A transformation method for the solution of power switching circuits based on network topological concepts

In this paper, a general and systematic method for the analysis of varying topology power semiconductor circuits is presented. the changes of the conduction state of the semiconductor switching devices are handled by successive modifications of the tree of the circuit graph. These tree modifications are systematically reflected on a square transformation tensor. On the basis of well known network topological concepts, this generalized transformation tensor can be constructed in a relatively simple way. This tensor constitutes a flexible and powerful tool to assemble automatically the necessary on-switch current and off-switch voltage equations required for any conduction pattern. These manipulations are accomplished with a step-by-step modification procedure of the equations describing the circuit in the most previous conduction state. the basic steps of an algorithm suitable for the practical implementation of the analysis of any power switching network on a digital computer are described, and an example is used to demonstrate the effectiveness of the proposed method.     

Handling three-winding transformers and loads in short circuit analysis by the admittance summation method

The admittance summation method is efficient in short circuit analysis of radial and weakly meshed networks. It is especially powerful if all node loads can be represented as any combination of constant impedance and constant current load component. However, in the existing literature one cannot find any explanation how to handle power transformer in that approach. For that reason, the corresponding equations have been developed in this paper along with a procedure for development of a three-winding transformer admittance matrix. In addition, a procedure for handling an arbitrary load was proposed. A large number of tests were performed and results were compared with that obtained by the previously published method. As an illustration, some of the results for single fault currents are presented. It can be concluded that the proposed approach makes the admittance summation method capable to take into account all network elements in a proper way.     

不平衡供电条件下多脉动整流器的谐波特性分析

为明确非理想供电情况下多脉动整流器的谐波产生特性,研究了6脉波、12脉波整流电路在不平衡供电条件下的频域谐波耦合导纳矩阵模型.考虑晶闸管换相过程及不平衡电压对晶闸管开通和关断时刻的影响,分析了供电不平衡时直流侧谐波电压的特征以及不平衡电压分量对直流电压波动的影响;采用附加谐波耦合导纳矩阵,建立了考虑不平衡电压的三相6脉波整流器的谐波耦合模型,模型可拓展应用至任意脉波整流器在不平衡供电电压下的谐波分析;修正了整流电路电流断续情况下的模型,提升了模型通用性.仿真分析与实验测量验证了所提模型的准确性和有效性.     

导纳型与阻抗型节点电压方程

在电力系统潮流计算中,通常用节点导纳矩阵形式的节点电压方程描述网络的数学模型,而在电力系统短路电流故障分量（基频交流分量初始有效值）计算中,为什么要使用网络的节点阻抗矩阵？本文对这个问题作了比较深入的分析,并据此阐述了《电路原理》与《电力系统分析》课程在理论性与实际性方面存在的差异。     

A DIAKOPTICAL TECHNIQUE FOR SHORT CIRCUIT STUDIES OF LARGE SIZE POWER SYSTEM NETWORKS

ABSTRACT

The paper presents a diakoptical technique for deriving the impedance matrices required for short circuit studies of large size power system networks by tearing the system into smaller subsystems by cutting appropriate tie lines. The bus admittance matrix is formed for the sequence networks of each subsystem and then modified later by means of diakoptics. The simulation of mutual couplings is taken into account in the zero sequence networks. Only columns of the impedance matrices corresponding to the faulted buses are computed in the proposed technique which is based on factorized bus admittance matrices and full exploitation of sparsity. The proposed technique can either be used in a single–processor computer for sequential solution of torn subsystems or in a multicomputer configuration for a faster solution by parallel processing of torn subsystems. Both symmetrical and unsymmetrical faults are studied by using the proposed technique which produces exact results as the untorn system. No iterative calculations are required as short circuit analysis is basically a linear problem. Included in this paper is a numerical example of a sample test system.     

