Efficient computer analysis of ideal switched-capacitor circuits using matrix compaction techniques

In this paper we describe how three simple observations can be used in order to obtain an efficient algorithm for the computer analysis of ideal switched-capacitor circuits. the resulting algorithm is linear in the number of phases. the first observation uses the structure of the r-domain MNA-matrix to come up with a new LU-decomposition scheme which is gradual per timeslot. the second observation allows a great reduction in size of the z-domain MNA-matrix by a matrix compaction algorithm which also operates gradually per timeslot and which can be interleaved with the first gradual LU-decomposition process. This leads to a small matrix which can then be used for a time- and direct frequency-domain analysis. Third, the computations of transfer functions, aliasing functions and sensitivities can be optimized by applying appropriate excitations and making appropriate combinations of the terms in the expressions. These algorithms have been implemented in the SC-analysis program DIANA.SC. the usefulness and efficiency of the program is then illustrated with some examples.     

A new method of inhomogeneous ladder network synthesis

A procedure to synthesize ladder networks in which each series arm impedance is f_iz(s) and each shunt arm admittance is g_iy(s) is presented. Given a specified network function T(s), the function G = z(s)y(s) is first established by a polynomial decomposition. Then the appropriate chain parameters associated with T(s) are constructed as polynomials in G. The constants f_i, g_i are determined from a straightforward continued fraction expansion of a related RL impedance function in G. Necessary and sufficient conditions for the steps in the procedure are established and examples are included.     

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。     

s-Domain analysis of lightning surges in three-phase systems using nonuniform single-phase line model

Surge response of the transmission tower in a three-phase transmission system is computed using s-domain nonuniform single-phase transmission line modelling. First, tower top voltage is obtained considering the tower and the ground wire by excluding the effect of the phase conductors, and then the induced voltages on the phase conductors as a result of the current flowing through the ground wire are computed using the magnetic coupling between the ground wire and the phase conductors. The first step of the analysis is the formulation of the system response in the s-domain, and the second step is the frequency to time domain conversion, which is carried out using fast inverse Laplace transform (FILT). The voltages on the phase conductors and the voltages across the tower insulators are computed, and some of the results obtained using s-domain analysis are compared with those obtaining using electromagnetic transients program (EMTP). The effect of frequency dependence of the line parameters is investigated.     

Efficient generation of compact symbolic network functions in a nested rational form

This paper presents the extension of generalized parameter extraction method for direct circuit function generation in a fully symbolic form of rational expressions or a nested s-expanded polynomial. The new formula for implicit extraction of parameters that allows effective factoring by grouping of determinants of circuits containing any linear models of active elements, such as controlled sources, nullors, and pathological mirrors, is proposed. The concept of nullor with parameter is used for implicit extraction. The rules of optimal selection of parameters for extraction are presented. The proposed algorithm of symbolic analysis is implemented in the CirSym program, which is available online. The paper discusses the results of automatic analysis of several large active circuits, as well as determinants of matrixes and passive topologies, in terms of compact size and minimization of the number of arithmetic operations. Experimental results demonstrate that the expressions of determinants derived by CirSym are more compact than the results of the factorization algorithms of commercial computer algebra systems. The comparison with several other symbolic analysis algorithms shows that CirSym is the only available program that provides the exact calculation of the symbolic function of large circuits in the s-expanded form with every coefficient being a compact-nested expression.     

A Contribution to the Frequency Analysis and Transient Response of Power Transformer Windings

Abstract—This article proposes a new approach to study the frequency response and the transient analysis of power transformer windings. For improved accuracy, the suggested model includes, among other equivalent circuit elements, the mutual magnetic couplings between any winding turn and all others. This implies that the equivalent inductance of any considered turn will be a location-dependent parameter. Accordingly, the winding will be analyzed as a non-uniform transmission line. Through the application of a recursive circuit reduction technique, a closed-form Laplace s-domain analytical expression for the winding's input impedance can be obtained for any neutral treatment. The resulting expression can be used to determine the winding's series and parallel resonance frequencies. The s-domain expression for the input impedance, in connection with the numerical inverse Laplace transform, will be utilized for determination of the winding's time-domain transient response for any input voltage or current time waveform. Accuracy increases with the assumed number of winding sections, which can be even increased to the actual number of turns, limited only by the available computation resources. The results of case studies are in good agreement with those available in the literature using the time-domain solution of the simultaneous differential equations in the state variables.     

