analyzed,and the power distribution strategies of two kinds of DC microgrid hybrid energy storage systems are introduced: low-pass filtering and variable-time-constant low-pass filtering.Aiming at the shortcomings that traditional filtering methods cannot adjust the power allocation in real time based on the remaining capacity and the time constant of the variable coefficient filtering method is difficult to set,this paper proposes a power allocation strategy for hybrid energy storage systems based on supercapacitor voltage.This strategy combines the advantages of a cascaded structure.Through the built-up droop relationship,the lithium battery can be smoothly charged and discharged while maintaining the supercapacitor voltage to work in the optimal working range as much as possible.Based on the analysis of the DC microgrid architecture,the architecture of a bipolar DC microgrid with mixed energy storage is mainly analyzed and introduced.The voltage balancer,an important part of the bipolar DC microgrid,is analyzed in detail.In this paper,the principle of Interleaved Parallel Voltage Balancer(IPVB)is mainly introduced,and an indirect phase-to-phase current sharing method suitable for IPVB is proposed for IPVB to achieve stable three-bus voltage.At the same time,based on the analysis of the control strategy of the DC microgrid hybrid energy storage system,a coordinated control strategy suitable for bipolar DC microgrid was further developed.This strategy uses supercapacitor voltage as the control medium to reasonably distribute lithium batteries.Power between the super capacitor and the super capacitor,and at the same time coordinate the working state between the hybrid energy storage system and the voltage balancer,which can not only achieve reasonable power distribution between the lithium battery and the super capacitor,but also allow the power between the double buses to be transferred on demand.A simulation model was built in Matlab/Simulink to verify the research object and the proposed control strategy.It can be seen from the simulation results that the proposed control strategy can guarantee the voltage stability of the three buses,and at the same time optimizes the charge and discharge of the lithium battery-supercapacitor hybrid energy storage system.The correctness and effectiveness of the proposed control strategy have been proven.