Suppression Control Method Of Dc Component In The Ac Output Of The Vsc-hvdc System

VSC-HVDC with the excellent performance of supplying power to the passivesystem or weak AC system, controlling the active and reactive powertransmission fast and independently, constituting a multiport network easily, at thesame time, it is provided with environment-friendly, application of VSC-HVDC innew energy grid, the grid non-synchronous interconnect, supplying power to passivesystems more widely.VSC-HVDC is based on can shut off the flow changing components and pulsewidth modulation (PWM) technology, through the control power switch pipe of thehige to achieve power conversion. Zero drift of the operational amplifier in controlcircuit, the discrete of the power electronics device parameters and the DCcomponent in the reference modulation voltage and the carrier will make the ACoutput of inverter contains a DC component, and the DC component give an adverseimpact on the VSC-HVDC. In order to improve the quality of AC output power of theVSC-HVDC, The thesis focuses on the causes of the DC component in the ACoutput of the VSC-HVDC and the influence on the converter transformer.This thesis firstly established the VSC-HVDC mathematical model in thecoordinate system of ABC three-phase static and d qrotation, The control strategyof the steady state not to consider DC component is studied. Then analyzes thereasons causing the dc component of VSC-HVDC system, On the mechanism causingthe converter transformer DC bias for the DC component, Described the mechanismcausing the converter transformer DC magnetic bias. According to Parktransformation to study the manifestations of the DC component in the d qcoordinate system, Analyzes the influence of the dc component to VSC-HVDC whenthe VSC-HVDC uses direct current control. The mathematical model of VSC-HVDCis derived when the DC component is considered, based on the inhibition of the DCcomponent of the control strategy based on repetitive control. Finally, using thePSCAD to simulate and analyze for the two kinds of control strategy. The simulationresults show that the control strategy has good control performance, can effectivelyrestrain the dc component and improve the ac output power quality of VSC-HVDC.