【作者】 张黎；

【导师】 李庆民；

【作者基本信息】 山东大学 ， 高电压与绝缘技术， 2009， 博士

【摘要】 电力电子技术的迅速发展为新型电气设备的涌现提供了机遇,继而推动现代电力系统的技术创新与进步。在过去的二十年间,电气科学家与工程师们提出了灵活交流输电系统(FACTS)的概念与技术,并研制了一系列的FACTS控制装置。所有的FACTS设备均是通过控制电力电子器件的开关过程,以有效实现电力系统的潮流控制、电压调节、提高系统暂态稳定性以及抑制系统低频振荡等功能。然而,大功率电力电子器件的频繁开关操作将产生很陡的瞬态脉冲,经近场耦合和远场辐射而形成较严重的高频传导和辐射骚扰,对电网设备及附近的电子单元造成电磁环境污染。另一方面,为实现电力系统运行的智能监测、故障诊断与自动控制,在现代化变电站的二次侧越来越多地安装了各种电子通讯与保护单元。FACTS设备产生的电磁骚扰将会严重影响这些非常敏感的二次电子单元,甚至导致其发生功能性故障或永久损坏。目前随着FACTS装置的高压大容量化,其电磁骚扰程度也愈加严重。因此,需要通过测试分析对FACTS变电站的电磁环境进行重新评估,并采取有效的电磁抗扰性措施以保证二次系统单元的安全与可靠运行。本文提出采用综合性的策略研究FACTS变电站的电磁兼容问题。研究内容主要包括以下几个方面:测量传感器的建模与数字化校正技术,电磁骚扰测量系统的建立,电磁骚扰的特征提取方法,高频电磁骚扰机制的仿真建模,电磁骚扰抑制方法与抗扰性试验措施,等。一般电磁场天线的幅频特性并不平坦,必须建立其等效传递函数以对测量数据进行数字化校正,才能正确归算出实际的电磁骚扰强度。本文提出了两种新的基于频域传递函数建模的数字化校正算法:一种是改进的复向量拟合法,它通过增加一阶导数信息以及将系数矩阵右乘一个对角阵来实现;另一种算法是极点置换法,它通过将一个给定极点的密切相关传递函数的零点置换为目标函数的初始极点来实现。仿真和应用结果表明,两种方法都具有较高的拟合准确度。现场测量的天气情况与标准校核条件可能存在较大差别,有必要研究不同天气因素对电磁天线测量特性的影响。基于实验研究、数字信号处理方法、改进的复向量拟合法以及人工神经网络,本文提出了一种定量分析、预测天气因素对电磁天线测量特性影响的一般方法。其中,实验测量和数字信号处理方法用以获取各种天气条件下的天线响应特性;改进的复向量拟合法用以获取天线频域特性的等效传递函数;BP神经网络用以建立天气因素与天线频域特征参数之间的非线性映射关系。实验与分析结果表明,利用该方法能够分析天气因素的具体影响,并可根据天气因素变化对电磁天线的频域特征参数作出有效预测。基于路-场传感器、光纤传输、数字存储示波器以及终端屏蔽单元等,本文建立了先进的电磁骚扰测量系统,并对多个FACTS变电站的电磁环境进行了现场测量,获得了宽频带的辐射骚扰与传导骚扰时域波形。通过分析一个工频周期内静态无功补偿器(SVC)的瞬态冲击脉冲特征,给出了电磁骚扰的幅值以及频率分布范围,积累了大量第一手的电磁骚扰原始数据。在时、频域内系统建立了电磁骚扰信号的特征提取与表征方法。提出基于双正交数字滤波器和基于Hough变换的两种瞬时频率估计算法,可分别应用于瞬时频率缓变和大幅度变化的电磁骚扰信号,具有较快的瞬时频率跟踪速度与较高的计算准确度。更进一步,通过引入短时傅立叶变换、Wigner分布、平滑伪Wigner分布及重排平滑伪Wigner分布等时频分析技术,在三维空间内建立了基于时频分析的电磁骚扰特征提取方法,以更加形象地描述电磁骚扰的非平稳时变特征,获取更丰富的电磁骚扰信息,为深入分析FACTS变电站的高频电磁骚扰机制和评估电磁环境提供了直接依据。为分析SVC的高频电磁骚扰机制,基于晶闸管的动态开关特性,本文提出了SVC传导骚扰的仿真建模方法。以非线性时变电阻作为晶闸管宏模型的内核,建立了含晶闸管控制电抗器支路、晶闸管开关电容器支路的SVC仿真模型。SVC传导骚扰的仿真结果与现场实测数据相比具有相似性,表明晶闸管的动态开关特性是导致高频骚扰的主要机制。为分析负荷随机变化对传导骚扰的影响,进一步建立了含可变负载的SVC传导骚扰仿真模型,可预测各种负荷条件下的电磁骚扰水平。根据FACTS设备的具体拓扑结构,基于现场测量和理论分析,本文有针对性地给出了抑制高频电磁骚扰的具体方法,包括接地、屏蔽、滤波、安装铁氧体磁环等,以减小对二次系统电子单元的影响。参照国际电磁兼容标准IEC61000-4系列,并综合国内外的最新研究结果,提出了有效的电磁抗扰性试验建议,对完善相关试验标准提供了有价值的参考依据。本文研究结果进一步丰富了电力系统电磁兼容研究的理论和方法,对FACTS设备的工程设计和大规模应用有重要意义。更多还原

