多样性子模块混合型MMC统一外特性高效电磁暂态模型

混合型模块化多电平换流器(MMC)的高效电磁暂态仿真是研究相关技术的重要基础。然而,由于多种子模块可以被采用,且每种子模块中均包含了大量的开关,混合型MMC的详细电磁暂态模型将严重降低其仿真效率。鉴于此,文中基于开关函数的定义与电容器件的动态特性,对多样性子模块的串联结构进行了统一的动态平均化等值,并根据等值后的动态模型,提出了一种适用于直流电网高效电磁暂态仿真的混合型MMC统一外特性模型以兼顾直流电网对仿真精度及效率的双重要求。同时,所提统一模型具有良好的可移植性以满足其作为研究工具的修改便利性要求。最后,基于ADPSS仿真软件,通过与基于分立元件的详细模型进行对比,验证了所提统一外特性模型的仿真精度与效率。     

超大规模MMC电磁暂态仿真提速模型

针对超大规模模块化多电平换流器高压直流输电(modular multilevel converter based HVDC,MMC-HVDC)在诸如PSCAD/EMTDC、MATLAB等电磁暂态仿真环境中仿真速度极慢问题,基于节点电压分析法,提出超大规模MMC电磁暂态仿真提速模型。所提出模型本质为将MMC在计算过程中的超大规模矩阵分解为相应数目的小矩阵,在与原有矩阵同解以保证仿真精度的前提下,仿真速度显著提升。所提出的模型具有极强的通用性,且可以进行开关器件级别的故障研究。在PSCAD/EMTDC中搭建的不同电平数MMC验证了提速模型的仿真精度及提速效果。     

MMC通用快速仿真模型及其在多端直流系统中的应用北大核心CSCD

为了研究复杂交直流网络下模块化多电平换流器(modular multilevel converter,MMC)与电网的交互影响问题,本文提出了一种普遍适用于多种拓扑变化的MMC通用快速仿真模型。首先,利用可控电压源、理想开关和二极管来等效不同拓扑在各种运行状态下的电路结构,得到桥臂通用简化电路,实现了MMC的动态特性和控制行为的准确模拟;其次,通过对多子模块开关和调制过程进行平均化等值,计算出桥臂动态平均值,避免了大规模节点导纳矩阵的动态求解,实现了仿真效率的提升。基于PSCAD/EMTDC平台,验证了所建立仿真模型的仿真精度和仿真速度;最后,应用MMC通用快速仿真模型,研究了多端柔性直流系统的关键控制策略和直流故障保护问题。     

柔性直流电网的快速电磁暂态仿真

柔性直流电网含多个模块化多电平换流器与直流断路器,需要快速准确的换流器与直流断路器仿真模型。为提高模块化多电平换流器的仿真速度,利用电容能量均分的思想简化子模块均压策略,并准确保留桥臂闭锁与不闭锁时的外特性,提出了一种能量均分模型。针对级联全桥型直流断路器,给出一种断路器支路子模块串等值电路简化方法,提出了一种快速仿真模型。在PSCAD/EMTDC中搭建模型并进行了电磁暂态仿真,验证了所提出模型的准确性与快速性。     

可仿真任意工况的MMC等值电磁暂态仿真模型与平均值模型

基于对MMC在启动以及直流故障期间桥臂电容电压动态过程的分析,提出了改进的MMC等值电磁暂态仿真模型,并根据桥臂总电容电压的动态特性提出了可仿真任意工况的MMC平均值模型。在PSCAD/EMTDC下搭建了21电平MMC的详细电磁暂态仿真模型、等值电磁暂态模型和平均值模型,通过启动、电流阶跃、交流故障和直流故障、环流抑制器投切仿真,验证了所提出的等值电磁暂态仿真模型和平均值模型可以分别在换流站级和电力系统级的研究上取代详细开关模型并提高仿真速度。     

基于Pscad/EMTDC自定义建模的MMC电磁暂态仿真技术

为了精确模拟仿真模块化多电平换流器(MMC)接入电网的暂态特性,需要开展计及MMC结构、特性及控制保护策略的电磁暂态仿真技术研究,以适应新一代电力电子技术在电力系统中应用的研究。本文通过Pscad/EMTDC自定义建模功能实现了MMC及其控制保护功能暂态建模。综合考虑MMC及其控制保护的特点,设计了MMC模型的整体结构,利用Pscad/EMTDC接口C语言实现了自定义元件,并结合模块化建模的方式,构建MMC及其控制保护功能的各个环节,基于此建立了MMC接入电网的电磁暂态仿真模型。利用该模型开展了MMC动态仿真,结果表明,模型能有效模拟MMC控制环节、子模块电容电压等暂态过程。建立的模型便于扩展且能适应不同应用场合,可用于开展基于MMC的柔性交直流输电电磁暂态特性及控制保护功能研究。     

