本文選題：高壓直流輸電 + 電壓源換流器�。� 參考：《湖南大學(xué)》2014年碩士論文

【摘要】：基于電壓源換流器的高壓直流輸電（Voltage source converter-high voltagedirect current，，VSC-HVDC）采用全控型電力電子器件IGBT，取代常規(guī)直流輸電中構(gòu)成換流器結(jié)構(gòu)的半控型器件晶閘管。該技術(shù)突出了全控型電力電子器件、電壓源換流器和脈沖寬度調(diào)制三大技術(shù)特點(diǎn)，解決了常規(guī)直流輸電中存在的波形質(zhì)量較差、需要無(wú)功補(bǔ)償、不能向無(wú)源系統(tǒng)供電等諸多瓶頸。目前已投入運(yùn)行的VSC-HVDC系統(tǒng)大多采用兩電平或三電平換流器，通過(guò)功率器件串聯(lián)方式實(shí)現(xiàn)高電壓和大容量，卻存在串聯(lián)器件難以均壓和開關(guān)損耗較大等問(wèn)題。 模塊化多電平換流器（Modular multilevel converter，MMC）是應(yīng)用于高壓直流輸電的一種新型電壓源換流器拓?fù)洌總�(gè)橋臂由多個(gè)彼此獨(dú)立子模塊（Sub-module，SM）串聯(lián)而成，子模塊由IGBT和電容構(gòu)成。在系統(tǒng)正常運(yùn)行前需對(duì)SM進(jìn)行預(yù)充電，使電容電壓和直流母線電壓由零上升到額定值，以完成MMC-HVDC系統(tǒng)的啟動(dòng)。MMC-HVDC的啟動(dòng)是一個(gè)復(fù)雜的暫態(tài)過(guò)程，合適的控制方式對(duì)提高啟動(dòng)速度、增強(qiáng)穩(wěn)定性、抑制過(guò)電流和過(guò)電壓至關(guān)重要。 本文闡述了利用外部直流電源從直流側(cè)進(jìn)行預(yù)充電的方式，即他勵(lì)模式，指出了這種方式存在的諸多不足。為了彌補(bǔ)這些弊端，本文介紹了MMC的工作原理，推導(dǎo)了MMC啟動(dòng)時(shí)的電壓、電流和功率方程，建立了相應(yīng)的數(shù)學(xué)模型和等值電路，為啟動(dòng)控制策略的研究和控制系統(tǒng)的設(shè)計(jì)提供了必要的理論依據(jù)。 在詳細(xì)分析MMC啟動(dòng)動(dòng)態(tài)過(guò)程的基礎(chǔ)上，本文提出了利用交流電網(wǎng)從交流側(cè)對(duì)SM進(jìn)行預(yù)充電的控制方式，即自勵(lì)模式，并將此過(guò)程分為不可控和可控兩個(gè)階段。給出了最小限流電阻的選擇方式，既避免了沖擊電流又最大限度地減弱了電阻對(duì)啟動(dòng)速度的影響；不可控階段結(jié)束點(diǎn)電壓低于理論終值，避免了后期電壓緩慢上升的過(guò)程；可控階段基于載波移相調(diào)制（Carrier phase shifted modulation，CPSM），提出了電流控制、電壓控制和子模塊平衡控制策略。在實(shí)現(xiàn)對(duì)SM中電容快速充電的同時(shí)，能夠有效抑制啟動(dòng)過(guò)程中出現(xiàn)的過(guò)電流和過(guò)電壓，并兼顧系統(tǒng)的平衡，以實(shí)現(xiàn)可靠和高效的預(yù)充電。最后在Matlab/Simulink中搭建了5電平模型，通過(guò)電壓電流雙閉環(huán)控制與僅考慮電壓?jiǎn)伍]環(huán)控制的對(duì)比可以看出，本文提出的啟動(dòng)控制策略具有良好的有效性和可行性。
[Abstract]:Voltage source converter-high voltagedirect VSC-HVDC based on voltage source converter replaces the thyristor of half-control device in conventional HVDC transmission using full-control power electronic device IGBT. The technology highlights the three technical features of full control power electronic devices, voltage source converters and pulse width modulation, and solves the problem of poor waveform quality in conventional HVDC transmission, which requires reactive power compensation. Can not supply power to passive systems and many other bottlenecks. At present, most of the VSC-HVDC systems in operation use two-level or three-level converters to achieve high voltage and large capacity by means of power devices in series, but there are some problems such as the difficulty of voltage sharing and the large switching loss of series devices. Modular multilevel converter (MMC) is a new voltage source converter topology used in HVDC transmission. Each arm is composed of several sub-modules, Sub-Modules and SMs, which are composed of IGBT and capacitor. Before the normal operation of the system, SM should be precharged to make the capacitor voltage and DC bus voltage rise from zero to rated to complete the start-up of the MMC-HVDC system. MMC-HVDC is a complicated transient process, and the proper control mode can improve the startup speed. Enhancing stability and suppressing overcurrent and overvoltage are essential. In this paper, the precharge mode of external DC power supply from DC side, that is, the mode of external excitation, is described, and the shortcomings of this mode are pointed out. In order to remedy these disadvantages, this paper introduces the working principle of MMC, deduces the voltage, current and power equations of MMC, and establishes the corresponding mathematical model and equivalent circuit. It provides the necessary theoretical basis for the research of startup control strategy and the design of control system. Based on the detailed analysis of the dynamic process of MMC startup, this paper proposes a control method of pre-charging SM from AC side by AC power grid, that is, self-excitation mode, and divides the process into two stages: uncontrollable and controllable. The method of selecting the minimum current limiting resistance is given to avoid the impact current and weaken the influence of the resistance on the starting speed, the end voltage of the uncontrollable stage is lower than the theoretical end value, and the process of the slow rise of the late voltage is avoided. The controllable phase is based on carrier phase shifted modulation.Current control, voltage control and sub-module balance control are proposed. In order to realize the reliable and efficient precharge, the overcurrent and overvoltage in the starting process can be effectively suppressed while the capacitor in SM can be charged quickly, and the balance of the system can be taken into account. Finally, a five-level model is built in Matlab/Simulink. The comparison between voltage and current double closed-loop control and single-loop voltage control shows that the startup control strategy proposed in this paper is effective and feasible.
【學(xué)位授予單位】：湖南大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2014
【分類號(hào)】：TM721.1

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