本文選題：直流電網(wǎng) + 虛擬慣性��； 參考：《華北電力大學》2017年碩士論文

【摘要】：近年來,隨著分布式電源、儲能、直流負荷的高密度接入以及電力電子技術(shù)的蓬勃發(fā)展,直流電網(wǎng)日益引起重視。與傳統(tǒng)交流電網(wǎng)相比,直流電網(wǎng)更適合新能源的接入及傳輸,并且能夠減少大量的DC/AC換流環(huán)節(jié),不存在無功環(huán)流、頻率、三相不平衡和功角穩(wěn)定性等問題。但由于變流器的隔離作用,直流電網(wǎng)失去了交流大電網(wǎng)對直流側(cè)穩(wěn)定性的支撐。本文研究直流電網(wǎng)的電壓功率控制技術(shù),針對直流電網(wǎng)慣性小、功率隨機擾動情況下直流電壓質(zhì)量差的問題,深入研究直流電網(wǎng)的虛擬慣性控制策略。旨在提高直流電網(wǎng)在受擾動情況下抑制直流電壓突變的能力,為直流電網(wǎng)提供虛擬慣性支持,從而提高直流系統(tǒng)的電壓質(zhì)量及其運行的穩(wěn)定性。完成的主要工作和成果如下:(1)建立風電、光伏與儲能等單元的數(shù)學模型,并分析其工作原理。在此基礎上搭建了包含風力發(fā)電單元、光伏發(fā)電單元、蓄電池單元、并網(wǎng)變流器單元以及交直流負荷單元的六端環(huán)形直流電網(wǎng)系統(tǒng),為后續(xù)直流電網(wǎng)虛擬慣性控制技術(shù)的研究奠定基礎,提供研究平臺。(2)提出了基于變下垂系數(shù)的直流電網(wǎng)的虛擬慣性控制方法。為提高直流電網(wǎng)的慣性以改善其電能質(zhì)量,在深入分析直流電網(wǎng)電壓下垂控制策略的基礎上,闡述了直流電網(wǎng)虛擬慣性的概念;從虛擬電容的角度對直流電網(wǎng)的固有慣性及虛擬慣性進行了理論分析,并得到了虛擬慣量與變流器下垂系數(shù)調(diào)節(jié)及直流母線電壓的關(guān)系,從而提出了基于變下垂系數(shù)的虛擬慣性控制方法,在保留變流器下垂特性的同時為直流側(cè)提供慣性。(3)提出了考慮虛擬慣性裕度的自適應虛擬慣性控制策略。對基于變下垂系數(shù)的虛擬慣性控制方法進行改進,考慮了虛擬慣性裕度的大小,及慣性的自適應調(diào)節(jié)能力。理論分析了在不同運行情況下該控制策略所能提供的具體的虛擬慣性裕度,在此范圍內(nèi)根據(jù)電壓大小自適應地調(diào)節(jié)下垂系數(shù),提供大小可變的慣性支持,從而使系統(tǒng)獲得最佳動態(tài)響應。(4)最后,在MATLAB/Simulink中搭建了直流電網(wǎng)系統(tǒng)并進行仿真驗證,結(jié)果表明所提控制策略在不同運行情況下,均能夠起到改善系統(tǒng)暫態(tài)響應,提高直流母線電壓質(zhì)量以及平滑直流系統(tǒng)與交流主網(wǎng)交換功率的作用,提高了系統(tǒng)運行的穩(wěn)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.
【學位授予單位】：華北電力大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TM727

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