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Networking Mechanism Of Distributed Generation And Esearch On Stability Of Microgrid

Posted on:2011-12-06Degree:MasterType:Thesis
Country:ChinaCandidate:J ShiFull Text:PDF
GTID:2232330392461929Subject:Power system and its automation
Abstract/Summary:PDF Full Text Request
After a lot of distributed generations (DGs) are integrated into the powergrid, the structure, form of energy, power flow, protection, control andinformation exchange of power grid will be much more complicated. On the onehand, problems of networking mechanisms like in which way DGs should beconnected to the grid, which control methods should be adopted and how tomeet the requirements of connection so that the impacts of DGs on power gridcan be reduced, are pressing for solutions. On the other hand, as the mostefficient way to integrate DGs into power grid, the technology of microgrid hasrecently received a wide publicity. Through this technology, the problem oflarge-scale integration of DGs will be solved and the advantages of DGs can beexerted. Microgrid is a special form of power system integrating the technologyof DG and power electronics. It works as an independent entirety, operatedeither in synchronization with grid, or as an island. With the expansion ofmicrogrid utilization, the use of a large amount of power electronics with lowinertia, and the intermittent power output of solar and wind power, are all potential threats to the stable operation of DC microgrid. Therefore, controllingthe converters in microgrid to guarantee its stable operation both insynchronization and in islanding way, will be an important research filed ofmicrogrid.Pointed at the networking mechanism of DGs, the problems of theintegrating way, the control method and the networking requirements arefocused on in this thesis. The following points are concluded:(1) DGs areconnected to the power grid mainly through DC/DC converters, DC/ACinverters and AC/DC-DC/AC back-to-back conversion,(2) control methods ofthe connection circuit between DGs and power grid, in order to control powerflow and guarantee energy quality,(3) standards and requirements in voltage,frequency, harmonics and so on when DGs are connected to grid.About the stability problem of microgrid, researches on small-signalstability and transient stability are conducted in this thesis with en eye to the DCmicrogrid which is less investigated but has broad applications and perspectives.Firstly, by using state-space approach, dynamic models of DGs in DC microgridare established. At the same time, the average models of converters and theircontrol systems those are important for power conversion and control inmicrogrid are also established. Based on these models, the state-spaceexpression of the whole DC microgrid is obtained. The eigenvalues of the system state matrix are computed to analyze the small-signal stability and thelocis the eigenvalues with the change of control parameters of converters areplotted to analyze the influence of control parameters on the stability of DCmicrogrid. The analysis shows that when control parameter increases to a certainvalue, the real part of eigenvalues will become positive which means the systemis instable. In order to analyze the transient stability of DC microgrid,time-domain simulations of the DC microgrid are conducted and voltage curvesunder different control parameters are obtained. On the one hand, the simulationresults verify the results of stability analysis, i.e. the system will deviate from itsoriginal stable working point when the control parameter is too large. On theother hand, the results also show that within the stable range, the larger thecontrol parameters, the better the voltage control performance is. It can beconcluded that proper choice of control parameters plays an important role inguaranteeing the stable operation of DC microgrid.
Keywords/Search Tags:distributed generation, networking mechanism, DC microgrid, small-signal stability, transient stability
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