电力系统机电暂态和电磁暂态混合仿真接口算法

传统的机电暂态或电磁暂态程序在分析日益复杂的大规模电力系统时,已开始显露出各自的局限性.将两者联合起来进行混合仿真,可以较好地解决仿真的规模、速度和精度的协调问题,这为研究电力系统的稳定性和动态特性提供了新的解决思路.文中系统研究了混合仿真中的接口算法,对机电侧和电磁侧的等值参数求取、等值电路形式及变换、电磁侧的基波等值复阻抗求解方法、机电侧正负序阻抗不等引起的不对称、电磁侧离散序列的基波提取等问题进行了深入分析,并且给出了具体的实现方案,为混合仿真平台的程序设计提供了坚实的理论依据.     

Development of a three-phase power-flow calculation method for distribution systems with automatic handling of arbitrary winding connections of transformers

Single-phase loads and photovoltaic generation cause three-phase imbalance in distribution systems, and prospective growth of normal chargers of electric vehicles may even increase the imbalance. The analysis of such unbalanced systems requires the three-phase power-flow calculation. Since existing methods require the admittance matrices of three-phase transformers, they must be derived for all possible winding connection patterns in advance to its computer-code implementation. This paper proposes a three-phase power-flow calculation method which formulates circuit equations using the modified nodal analysis, making it possible to automatically handle any winding connection. The power-flow constraints are then embedded into the circuit equations using a fixed-point iteration. Newton-Raphson, backward/forward sweep and fixed-point iteration methods are the existing three categories of solution methods. Newton-Raphson methods may show convergence problems due to the high R/X ratios of distribution lines. Backward/forward sweep methods cannot be used, because loops are temporarily formed in a distribution system during circuit switching. These justify the use of a fixed-point iteration. In this paper, the proposed method is validated by practical examples.     

大规模交直流混联电网在线静态安全分析

南方电网总调能量管理系统(EMS)采用了先进的分布式建模技术,其在线静态安全分析需要对包括五省区220kV以上的交直流混联电网大模型进行计算,普通的潮流开断或补偿法难以满足南方电网大模型计算的效率要求。文章采用了基于图上作业的稀疏矢量和因子表修正技术来解决这一问题。图上作业法的稀疏矢量将开断计算工作量缩小到点集的路集上。因子表修正则利用递归与递推方法来减少因子表重新分解的工作量,加快计算速度。与EMS全潮流计算和BPA的对比计算表明,所提出的算法是合理的,且已在南方电网总调EMS有效地运行了两年多。     

Development of a new algorithm for power flow analysis

This paper presents a new iterative solution technique for power flow analysis to reduce the computation complexity, hence time of the conventional solution techniques. In the proposed method, the impedance matrix has been used instead of admittance matrix. This method does not involve any other jacobian matrix or any other inversion of matrix, hence there is no problem of singularity. Memory requirement of the proposed method is also less. The new method has been tested on IEEE standard 5-bus, 14-bus, 30-bus, 57-bus, 118-bus and 300-bus test systems with high precession. The test results have been compared with the same of popular conventional solution methods. The method has also been tested under different practical security constraints. The test results presented reveal the superiority of the proposed method.     

电力网络的谐振稳定性分析方法研究

随着电力系统电力电子化程度的不断加深,近年来出现了多起机理不明的新的振荡现象。提出了电力网络谐振稳定性的概念,试图将上述机理不明的振荡现象纳入到电力网络的谐振不稳定范畴,从而基于线性网络理论对众多复杂振荡现象进行分析,为借助数学上完全成熟的线性系统理论解决电力系统实际问题提供一条途径。围绕判断谐振稳定性的分析方法展开,通过引入电力网络的s域节点导纳矩阵,将电力网络的谐振稳定性问题归结为判断s域节点导纳矩阵行列式的零点在复平面上的分布问题。首先,理论证明了s域节点导纳矩阵行列式的零点就是系统的特征值。其次,给出了求解s域节点导纳矩阵行列式零点的实部-虚部交叉迭代法。接着,推导了特定谐振模式下的节点电压振型和参与因子矩阵,这2个指标可用来定位特定谐振模式发生的位置。最后,通过算例展示了所提方法在分析电力网络谐振稳定性方面的有效性。     

