【摘要】：在現(xiàn)代化工業(yè)、電力系統(tǒng)、城市軌道交通系統(tǒng)等高壓大功率場合中,與傳統(tǒng)的兩電平逆變器控制系統(tǒng)相比,NPC型三電平逆變器以具有開關(guān)頻率低、輸出電壓波形質(zhì)量高、開關(guān)管承受電壓小等優(yōu)點,成為一種應用最為廣泛的多電平變換器之一。然而NPC型三電平逆變器在中矢量和小矢量的作用下,容易引起直流側(cè)兩電容充放電的不平衡,從而導致中點電壓的不平衡,會給整個逆變器控制系統(tǒng)帶來很多不利影響。同時,逆變器工作時輸出端產(chǎn)生的共模電壓會給電機及其周圍的用電設(shè)備造成很大的危害。因此,對NPC型三電平逆變器進行深入的研究是非常有意義的。針對NPC型三電平逆變器中存在的中點電位不平衡和共模電壓問題,本文提出了一種改進型虛擬空間矢量調(diào)制策略。該策略在傳統(tǒng)虛擬空間矢量調(diào)制策略的基礎(chǔ)上,重新選取基本矢量(大矢量、中矢量和零矢量OOO)來合成新的虛擬矢量,每一個新合成的虛擬矢量產(chǎn)生的中點電流為零,進而實現(xiàn)對中點電壓平衡的控制,此外,還使新合成的虛擬矢量產(chǎn)生的共模電壓的最大值為Udc/6,比傳統(tǒng)虛擬空間矢量法產(chǎn)生的共模電壓值(Udc/3)減小一半,從而達到對共模電壓的有效抑制。在新合成的虛擬中矢量中引入分配系數(shù)k2,并選用虛擬中矢量的分配系數(shù)k2為控制量,當中點電壓出現(xiàn)較大的波動時,通過調(diào)整分配系數(shù)k2的取值,來控制中點電流,使中點電流向減小中點電壓波動的方向流動,進而實現(xiàn)對中點電位波動的抑制,此外,還能夠使逆變輸出端產(chǎn)生的共模電壓不增加。本文對傳統(tǒng)虛擬空間矢量調(diào)制策略和本文所提策略進行了介紹,分析其控制中點電壓的原理,在Matlab/Simulink上搭建仿真模型,驗證兩種方法對共模電壓抑制和中點電壓平衡控制的效果,并進行對比分析,進而提出了利用虛擬中矢量的分配系數(shù)k2,對中點電壓波動進行抑制。最后,在NPC型三電平逆變器實驗系統(tǒng)上對傳統(tǒng)虛擬空間矢量調(diào)制策略及本文提出的調(diào)制策略進行了實驗驗證,結(jié)果證明了本文所提出的調(diào)制策略能夠有效地抑制共模電壓和中點電壓的波動。
[Abstract]:In modern industry, power system, urban rail transit system and other high-voltage and high-power situations, compared with the traditional two-level inverter control system, NPC three-level inverter with low switching frequency, high quality output voltage waveform, Because of its small voltage, switching transistor has become one of the most widely used multilevel converters. However, under the action of neutral vector and small vector, NPC three-level inverter is easy to cause the imbalance of charge and discharge of DC side two capacitors, which leads to the imbalance of neutral point voltage, which will bring a lot of adverse effects to the whole inverter control system. At the same time, the common-mode voltage generated by the output of the inverter will cause great harm to the motor and its surrounding electrical equipment. Therefore, it is very meaningful to study the NPC type three-level inverter in depth. Aiming at the imbalance of neutral point potential and common-mode voltage in NPC three-level inverter, an improved virtual space vector modulation strategy is proposed in this paper. Based on the traditional virtual space vector modulation strategy, the basic vectors (large vector, middle vector and zero vector OOO) are re-selected to synthesize the new virtual vector. The midpoint current generated by each new synthesized virtual vector is zero. In addition, the maximum value of common-mode voltage generated by the new virtual vector is reduced by half compared with the common mode voltage (Udc/3) generated by the traditional virtual space vector method, and the maximum value of the common-mode voltage generated by the new virtual vector is reduced by half compared with the traditional virtual space vector method. Thus, the common mode voltage can be effectively suppressed. The distribution coefficient K2 is introduced into the newly synthesized virtual vector, and the distribution coefficient K2 of the virtual vector is selected as the control quantity. When the voltage of the middle point fluctuates greatly, the midpoint current is controlled by adjusting the value of the distribution coefficient K2. The midpoint current flows towards the direction of decreasing the midpoint voltage fluctuation, which can suppress the midpoint potential fluctuation. In addition, the common-mode voltage generated by the inverter output can not be increased. In this paper, the traditional virtual space vector modulation strategy and the strategy proposed in this paper are introduced, the principle of controlling the midpoint voltage is analyzed, and the simulation model is built on Matlab/Simulink. The effect of the two methods on the common mode voltage suppression and midpoint voltage balance control is verified, and the comparison and analysis are carried out, and then a method is proposed to suppress the midpoint voltage fluctuation by using the distribution coefficient K2 of the virtual vector. Finally, the traditional virtual space vector modulation strategy and the modulation strategy proposed in this paper are verified on the NPC three-level inverter experimental system. The results show that the proposed modulation strategy can effectively suppress the fluctuation of common-mode voltage and midpoint voltage.
【學位授予單位】：天津工業(yè)大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TM464

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