【作者】 刘洋；

【导师】 黄少锋； 王宁；

【作者基本信息】 华北电力大学(北京) ， 工程硕士（专业学位）， 2019， 硕士

【摘要】 改革开放以来,由于电力系统规模的日益增加与新能源并网规模的逐步增长,电力系统的安全稳定问题越来越受到人们的重视,怎样使电力系统能够在更加经济的情况下安全稳定运行已经越来越重要,因此电力系统的稳定性分析已经成为了现在人们研究的重要热点。在等效双电源系统中,若系统受到某些扰动发生振荡,系统两侧等效电动势的夹角δ(功角)可能会在0°到360°内发生变化,这时系统将会处于不稳定状态。在δ摆开到90°以后的某一角度时,若我们用电力电子控制电路将联络线开关的一次相位迅速翻转,通过“相序交换”实现功角突变120°,将原本持续增大的功角拉回到较小的状态,抑制失步的发生,这种新的提高系统稳定性的方法称为换相序稳定控制措施。由于系统联络线上的传输功率与功角有关,当利用换相序技术将系统功角突变120°时,这一瞬间联络线上传输功率将发生变化,因此,本文通过研究直流功率调制作用对电力系统的影响,提出了一种将模块化多电平换流器直流输电与交流换相序功能相组合的电路,即利用交直流变换来实现换相序稳定控制。本文主要包括以下几个方面内容:(1)分别对交流换相序稳定控制与基于交直流变换的换相序稳定控制的基本概念与原理进行分析,解释什么是换相序技术,换相序技术如何提升系统的稳定性。提出了一种将模块化多电平换流器直流输电与交流换相序功能相组合的电路拓扑并对此电路拓扑的各种运行状态、状态之间的互相切换与此电路拓扑如何将直流输电与交流换相序功能组合进行研究。(2)在研究基于交直流变换的换相序稳定控制过程中,对直流线路的过载能力、稳态运行初始功角、故障切除角和线路的传输功率分配对系统暂态稳定性提升效果的影响进行分析并通过对比交直流并联系统中直流系统的功率调制作用分析了所设计电路对系统功率的调制,再通过对输送功率极限与短路比的关系和交流系统强度与有效惯性常数的关系进行分析提高直流输电系统的功率输送能力。(3)在Matlab/Simulink平台上进行了仿真验证,通过对同一单机对无穷大系统加入不同直流输电系统组成的换相序电路后发生三相短路故障的暂态仿真结果进行分析,研究基于交直流变换的换相序稳定控制对系统发生故障后的控制效果以及所设计电路拓扑的优点。更多还原

【Abstract】 With the process of reform and opening.due to the increasing scale of power systems and the scale of new energy grids,the security and stability of power systems has received more and more attention.How to make the power system safe and stable in more economical situations has become more and more important,so the stability analysis of the power system has become an important hot spot for people to study now.In an equivalent dual-supply system,if the system oscillates with some perturbation,the angle of the equivalent electromotive force on both sides of the system may change from 0° to 360°,and the system is in an unstable state.When δ is swung to an angle after 90°.achieving a sudden change in power angle by "phase sequence exchange",pull the originally increasing power angle back to a smaller state,and suppress the occurrence of out-of-synchronization.This new method of improving system stability is called phase sequence changing stability control.Since the transmission power of the system tie line is related to the power angle,when the system power angle is abruptly changed 120° by using the phase sequence changing technique,the transmission power of the contact line will change at this moment.Therefore,by studying the influence of DC power modulation on the power system,this paper proposes a circuit that combines the MMC-HVDC w ith the AC phase sequence changing function.That is,the AC/DC conversion is used to realize the phase sequence changing stability control.(1)The basic concepts and principles of AC phase sequence changing stability control and phase sequence changing stability control based on AC-DC conversion are analyzed respectively,which explains what is the phase sequence changing technique,and how the phase sequence changing technique improves the stability of the system.Proposes a circuit that combines the MMC-HVDC with the AC phase sequence changing function.And the various operating states of the circuit topology,the mutual switching between states,and how the circuit topology combines the DC power transmission and the AC phase sequence changing function are also studied.(2)In the process of studying the phase sequence changing stability control based on AC/DC conversion,the overload capacity of DC line.the influence of the initial power angle of steady-state operation,the fault resection angle and the transmission power distribution of AC and DC lines on phase sequence changing stability control are analyzed and by comparing the power modulation of the DC system in the AC-DC parallel system,the modulation of the system power by the designed circuit is explained.Then,the relationship between the transmission power limit and the short-circuit ratio and the relationship between the strength of the AC system and the effective inertia constant are analyzed to improve the power transmission capability of the DC transmission system.(3)The simulation verification is carried out on the Matlab/Simulink platform,by analyzing the transient simulation results of the three-phase short-circuit fault of the same single machine to the infinite system which add phase sequence changing circuits that have different types of DC transmission systems,study on the control effect of phase sequence changing stability control based on AC/DC transmission on system failure and the advantages of the designed circuit topology.更多还原