电力系统串联谐波谐振的特性分析与灵敏度计算

分析电力系统谐波背景下模态分析与谐波谐振关联的机理,根据回路阻抗矩阵,绘制矩阵特征值频谱和串联谐波谐振下的关键模态导纳。根据串联谐振及谐波激励的自身特点,提出使用虚拟支路对系统拓扑结构进行修正处理,对网络进行谐波谐振模态分析,将模态分析结果与系统导纳频谱扫描结果进行比较,验证谐波谐振频率计算方法的可行性和准确性。定义灵敏度矩阵,通过基本回路矩阵确定系统元件与回路阻抗矩阵元素间的关联性,推导关键模态下特征值对各网络元件电气参数的灵敏度,通过标准化处理,提高了各支路元件灵敏度的可比性。对IEEE30母线系统进行仿真分析,得出串联谐振对元件的灵敏度影响程度和串联谐振的定位及传播范围。     

A robust power flow model for active power flow control via thyristor‐controlled series compensator

In this paper, a new power flow model for active power flow control through a thyristor‐controlled series compensator (TCSC) in an AC network system is proposed. The proposed power flow model is based on the Newton–Raphson method. In this model, TCSC's admittance effect is included as a state variable into the Jacobian matrix to avoid the divergence problem. Unlike similar studies in the literature, TCSC's admittance is ignored in the bus admittance matrix, and the need for rebuilding the bus admittance matrix in each power flow iteration caused by the change of TCSC's admittance is prevented. So, faster convergence for power flow calculation is achieved. For this aim, new power equations are obtained. Also, in the proposed approach, we need not consider each terminal of TCSC as an individual bus in the power flow calculation. Thus, increasing the Jacobian and bus admittance matrixes sizes caused by the total bus number is prevented. The proposed approach is tested on an IEEE 57‐bus test system. The obtained results prove that this approach provides efficient, reliable, and fast convergence. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

DCM Boost PFC数字化的研究

传统断续导通模式的Boost PFC采用单电压环控制算法实现,但存在输入电流畸变大、功率因数不高的问题,从理论的角度深入分析了单电压环控制法不足的原因,根据Boost PFC电路在断续导通模式下的输入输出电压比,利用功率守恒原则,提出了适用于断续导通模式的DCM预测电流法,与单电压环控制法相比电流畸变、功率因数均得到改善。实验结果验证了理论分析的正确性。     

基于相分量模型的变电站短路电流分流系数计算

发变电站内发生短路故障时真正引起危害的是入地故障电流,而不是短路故障电流;当前已有的数值算法及软件或存在一定的技术性门槛,或在表征系统方面存在不足。提出一种适用于不同电压等级的复杂电力系统分流系数计算方法,推导并拓展了基于相分量的变压器导纳模型,将其应用于回路电流法,计算出电流分布及分流系数;通过与商业软件CDEGS进行比较,验证了该算法的正确性。作为应用,还定量分析了考虑变压器故障侧和非故障侧同时分流对分流系数的影响,指出了准确计算分流系数时变压器是不可或缺的系统元件。     

Analytical model and algorithm for tracing active power flow based on extended incidence matrix

This paper proposes an analytical model and algorithm for tracing power flow (TPF). The concept, construction approach and properties of extended incidence matrix (EIM) are developed. By using results of an AC or DC power flow solution from any off-line program or state estimation, the extended incidence matrix, generation and load power vectors, and distribution factor matrix are derived so that the analytical model of power transfers between generators and loads can be built. The major advantage of the proposed method is that the matrix theory is used to directly build the TPF model and no proportional sharing assumption on the flow distribution is needed. The method was tested using a 4-bus system, and the IEEE 30-bus and IEEE 14-bus power systems. The case studies indicate that the developed technique can be applied to any power system with or without loop flows.     

