本文選題：多端直流輸電系統(tǒng) + 模塊化多電平換流器　； 參考：《蘭州理工大學》2017年碩士論文

【摘要】：多端柔性直流輸電技術尤其是以基于全控型器件的電壓源換流器多端直流輸電(Voltage Source Converter based Multi-Terminal Direct Current,VSC-MTDC)技術近年來受到各國重視并得以飛速發(fā)展,主要是由于其在功率的可控性和輸電擴展性方面具有無可比擬的優(yōu)勢,多端柔性直流輸電技術可在風電場聯(lián)網(wǎng)、大電網(wǎng)互聯(lián)以及孤島供電中發(fā)揮其特點。從電壓源換流器中發(fā)展而來的模塊化多電平換流器(Modular Multilevel Converter,MMC)具備換流器容量大及損耗小等優(yōu)點,因此本文以基于MMC換流站的多端直流輸電系統(tǒng)(MMC-MTDC)為研究對象,對其各級控制方式、直流線路故障特性以及故障發(fā)生時的保護策略進行重點分析和研究。本文以三端MMC直流輸電系統(tǒng)為例,對單個MMC換流站以及三端MMC直流輸電系統(tǒng)的數(shù)學模型進行深入分析。在調(diào)制方式上選取最近電平逼近的方式,在站級控制方面,采用內(nèi)環(huán)電流控制,外環(huán)為內(nèi)環(huán)提供電流參考值得方式。在系統(tǒng)級控制方面,本文對比了不同的控制方式且基于對直流電壓和功率需求的考量,選擇了電壓裕度控制,并在PSCAD/EMTDC中搭建了三端MMC直流輸電系統(tǒng)的仿真模型,對此模型在正常運行以及主換流站因故退出運行這兩種情況進行仿真研究。最后,本文針對MMC-MTDC系統(tǒng)的直流側線路上的三種故障——單極接地故障、極間短路故障以及斷線故障發(fā)生時的情形進行仿真,對每種故障的特性深入分析,然后提出了相應的保護策略使得系統(tǒng)穩(wěn)定運行。經(jīng)過在仿真軟件PSCAD/EMTDC上的仿真結果表明本文所提出的電壓裕度控制策略及所設計的控制器,能夠讓系統(tǒng)在功率需求有變動時自行轉換各換流站的控制方式來平衡整個系統(tǒng)的有功功率,即時在主換流站退出運行時也能讓剩余系統(tǒng)穩(wěn)定運行維持供電;在直流側故障發(fā)生時,電壓裕度控制策略配合相應的保護策略也能讓系統(tǒng)快速恢復穩(wěn)定,消除故障帶來的影響,提高了系統(tǒng)對于直流側線路故障的處理能力。
[Abstract]:In recent years, the technology of multi-terminal flexible DC transmission, especially voltage source converter based on full-control devices, has been paid more and more attention to and developed rapidly in recent years. Because of its unparalleled advantages in power controllability and transmission expansibility, multi-terminal flexible direct current transmission technology can play its role in wind farm interconnection, large power grid interconnection and island power supply. The modular multilevel converter (Modular Multilevel converter) developed from the voltage source converter has the advantages of large capacity and low loss. Therefore, this paper takes the multiterminal DC transmission system based on the MMC converter station as the research object and its control methods at all levels. The fault characteristics and protection strategy of DC line are analyzed and studied. Taking the three-terminal MMC DC transmission system as an example, the mathematical models of a single MMC converter station and a three-terminal MMC DC transmission system are deeply analyzed in this paper. In the modulation mode, the nearest level approximation is selected. In the field of station level control, the inner loop current control is adopted, and the outer loop provides the current reference mode for the inner loop. In the aspect of system-level control, this paper compares different control methods and based on the consideration of DC voltage and power demand, selects voltage margin control, and builds the simulation model of three-terminal MMC HVDC transmission system in PSCAD/EMTDC. The model is simulated in normal operation and main converter station exit operation. Finally, this paper simulates three kinds of faults on DC side line of MMC-MTDC system, such as single-pole grounding fault, inter-pole short-circuit fault and break-line fault, and deeply analyzes the characteristics of each kind of fault. Then the corresponding protection strategy is put forward to make the system run stably. The simulation results on the simulation software PSCAD/EMTDC show that the proposed voltage margin control strategy and the controller designed in this paper. The system can balance the active power of the whole system by changing the control mode of each converter station when the power demand changes. Even when the main converter station is out of operation, it can make the remaining system run stably and maintain the power supply. When the DC side fault occurs, the voltage margin control strategy combined with the corresponding protection strategy can also make the system quickly restore stability, eliminate the influence of the fault, and improve the system's ability to deal with the DC side line fault.
【學位授予單位】：蘭州理工大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TM721.1

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