Generalized bessel polynomials with application to the design of bandpass filters with approximately flat group delay response

The continued fraction expansion of the ordinary Bessel polynomials is modified by replacing the complex frequency variable p by p/(1+γp), where γ=?0. The resulting polynomials, when a reactance transformation is applied, are capable of providing bandpass filters with an approximately flat group delay response.     

Frequency domain subspace identification with the aid of the w‐operator

Frequency domain subspace identification algorithms have been studied recently by several researchers in the literature, motivated by the significant development of the more popular time domain counterparts. Usually, this class of methods are focused on discrete‐time models, since in the case of continuous‐time models, the data matrices often become ill‐conditioned if we simply rewrite the Laplace operator s as s = jω, where ω denotes the frequency. This paper proposes an efficient and convenient approach to frequency domain subspace identification for continuous‐time systems. The operator w = (s−α)/(s+α) is introduced to avoid the ill‐conditioned problem. Hence, the system can be identified based on a state‐space model in the w‐operator. Then the estimated w‐operator state‐space model can be transformed back to the common continuous‐time state‐space model. An instrumental variable matrix in the frequency domain is also proposed to obtain consistent estimates of the equivalent system matrices in the presence of measurement noise. Simulation results are included to verify the efficiency of the proposed algorithms. © 2000 Scripta Technica, Electr Eng Jpn, 132(1): 46–56, 2000     

A simplified design-oriented analysis of switched-capacitor active filters

The method presented in this paper provides a simplified approach to obtain the z-domain equivalent circuit of an SC active filter by one-for-one substitution of each basic SC element with its z-domain equivalent admittance, if a specific terminal condition is met. Then, traditional circuit analysis techniques can be used to derive the z-domain transfer function of the filter. This method makes the analysis and the design of the SC active filter simple and similar to the S-domain method. Two application examples are given.     

基于高斯方法及Sherman-Morrison公式的暂态稳定性并行计算方法

并行计算是实现大规模电力系统暂态稳定性实时分析计算的有效途径。将s级2s阶的高斯方法和扩展的Sherman-Morrison矩阵求逆公式相结合,提出了一类新的暂态稳定性并行计算方法。该方法首先利用s级2s阶的高斯方法对微分-代数方程组进行多级离散,并利用严格的牛顿法对离散后的非线性方程组进行整体求解。在此基础上,按s个时间点将整体雅可比矩阵分裂成为一个分块对角矩阵和一个分块常系数矩阵。然后,以分裂后的分块对角矩阵为基础,利用扩展的Sherman-Morrison矩阵求逆公式将s个时间点上的计算任务进行“解耦”。所提方法在保持严格牛顿法的收敛性的同时具有很好的并行性。利用OpenMP并行计算技术在多核计算机上对2个不同的系统算例进行了测试,结果表明,所提出的并行方法可以获得较好的加速比以及并行效率。     

A new feasible method for the design of stray-insensitive optimum switched capacitor networks

On the basis of signal flow graphs a general method is described for the design of stray-insensitive switched capacitor networks. to be able to choose the optimum one, the method involves the search of all possible topologies for the specially formed signal flow graph of the given z-domain transfer function and is easily implemented by digital computer.     

Al-Alaoui operator and the new transformation polynomials for discretization of analogue systems

The “new transformation polynomials for discretization of analogue systems” was recently introduced. The work proposes that the discretization of 1/s ⁿ should be done independently rather than by raising the discrete representation of 1/s to the power n. Several examples are given in to back this idea. In this paper it is shown that the “new transformation polynomials for discretization of analogue systems” is exactly the same as the parameterized Al-Alaoui operator. In the following sections, we will show that the same results could be obtained with the parameterized Al-Alaoui operator. This research was supported, in part, by the University Research Board of the American University of Beirut.     

Three winding transformer s-domain model for modal analysis of electrical networks

This paper describes an s-domain sequence model for three winding transformers to be used in modal analysis of ac networks. The model takes into account off-nominal tap positions and the phase shifts among the windings. The main contribution of this proposed model is to complete the set of s-domain models of electrical system components already developed (loads, transmission lines, generators, harmonic filters, shunt elements) suitable for modal analysis of complex electrical networks. Modal analysis provides an important set of system information that is hard to be obtained using the conventional time simulation and frequency response methods. This information may be effectively used to improve the harmonic performance of electrical networks, to build linear equivalents for harmonic and electromagnetic transient studies and to perform linear dynamic performance analysis.     

