Experimental Research On System Design And Hierarchical Control Strategy Design Of DC Microgrid Cluster

With the increasing installed scale of new energy power generation such as photovoltaic power generation and wind power generation,distributed power generation technology has been widely used.Building an efficient,low-consumption,and reliable DC microgrid system is an effective way to achieve flexible networking and supplydemand interaction of DC distributed power and DC loads.DC microgrid cluster is a kind of DC microgrid system composed of multiple sub-microgrids.The sub-microgrids are independent of each other and are reserved for each other.The stability and reliability of DC microgrid cluster are better than traditional DC microgrid.In this paper,DC microgrid cluster is studied.Focusing on the contol of DC bus voltage,the current distribution of sub-microgrids and the current distribution of converters in sub-microgrid.The hierarchical control method is designed to control DC microgrid cluster.This paper is organized as follows:(1)The improved droop control strategy of DC microgrid is investigated.A theoretical analysis is conducted on the reasons that control accuracy of bus voltage of DC microgrid using traditional droop control is low,and the current sharing accuracy of converters in microgrid is greatly affected by the difference of line resistances.By adding compensation control of bus voltage and correction control of droop coefficient on the basis of traditional droop control,two major problems of droop control are completely solved.The small-signal modeling of DC microgrid system controlled by this method is carried out to verify stability of this control method.A simulation model of DC microgrid with improved droop control is established in PLECS simulation environment,and the simulation results verify the effectiveness of this control method.(2)The hierarchical control strategy of BOOST-type DC microgrid cluster is investigated.In order to effectively control voltage of DC bus and output current of converters in this BOOST-type DC microgrid cluster,a master-slave hierarchical control strategy and a peer-to-peer hierarchical control strategy are designed on the basis of improved droop control.Different calculation methods of reference value are adopted separately in the two methods.In order to compare the two hierarchical control strategies,a simulation model of DC microgrid cluster is built in PLECS simulation environment,and control effects of two control methods on DC microgrid cluster under five operating conditions are compared in detail.The simulation results prove that the control effect of the peer-to-peer hierarchical control is better than the master-slave hierarchical control.(3)The hierarchical control strategy of hybrid DC microgrid cluster is investigated.In order to achieve coordination between three sub-microgrids and ensure stability of DC bus voltage,based on the proposed peer-to-peer hierarchical control of BOOST-type DC microgrid cluster,the peer-to-peer hierarchical control of hybrid DC microgrid cluster is designed.And the working principle of this hierarchical control strategy is analyzed in detail.A simulation model of hybrid microgrid cluster controlled by this hierarchical control strategy is built in PLECS.The simulation results prove the effectiveness of proposed control strategy.(4)The hardware circuits and control software of BOOST-type DC microgrid cluster is designed and completed,and an experiment platform of DC microgrid cluster which is composed of 6 BOOST converters is built.In this platform,the voltage level of DC bus is 60 V,and the maximum power of load is 350 W.Five sets of experiments were carried out,they are reference value of current distribution ratio change,load mutation,reference value of voltage change,converter removal and re-connection,sub-microgrid removal and re-connection.The experimental results prove the effectiveness and reliability of control strategy proposed in this paper from the hardware level.