三相交流微电网控制及小信号稳定性研究

发布时间：2018-05-25 15:08

本文选题：交流微电网 + 下垂控制　；参考：《浙江大学》2014年博士论文

【摘要】：全球性的能源危机与环境危机迫使世界各国寻找传统化石能源发电的替代品。近年来可再生能源发电技术逐渐兴起,其合理利用可以作为现有化石能源发电形式的有益补充,并最终成为解决能源危机的有效途径。微电网可以将各种类型的可再生能源发电单元以及储能元件有机集成为一个系统,为用户提供稳定、可靠、优质的电能。在微电网系统中,稳定运行是首要的,因而微电网的小信号稳定性问题是学术界的研究重点之一。论文在总结现有的交流微电网系统小信号稳定性分析方法的基础上,提出了基于元件等效阻抗模型的系统小信号稳定性分析方法,并将该方法应用于单母线微电网和网状网络拓扑结构微电网的小信号稳定性分析。同时,提出了通过控制输出阻抗的方式抑制孤岛微电网带非线性负载时的电压谐波,并通过电网电压与频率前馈的方式稳定并网潮流。首先,论文推导了基于下垂控制电压型变流器(Power Conditioning System, PCS)、负载及线路阻抗、电网等在d-q同步旋转坐标系下的等效模型,分别为戴维南等效模型、阻抗模型、电压源模型等。以此为基础,建立了三相交流微电网在d-q坐标系下的网络等效模型,并推导出系统中各元件功率闭环特征方程,根据功率闭环特征方程即可求解出某一特定参数下系统各元件功率闭环特征根,特征根的分布即可用来预测系统的动态特性与小信号稳定性。进一步地,设置某些参数变化,即可求解出系统闭环特征根随该参数变化的根轨迹,从而可以利用这一方法来判断各个控制参数对系统的动态特性与稳定性的影响,并据此设计出恰当的控制参数。基于该思想,论文以单母线微电网为例,推导了并网及孤岛模式下的微电网模型,并求解出功率闭环特征方程随某些控制参数变化的根轨迹。其次,论文所提出的微电网建模方法是先给出系统的在d-q同步旋转坐标系下的等效电路模型,然后利用基本电路方程导出系统闭环功率特征方程,且系统描述方程的矩阵规模与网络拓扑结构无关,只与组网PCS数量相关,因而特别适用于求解网络结构比较复杂的系统。而在目前的文献检索范围内,并无系统地讨论网状拓扑结构微电网的相关工作。基于此,论文提出了一种交流微电网系统的一般化网状网络拓扑结构,并利用论文提出的建模方法推导出该系统中各元件的功率闭环特征方程以及根轨迹,从而可以预测系统的动态特性及小信号稳定性。此外,论文还给出了该通用微电网拓扑结构演变为其它拓扑结构的一般方法。再者,论文推导了下垂控制电压型PCs的输出阻抗模型,并分析了逆变器输出阻抗对电压波形的影响。孤岛运行时,若微电网存在非线性负荷,谐波电流会在逆变器的输出阻抗上产生谐波压降,进而导致输出电压波形畸变,从而严重影响微电网的电压波形质量。论文提出通过控制逆变器输出阻抗的方法,改善微电网孤岛运行时的电压波形质量。此外,下垂控制逆变器并网运行时,并网潮流受电网电压与频率随机波动的影响,也会存在随机波动,影响并网潮流控制的精确性。论文提出通过电网电压与频率前馈的方法抑制电网波动对并网潮流影响。论文所提出的微电网建模方法,能够很好地应用于求解并网运行或孤岛运行的三相交流微电网,且该方法适用于求解网络结构较为复杂的微电网系统。推导系统闭环功率特征方程与求取根轨迹,为微电网中PCS的控制参数设计、微电网小信号稳定性问题的分析提供了新思路。最后,论文介绍了基于RT-LAB的三相交流微电网实验平台的研发。该系统包含三台电压型逆变器,以RT-LAB作为虚拟控制器,可以用于验证论文所推导的微电网小信号模型,以及微电网电压波形质量问题。同时,由于该实验平台的通用性,也可以用于其它不同网络形态和负载条件的微电网实验研究,加快科研进度。
[Abstract]:The global energy crisis and environmental crisis have forced the countries all over the world to look for the alternative to traditional fossil energy generation. In recent years, the renewable energy generation technology has gradually emerged. Its rational use can be a useful supplement to the existing fossil energy generation form, and eventually become an effective way to solve the energy crisis. The type of renewable energy generating unit and energy storage element are integrated into a system to provide users with stable, reliable and high quality electric energy. The stability of the microgrid is the first priority in the microgrid system, so the problem of the small signal stability of the microgrid is one of the key points in the academic field. On the basis of the number stability analysis method, a system small signal stability analysis method based on the component equivalent impedance model is proposed, and the method is applied to the small signal stability analysis of the single bus microgrid and the mesh network topology microgrid. At the same time, the control output impedance is proposed to suppress the islanding microgrid zone. The voltage harmonics in linear load are stabilized by grid voltage and frequency feedforward.
First, the paper derives the equivalent model based on Power Conditioning System (PCS), load and line impedance, power grid and so on in d-q synchronous rotating coordinate system, which are the equivalent model, impedance model and voltage source model, respectively. Based on this, the three-phase AC microgrid is established in the d-q coordinate system. The network equivalent model is used to derive the closed loop characteristic equation of each component in the system. According to the power closed-loop characteristic equation, the closed-loop characteristic root of each component of the system can be solved. The distribution of the characteristic root can be used to predict the dynamic characteristics of the system and the stability of the small signal. This method can be used to determine the influence of the control parameters on the dynamic characteristics and stability of the system, and the appropriate control parameters are designed based on this method. Based on this idea, a single bus micro electric network is taken as an example to deduce the micro electricity under the mode of grid and Isle. The root locus of the power closed loop characteristic equation with certain control parameters is solved.