COMPNET: an interactive computer networks analysis and designpackage

COMPNET is an educational software package being used as a teaching tool to study, analyze, and design computer networks. This package is an interactive, user-friendly, entirely menu-driven, and graphics-oriented software tool, implemented for the Apple's MacPlus and Digital's VAX 11/780. The authors describe the applications of this package, and cover topics in graph theory, centralized network design, and queuing systems. The software work has been successfully implemented and classroom-tested by the authors at both the undergraduate and graduate level. Several computer exercises using COMPNET are suggested to accompany classroom lectures and traditional problem assignments     

In-situ Raman Spectroscopic Investigation of the Effect of Cooling Speed on Domain Formation in PbTiO3 Films

The influence of the post-deposition cooling speed on the domain formation process of PbTiO₃ films was investigated using MOCVD equipment combined with in-situ Raman spectroscopy. The accumulation and relaxation of strain during the post-deposition cooling process is responsible for the domain structure. The Curie temperature for fast cooling is lower than that for slow cooling. Additionally, the residual strain with fast cooling is smaller than that with slow cooling. These observations suggest that the volume fraction of the c-domain is larger for fast cooling and that the atmospheric conditions during the first post-deposition cooling process may control the domain structure.     

A Decomposition Approach to Preventive Planning of Reactive Volt Ampere (VAR) Source Expansion

This paper presents a two-level approach for determining the minimum cost expansion pattern (location and size) of new reactive compensation sources that would ensure steady-state secure operation of large scale power systems not only under a given set of operating conditions for the intact system, but also under contingency conditions. This preventive planning problem is decomposed into a var dispatch (Level 1) problem and a var allocation (Level 2) problem which are related together using the generalized Benders decomposition. The methodology has been implemented in a prototype computer package which can handle power systems with up to 1500 buses. Results of testing the package with practical power systems of different sizes and characteristics are presented.     

A New Rate of Change of Impedance-based Islanding Detection Scheme in Presence of Distributed Generation

Abstract—Integration of distributed generation with utility network demands satisfactory operation of an islanding detection scheme, as it can otherwise lead to such problems such enhancement in non-detection zone, out-of-phase reclosing, personnel safety, and degradation of power quality. This article presents a new islanding detection scheme based on the rate of change of impedance (dz/dt) of each phase. To calculate dz/dt, phasor computation is carried out using a half-cycle modified discrete Fourier transform algorithm. Test data are generated using the PSCAD/EMTDC software package (HVDC Research Center, Inc., Manitoba). Various islanding conditions have been simulated by disconnecting the main circuit breaker with different values of active and reactive power mismatch. At the same time, different non-islanding conditions have also been simulated through switching (ON/OFF) of load, energization/de-energization of medium transmission lines, short-circuit on an adjacent feeder, and switching (ON/OFF) of the transformer and capacitor bank in the network. The simulation results indicate that the proposed scheme is capable of providing effective discrimination between islanding and non-islanding conditions. The proposed scheme is able to detect islanding conditions within a half-cycle from event inception.     

An iterative system inversion technique

An inversion iterative algorithm for discrete‐time non‐linear systems is presented. The algorithm is tuned depending on system characteristics. Under the assumption that the system inverse exists, the iterative algorithm constructs the system inverse by attempting to achieve on‐line the perfect tracking. The inversion process is based on the observation of the input–output pairs. The resulting control scheme requires a very low a priori knowledge of the system dynamics. Moreover, low‐engineering efforts are needed to apply the control scheme to a particular control problem or to modify it in order to accommodate changes in the physical system. Copyright © 2001 John Wiley & Sons, Ltd.     

电站大型管道的推弯工艺及其计算机辅助设计

分析了中频弯管推弯工艺的特点。特别指出了“过渡阶段”工艺的重要性,并且结合试验提出了定量化的推变工艺方案和用计算机辅助设计进行推弯工艺分析和设计的方法。该工艺方案和计算机辅助工艺分析软件包已应用在中频弯管计算机监控系统上,在国内首次实现了中频这的自动化并且弯制出质量合格的弯管。     

New Algorithms for Computer Based Power System Measurements for Relaying

Abstract

The paper presents two new algorithms for power system measurements for computer relaying. The algorithms involve the design of a discrete-time digital filter which interpolates the signal samples and generates Fourier Co-efficients either by using spectral observations or a functional expansion technique. Sample designs are presented for voltage and current phasor estimation during system transients. A method for including decaying dc and harmonic frequency components in the filter design is also described in the paper. Both computational and on-line test results using an LSI-11/23 microcomputer for power system phasor estimation are presented in the paper.