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Research On Main Circuit And Control Strategy Of Cascaded STATCOM

Posted on:2013-01-21Degree:MasterType:Thesis
Country:ChinaCandidate:Z F LiuFull Text:PDF
GTID:2212330371457013Subject:Power system and its automation
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The transmission capacity and load demand of national power grid are increasing rapidly. As a matter of fact, the inadequacy of reactive power capacity has become a serious problem. As reactive power can not be transmitted in long distance, it is essential to develop high-voltage and large-capacity reactive power compensators for national power grid. As an important member of FACTS family, cascaded STATCOM based on VSC, PWM and multilevel converter technology is widely applied in the field of high-voltage and large-capacity reactive power compensation, which has plenty of advantages, such as fast response, good harmonic quality, compensated currents independent of the PCC voltage and so on. Main contents and related conclusions of this thesis are as follows:(1)The transient mathematical models of the cascaded STATCOM are established in abc and dq coordinates respectively, including high frequency switching model and low frequency dynamic model. The power exchanged between the cascaded STATCOM and the AC system is analyzed based on instantaneous power theory.(2)The selection of main circuit configuration and corresponding parameters for cascaded STATCOM is proposed, including connecting structure, linked reactor, DC capacitor, number of cascaded HBIs and power electronic devices. The key considerations of the design are also discussed.(3)The hierarchy of the control system for the cascaded STATCOM is presented based on its transient mathematical model. The converter controller is designed in detail. The inner loop for active and reactive current control is decoupled, while the outer loop uses combination of inverse system and PI control.(4)The problem of DC capacitor voltage balancing of the cascaded STATCOM is studied. It is pointed out that the traditional CPS-SPWM and pulse cycle transposition strategy can not solve the problem, and thus the advanced CPS-SPWM strategy for DC capacitor voltage balancing control is proposed. Principle and realization of the novel strategy are also presented, and the strategy is verified by simulation results in PSCAD/EMTDC.
Keywords/Search Tags:VSC, cascaded STATCOM, low frequency dynamic mathematical model, main circuit structure, converter control, CPS-SPWM, capacitor voltage balance control, PSCAD/EMTDC
PDF Full Text Request
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