NPC三电平逆变器共模电压抑制的调制策略

发布时间：2019-01-10 18:26

【摘要】：在现代化工业、电力系统、城市轨道交通系统等高压大功率场合中,与传统的两电平逆变器控制系统相比,NPC型三电平逆变器以具有开关频率低、输出电压波形质量高、开关管承受电压小等优点,成为一种应用最为广泛的多电平变换器之一。然而NPC型三电平逆变器在中矢量和小矢量的作用下,容易引起直流侧两电容充放电的不平衡,从而导致中点电压的不平衡,会给整个逆变器控制系统带来很多不利影响。同时,逆变器工作时输出端产生的共模电压会给电机及其周围的用电设备造成很大的危害。因此,对NPC型三电平逆变器进行深入的研究是非常有意义的。针对NPC型三电平逆变器中存在的中点电位不平衡和共模电压问题,本文提出了一种改进型虚拟空间矢量调制策略。该策略在传统虚拟空间矢量调制策略的基础上,重新选取基本矢量(大矢量、中矢量和零矢量OOO)来合成新的虚拟矢量,每一个新合成的虚拟矢量产生的中点电流为零,进而实现对中点电压平衡的控制,此外,还使新合成的虚拟矢量产生的共模电压的最大值为Udc/6,比传统虚拟空间矢量法产生的共模电压值(Udc/3)减小一半,从而达到对共模电压的有效抑制。在新合成的虚拟中矢量中引入分配系数k2,并选用虚拟中矢量的分配系数k2为控制量,当中点电压出现较大的波动时,通过调整分配系数k2的取值,来控制中点电流,使中点电流向减小中点电压波动的方向流动,进而实现对中点电位波动的抑制,此外,还能够使逆变输出端产生的共模电压不增加。本文对传统虚拟空间矢量调制策略和本文所提策略进行了介绍,分析其控制中点电压的原理,在Matlab/Simulink上搭建仿真模型,验证两种方法对共模电压抑制和中点电压平衡控制的效果,并进行对比分析,进而提出了利用虚拟中矢量的分配系数k2,对中点电压波动进行抑制。最后,在NPC型三电平逆变器实验系统上对传统虚拟空间矢量调制策略及本文提出的调制策略进行了实验验证,结果证明了本文所提出的调制策略能够有效地抑制共模电压和中点电压的波动。
[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.
【学位授予单位】：天津工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM464

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