三相四线制三电平中点钳位型变换器控制研究

发布时间：2018-06-19 03:42

本文选题：三相四线制 + 三电平中点钳位　；参考：《北京交通大学》2017年硕士论文

【摘要】：三相四线制结构广泛应用于工厂供电以及城市供电系统中。三电平中点钳位型(Neutral-Point-Clamped,NPC)结构具备结构简单,开关应力小,开关损耗少,电磁干扰低等优势,近年来成为多电平三相四线系统的重要拓扑形式。然而由于这种结构的固有缺点,需要解决直流侧母线电容中点电压不平衡问题。本文围绕中点电压平衡控制展开研究。首先分析了三相四线制三电平NPC变换器的中点平衡控制的两种方法:α-β-0坐标系下的最优三维空间矢量调制策略和正交a-b-c坐标系下的最优三维空间矢量调制策略。介绍了两种策略的基本控制原理,并分别分析了两种方法存在的问题。针对正交a-b-c坐标系下的控制策略不能实现对中点电压偏移差值的定量补偿这一局限,从载波PWM调制出发,提出一种基于零电平分解的中点电压平衡控制新思路。该控制策略可以根据检测到的中点电压偏移值,基于中点控制裕量NPCM的概念,选择合适的相,通过将其一部分零电平作用时间等分给正负电平,在不改变输出电压的情况下,实现对偏移值的定量补偿,从而完成对三相四线制三电平NPC变换器的中点电压平衡控制。该控制方法对于不同工况下的中点电压偏移都有一定程度的抑制效果,虽然不能完全消除中点电压的波动,但是在尽可能不增加开关频率的前提下大大改善了中点电压的稳定性。将零电平分解的思想推广至三相三线制三电平NPC变换器结构中,提出了一种基于零电平分解的中点电压平衡控制策略。该方法根据各相分解零电平后对中点电流的影响范围,选择合适的相进行零电平分解,补偿中点电压偏差。在注入零序电压的情况下,提出了一种特定相零电平分解的中点平衡控制策略,该策略分析了注入零序电压后三相调制电压的零电平规律,直接选择调制电压的中间值对应相进行零电平分解补偿,从而实现中点电压平衡控制目标。对所提控制策略进行了仿真,并搭建三电平NPC变换器实验平台进行实验验证,仿真和实验结果验证了所提方法的正确性和有效性。
[Abstract]:Three-phase four-wire system is widely used in power supply and urban power supply system. The three-level Neutral-Point-Clampedn NPC (NPC) structure has the advantages of simple structure, low switching stress, low switching loss and low electromagnetic interference. It has become an important topological form of multilevel three-phase four-wire system in recent years. However, due to the inherent shortcomings of this structure, it is necessary to solve the problem of unbalanced midpoint voltage of DC side busbar capacitor. This paper focuses on the midpoint voltage balance control. Firstly, two methods of neutral-point balance control for three-phase four-wire three-level NPC converter are analyzed: the optimal three-dimension space vector modulation strategy in 伪-尾 -0 coordinate system and the optimal three-dimensional space vector modulation strategy in orthogonal a-b-c coordinate system. The basic control principle of the two strategies is introduced, and the problems of the two methods are analyzed. Aiming at the limitation that the control strategy in orthogonal a-b-c coordinate system can not compensate the offset of neutral voltage quantitatively, a new idea of neutral point voltage balance control based on zero level decomposition is proposed from carrier PWM modulation. According to the detected neutral voltage offset and the concept of neutral control margin NPCM, the control strategy can select the appropriate phase and divide part of the zero level operation time into positive and negative levels without changing the output voltage. The offset value can be compensated quantitatively so that the neutral point voltage balance control of three-phase four-wire three-level NPC converter is completed. This control method can restrain the midpoint voltage deviation to a certain extent under different operating conditions, although it can not completely eliminate the midpoint voltage fluctuation. However, the stability of the midpoint voltage is greatly improved without increasing the switching frequency as much as possible. The idea of zero-level decomposition is extended to three-phase three-wire three-level NPC converter. A neutral point voltage balance control strategy based on zero-level decomposition is proposed. According to the influence range of the zero level of each phase on the neutral point current, the suitable phase is selected to decompose the zero level to compensate the bias of the neutral point voltage. Under the condition of injecting zero-sequence voltage, a neutral-point balance control strategy with specific phase zero-level decomposition is proposed, which analyzes the zero-level rule of three-phase modulation voltage after injecting zero-sequence voltage. The intermediate phase of modulation voltage is directly selected for zero-level decomposition compensation to achieve the neutral-point voltage balance control goal. The proposed control strategy is simulated, and the experimental platform of three-level NPC converter is built for experimental verification. The simulation and experimental results verify the correctness and effectiveness of the proposed method.
【学位授予单位】：北京交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM46

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