模块化多电平换流器的快速电磁暂态仿真方法

通过分析电压源换流器换流过程,得到电压源换流器的简化电路。换流器的上、下桥臂互补通断时,简化电路与原电路等效。简化电路不仅减少了支路数,而且可简化支路方程,因此,基于简化电路的快速仿真方法可减少电磁暂态仿真计算量,节省仿真用时。该快速电磁暂态仿真方法的缺点是不能模拟开关死区和故障闭锁过程。在PSCAD/EMTDC仿真平台上通过3个仿真实例对基于简化电路的快速电磁暂态仿真方法进行了具体评估。结果表明,对2电平换流器而言,快速方法加速效果一般,实用价值不大;对高级联数模块化多电平换流器而言,快速方法加速效果很好,能显著节省仿真用时,实用价值较大。     

模块化多电平换流器快速电磁暂态仿真模型

针对模块化多电平换流器(modular multilevel converter,MMC)电磁暂态仿真耗时过长的问题,提出了2种MMC快速仿真模型。通过分析MMC子模块原理,提出将MMC桥臂等效为自定义数值计算模块与受控电压源组合的数值计算详细模型;并在该模型的基础上设计了一种将独立子模块电磁暂态模型和一般子模块数值计算模型结合的混合模型仿真方法,弥补了数值计算模型难以模拟子模块电磁暂态过程的缺陷。为了进一步提高模型的仿真速度,通过简化MMC的电压均衡控制及子模块状态的差异性,建立了数值计算平均值模型。在PSCAD/EMTDC上搭建MMC-HVDC模型,对所提出的快速仿真模型及仿真方法的有效性进行了验证。     

级联多电平换流器的高效仿真模型

级联多电平换流器是目前在柔性交直流输配电领域极具发展潜力的换流器拓扑,然而由于其拓扑中有大量独立的开关器件支路,如果在EMTP类仿真软件(如PSCAD/EMTDC)中采用器件模型直接建模将使得仿真计算极其缓慢,给研究及工程应用带来障碍。提出一种基于Dommel等值计算原理的级联多电平换流器仿真等值计算模型,可有效地解决仿真计算缓慢的问题,具有建模原理明确、计算结果可靠的优点。使用PSCAD/EMTDC软件对所提仿真模型进行仿真验证,结果表明,所提仿真计算模型与详细器件模型在暂态仿真中的响应高度一致,并且在仿真计算时间上具有明显的优势。     

提高MMC高效电磁暂态模型仿真精度的方法

对基于戴维南等效原理的模块化多电平换流器（modular multilevel converter, MMC）桥臂电磁暂态仿真详细模型的数学原理进行了分析,发现当仿真过程中发生故障或开关动作等引起网络结构变化时,由于电容电流会发生突变,当采用梯形积分法计算时会引入计算误差。为了解决这一问题,提出了一种通过求解突变后的非状态变量来消除计算误差的方法,在PSCAD/EMTDC下对比分析了误差消除前后在开关变化时刻的电容电压,验证了本方法的正确性和有效性。同时,搭建了单端101电平MMC-HVDC仿真系统,验证了本文提出的改进计算模型的正确性。     

Developments of power system protectionand control

Synchronized wide area communication has become a mature technology, which makes the real-time interaction between the substations and the wide area protection and control system possible. However, the present protection and control system to handle this real-time data has been recognized to be deficient. This paper begins by reviewing the development history of power system protection, with special attention paid to the recent development in the field of wide-area and integrated protections, in order to look into the future development of protection and control systems. Then the concept of integrated wide area protection and control is introduced, where it can be shown that a hierarchical protection and control system provides the protection and control for wide area or regional power substations/plants and their associated power networks. The system is mainly divided into three levels: the local, the substation/plant, and the wide area/regional. The integrated functions at each level are described in details with an aim to develop an optimal coordination mechanism between each level. The key element in the proposed system is the wide area real-time protection and control information platform, which not only enables the merger of three lines of defence for power system protection and control, but also provides a perfect tool for the application of cloud computing in substations and power networks.     

Developments of power system protection and control

This paper begins by reviewing the development history of power system protection, with special attention paid to the recent development in the field of wide-area and integrated protections, in order to look into the future development of protection and control systems. The paper will then turn to recent developments in the field of protection and control integration. The concept of integrated wide area protection and control is introduced, where it can be shown that a hierarchical protection and control system provides the protection and control for wide area or regional power substations/plants and their associated power networks. The system is mainly divided into three levels: the local, the substation/plant, and the wide area/regional. The integrated functions at each level are described in details with an aim to develop an optimal coordination mechanism between each level. The key element in the proposed system is the wide area real-time protection and control information platform supported by a synchronized wide area communication network between the substations and the wide area protection and control system, which not only enables the merger of three lines of defence for power system protection and control, but also provides a perfect tool for the application of cloud computing in substations and power networks.     

