【作者】 马玉龙；

【导师】 肖湘宁；

【作者基本信息】 华北电力大学（北京） ， 电力系统及其自动化， 2006， 博士

【摘要】 维持高压直流输电系统的稳定、可靠运行是一项基本的要求。HVDC工程单极大地回路引起的直流偏磁、电力系统背景谐波和各种电力系统扰动等都有可能使HVDC系统运行于非理想的环境,在一定条件下甚至会导致HVDC系统稳定被破坏的严重后果。本文立足于交、直流系统的相互作用关系,以HVDC系统的稳定性为目标,重点研究了以下问题。(1)逆变器正斜率伏安特性对HVDC稳定性的影响工程上使用逆变器正斜率伏安特性的本意为解决整流器和逆变器伏安特性多个交点的问题,但本文也证明,从小信号扰动的观点看,与负斜率伏安特性相比正斜率伏安特性可以使控制系统无条件满足稳定性的要求,不必对控制系统和一次回路参数作出任何要求。(2) HVDC的小信号模型及稳定性分析在HVDC准稳态模型的前提下,针对HVDC换流器的常见控制模式,推导了各自的小信号状态方程。在建立小信号状态方程后,利用特征根分析的方法分析系统的小干扰稳定性,分析了控制系统参数对HVDC系统稳定性的影响。(3) HVDC换流器阻抗频率特性与谐波不稳定谐波不稳定曾引起多个直流工程的闭锁,而HVDC换流器的阻抗频率特性是分析和解决谐波不稳定的一个重要因素。从分析换流器工作过程出发,基于开关函数理论,提出换流器阻抗频率特性的计算方法。该方法能准确确定从换流器交、直流端口向对侧看入的阻抗频率特性,因而将交、直流系统等效到同一电路系统中研究。该方法可用于交直流系统的谐波不稳定分析,仿真结果也证明行之有效。(4)交流系统单相接地故障对HVDC的影响分析交流系统故障时,HVDC的稳定运行将遭到破坏。针对交流系统常见的单相接地故障,深入分析了交流系统单相接地故障时换流器的动态行为,为求解换流器不对称运行产生的非特征谐波,提出改进的开关函数法。该方法解决了开关函数法不能应用于阀不对称运行的难题,可用于直流谐波保护定值校验的辅助手段。(5)抑制变压器直流偏磁的接地电阻配置方法直流偏磁引起的系统谐波增大和换流母线电压畸变会恶化HVDC换流器的运行环境,导致发生谐波不稳定等。针对传统方法不能解决全网变压器直流偏磁的问题,以使全网变压器中性点接地电流均不超标为目标,基于伴随网络的灵敏度分析,提出接地电阻的优化配置方法。以直流偏磁比较严重的南方电网的仿真分析表明该方法能够有效抑制中性点的直流电流,彻底解决电网中普遍存在的直流偏磁问题。更多还原

【Abstract】 To keep HVDC transmission in stable and reliable operation is the most basic andimportant requirement. Transformer’s dc bias by HVDC’s monopole operation mode, thebackground harmonic and various disturbances in power system will make HVDC operate inunrealistic circumstance, which can lead to the breakdown of HVDC’s stability. The paperfocuses on the mutual relationship between ac and dc systems, aims at the HVDC’s stabilityand the following problems are studied detailedly.(1) The influence of inverter’s positive slope characteristic on HVDC stabilityThe original purpose to use positive slope characteristic is to eliminate the multiplecross-point between the rectifier and inverter voltage-ampere characteristic. This paperproves that from the viewpoint of small signal inverter’s positive slope characteristic makesthe control system satisfy the stability requirement unconditionally compared with negativeslope characteristic, thus no need to demand any requirement on the parameters of controlsystem and primary circuits.(2) Small signal stability analysis of HVDC based on quasi-steady modelOn the basis of HVDC quasi-steady model, different state equation of small signalmodels of common-used control system are elaborated. Then the method of eigenvalueanalysis is used to analyse the small signal stability of the system. The influence of controlsystem parameters is presented. The model and analysis method can be helpful to theoptimization of control system parameters.(3) The impedance-frequency characteristic of HVDC converter and harmonic instabilityHarmonic instability has already led to several HVDC project shutdown in the pastdecades, while the impedance–frequency characteristic is important for analysis and solve thisproblem. The paper analyses the working course of converter and presents a method tocalculate the impedance-frequency characteristic on the basis of switching function. Themethod can determine the converter’s impedance-frequency characteristic seen from the dcand ac side, then the ac and dc circuits are converted to the same frame, and thus the harmonicinstability problem can be studied easily. Simulation results show that the method is quiteeffective.(4) The impact of ac system single-phase earth fault on HVDCWhen ac system fault occurs, the stable operation of HVDC can be destroyed.Single-phase earth fault is very common in ac system and the paper analysis the dynamiccourse of converter under this fault. To calculate the non-characteristic harmonic, the paperpresented a so-called promoted switching function which solved the problem that switchingfunction cannot be used to unsymmetrical operation condition of valve. The method can beused as auxiliary means for harmonic protection in HVDC control and protection system.(5) Optimized grounding resistance configuration against dc bias of transformerThe amplification of harmonic and bus voltage distortion in commutation bus bytransformer dc bias will deteriorate the operation condition and easily lead to harmonicinstability. The traditional cure measures for transformer dc bias are to install suppressiondevice at the happening place only. Aimed at this, the paper presented an optimized configurationmethod of grounding resistance to make all the currents through the transformer neutral point inthe grid within its limits on the basis of adjoint network sensitivity analysis. The proposed methodis verified by the data from Southern China Power Grid, the verification results show that allneutral currents are limited within the specified value, thus the dc bias of transformer is avoided.更多还原