【摘要】：模塊化多電平換流器柔性直流(Modular Multilevel Converter-High Voltage Direct Current,MMC-HVDC)輸電系統(tǒng)具有模塊化程度高、輸出波形質量好、獨立調節(jié)有功功率和無功功率等優(yōu)點,因其能夠適應高電壓、大功率傳輸要求,具有很好的應用前景,已有諸多實際工程投運。本文以MMC-HVDC系統(tǒng)為研究對象,針對系統(tǒng)正常運行和橋臂不對稱運行存在環(huán)流、子模塊電容電壓不平衡等問題進行研究。研究了MMC-HVDC系統(tǒng)模型預測控制,將比例-積分控制器與模型預測控制相結合,依據(jù)交流電流跟蹤目標函數(shù)、子模塊電容電壓均衡目標函數(shù)以及相應的權重系數(shù)建立綜合目標函數(shù),根據(jù)環(huán)流抑制補償電平調節(jié)開關狀態(tài),在保持子模塊電容電壓均衡的同時,實現(xiàn)了對環(huán)流的有效抑制。分析了MMC-HVDC系統(tǒng)上下橋臂阻抗不對稱運行時橋臂電流成分,指出橋臂阻抗不對稱所在橋臂不均分交流側電流,會造成環(huán)流成分不僅含有二倍頻分量,還存在基頻分量,引起直流側電流波動。提出了一種橋臂阻抗不對稱時模型預測控制策略,該策略結合預測時刻子模塊電容電壓排序,根據(jù)綜合目標函數(shù)和環(huán)流抑制目標函數(shù),選擇最優(yōu)開關狀態(tài),實現(xiàn)了橋臂阻抗不對稱運行時環(huán)流的抑制,減小了直流側電流波動。對于存在冗余子模塊的MMC-HVDC系統(tǒng),建立了模塊化多電平換流器冗余容錯數(shù)學模型,提出了一種冗余容錯模型預測控制策略,根據(jù)正常運行子模塊數(shù)量設定子模塊電容電壓均衡目標函數(shù),依據(jù)環(huán)流抑制目標函數(shù)調整橋臂最優(yōu)子模塊開通狀態(tài),在實現(xiàn)交流電流跟蹤、子模塊電容電壓均衡的同時,可以實現(xiàn)子模塊數(shù)目不對稱時對環(huán)流基頻成分和二倍頻成分的抑制�；贛ATLAB/SIMULINK搭建MMC-HVDC系統(tǒng)仿真模型,分別對系統(tǒng)正常運行、上下橋臂阻抗不對稱運行、上下橋臂子模塊數(shù)目不對稱運行三種情況進行仿真分析,仿真結果驗證了所提控制策略的可行性和有效性。
[Abstract]:Modularized multilevel converter flexible direct current (Modular Multilevel Converter-High Voltage Direct Current,MMC-HVDC) transmission system has the advantages of high modularization, good quality of output waveform, independent regulation of active and reactive power, etc., because it can meet the requirements of high voltage and high power transmission. It has a good prospect of application, and many practical projects have been put into operation. In this paper, MMC-HVDC system is taken as the research object. The problems of circulating current and capacitor voltage unbalance in the normal operation and asymmetric operation of the bridge arm are studied in this paper. The model predictive control of MMC-HVDC system is studied. The integrated objective function is established according to the objective function of AC current tracking, the objective function of capacitance voltage equalization of submodule and the corresponding weight coefficient, by combining the proportional and integral controller with the model predictive control. According to the switching state of the current suppression compensation level, the effective suppression of the circulation is realized while maintaining the capacitor voltage equalization of the submodule. In this paper, the current components of the upper and lower arm of the MMC-HVDC system are analyzed when the impedance of the upper and lower leg is asymmetrical. It is pointed out that the current of the bridge arm in which the impedance of the bridge arm is asymmetrical is not only divided equally into the AC side current, but also the basic frequency component is found in the circulation component. Cause DC side current fluctuation. In this paper, a predictive control strategy for bridge arm impedance asymmetry is proposed. The optimal switching state is selected according to the integrated objective function and the circulation suppression objective function, combined with the capacitor voltage order of the predictive time submodule. The current fluctuation of DC side is reduced by suppressing the circulation when the bridge arm impedance is asymmetrical. For the MMC-HVDC system with redundant sub-modules, a mathematical model of modularized multilevel converter redundancy fault tolerance is established, and a redundant fault-tolerant model predictive control strategy is proposed. According to the number of submodules in normal operation, the objective function of capacitor voltage equalization of sub-modules is set, and the opening state of the optimal submodule of the bridge arm is adjusted according to the objective function of circulation suppression. The AC current tracking and capacitor voltage equalization of sub-modules are realized at the same time. The fundamental and double frequency components of the circulation can be suppressed when the number of submodules is asymmetric. The simulation model of MMC-HVDC system based on MATLAB/SIMULINK is built. The simulation analysis is carried out for the normal operation of the system, the asymmetric operation of the upper and lower arm impedance, and the asymmetric operation of the upper and lower arm submodules. Simulation results verify the feasibility and effectiveness of the proposed control strategy.
【學位授予單位】：華北電力大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TM721.1

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