低压微电网环流控制策略研究

发布时间：2018-04-25 04:03

本文选题：微电网 + 下垂控制　；参考：《西南交通大学》2017年硕士论文

【摘要】：为了解决日益严峻的能源问题,分布式发电(Distributed Generation,DG)得到迅速的发展和广泛的应用。但DG大量接入电网会对电网产生不利的影响,微电网技术可以有效解决DG的接入和控制。与传统电网不同,微电网有两种运行模式,不仅可以运行于并网模式,与大电网相互配合为负载供电,也可以运行于孤岛模式,单独为负载供电。孤岛运行的微电网,失去了大电网对其电压和频率的支撑,当DG的线路阻抗不相等或DG有本地负荷时,微电网中存在较大的环流,影响微电网的稳定运行。本文主要研究孤岛运行模式下,低压微电网的环流控制策略,主要进行了如下的工作:首先,简要介绍了微电网中不同类型的DG常用的控制方法,在此基础上对微电网的运行控制策略进行了分析,以采用下垂控制的微电网为研究对象,分析了微电网中环流产生的原因,并推导了线路阻抗与微电网环流大小的关系。通过仿真证明,当DG的线路阻抗不相等或DG有本地负荷时,传统的下垂控制和基于虚拟阻抗的下垂控制对微电网环流的控制效果都不理想。其次,在对微电网环流进行分析的基础上,提出了一种基于自适应虚拟阻抗的控制策略来抑制微电网中的环流,介绍了控制策略的原理和控制流程。该控制策略利用DG输出无功功率的差值对虚拟阻抗进行调整,设计了3种算法来控制虚拟阻抗,使虚拟阻抗能够跟随线路阻抗的差值,实现DG输出无功功率按容量分配,从而抑制微电网中的环流。对虚拟阻抗上的电压降落进行了分析,指出当虚拟阻抗的取值过大时,DG输出端电压存在严重跌落,设计了一种简单的电压补偿方法,补偿虚拟阻抗上的电压降落。最后,在MATLAB软件中,建立微电网的仿真模型,对本文提出的环流控制策略和电压补偿方法进行仿真。通过仿真结果,验证了本文提出的控制策略能够有效抑制微电网中的环流,即使在虚拟阻抗调整过程中出现通信故障,环流控制性能也比基于虚拟阻抗的下垂控制策略更好。当微电网采用本文提出的控制策略时,电压补偿方法可以在不影响无功功率分配的基础上补偿虚拟阻抗上的电压降落。
[Abstract]:In order to solve the increasingly serious energy problem, distributed Generation (DG) has been rapidly developed and widely used. However, a large number of DG access to the grid will have a negative impact on the grid, micro-grid technology can effectively solve the DG access and control. Different from the traditional power grid, there are two operation modes of microgrid, not only in grid-connected mode, but also in isolated island mode. When the line impedance of DG is not equal or the DG has local load, there is a large circulation in the microgrid, which affects the stable operation of the microgrid. In this paper, the circulation control strategy of low-voltage microgrid in isolated island mode is studied. The main work is as follows: firstly, the common control methods of different types of DG in microgrid are introduced briefly. On this basis, the operation control strategy of microgrid is analyzed. Taking microgrid with droop control as research object, the causes of circulation in microgrid are analyzed, and the relationship between line impedance and circulation size of microgrid is deduced. It is proved by simulation that when the line impedance of DG is not equal or DG has local load, the traditional droop control and the droop control based on virtual impedance are not ideal for microgrid circulation control. Secondly, based on the analysis of microgrid circulation, a control strategy based on adaptive virtual impedance is proposed to suppress the circulation in microgrid. The principle and control flow of the control strategy are introduced. The control strategy adjusts the virtual impedance by using the difference of DG output reactive power, designs three algorithms to control the virtual impedance, enables the virtual impedance to follow the line impedance difference, and realizes the DG output reactive power distribution according to the capacity. Thus the circulation in the microgrid is restrained. The voltage drop on the virtual impedance is analyzed, and it is pointed out that when the value of the virtual impedance is too large, there is a serious drop in the output voltage of DG. A simple voltage compensation method is designed to compensate the voltage drop on the virtual impedance. Finally, in MATLAB software, the simulation model of microgrid is established, and the circulation control strategy and voltage compensation method proposed in this paper are simulated. The simulation results show that the proposed control strategy can effectively suppress the circulation in the microgrid. Even if there is a communication fault in the process of virtual impedance adjustment, the performance of the loop control is better than that of the droop control strategy based on virtual impedance. When the control strategy proposed in this paper is adopted, the voltage compensation method can compensate the voltage drop on the virtual impedance without affecting the reactive power distribution.
【学位授予单位】：西南交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM727

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