虚拟同步发电机（VSG）广义惯性与无功均分控制策略研究

发布时间：2018-06-15 19:06

本文选题：分布式发电 + VSG　；参考：《合肥工业大学》2017年博士论文

【摘要】：随着环境、能源问题的日益凸显和可再生能源的大规模应用,尤其是可再生能源发电的渗透率越来越高,使得电网系统的惯量也随之减少,难以维持短时的功率平衡以抑制频率波动。为此,可以在以电力电子为并网接口的发电系统中应用虚拟同步发电机(Virtual Synchronous Generator,VSG)控制策略,通过模拟同步发电机的惯性和调频调压特性以增加系统的电压和频率支撑能力。然而,在调频控制方面,现有的VSG控制主要基于一阶虚拟惯性的VSG策略。而基于一阶虚拟惯性的VSG策略虽然可以模拟系统的惯量,抑制频率的波动,但其存在有功功率稳态和动态特性调节矛盾的问题;在调压控制方面,现有的VSG控制主要基于Q-U下垂控制的VSG策略。然而由于各VSG的联线阻抗与额定容量不匹配,则难以实现无功均分。而现有增大下垂系数和增大虚拟阻抗的无功均分方案存在无功均分误差与电压控制精度之间矛盾的问题。本文在国家863项目《光伏微电网关键技术研究和核心设备研制》(2015AA050607)等国家项目的支持下,并依托阳光电源股份有限公司开展的虚拟同步发电机产学研项目展开了相关研究,本文的主要研究和创新如下:(1)研究和分析了VSG的产生背景、国内外研究现状、与同步发电机的区别,总结了VSG的应用领域和关键问题。(2)对比分析了现有的各种VSG数学模型,并基于本文采用的控制策略建立了VSG并网和组网小信号模型。研究了电压闭环控制、重复控制、虚拟阻抗算法、预同步算法等基本控制策略,并针对预同步算法中的相角差跳变问题,提出了基于乘法鉴相器的预同步控制策略,消除了相角差跳变,缩短了程序运行时间和预同步时间。(3)在研究了几种典型的虚拟惯量和阻尼系数优化设计控制策略的基础上,分析了现有基于一阶虚拟惯性的VSG在孤岛运行、并网运行和组网运行模式下,VSG输出有功稳态和动态特性调节存在矛盾的问题;分析了增大下垂系数和增大虚拟阻抗算法的开环无功均分方案存在无功均分误差与电压控制精度之间矛盾的问题,以及下垂系数和虚拟阻抗的变化对系统稳定性的影响。(4)针对基于一阶虚拟惯性的VSG有功稳态和动态特性调节之间的矛盾问题,提出了基于微分补偿的一阶虚拟惯性,通过在原有一阶惯性的基础上串联一个超前补偿环节,在保持功率稳态特性的同时增大系统阻尼比,减小功率超调,提高功率响应速度。(5)针对基于微分补偿的一阶虚拟惯性在响应初始阶段惯量较小的问题,根据增加调节自由度以提高系统控制性能的基本思路,提出了广义虚拟惯性的概念,给出了广义虚拟惯性的一般表达式。并以二阶虚拟惯性为例,分析了二阶广义虚拟惯性的VSG在孤岛运行、并网运行和组网运行模式下系统的动态和稳态特性。研究表明,二阶广义虚拟惯性在维持VSG稳态特性的同时减小了动态功率超调,并且克服了基于微分补偿的一阶虚拟惯性策略在响应初始阶段惯性不足的缺点。(6)针对现有开环无功均分方案存在的功率均分误差与电压控制精度之间的矛盾问题,提出了基于虚拟电容的无功均分控制策略。该控制策略通过算法模拟VSG输出端并联电容的特性,在减小无功均分误差的同时,也提高了电压控制精度。在对虚拟电容算法稳定性分析的基础上,提出了一种具有虚拟阻抗的虚拟电容改进算法,在实现无功均分的同时,提高了电压控制精度和系统稳定性。(7)搭建了VSG实验平台,并分别对VSG在各运行模式下的基本特性及改进预同步算法、基于微分补偿的一阶虚拟惯性及基于虚拟电容的无功均分控制策略进行了验证,并且相关研究成果已在西藏措勤微电网示范项目中应用。
[Abstract]:With the increasing prominence of the environment, the energy problem and the large-scale application of renewable energy, especially the high permeability of the renewable energy generation, the inertia of the power grid system is also reduced, it is difficult to maintain the short-term power balance to suppress the frequency fluctuation. Therefore, the power generation system with power electronics as the grid interface can be used. Virtual Synchronous Generator (VSG) control strategy is used to increase the voltage and frequency support capability of the system by simulating the inertia and FM voltage modulation characteristics of the synchronous generator. However, in the frequency modulation control, the existing VSG control is mainly based on the VSG strategy of first order pseudo inertia, and VSG based on the first order virtual inertia. Although the strategy can simulate the inertia of the system and suppress the fluctuation of the frequency, it has the problem of regulating the steady-state and dynamic characteristics of the active power; in voltage regulation control, the existing VSG control is mainly based on the VSG strategy of Q-U droop control. However, it is difficult to achieve the equalization of reactive power because the connection impedance of each VSG is not matched with the rated capacity. The existing reactive power equalization scheme with increasing droop coefficient and increasing virtual impedance has the problem of the contradiction between the error of reactive power equalization error and voltage control accuracy. This paper is supported by national projects such as the National 863 project "Research on key technology of photovoltaic microgrid and the development of core equipment" (2015AA050607), and relying on the sun power Limited by Share Ltd. The main research and innovation in this paper are as follows: (1) study and analyze the background of VSG, the present situation at home and abroad, the difference between the synchronous generator and the synchronous generator, summarize the application field and key problems of VSG. (2) the existing VSG mathematical models are compared and analyzed, and based on this paper The VSG network and the small signal model are established by the