Secondly, the method of modeling microgrid proposed in this paper first gives the equivalent circuit model of the system in d-q synchronous rotating coordinate system, and then uses the basic circuit equation to derive the closed loop power characteristic equation of the system, and the matrix scale of the system description equation is independent of the network topology, and is only related to the number of network PCS, so it is especially suitable for the system. In the context of current literature retrieval, there is no systematic discussion of the related work of network topology microgrid. Based on this, a general network topology of the AC microgrid system is proposed, and the components in the system are derived from the modeling method proposed in this paper. The power closed-loop characteristic equation and the root locus can be used to predict the dynamic characteristics of the system and the stability of the small signal. In addition, the general method of the evolution of the general microgrid topology into other topological structures is also given.
Furthermore, the output impedance model of the droop controlled voltage type PCs is derived, and the influence of the output impedance of the inverter on the voltage waveform is analyzed. If there is a nonlinear load in the isolated island, the harmonic current will produce the harmonic voltage drop on the output impedance of the inverter, which leads to the distortion of the output voltage waveform, thus seriously affecting the micropower. By controlling the output impedance of the inverter, the paper puts forward the method of controlling the output impedance of the inverter to improve the quality of the voltage waveform of the microgrid. In addition, when the droop control inverter is connected to the grid, the grid flow is affected by the random fluctuation of the voltage and frequency of the power grid, and it will also exist in the random fluctuation, which affects the accuracy of the grid power flow control. In this paper, a feed-forward method of grid voltage and frequency is proposed to suppress the influence of grid fluctuation on grid connected power flow.
The method of micro grid modeling proposed in this paper can be used to solve the three-phase AC microgrid with grid connected operation or island operation, and this method is suitable for solving the complex network structure of the network structure. The closed-loop power characteristic equation and the root locus are derived, and the PCS control parameters in the microgrid are designed and the micro grid is small. The analysis of the problem of signal stability provides a new way of thinking.
Finally, the paper introduces the research and development of a three-phase AC microgrid experiment platform based on RT-LAB. The system includes three voltage inverters and RT-LAB as a virtual controller. It can be used to verify the microgrid small signal model derived from the paper and the quality of the voltage waveform of the microgrid. In order to speed up the progress of scientific research, microgrid experiments are carried out for other network configurations and load conditions.
【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM712

【参考文献】