Research On Balance Control Strategy Of Energy Storage System In DC Microgrid

With the continuous development of the global industry,energy sources such as oil,natural gas,and coal have faced increasingly serious exhaustion problems.The microgrid is integrated with the distributed energy,the energy storage system,the power converter,the load unit,and the monitoring system.Microgrid compensated the energy shortage problem largely.However,the intermittency and volatility of distributed energy,which bring many security risks,has always affected the stability of the DC microgrid.Therefore,this thesis focused on the stable operation of the DC microgrid and the control strategy of the energy storage system.First of all,this thesis introduced the structure of the DC microgrid and analyzed the working principle of the bidirectional Buck/Boost converter in the energy storage system.Moreover,the main circuit parameters of the converter are designed.With the small-signal model under the different working modes,the closed-loop compensation controller is introduced to ensure the stable work of the energy storage system.Using Mathcad software,the Bode diagram of the system is proposed to verify the rationality of the closed-loop compensation network design.A Buck/Boost simulation circuit is performed to analyze the effectiveness of the designed closed-loop compensation network.Secondly,in order to solve the imbalance problem of the battery packs under the working state,this thesis proposed two improved droop control strategies.The first improved strategy introduced the battery SoC into the sag coefficient,which forces the large SoC battery to provide a larger output current and the small SoC battery to share a small output current.The balance of the output current and SoC is realized finally.Integrated the SoC of the battery pack with the DC bus,the second strategy changed the reference value of the DC bus voltage,which can realize the balance of the SoC and the output current.In this thesis,the two methods are proposed by the small-signal stability analysis.Using the motion trajectory diagram of the dominant characteristic root of the system,the stability of the whole system during the change of the battery SoC was proved.Finally,based on theoretical analysis,a simulation system was built with the MATLAB/Simulink simulation platform,and the two improved control strategies were verified.Moreover,a DC microgrid hardware experimental platform is built.The hardware design process is introduced in detail in this thesis,which includes the production of the interface converter circuit model,drive circuit model,sampling and conditioning circuit model,and power supply circuit model.The digital control algorithm is achieved with the TI＿DSP28335controller.The simulation results and the experimental results verified the effectiveness and practicality of the strategies.