基于下垂控制微电网的小信号稳定性分析

发布时间：2018-09-19 21:13

【摘要】：随着化石能源的枯竭、环境污染的加重以及传统电网安全性的降低,各国纷纷加快对分布式发电技术的研究。分布式发电技术具有运行方式灵活、环境友好性强等优点,但对大电网干扰较大,制约了其的大规模使用。微电网概念的提出,解决了分布式发电和大电网之间矛盾的局面。微电源多通过电力电子变换器接入微电网,具有灵活的控制和运行方式。但由于其惯性较小,在当受到扰动时,系统会发生振荡失稳。所以与传统电网相比,微电网的稳定性分析有较大不同。围绕这一问题,本文对采用下垂控制的微电网进行小信号稳定性建模和分析。首先,对微电源的输出功率传输特性、逆变器的控制方法,进行了分析、介绍。对采用下垂控制的逆变器进行设计,并在控制环中加入虚拟阻抗,减小线路参数对输出阻抗的影响,保持为感性。然后,对逆变器、负荷和大电网的表达式进行线性化,得到各自的小信号模型,并得出戴维南等效电路。在此基础上,选定一个d-q坐标系为公共坐标系D-Q,将各元件模型转换到公共坐标系下,得到整个微电网的功率闭环特征方程。根据方程求出闭环特征根,绘制根轨迹图。最后,利用Matlab/Simulink软件搭建微电网仿真并验证所搭模型的正确性;对有、无虚拟阻抗两种情况进行仿真对比,验证了加入虚拟阻抗的有效性和必要性;利用根轨迹图,分析负载电抗和虚拟电感对系统稳定性的影响:负载电抗的增大和虚拟电感的减小使系统的稳定性降低,并通过仿真验证了所得结论的正确性。
[Abstract]:With the depletion of fossil energy, the aggravation of environmental pollution and the decrease of the security of traditional power grid, many countries have accelerated the research of distributed power generation technology. Distributed generation technology has many advantages, such as flexible operation mode and strong environmental friendliness, but it interferes with large power grid and restricts its large-scale application. The concept of microgrid resolves the contradiction between distributed generation and large power grid. Micro power supply is connected to microgrid through power electronic converter, and has flexible control and operation mode. However, because of its small inertia, oscillation instability will occur when the system is disturbed. Therefore, compared with the traditional grid, the stability analysis of microgrid is quite different. Aiming at this problem, the small signal stability modeling and analysis of microgrid with droop control is carried out in this paper. Firstly, the transmission characteristics of output power and the control method of inverter are analyzed and introduced. The inverter with droop control is designed and virtual impedance is added to the control loop to reduce the influence of line parameters on the output impedance and to maintain inductance. Then, the expressions of inverter, load and large power grid are linearized, and their small signal models are obtained, and the Thevenin equivalent circuit is obtained. On the basis of this, a d-q coordinate system is selected as the common coordinate system D-Q. each element model is converted to the common coordinate system, and the power closed-loop characteristic equation of the whole microgrid is obtained. The closed-loop characteristic root is obtained according to the equation and the root locus is drawn. Finally, the Matlab/Simulink software is used to build the simulation of microgrid and verify the correctness of the proposed model. The validity and necessity of adding virtual impedance are verified by comparing the two cases of virtual impedance with or without virtual impedance, and the root locus diagram is used to verify the validity and necessity of adding virtual impedance. The influence of load reactance and virtual inductor on the stability of the system is analyzed. The stability of the system is reduced by the increase of load reactance and the decrease of virtual inductance, and the correctness of the conclusions is verified by simulation.
【学位授予单位】：安徽理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM727

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