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Research On Control Strategy Of High Voltage Cascaded H-bridge STATCOM

Posted on:2014-07-09Degree:MasterType:Thesis
Country:ChinaCandidate:Z P LiuFull Text:PDF
GTID:2252330425980489Subject:High Voltage and Insulation Technology
Abstract/Summary:PDF Full Text Request
With the development of power system scale, STATCOM also unceasinglygo to the high voltage and high power direction. Because Multilevel inverteradopted in STATCOM can not only reduce the harmonic, but also need no bulkyand expensive zigzag, so it become a development trend of reactive powercompensation.Compared to the diode clamped and the flying capacitor multilevel inverter,cascade H-bridge STATCOM has less circuit structure of the diode and thecapacitor, and every H-bridge has the same structure, that is easy to realizemodular.This paper analyses the principle of reactive power compensation with theSTATCOM, using the phase relationship between grid voltage and the outputvoltage of the STATCOM on the steady state, Q-δ closed-loop STATCOM systembased on10kV is established, which has eight H-bridges. The simulation resultshow that, the output voltage and phase can be generated by the simulationsystem corresponding the different load, and the harmonic content is low, ThePower Factor compensation can be proof that the system can compensate thereactive completely.Due to the load is always changing, so the chosen of control method willdecide the dynamic compensation ability of STATCOM. This paper instead oftraditional PI control with Fuzzy-PI control which is a combination with traditionPI and fuzzy control technology. Changing the load in grid, and respectivelyadjusted with two kinds of control methods, compared the effect of dynamiccompensation. Simulation result show that, the Fuzzy-PI control can be betterperformance when the load switching between capacitive and inductive.When STATCOM in dynamic compensation, if the modulation ratio isconstant, the DC capacitor voltage will change with the change of load, and the DC side capacitor charge-discharge can increase the response time of the systemThis paper uses BP neural network prediction technology, according to theworking conditions of STACOM, adjust modulation to ensure that the DCcapacitor voltage unchanged. Simulation show that the effect is good.The biggest characteristic of DC side of cascade H-bridge STATCOM iseach sing-phase H-bridge is independent, but the problem of DC side capacitorvoltage balance of each is one of key technical limitations of cascade H-bridge toSTATCOM development, This paper added two control loops to control thevoltage of capacitor. The inner loop to control the voltage of capacitor on samephase, and outer loop to control the voltage of capacitors between the phases.which is in order to ensure all DC side capacitors voltage balance. Simulationresults show that, adding two control loops can made the balance of all DCcapacitors.This paper analyses processing technologies of the H-bridge fault in the past,and for each method are simulated and compared, finally proposed the newmethod that based on neutral drifting technology. Simulation results show thatcan be used in the fault processing of STATCOM and it has greatly improved theutilization ratio of H-bridge power unit.
Keywords/Search Tags:STATCOM, Reactive power compensation, Fuzzy-PI, Voltagebalancing control, Fault processing technology
PDF Full Text Request
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