本文選題：多電平　切入點：逆變器　出處：《蘭州理工大學》2014年碩士論文

【摘要】：多電平逆變器以其高性能和大容量方面的突出優(yōu)勢已成為人們研究與應用的熱點之一。在多電平逆變器的多種控制策略中,空間矢量脈寬調制(SVPWM)算法具有調制比大、能夠優(yōu)化輸出電壓波形等優(yōu)點,通過對SVPWM算法改進可以改善控制性能。三電平NPC逆變器以其結構簡單、成本較低等優(yōu)點得到了廣泛的研究和應用,但電容電壓平衡是影響其安全運行和輸出性能的關鍵問題之一,對該問題的研究具有重要的理論和工程價值。 論文以三電平NPC逆變器為例對不同坐標系下多電平SVPWM調制方法進行了研究。為解決計算復雜的問題,根據(jù)基本矢量在α'β'兩相坐標平面的坐標都是整數(shù)的規(guī)律,研究得到一種在α'β\侈坐標系下多電平SVPWM的通解,實現(xiàn)多電平SVPWM算法的統(tǒng)一簡化。利用得到的多電平SVPWM通解,提出了一種電路中各個開關器件的開關次數(shù)最少的調制方案,即每次只有一相輸出電壓改變,且只改變一個電平單位的切換。 為了尋求合適的切換路徑以降低開關次數(shù),在α'β'平面上,提出了特征網(wǎng)絡和特征四邊形的概念,利用扇區(qū)序列S的每個頂點去逼近參考電壓矢量ur。。研究表明參考電壓軌跡的半徑所在的范圍不同,特征網(wǎng)絡具有兩種不同的形狀。在這兩種特征網(wǎng)絡中,以特征四邊形為基礎分析了總開關切換次數(shù)最小的切換路徑,提出了優(yōu)化開關頻率的SVPWM算法。仿真結果表明,該算法在一個參考電壓周期內的總開關切換次數(shù)與相同參數(shù)下同相層疊正弦調制算法相比降低了25%。 針對NPC型逆變器存在的電容電壓波動問題,提出一種小矢量在線自調節(jié)的方法,此方法可以實現(xiàn)NPC電容電壓在各個工況點的有效控制。論文從矢量和中點電流的影響角度深入分析了中點電位平衡控制的規(guī)律,通過設計平衡系數(shù),動態(tài)調節(jié)不同小矢量的作用時間,以此實現(xiàn)對電容電壓的控制。仿真實驗及結果驗證了分析結論和控制方法的正確性。 最后,設計了三電平NPC逆變器及實驗方案,進行了硬件和軟件設計,并進行仿真研究。
[Abstract]:Multilevel inverter has become one of the hotspots in research and application because of its outstanding advantages in high performance and large capacity. In many control strategies of multilevel inverter, space vector pulse width modulation (SVPWM) algorithm has a large modulation ratio. The output voltage waveform can be optimized and the control performance can be improved by improving the SVPWM algorithm. The three-level NPC inverter has been widely studied and applied because of its simple structure and low cost. However, capacitor voltage balance is one of the key problems affecting its safe operation and output performance. The study of this problem has important theoretical and engineering value. In this paper, a three-level NPC inverter is taken as an example to study the multilevel SVPWM modulation method in different coordinate systems. In order to solve the complex problem of calculation, according to the law that the coordinates of the basic vectors in the 偽'尾 'two-phase coordinate plane are integer. In this paper, a general solution of multilevel SVPWM in 偽'尾\ luxury coordinate system is obtained, and the unified simplification of multilevel SVPWM algorithm is realized. Using the obtained general solution of multilevel SVPWM, a modulation scheme with minimum switching times for each switch device in the circuit is proposed. That is, only one phase output voltage changes, and only one level unit switching. In order to find a suitable switching path to reduce the number of switches, the concepts of characteristic network and characteristic quadrilateral are proposed on the 偽'尾 'plane. Using each vertex of sector sequence S to approach the reference voltage vector ur.The study shows that the radius of the reference voltage locus is different, and the characteristic network has two different shapes. Based on the characteristic quadrilateral, the switching path with minimum switching times is analyzed, and the SVPWM algorithm is proposed to optimize the switching frequency. The simulation results show that, Compared with the in-phase stacked sinusoidal modulation algorithm with the same parameters, the total switching times of the algorithm in a reference voltage cycle are reduced by 25%. Aiming at the problem of capacitor voltage fluctuation in NPC inverter, a method of on-line self-adjusting with small vector is proposed. This method can realize the effective control of NPC capacitor voltage at each working point. The law of midpoint potential balance control is deeply analyzed from the angle of vector and midpoint current, and the balance coefficient is designed. The effect time of different small vectors is dynamically adjusted to realize the control of capacitor voltage. The simulation experiment and result verify the correctness of the analysis conclusion and the control method. Finally, the three-level NPC inverter and its experimental scheme are designed, and the hardware and software are designed and simulated.
【學位授予單位】：蘭州理工大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：TM464

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