【作者】 张冰；

【导师】 赵书强；

【作者基本信息】 华北电力大学 ， 电力系统及其自动化， 2017， 硕士

【摘要】 基于电压源换流器的高压直流输电技术(VSC-HVDC)由Boon-Teck Ooi等人于1990年首次提出,其主要特点是采用由全控电力电子器件构成的电压源换流器(VSC),取代常规直流输电中基于半控晶闸管器件的电流源换流器。作为新一代直流输电技术,柔性直流输电有效克服了一些传统直流输电的缺陷,适用于风电发电并网、孤岛供电、交流系统的异步互联、分布式发电并网、多端直流输电以及城市配电网增容等领域。应用柔性直流输电技术进行远距离大容量架空线输电是电网技术发展的未来趋势,但与直流电缆相比,架空输电线一般较长且运行环境恶劣,因而与其他输电设备相比故障率高,因此直流线路保护在直流系统中起着至关重要的作用。如何快速识别故障是直流保护的一项重要问题,本文针对柔性直流输电线路保护的相关问题进行了研究。首先,对两电平电压源换流器的运行原理和调制方式进行总结分析,在PSCAD/EMTDC中建立双端和多端柔性直流输电系统仿真模型,选用具有分布参数的架空线输电线路,对各种线路故障进行仿真分析,研究柔性直流输电系统运行特性和线路故障特性。其次,运用叠加原理分析单根无损线路中故障行波的传播特性,针对传统行波保护可靠性不高的缺点,研究采样率对提高行波保护可靠性的作用,对比10k~100kHz区间的采样率发现提高采样率后保护可以更准确地判明故障。最后,由于传统行波保护在面对高阻接地故障时灵敏性较低,根据故障行波在直流线路上传播的特点,提出一种适用于双端柔性直流输电线路的行波保护方案,该保护方案通过故障行波小波变换模极大值识别故障,利用极波差值区分故障极与非故障极。在PSCAD/EMTDC环境下进行仿真分析,仿真结果验证了本文所提出的快速行波保护具有良好的动作性能,可以在1ms时间内判断出区内和区外故障,并且能够耐受不低于1000Ω的接地电阻,具有较高的可靠性和速动性。更多还原

【Abstract】 High voltage DC transmission technology based on voltage source converter(VSC-HVDC)was firstly proposed by Ooi Boon-Teck and others in 1990,the voltage source converter(VSC)which is composed of wholly-controlled power electronic device is used to replace the current source converter which is based on semi-controlled thyristor device.As a new generation of DC transmission technology,VSC-HVDC can effectively overcome some disadvantages of traditional HVDC.It applied to wind power integration,Island power supply,Asynchronous interconnection of AC systems,interconnection of distributed generation,MTDC,expansion of urban distribution network and other fields.Application of VSC-HVDC in long distance and large capacity overhead line transmission is the future trend of the development of power grid technology.Compared with DC cable,overhead lines are generally long and have a poor transmission environment.So the failure rate of overhead lines is higher than other transmission equipment.Line protection plays an important role in DC system.How quickly to identify the fault is an important problem of DC protection.In this paper,the problem of VSC-HVDC line protection is studied.First of all,the operation principle and modulation mode of two level VSC are summary analyzed and simulation models of two-terminal VSC-HVDC and VSC-MTDC are established in PSCAD/EMTDC which with overhead lines of distributed parameters.Study on the operating and fault characteristics of VSC-HVDC according to the simulation of various circuit faults.Secondly,applying the principle of superposition to study the propagation characteristics of single non-loss transmission line.Because of the low reliability of traditional traveling wave protection,The effect of sampling rate on improving the reliability is studied.By comparing the sampling rate of 10k~100kHz range denotes that the improvement of sampling rate can make protection identify fault more accurately.Finally,the sensitivity of traditional traveling wave protection is relatively low when there is high resistance grounding fault.This paper presents a new traveling wave protection scheme for VSC-HVDC transmission lines according to the propagation characteristics of fault wave.This protection using wavelet transform modulus maximum to identify a fault internal or external,using the pole wave difference value to detect the fault pole.The simulation analysis of a two-terminal VSC-HVDC on PSCAD/EMTDC platform validates that this new wave protection can accurately identify transmission line fault within 1ms and its adaptability to earth resistance are not less than 1000Ω,it has good sensitivity and speed.更多还原