control strategy. The basic control strategies such as voltage closed loop control, repetitive control, virtual impedance algorithm and pre synchronization algorithm are studied. The pre synchronization control strategy based on multiplicative phase discriminator is proposed to eliminate phase angle difference jump and shorten the phase angle difference jump problem in the pre synchronization algorithm. Program running time and pre synchronization time. (3) on the basis of studying several typical optimal design control strategies of virtual inertia and damping coefficient, this paper analyzes the existing problem that the existing VSG based on the first order virtual inertia is running in the island, the network operation and the network operation mode, the VSG output has the contradiction between the power steady state and the dynamic characteristic regulation. The problem of the contradiction between the reactive power equalization error and the voltage control precision in the open loop reactive power equalization scheme with increasing droop coefficient and increasing the virtual impedance algorithm, and the influence of the variation of the droop coefficient and the virtual impedance on the stability of the system. (4) the spear between the active steady-state and dynamic characteristics of VSG based on the first order virtual inertia The first order virtual inertia based on differential compensation is proposed, which is connected with a pre compensation link on the basis of the original first order inertia. The damping ratio of the system is increased while the power steady characteristic is kept, the power overshoot is reduced and the power response speed is increased. (5) the first order virtual inertia based on differential compensation is used in the initial order of response. Based on the basic idea of increasing the degree of freedom of adjustment in order to improve the control performance of the system, the concept of generalized virtual inertia is proposed. The general expression of the generalized virtual inertia is given. The two order virtual inertia is taken as an example to analyze the operation of the Nikai Hiroyoshi virtual inertia VSG in the isolated island, the operation of the network and the running mode of the network. The dynamic and steady state characteristics of the lower system show that the Nikai Hiroyoshi virtual inertia reduces the dynamic power overshoot while maintaining the steady state of the VSG, and overcomes the shortcoming of the inertia of the first order virtual inertial strategy based on differential compensation in the initial stage of response. (6) the power equalization error exists in the present open-loop reactive power equalization scheme. In the contradiction between the difference and the voltage control precision, a reactive power equalization control strategy based on the virtual capacitor is proposed. The control strategy simulates the characteristics of the shunt capacitor at the output end of the VSG, and improves the voltage control accuracy while reducing the error of the reactive power equalization. A virtual capacitance improvement algorithm with virtual impedance improves the precision of voltage control and system stability while realizing the equalization of reactive power. (7) a VSG experimental platform is built, and the basic characteristics of the VSG in each operation mode and the improved pre synchronization algorithm, the first order virtual inertia based on the micro compensation and the virtual capacitance based on the no The power sharing strategy is verified, and the relevant research results have been applied in the Tibet Cuoqin microgrid demonstration project.
【学位授予单位】：合肥工业大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TM31

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