弱电网条件下并网逆变器锁相技术研究

发布时间：2018-03-25 16:00

本文选题：锁相技术　切入点：弱电网　出处：《中国矿业大学》2017年硕士论文

【摘要】：随着新能源分布式发电的发展,逆变器被广泛应用到并网系统中。锁相环作为逆变器的一部分为其并网电流提供了相位参考,因此锁相环的准确输出与稳定运行关乎到逆变器的工作状态。尤其在弱电网条件下,其电网阻抗较高,如果不能准确锁定电网相位,逆变器向弱电网注入的电流会失真,甚至影响系统的稳定性。本文在弱电网条件下,研究了并网逆变器锁相过程中存在的问题,并针对弱电网条件设计了相应的锁相策略。本文首先选取了三种结构不同且具有代表性的锁相技术,按照每种锁相结构的特征依次在电网理想情况与非理想情况下对其进行了锁相特性分析。其次,分析了弱电网的高阻抗条件,利用同步参考坐标锁相环推导出锁相环线性化前后的数学模型,并在该模型基础上研究了弱电网条件下锁相过程中出现的自同步现象,从理论上分析了并网逆变器锁相过程中可能出现的问题,同时将其他两种锁相技术置于弱电网条件下研究这一问题的普遍性。搭建锁相环仿真平台,将三种锁相结构分别应用到并网逆变器中,验证弱电网条件下逆变器的锁相问题。针对弱电网的高阻抗特点以及由此引发的锁相问题设计了锁相环阻抗抵消策略,根据需要研究了常见的电网阻抗估计方法,并分析了基于双二阶广义积分的电压正序分量提取结构,将其运用到锁相策略中。最后搭建了弱电网条件下的并网逆变器仿真平台,利用弱电网锁相策略进行了仿真验证。通过锁相环基本性能仿真,以及在弱电网条件下使用锁相环阻抗抵消策略前后的对比仿真,验证了锁相策略的可行性。
[Abstract]:With the development of new energy distributed generation, inverter is widely used in grid-connected system. As a part of inverter, PLL provides phase reference for grid-connected current. Therefore, the accurate output and stable operation of the PLL are related to the working state of the inverter, especially under the condition of weak grid, the impedance of the grid is high, if the phase of the grid can not be locked accurately, the current injected by the inverter into the weak grid will be distorted. Even affects the stability of the system. In this paper, under the condition of weak electric grid, the problems existing in the phase locking process of grid-connected inverter are studied. In this paper, three kinds of phase-locking techniques with different structure and representative structure are selected. According to the characteristics of each kind of phase-locked structure, the phase locking characteristics are analyzed under the ideal and non-ideal conditions of the power network in turn. Secondly, the high impedance conditions of the weak current network are analyzed. The mathematical model before and after the linearization of PLL is derived by using synchronous reference coordinate PLL. Based on the model, the phenomenon of self-synchronization in the process of PLL under the condition of weak electric network is studied. In this paper, the possible problems in the phase locking process of grid-connected inverter are analyzed theoretically. At the same time, the other two kinds of phase-locking techniques are put into the condition of weak electric network to study the universality of this problem. A phase-locked loop simulation platform is built. Three kinds of phase-locked structures are applied to grid-connected inverters to verify the phase-locked problem of the inverter under the condition of weak grid. A phase-locked loop impedance cancellation strategy is designed for the characteristics of high impedance of weak grid and the resulting phase-locking problem. According to the need, the common methods of impedance estimation are studied, and the structure of voltage positive sequence extraction based on double second order generalized integral is analyzed, which is applied to the phase-locked strategy. Finally, a grid-connected inverter simulation platform is built under the condition of weak grid. Through the simulation of the basic performance of PLL and the contrast simulation before and after using PLL impedance cancellation strategy under the condition of weak electric network, the feasibility of PLL is verified.
【学位授予单位】：中国矿业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM464

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