【Abstract】 The rapid development of power electronics technology creates feasible and exciting opportunities to develop novel electrical equipment for better utilization of the existing power systems. During the last decade, a great number of control devices incorporating specifically the concept of "Flexible AC Transmission Systems" (FACTS) technology have been proposed and implemented all over the world. Almost all the FACTS elements are based on controlled switching of the power electronic devices to effectively realize power flow control, voltage regulation, enhancement of transient stability and mitigation of low-frequency system oscillations. However, very steep transient pulses are generated due to frequent switching of the large power electronic devices, hence resulting in considerable high-frequency conducted and radiated emissions through near-field coupling and far-field radiation, which causes electromagnetic contamination to both the power grids and the victim electronic devices positioned nearby. In the mean time, more and more electronic units have also been utilised in the secondary side of nowadays power substations to realize online monitoring and diagnosis, data acquisition and communication, automation control and protection of the power system operation. Unfortunately, these electronic units are normally quite vulnerable to electromagnetic disturbances, and sometimes can not withstand the emission levels generated from the FACTS equipment, subsequently rendering malfunctions or even being damaged. Furthermore, the case may become even worse if higher power FACTS equipments are installed. So the electromagnetic environment within substations employing FACTS equipments needs to be re-evaluated and thereafter some immune measures should be taken to guarantee all the secondary electronic units function properly.A comprehensive strategy is adopted in this dissertation to address the prominent electromagnetic compatibility (EMC) issues in FACTS-based substations. The research work mainly concentrates on the following several aspects: Equivalent modelling and digital rectifying technology for transducers and antennas, establishment of on-site measurement system, feature extraction methodology for electromagnetic interference (EMI) data, modelling and simulation scheme of high-frequency EMI mechanisms, EMI suppressing methods and electromagnetic susceptibility test measures within FACTS-based substations, etc.Due to non-flat amplitude-frequency characteristics of the antennas used in EMC measurement, it is desired to establish the equivalent transfer functions of the antennas so as to make digital correction to the measured data, from which the actual electromagnetic emissions can be traced back. Two digital rectifying algorithms based on frequency domain transfer function are proposed, one is Improved Vector Fitting Method which is achieved by introduction of the first-order derivative and also right-multiplication to the coefficient matrix by a diagonal matrix, the other one is called Poles Replacement Method which is achieved by replacing the initial poles of the target transfer function with the zeroes derived from another relative transfer function whose starting poles are manually preset. Simulation results show the proposed algorithms both render good performance in fitting accuracy.The weather conditions of on-site measurement may differ a lot from the standard calibration condition of an antenna, so it is necessary to analyze the impact of weather factors, such as temperature, humidity and atmosphere pressure, on the measurement accuracy of the antenna. Based on experimental study, digital signal processing, improved vector fitting method and artificial neural network (ANN), a comprehensive scheme is presented to quantitatively analyze and effectively predict the impact of weather factors on an antenna’s frequency-domain characteristics. Analysis and experimental verification indicate that, the proposed scheme can address the concrete impact from weather factors, and thereby realize reliable prediction of the antenna’s specific frequency-domain parameters with regards to variation of weather conditions.Based on circuit and field transducers, optical fibre transmission, digital oscilloscope and shielded terminal unit, an advanced data acquisition system is established to implement on-site measurements of the electromagnetic emissions generated from FACTS equipments within several different substations, which demonstrates that the measurement system can realise effective acquisition of both the conducted and radiated wide-bandwidth interference. The switching bursts of the EMI waveforms within a power cycle are analyzed to present in details the frequency and amplitude range of the electromagnetic emissions, which facilitates accumulation of large amount of first-hand EMI data.A systematic methodology for feature extraction and expression of the electromagnetic emissions is established in both time- and frequency-domains. Two novel algorithms to accurately track the instantaneous frequency of EMI signals are proposed, with one based on bi-orthogonal digital filters and the other one on Hough transform, which can respectively cope with low and fast frequency-varying EMI signals accurately. Further, with the utilization of short-time Fourier transform, Wigner-Ville distribution, smoothed pseudo Wigner-Ville distribution and rearranged smoothed pseudo Wigner-Ville distribution, a feature extraction scheme based on time-frequency analysis is presented, and more detailed and useful information of the electromagnetic emissions can be obtained through 2-D and 3-D displays, which presents fundamental reference for characterizing the interfering mechanisms and effectively evaluating the electromagnetic environment.Based on the dynamic switching characteristics of the thyristors, a modelling and simulation methodology is established to investigate on the high-frequency EMI mechanisms in substations operational with Static Var Compensator (SVC) devices. With a nonlinear time-varying resistor as the kernel of the high-frequency macro model for thyristors, a concrete simulation model of SVC including a Thyristor-switched Capacitor (TSC) element and a Thyristor-controlled Reactor (TCR) element is further proposed. The conducted emissions by simulation are correlated well with that from on-site measurements, which indicates the dynamic switching process of the thyristors is the main cause and principal mechanism of the high-frequency conducted interference. Specifically, a SVC simulation model incorporating randomly varying loads is also established to predict the EMI levels under different loadings.Referring to the topologies of FACTS equipment, and based on on-site measurement as well as theoretical analysis, pertinent measures for EMI suppression are put forward, such as earthing, shielding, filtering and installation of ferrite rings so as to reduce coupling impacts on the electronic units of the secondary side. With combination of the state-of-the-art achievement of FACTS-based EMI research, a correlation is made to the present EMC standards IEC 61000-4 series and concrete recommendations of changes for immunity tests are presented to ameliorate the IEC standards.The research work of this dissertation further develops and enriches both the theories and methodologies for power system EMC study, which possesses practical significance for engineering design and wide application of the FACTS equipment.更多还原