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Research On Hierarchical Coordinated Control Strategy Of DC Microgrids

Posted on:2018-06-21Degree:MasterType:Thesis
Country:ChinaCandidate:X L YangFull Text:PDF
GTID:2322330512476834Subject:Electrical engineering
Abstract/Summary:PDF Full Text Request
With the integrated utilization of PV generation,fuel cells,energy storage batteries which have the DC output characteristics,combined with the rising DC load demand such as the LED lighting,EVs and DC motor driving,DC microgrids gradually become the focus of microgrid technology.In order to insure stable and reliable operation of the DC microgrid,a lot of research work has been done in areas such as coordinated control strategies,stability analysis and dampling control by the scholars around the world.The aforementioned areas are vital important for the reliable operation of a DC micorgrid,which deserve more theoretial analysis and detailed research.As for the reliable operation of the DC microgrid,this paper launches the research from the following several aspects.(1)In order to realize the coordinated control of a DC microgrid,DBS(DC Bus Signaling)method and hierarchical control strategy are combined to from the proposed control architecture.The proposed control architecture consists of two control layers.The first control layer is the coordinated control layer,which aims to coordinate the distributed units and achieve the real-time power balance of the DC microgrid.The second control layer is the optimization control layer,which focus on the DC bus voltage compensation and charging or discharging process optimization of the storage units.The combination of DBS and hierarchical control on one hand,makes full use of high reliability and communication channels absence of the DBS method,on the other hand,the secondary control objectives such as DC bus voltage compensation can be easily integrated into the control architecture.The functional division of the control layers makes the control of the DC microgrid more consise and efficient.(2)In the coordinated control layer,control strategies of RES(Renewable Energy Source)units,BSE(Battery Storage Element)units,LIFC(Load Interfacing Converter)and AC/DC GSC(Grid Side Converter)are thoroughly investigated.Droop control is implemented by the BSE units to stabilize the DC bus voltage,other units by detecting the DC bus voltage to generate their own power or voltage reference,realizing the working state transition.By adopting this control method,the coordinated control of distributed units and DC bus voltage control can be achieved.Simulation and experimental results verify the correctness and effectiveness of the coordinated control layer.(3)In the optimization control layer,the DC bus voltage can be compensated to the reference value by up-down shifting the droop curve of BSE units.Control curves of other units are left-right shifted according to the DC bus voltage compensation term.By using this method,the DC bus voltage can be restored to the reference value without canceling the effectiveness of DBS.At the same time,in order to realize the optimization of charging or discharging process of BSE units and maintain the SOC in a reasonable range,secondary shifting control is applied to the GSC to adjust the power flow between the DC bus and the main grid.The effectiveness of the optimization layer is verified by simulation and experiment.(4)To investigate the large signal stability of a DC microgrid which contains the CPL(Constant Power Load),large signal model and domain of attraction calculation algorithm are constructed.The variation of domain of attraction under the change of circuit parameters and CPL load is discussed.Simulation results validate the correctness of the large signal model and large signal analysis method.The large signal analysis provide theoretical guidance for the design of large signal stability and the selection of DC microgrid parameters.(5)In order to study the small signal stability of the aforementationed DC microgrid,the small signal model of closed-loop control of each converter is established and impedance of each conveter is calculated.The small signal stability of DC microgrid is analyzed by using the method of impedance stability criterion.The influence of parameters variation on the small signal stability of DC microgrid is analyzed and verified by simulation,which provides guidance for the design of small signal stability of DC microgrid.Besides,to solve the instability problem caused by small signal disturbance,the active damping method is implemented to achieve oscillation suppression and stability improvement.This active damping method can insure the reliable operation of DC microgrid.
Keywords/Search Tags:DC microgrid, coordinated control, hierarchical control, large signal stability, small signal stability, active damping
PDF Full Text Request
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