Coordination Control Strategy Of DC Microgrid Cluster

In recent years,microgrid has received extensive attention because of its advantages in the consumption of renewable energy,reliability,and high scalability.Due to the intermittency of new energy power generation,the power supply reliability of an independent DC microgrid depends on the energy storage unit.However,increasing the capacity of the energy storage unit will bring additional costs and maintenance.The current research on DC microgrid mainly focuses on the optimization and control of a single DC microgrid,while ignoring the energy exchange between DC microgrid groups.In order to alleviate the pressure that the energy storage unit absorb unbalanced power,the adjacent DC microgrids are connected to each other in a specific way to establish a reasonable DC microgrid cluster system.Based on this system,an effective cluster control strategy is designed to achieve power reduction.Realizing the transmission of energy between microgrids is of great significance.Firstly,the operating principles of each unit in the DC microgrid is analyzed in this article.Considering the influence of each unit,a mathematical model of an independent DC microgrid is established.In order to realize the energy exchange between DC microgrids and relieve the pressure of a single microgrid energy storage unit,a cluster structure in which interconnected converters are connected to the DC microgrid is proposed.Secondly,a two-stage DC converter for the interconnection of two DC microgrids is designed in this article.The converter is composed of a three-phase LLC resonant converter cascaded interleaved bidirectional DC converter.The transformer of the three-phase LLC resonant converter adopts Y-Y connection,which widens the zero-voltage conduction range of the converter and reduces the output current ripple.Also the isolation function of the transformer makes the interconnection system have a protective effect.The bidirectional DC converter adopts the interleaving technology to reduce the output current ripple when the converter is working,and reduces the switching loss when the input current pulsation of the inductor is the same.Through Matlab/Simulink simulation,it is verified that the interconnected converter can not only realize the two-way transmission of energy and fault isolation,but also the operation efficiency is better than the traditional two-way DC converter.Finally,a hierarchical coordinated control strategy for the DC microgrid cluster system is proposed.By setting the voltage threshold,this strategy establishes the power balance relationship of the system voltage division under the grid-connected and island operation state,and designs the coordinated control strategy of each unit in the system.According to the real-time bus voltage change,the system is made to work in the corresponding voltage area partition,and the power balance is realized according to the control strategy of this partition.Matlab/Simulink is used to build a cluster interconnected DC microgrid system model,and the proposed control strategy is simulated and verified in grid-connected and island operation state.The simulation results show that the proposed strategy is effective and feasible.