Research On Layered Coordinated Control Of Interconnected DC Microgrid

In recent years,with the shortage of traditional fossil energy sources and increasing environmental pollution,a microgrid composed of distributed power sources such as photovoltaic and wind power is of great significance to solve the above problems.Compared with the AC microgrid,the DC microgrid has the advantages of simple structure,low loss and better controllability,and there is no multi-level converter conversion link and no need to consider reactive power loss and frequency stability.Good development prospects.Achieving coordinated control among the units of the DC microgrid system to ensure the balanced distribution of load power and thus the stability of the system voltage has become a key issue in the DC microgrid.In this paper,a DC microgrid system composed of distributed power sources,energy storage units and loads is used as the research object,and the stable operation of the system is studied from the island DC microgrid and the interconnected DC microgrid system.The specific research content is as follows:Firstly,this paper introduces the research status of DC microgrid at home and abroad,introduces the structural model of DC microgrid and interconnected DC microgrid,establishes the theoretical and engineering mathematical model of photovoltaic power generation unit,and analyzes the photovoltaic power generation unit through numerical simulation Output characteristics.At the same time,two operating modes of the photovoltaic power generation unit,namely the maximum power operating mode and the power limiting mode,are discussed,and the maximum power tracking control is theoretically analyzed and verified by simulation.Secondly,the stable operation of the DC microgrid under isolated island operation was analyzed.Aiming at the requirements of voltage stability and current sharing of island DC microgrid system,according to the fluctuation of bus voltage,a layered coordinated control strategy of island DC microgrid based on multi-operation mode switching is proposed.The strategy adopts a three-layer control structure and divides the island DC microgrid into three modes of operation based on bus voltage information.In addition,considering the influence of the unbalanced line parameters on the precise load distribution,through the establishment of a sparse communication network,each power generation unit only interacts with the neighboring units to complete the system current control based on the difference discrete consistency algorithm.Finally,the problem of insufficient anti-interference ability of a single DC microgrid is further analyzed,and a multi-mode coordinated control strategy for interconnected DC microgrid is proposed.Under the two operating states of on-grid and off-grid,fully consider the limitations of the virtual capacity of the energy storage unit and the capacity of the converter,and then realize the smooth switching based on the multi-operation mode between the voltage partitions and the autonomous power balance distribution to ensure the interconnection The stable and safe operation of the microgrid system.In order to verify the effectiveness of the control strategy,PSCAD / EMTDC was used to simulate the proposed coordinated control strategy.The results show that the proposed control strategy can achieve the stable operation of the DC microgrid system.