三相电压源型并网变换器的非线性行为研究

发布时间：2018-02-13 23:48

本文关键词： 非线性现象稳定性变换器电网阻抗　出处：《华中科技大学》2014年博士论文　论文类型：学位论文

【摘要】：三相高频整流器被广泛应用于分布式电力系统及各种工业设备中,并且得到了广泛的研究,而其非线性行为研究颇为少见。本文主要对这种变换器的非线性行为进行了定义和分析。随着微网及分布式发电的迅猛发展,电网不在应该被认为是理想电压源,而被认为是一种含有内部阻抗的非理想电压源。因此,连接在这样的弱电网上的三相高频整流器则不能被认为是一个独立的系统,而是一个能够和非理想电网相互影响的子系统。关于此系统,本文将展示一些特别的非线性现象,并且通过分岔分析来定义有关非线性现象。而后,本文将通过基于设计的分析,得出系统各关键参数的稳定边界以及区分不同运行状态的区域,给设计者提供设计思路。首先,当本地电阻性负载与三相整流器同时连接在非理想电网的相同节点时,变换器的一种不可逆分岔现象将发生。而此系统模型是作为实际应用中非常现实的一种模型。由于在此模型中,非理想电网提供给变换器的有功功率被限制住了,当变换器不能得到它所需要的有功功率时,变换器的输出直流电压将会下跌。此时,变换器吸收的无功功率会瞬时增大,并且几乎工作在零功率因数模式下。变换器的这种工作模式可以称之为“不正常运行”。本章将应用大信号模型分析了此物理现象的基本原理,并且通过基于设计的分析方法把此系统的关键参数的稳定边界划定出来。同时,本章也通过实验验证了此现象的存在。其次,在三相高频整流器连接在非理想电网时发生的Hopf分岔现象,本章将会重点描述。当三相变换器所连接的非理想电网自身的内部阻抗足够大时候,变换器的直流输出电压将会出现明显的低频振荡,或者被称之为Hopf分岔。本章应用三相变换器的平均模型和时域分析方法来预测Hopf分岔现象的发生。同时,一些参数的稳定区间及其边界也得到了分析。最后,本章也通过实验验证了此现象的发生。最后,本文将介绍两个或多个并网变换器同时连接在同一非理想电网的节点时发生的Hopf分岔现象。当单个变换器连接在非理想电网上能够稳定运行时,连接在同一非理想电网的相同节点的两个变换器则会相互影响而可能导致不稳定运行。由于其相互影响,两个或多个变换器输出电压会出现低频振荡或者Hopf分岔现象。本章将利用变换器的阻抗模型和广义奈圭斯特判据来判别此种不稳定现象。而后,通过基于设计的分析,寻找到系统关键参数并得到系统的稳定区域划分以及参数变化对稳定裕度的影响。并且,本章的研究充分说明了并网变换器的稳定性问题不再是一个独立系统的稳定性问题,而是要根据所连接的系统环境来判断的系统级稳定性问题。
[Abstract]:Three-phase high-frequency rectifier is widely used in distributed power system and various industrial equipment, and has been widely studied. In this paper, the nonlinear behavior of this converter is defined and analyzed. With the rapid development of microgrid and distributed generation, the power grid should not be considered as an ideal voltage source. Therefore, a three-phase high-frequency rectifier connected to such a weak network cannot be considered an independent system. It's a subsystem that can interact with a non-ideal grid. For this system, we will show some special nonlinear phenomena and define the nonlinear phenomena by bifurcation analysis. Through the analysis based on design, the stable boundary of the key parameters of the system and the region of distinguishing different running states will be obtained, and the design ideas will be provided to the designers. First, when the local resistive load is connected to the same node as the three-phase rectifier at the same time as the non-ideal grid, An irreversible bifurcation will occur in the converter, and the system model is a very practical model in practical application. In this model, the active power provided by the non-ideal power grid to the converter is limited. When the converter fails to get the active power it needs, the output DC voltage of the converter will fall. In this case, the reactive power absorbed by the converter will increase instantaneously. And it almost works in zero power factor mode. This operation mode of converter can be called "abnormal operation". In this chapter, the basic principle of this physical phenomenon is analyzed by using large signal model. The stable boundary of the key parameters of the system is delineated by the Design-based analysis method. At the same time, the existence of this phenomenon is verified by experiments in this chapter. Secondly, when the three-phase high-frequency rectifier is connected to the non-ideal power network, the Hopf bifurcation will be described in this chapter. When the internal impedance of the non-ideal power network connected by the three-phase converter is large enough, The DC output voltage of the converter will appear obvious low-frequency oscillation, or called Hopf bifurcation. In this chapter, the average model of three-phase converter and the time-domain analysis method are used to predict the occurrence of Hopf bifurcation. The stability interval and its boundary of some parameters are also analyzed. Finally, the occurrence of this phenomenon is verified by experiments. Finally, this paper introduces the phenomenon of Hopf bifurcation when two or more grid-connected converters are connected to the same node in the same non-ideal power network at the same time. When a single converter is connected to a non-ideal power network, it can operate stably. Two converters connected to the same node in the same non-ideal grid will interact with each other and may lead to unstable operation. The output voltage of two or more converters will appear low frequency oscillation or Hopf bifurcation. In this chapter, the impedance model of the converter and the generalized Nigel criterion will be used to judge the instability. The key parameters of the system are found and the stable region partition of the system and the influence of the parameter variation on the stability margin are obtained. Furthermore, the research in this chapter fully shows that the stability problem of grid-connected converter is no longer a stability problem of an independent system. It is a system-level stability problem to be judged by the connected system environment.
【学位授予单位】：华中科技大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM46

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