【摘要】：近年來,隨著電力電子技術在風力發(fā)電、輕型高壓直流輸電等領域的應用,高壓大功率電力電子設備得到國內外學者的廣泛關注。模塊化多電平變流器(modular multilevel converters, MMC)因其結構模塊化,采用子模塊級聯的形式,具有良好的擴展性、運行損耗低、輸出波形質量好、良好的冗余容錯性、可靠性好等諸多優(yōu)點,被認為是未來最具備應用價值的高壓大功率電力電子變換拓撲之一。本文研究了模塊化多電平變流器的拓撲結構和基本工作原理,建立了MMC的數學模型,對MMC環(huán)流和電容電壓波動進行了分析,闡述了目前常用的調制策略和工作特性,重點研究了最近電平逼近調制技術(nearest level modulation,NLM),NLM調制實現簡便,控制系統(tǒng)計算量小,適合MMC電平數較多的場合,當MMC電平數較少時,最近電平逼近調制方式輸出電流的波形質量差、諧波含量高且不能精確跟蹤參考電流。針對最近電平逼近調制方式在中低壓領域MMC中的應用,本文提出了一種改進的最近電平逼近調制策略,即采用電流滯環(huán)控制器對最近電平逼近調制結果進行修正,即在雙閉環(huán)控制結構的基礎上加入環(huán)流控制器、穩(wěn)壓控制器、均壓控制器等附加控制器,附加控制器在主控制器計算出的上、下橋臂電壓參考值的基礎上加入一定的修正量。該調制策略易于實現,動態(tài)性能好,控制器計算量小,能夠對參考電流進行良好的跟蹤,降低了電流諧波含量,顯著改善MMC輸出電流波形。本文針對模塊化多電平變流器子模塊電容電壓波動影響子模塊參數選擇及降低交流電壓輸出質量的問題,分析了子模塊電容電壓波動、環(huán)流及傳輸功率等物理量之間的關系；引入準比例諧振控制器和陷波器,通過對MMC內部環(huán)流控制來抑制MMC子模塊電容電壓波動,不需要進行傳統(tǒng)的坐標變換,有效的減少了計算量,有利于控制器的簡化設計,在保證MMC子模塊參數設計不變的情況下,能夠有效抑制MMC子模塊電容電壓波動,改善MMC輸出的交流電壓波形。本文在MMC應用于電力牽引系統(tǒng)、高壓變頻調速系統(tǒng)及其他中高壓大功率等方面做出了有益的嘗試。
[Abstract]:In recent years, with the application of power electronics technology in wind power generation, light HVDC transmission and other fields, high-voltage and high-power electronic equipment has been widely concerned by scholars at home and abroad. Modular multilevel converter (modular multilevel converters, MMC) has many advantages, such as modularization, adopting sub-module cascade, good expansibility, low running loss, good quality of output waveform, good redundancy and fault tolerance, good reliability, and many other advantages, such as good expansibility, low running loss, good output waveform quality, good redundancy and fault tolerance, good reliability and so on. It is considered to be one of the most valuable high-voltage and high-power electronic transformation topologies in the future. In this paper, the topological structure and basic working principle of modular multilevel converter are studied, the mathematical model of MMC is established, the MMC circulation and capacitance voltage fluctuation are analyzed, and the common modulation strategies and working characteristics are described. This paper focuses on the study of the nearest level approximation modulation technology (nearest level modulation,NLM), NLM modulation is easy to realize, the control system calculation is small, suitable for more MMC level, when the MMC level number is less, the control system is suitable for the situation of more level, when the number of MMC level is less. The output current of the nearest level approximation modulation mode has poor waveform quality, high harmonic content and can not accurately track the reference current. In view of the application of the nearest level approximation modulation method in the medium and low voltage domain MMC, an improved nearest level approximation modulation strategy is proposed in this paper, in which the current hysteresis controller is used to modify the nearest level approximation modulation result. On the basis of double closed loop control structure, an additional controller, such as loop controller, voltage regulator, equalizing controller and so on, is added. The additional controller adds a certain amount of correction on the basis of the reference value of the voltage of the lower arm and the upper part of the controller calculated by the main controller. This modulation strategy has the advantages of easy realization, good dynamic performance and low computational complexity. It can track the reference current well, reduce the harmonic content of the current, and improve the output current waveform of the MMC significantly. In this paper, the relationship among capacitance voltage fluctuation, current circulation and transmission power of modular multilevel converter sub-module is analyzed, which affects the parameter selection of sub-module and reduces the output quality of AC voltage, and analyzes the relationship among capacitance voltage fluctuation, circulating current and transmission power of sub-module. The quasi-proportional resonant controller and notch filter are introduced to restrain the capacitance voltage fluctuation of MMC sub-module by controlling the internal circulation of MMC. The traditional coordinate transformation is not necessary, and the calculation is reduced effectively, which is beneficial to the simplified design of the controller. The capacitance voltage fluctuation of the MMC sub-module can be effectively suppressed and the AC voltage waveform of the MMC output can be improved under the condition that the parameters of the MMC sub-module are not changed. This paper makes a beneficial attempt in the application of MMC in electric traction system, high voltage variable frequency speed regulation system and other medium and high voltage and high power systems.
【學位授予單位】：湖南大學
【學位級別】：碩士
【學位授予年份】：2016
【分類號】：TM46

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本文編號：2444358