直流电网的虚拟惯性控制方法研究

发布时间：2018-06-15 07:04

本文选题：直流电网 + 虚拟惯性　；参考：《华北电力大学》2017年硕士论文

【摘要】：近年来,随着分布式电源、储能、直流负荷的高密度接入以及电力电子技术的蓬勃发展,直流电网日益引起重视。与传统交流电网相比,直流电网更适合新能源的接入及传输,并且能够减少大量的DC/AC换流环节,不存在无功环流、频率、三相不平衡和功角稳定性等问题。但由于变流器的隔离作用,直流电网失去了交流大电网对直流侧稳定性的支撑。本文研究直流电网的电压功率控制技术,针对直流电网惯性小、功率随机扰动情况下直流电压质量差的问题,深入研究直流电网的虚拟惯性控制策略。旨在提高直流电网在受扰动情况下抑制直流电压突变的能力,为直流电网提供虚拟惯性支持,从而提高直流系统的电压质量及其运行的稳定性。完成的主要工作和成果如下:(1)建立风电、光伏与储能等单元的数学模型,并分析其工作原理。在此基础上搭建了包含风力发电单元、光伏发电单元、蓄电池单元、并网变流器单元以及交直流负荷单元的六端环形直流电网系统,为后续直流电网虚拟惯性控制技术的研究奠定基础,提供研究平台。(2)提出了基于变下垂系数的直流电网的虚拟惯性控制方法。为提高直流电网的惯性以改善其电能质量,在深入分析直流电网电压下垂控制策略的基础上,阐述了直流电网虚拟惯性的概念;从虚拟电容的角度对直流电网的固有惯性及虚拟惯性进行了理论分析,并得到了虚拟惯量与变流器下垂系数调节及直流母线电压的关系,从而提出了基于变下垂系数的虚拟惯性控制方法,在保留变流器下垂特性的同时为直流侧提供惯性。(3)提出了考虑虚拟惯性裕度的自适应虚拟惯性控制策略。对基于变下垂系数的虚拟惯性控制方法进行改进,考虑了虚拟惯性裕度的大小,及惯性的自适应调节能力。理论分析了在不同运行情况下该控制策略所能提供的具体的虚拟惯性裕度,在此范围内根据电压大小自适应地调节下垂系数,提供大小可变的惯性支持,从而使系统获得最佳动态响应。(4)最后,在MATLAB/Simulink中搭建了直流电网系统并进行仿真验证,结果表明所提控制策略在不同运行情况下,均能够起到改善系统暂态响应,提高直流母线电压质量以及平滑直流系统与交流主网交换功率的作用,提高了系统运行的稳定性。
[Abstract]:In recent years, with the rapid development of distributed power generation, energy storage, high density DC load access and power electronics technology, DC network has attracted more and more attention. Compared with the traditional AC power grid, DC network is more suitable for new energy access and transmission, and can reduce a large number of DC / AC converter links, without reactive power circulation, frequency, three-phase imbalance and power angle stability. However, because of the isolation of converter, DC network loses the support of DC side stability of large AC power grid. In this paper, the voltage power control technology of DC network is studied. Aiming at the problem of low inertia and poor DC voltage quality under random power disturbance, the virtual inertial control strategy of DC network is deeply studied. The purpose of this paper is to improve the ability of DC network to restrain DC voltage mutation under disturbance, and to provide virtual inertial support for DC network, so as to improve the voltage quality and stability of DC system. The main work and results are as follows: 1) the mathematical models of wind power, photovoltaic and energy storage units are established, and their working principles are analyzed. On this basis, a six-terminal ring DC network system including wind power unit, photovoltaic unit, battery unit, grid-connected converter unit and AC / DC load unit is built. The virtual inertial control method of DC network based on variable sag coefficient is presented in this paper, which lays a foundation for further research on virtual inertial control technology of DC network. In order to improve the inertia of DC network and improve its power quality, the concept of virtual inertia of DC network is expounded based on the analysis of voltage sag control strategy in DC network. The inherent inertia and virtual inertia of DC network are theoretically analyzed from the point of view of virtual capacitance, and the relationship between virtual inertia and sag coefficient of converter and DC bus voltage is obtained. A virtual inertial control method based on variable sag coefficient is proposed. An adaptive virtual inertial control strategy considering virtual inertial margin is proposed, which preserves the droop characteristics of converter and provides inertia for DC side at the same time. The virtual inertial control method based on variable sag coefficient is improved, and the magnitude of virtual inertia margin and the adaptive adjustment ability of inertia are considered. The virtual inertia margin can be provided by the control strategy under different operation conditions. In this range, the sag coefficient can be adjusted adaptively according to the voltage, and the inertia support with variable size is provided. Finally, the DC network system in MATLAB / Simulink is built and simulated. The results show that the proposed control strategy can improve the transient response of the system under different operation conditions. The stability of the system is improved by improving the quality of DC bus voltage and smoothing the switching power between DC system and AC main network.
【学位授予单位】：华北电力大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM727

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