非同步机电源接入电网后的谐振问题分析及抑制

随着非同步机电源在电网中的占比越来越大，有别于传统功角振荡的电网谐振不稳定问题逐渐显现。为此，文中提出了一种基于s域节点导纳矩阵的网络谐振分析方法，用以分析及抑制含非同步机电源电力系统的谐振问题。首先，介绍了两种非同步机电源的s域阻抗建模方法——小干扰线性化法和测试信号法，重点考虑了内环控制器和锁相环的影响。然后，给出了一套基于s域节点导纳矩阵的网络谐振结构分析方法，并提出了两个描述谐振模式的特征指标，用以确定其主要影响区域和敏感元件参数。最后，以某风电场并网系统为例，对该系统的谐振结构进行了分析，并针对其存在的谐振问题提出了相应的改善措施。分析表明，由于电力电子装置的负电阻效应，含非同步机电源的电力系统确实存在谐振不稳定的风险，需要加以抑制。     

谐波谐振的模态分析法及其应用

通过计算与分析,论证了系统并联谐振频率与回路串联谐振频率完全相同。比较几种不同的模态分析法并得出结论：基于节点导纳矩阵或基于节点阻抗矩阵的模态分析法适用于系统并联谐振分析,且两种方法结果相同;基于回路阻抗矩阵的模态分析法适用于回路串联谐振分析,由于系统回路串联谐振频率与并联谐振频率完全相同,因而与系统并联谐振分析结果相同,单一使用基于回路阻抗矩阵的模态分析法并不能求得支路串联谐振频率;结合运用基于节点导纳矩阵的模态分析法和虚拟支路法,可求得包括支路串联谐振频率在内的系统全部谐波谐振频率。论证了虚拟支路法对于支路串联谐振分析的适用性。     

机电-电磁暂态混合仿真复合非对称故障计算方法

为了提高机电-电磁暂态混合仿真对机电侧非对称故障的处理能力,进一步提升混合仿真对各类工况的适应性,本文提出了一种同时考虑机电侧非对称故障和电磁侧非对称故障的计算方法。首先提出了一种机电侧发生非对称故障后的机电侧故障仿真方法,该方法根据非对称故障的类型获取故障电路导纳矩阵,继而通过修改与故障节点相关的导纳元素,将故障电路导纳矩阵的叠加到原导纳矩阵中获得故障后的导纳矩阵,并通过求解网络方程获得故障后的网络解。然后根据线性电路叠加定理,提出了接口节点戴维南等值电势的计算方法。为减少电磁侧的建模量,采用接口正序等值导纳进行戴维南电势向诺顿等值电流的转化。最后结合含有一回直流线路的IEEE39节点系统的基于PSCAD+C架构的机电-电磁暂态混合仿真平台,验证了所提方法的精度和有效性。     

基于节点导纳方程预处理的ISOP型DAB变换器双端口解耦等效模型

电力电子变压器是柔性直流配电网的主要设备,常包含大量开关器件与储能设备,且高频特征限制了仿真步长,仿真效率极低。文中针对典型的输入串联输出并联(input-series-output-parallel, ISOP)型双有源桥(dual active bridge,DAB)变换器,提出一种基于节点导纳方程预处理的双端口解耦等效模型。首先,将变压器用双端口等效电路表示,列写单个DAB单元的节点导纳方程。然后,通过嵌套快速求解法,列写DAB端子对外等效节点导纳方程,并利用矩阵的对称性与稀疏性进行节点导纳方程的预处理,求解等效参数表达式。其次,利用DAB单元端口电容电压不突变性质进行单步长约等,建立串并联侧解耦的单模块等效电路。最后,给出ISOP型DAB变换器的对外等效电路参数与求解流程。在PSCAD/EMTDC环境中对所提等效建模方法进行仿真加速比与精度的测试,结果表明,当DAB模块数大于50时,所提模型可实现2个数量级的提速,并且与详细模型相比具有极高的仿真精度。     

基于回路模态分析法的串联谐波谐振评估

串联谐波谐振发生时会造成系统过电压,损坏电力设备,影响系统正常工作。为了解决此问题,需获得准确的串联谐波谐振频率,从而控制谐波源产生与此相应的谐波。由于串联谐振的发生与回路密切相关,不能用节点阻抗矩阵来分析串联谐振问题,据此提出一种分析网络回路阻抗矩阵以获得串联谐振频率及相关支路信息的模态分析方法。仿真分析所得串联谐波谐振频率与频谱分析的比较结果证明此方法正确。理论分析和算例研究证明,该方法是电力系统谐波谐振分析的有效工具。