Coupling capacitor voltage transformer: A model for electromagnetic transient studies

In this work, an accurate coupling capacitor voltage transformer (CCVT) model for electromagnetic transient studies is presented. The model takes into account linear and nonlinear elements. A support routine was developed to compute the linear 230 kV CCVT parameters (resistances, inductances and capacitances) from frequency response data. The magnetic core and surge arrester nonlinear characteristics were estimated from laboratory measurements as well. The model is used in connection with the electromagnetic transients program (EMTP) to predict the CCVT performance when it is submitted to transient overvoltages, as are the cases of voltages due to the ferroresonance phenomenon and circuit breaker switching. The difference between simulated and measured results is fairly small. Simulations had shown that transient overvoltages produced inside the CCVT, when a short circuit is cleared at the CCVT secondary side, are effectively damped out by the ferroresonance suppression circuit and the protection circuit.     

电力系统继电保护系统信息安全研究

信息化技术的进步促进了电力系统自动化的飞速发展,同时也带来了电力系统信息安全问题。通过阐述网络环境下电力系统的数据和通讯安全特点,结合国际上相关的标准,对继电保护系统的相关安全问题和防护进行了分析。     

电力系统的安全性及防治措施

作者介绍了电力系统安全性问题及其研究动态,从分析影响电力系统安全性的各种因素出发,结合目前的技术手段,就如何加强电力系统的安全性,防治大停电事故提出了一些措施,并对今后在该领域研究中应采用的方法和研究方向提出了一些看法.     

广域测量技术在电力系统应用中关键技术问题

广域实时动态监测系统对电力系统安全稳定运行及监测具有重要作用.针对国内外广域动态测量系统建设所遇到的一些关键性技术问题进行了讨论,从子站的布点、测量方法、GPS授时、通信以及主站的平台、与EMS系统的互联和高级应用功能等方面进行了探讨,提出了有益的建议,为广域电网实时动态监测系统的建设提供有益的指导.     

现代电力系统暂态稳定控制研究综述

现代电力系统的发展使其稳定性问题日趋重要,而暂态稳定控制又是稳定性研究的重中之重.文章简要介绍了当前电力系统的发展特点及其稳定控制的重要性,总结了近年来非线性控制技术在暂态稳定控制中的应用情况,按控制对象分类讨论了各控制对象的稳定控制研究现状,并讨论了控制的综合与协调问题,最后指出了当前稳定分析与控制研究的主要任务.     

Power differential based wide area protection

Current differential based wide area protection (WAP) has recently been proposed as a technique to increase the reliability of protection systems. It increases system stability and can prevent large contingencies such as cascading outages and blackouts. This paper describes how power differential protection (PDP) can be used within a WAP and shows that the algorithm operates correctly for all types of system faults whilst preventing unwanted tripping, even if the data has been distorted by CT saturation or by data mismatches caused by delays in the WAP data collection system. The PDP algorithm has been simulated and tested on an Iranian 400 kV transmission line under different fault and system operating conditions. The proposed operating logic and the PDP algorithm have also been evaluated using simulation studies based on the Northern Ireland Electricity (NIE) 275 kV network. The results presented illustrate the validity of the proposed protection.     

Wavelet transform applications in power system dynamics

This paper proposes the use of the discrete wavelet transform (DWT) to analyze and locate the low frequency oscillations of power systems, which can result in a loss of stability or in a black-out. The proposed DWT applied to active power signal is tested and compared with more conventional approaches of Prony and Eigenvalue analyses. The DWT also enables estimation of the total active power imbalance of a system. Estimation performances of different wavelet families are tested. Based on the proposed DWT of electromechanical transient oscillations, the DWT is also applied to identify the network nodes in the neighbourhood of the original disturbance. The performance of the proposed DWT is evaluated on the New England (NE) 39-bus test system.     

直流机电暂态与电磁暂态模型在低频振荡分析中的比较

对交直流混合运行系统进行低频振荡分析时,直流系统通常采用机电暂态仿真模型。介绍了直流系统的机电暂态和电磁暂态两种仿真模型,在电力系统全数字仿真装置（ADPSS）平台上建立了EPRI36系统和某实际电网系统的机电暂态模型和机电-电磁暂态混合仿真模型,分别用于低频振荡分析。采用基于总体最小二乘-旋转不变技术的信号参数估计（TLS-ESPRIT）算法,分析故障后的振荡功率信号。提取低频振荡主导振荡频率、阻尼比等信息进行模态分析,并对分别利用两种仿真模型进行仿真得到的低频振荡分析的结果进行比较。结果表明,直流线路分别采取两种仿真模型时,仿真结果较为吻合,低频振荡分析的结果基本相同,机电暂态模型具有较高的实用价值。