T型三电平逆变器的共模电流抑制及中点电位平衡

发布时间：2018-05-02 22:06

本文选题：T型三电平逆变器 + PWM调制策略　；参考：《华北电力大学》2017年硕士论文

【摘要】：从1954年第一块实用光伏电池面世以来,我国在1958年也开始着实研制太阳能电池,近几年来的国家政策及财政扶持也加快了光伏产业的产业化和规模化发展。但是光伏系统初期的大投资和高成本是阻碍发展的关键因素,因此探索低成本、高效率、高可靠性的光伏并网系统尤为重要。光伏并网逆变器作为光伏并网系统中的重要组成部分,在无隔离变压器的情况下,对地寄生电容及电网阻抗组成的谐振回路所产生的共模电流不容忽视,也是亟待改善的一个重要方面。本文通过对T型三电平并网逆变器的结构及数学模型进行分析,由得到的共模电压表达式及不同电压空间矢量下的共模电压幅值的不同,在传统共模电压抑制的PWM原理之上,提出了一种改进型共模电压减小的PWM原理,并且提出了一种改进型模型预测算法,通过理论分析及仿真运行,验证了所提出的改进算法的有效性。本文的主要工作和成果如下:通过分析共模电压消除的PWM及共模电压减小的PWM的原理,并对两种算法的中点点位波动进行分析,对于其存在的问题提出了一种改进型共模电压减小的PWM原理,通过对三相的开关状态持续时间进行数学规划,能够减小共模电压,且通过确保任意载波周期中点电流的平均值为零来实现减小中点电位波动幅值的目的。提出了一种改进模型预测控制算法,给出了改进T型三电平并网逆变器模型预测的控制可行域查询表,采用分层优化的思想减小运算量以及加权系数设计的困难,提高算法的可靠性。通过仿真验证可以得知本文所提出的改进型共模电压减小原理在大功率、高功率密度的光伏并网场合的优势,并且也为其他类型逆变器的并网控制策略提出了一种新的思路。
[Abstract]:Since the advent of the first practical photovoltaic cell in 1954, China began to develop solar cells in 1958. The national policies and financial support in recent years have also accelerated the industrialization and large-scale development of photovoltaic industry. However, the large investment and high cost of photovoltaic system are the key factors to hinder the development of photovoltaic system, so it is very important to explore low-cost, high-efficiency and high-reliability photovoltaic grid-connected system. Photovoltaic grid-connected inverter is an important part of photovoltaic grid-connected system. In the absence of isolation transformer, the common mode current generated by resonant circuit composed of parasitic capacitance and grid impedance can not be ignored. It is also an important aspect that needs to be improved. By analyzing the structure and mathematical model of T-type three-level grid-connected inverter, the common mode voltage expression and the amplitude of common-mode voltage under different voltage space vectors are obtained, based on the PWM principle of conventional common-mode voltage suppression. An improved PWM principle of common mode voltage reduction is proposed, and an improved model prediction algorithm is proposed. The effectiveness of the improved algorithm is verified by theoretical analysis and simulation. The main work and achievements of this paper are as follows: by analyzing the principle of PWM eliminated by common-mode voltage and PWM with reduced common-mode voltage, the midpoint fluctuation of the two algorithms is analyzed. An improved PWM principle of decreasing common-mode voltage is put forward for its existing problems. The common mode voltage can be reduced by mathematical programming of the switching state duration of three-phase. The aim of reducing the amplitude of midpoint potential fluctuation is to ensure that the mean value of midpoint current is zero in any carrier cycle. In this paper, an improved model predictive control algorithm is proposed, and the control feasible region query table for model prediction of improved T type three-level grid-connected inverter is given. The idea of hierarchical optimization is used to reduce the computational complexity and the difficulty of the weight coefficient design. Improve the reliability of the algorithm. Simulation results show the advantages of the improved common-mode voltage reduction principle in high power and high power density photovoltaic grid-connected situations, and a new idea for grid-connected control strategy of other types of inverters is also proposed.
【学位授予单位】：华北电力大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM464

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