Simulation Research On Filters And Operation Modes Of HVDC Transmission System

HVDC transmission technology has attracted the attention from all over the world with unique advantages of long distance, high-capacity power grid and power grid interconnection. But current converter in HVDC system device is made up of a number of power electronic components. This is a typical strongly nonlinear system which may result in serious harmonic wave pollution. Thus study on inhibiting harmonic wave contamination in HVDC system has become one of the most important projects. Aiming at the harmonic wave issue, this thesis firstly designs and researches into various filters, and then comprehensively analyzes the performance of filter and its overall function and at last puts forward the optimal filtering scheme and system combination by means of the system model under the various operational modes established by HVDC with the premise of given fuzzy control method.This paper analyzes mechanisms and characteristics of harmonic wave generation in HVDC, presents the concept of harmonic wave and possible harms to the system, researches into the methods to inhibit harmonic wave and their advantages and disadvantages respectively, mainly analyzes characteristic and non-characteristic harmonic wave of 12-pulse wave converter and then compares and analyzes the distinction and their own features of AC and DC filters, all of which will lay a theoretical foundation for the design and simulation research on filter in the future.By analysis of operating principle and structure of the various filters and research on methods in order to detect harmonic wave with the help of active filter, the essay establishes Matlab simulation model. Under the operational mode of unipolar earth, the paper simulates by adopting the DC transmission line model, compares the simulative waves, analyzes side voltage harmonic component as well as THDV of AC and DC respectively and then records control data. The results show that adopting passive three tuning AC filters and passive three tuning DC filter can perform best.In order to compare further and verify the filtering effect, the dissertation presents structural model of DC transmission line under seven operational modes, of which are unipolar earth grounding, unipolar metal grounding, unipolar parallel double conductor grounding, bipolar ends neutral-point earthing, bipolar one-port neutral-point earthing, bipolar neuter line grounding and back-to-back HVDC system. The method of this essay is comparing the advantages and disadvantages of various operational modes, establishing the corresponding Matlab simulation model, adding three tuning AC or DC filter, debugging system control parameters, observing line waveform simulation curve, recording the related data as well as comparing its controlling and filtering effect. The results show that, after adding three tuning filter, HVDC transmission model under the bipolar neutral-point earthing ends has the best effect.Through analysis and demonstration of this project, this essay finally puts forward a set of system model. That is, the optimal control strategy commutation editor at both ends by fuzzy control; optimal filter combination-the filter by using passive three tuning filter; optimal control way-a bipolar ends the neutral-point earthing operation mode, which make up of the best overall HVDC transmission lines system model. This study will be designed to provide theoretical and simulative support for the future analysis and research on HVDC project.