【摘要】：隨著分布式發(fā)電并網(wǎng)和孤島供電等需求的增加,多端直流輸電技術(shù)逐漸受到人們的重視,并在多項工程中得到了應(yīng)用。而基于模塊化多電平變流器的多端直流輸電系統(tǒng)(Multi-terminal Direct Current based on Multilevel Converter,MMC-MTDC)不僅擁有MMC高電壓、大容量的技術(shù)優(yōu)勢,同時也具有直流輸電系統(tǒng)運行靈活、穩(wěn)定性好、可實現(xiàn)多電源供電和多落點受電的特點。因此,基于MMC的MTDC系統(tǒng)已經(jīng)成為人們研究的熱點之一,研究的內(nèi)容主要集中在協(xié)調(diào)控制策略、故障保護、分布式發(fā)電并網(wǎng)、潮流優(yōu)化以及附加控制等方面。本文對多端直流輸電系統(tǒng)的控制策略進行了研究,主要的研究內(nèi)容包括:(1)針對MMC-MTDC系統(tǒng),分析了其上層控制、站級和閥級等各級控制系統(tǒng)的需求,并按照需求對各級的控制系統(tǒng)進行了設(shè)計,使各級控制系統(tǒng)能夠?qū)崿F(xiàn)相應(yīng)的控制功能。同時,設(shè)計了遠程和本地兩級的監(jiān)控系統(tǒng),實現(xiàn)對整個系統(tǒng)運行狀態(tài)的監(jiān)控。(2)對MMC-MTDC輸電系統(tǒng)的閥級、站級和各換流站間的協(xié)調(diào)控制等控制策略進行了研究。并對適用于閥級、站級和各換流站間的協(xié)調(diào)控制等控制策略進行了對比分析,根據(jù)各換流站的運行方式選取合適的控制策略,從而確保系統(tǒng)能夠穩(wěn)定運行。利用仿真和實驗對各級控制策略的正確性和有效性進行了驗證。(3)考慮了利用多端直流輸電系統(tǒng)向孤島供電的情況,若負載不對稱時,會使系統(tǒng)中出現(xiàn)波動功率,而該波動功率會進一步引起主換流站的交流側(cè)電流和直流電壓的電能質(zhì)量問題。本文對負載不對稱條件下的運行特性進行了分析,然后通過對環(huán)流的控制,實現(xiàn)了由子模塊承擔因負載不對稱而產(chǎn)生的二倍頻波動功率,從而避免了負載不對稱引起的直流電壓和主換流站的交流電流的電能質(zhì)量的惡化。(4)考慮了負載不對稱條件下,傳統(tǒng)的定交流電壓控制策略無法實現(xiàn)交流電壓的平衡控制。因此,本文對PI調(diào)節(jié)器和R調(diào)節(jié)器的幅頻特性進行了分析,并對傳統(tǒng)的定交流電壓控制策略進行改進,采用PI調(diào)節(jié)器和R調(diào)節(jié)器并聯(lián)的結(jié)構(gòu),確保在負載不對稱情況下,換流站能夠輸出對稱的交流電壓,從而使供電質(zhì)量得到提高。
[Abstract]:With the increasing demand of distributed generation and island power supply, multi-terminal DC transmission technology has been paid more and more attention, and has been applied in many projects. The Multi-terminal Direct Current based on Multilevel converter MMC-MTDC based on modularized multilevel converter not only has the technical advantages of high voltage and large capacity of MMC, but also has the advantages of flexible operation and good stability of HVDC system. It can realize the characteristics of multi-power supply and multi-point power supply. Therefore, the MTDC system based on MMC has become one of the hot research topics. The research focuses on coordinated control strategy, fault protection, distributed generation grid connection, power flow optimization and additional control. In this paper, the control strategy of multi-terminal HVDC transmission system is studied. The main research contents are as follows: (1) for MMC-MTDC system, the requirements of the upper control system, station level and valve level control system are analyzed. The control system of each level is designed according to the requirement, so that the control system can realize the corresponding control function. At the same time, a remote and local monitoring system is designed to monitor the operation state of the whole system. (2) the control strategies of valve level, station level and coordinated control between converter stations of MMC-MTDC transmission system are studied. The control strategies suitable for valve level, station level and converter station are compared and analyzed. According to the operation mode of each converter station, appropriate control strategies are selected to ensure the stable operation of the system. Simulation and experiments are used to verify the correctness and effectiveness of the control strategy. (3) considering the use of multi-terminal HVDC system to supply power to isolated islands, if the load is asymmetric, the fluctuating power will appear in the system. The fluctuating power will cause the power quality problems of AC side current and DC voltage in the main converter station. In this paper, the operating characteristics under the condition of load asymmetry are analyzed, and by controlling the circulation, the double frequency fluctuation power caused by the load asymmetry is realized by the sub-module. Therefore, the deterioration of DC voltage and AC current quality caused by load asymmetry is avoided. (4) considering the load asymmetry, the traditional constant AC voltage control strategy can not realize the balance control of AC voltage. Therefore, this paper analyzes the amplitude-frequency characteristic of Pi regulator and R regulator, and improves the traditional constant AC voltage control strategy. The parallel structure of Pi regulator and R regulator is adopted to ensure the load asymmetry. The converter station can output symmetrical AC voltage, thus improving the quality of power supply.
【學位授予單位】：北京交通大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TM721.1

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