Load modeling at electric power distribution substations using dynamic load parameters estimation

This paper is focused on electric power distribution substations load modeling using dynamic load parameters estimation. The load parameters are estimated using two models: the exponential and the ZIP load models. Since the load bus voltage and parameters are known one can determine the active and reactive power injections of this bus and include these pseudo-measurements in the state estimation in order to improve observability and estimation accuracy. The dynamic parameter estimation is developed using the weighted least squares method in a recursive form and the tests are carried out based on actual measurements. It is shown that the estimated parameters (for both load models) at a distribution substation are valid, since the obtained active and reactive power residuals are very close to zero.     

电力系统广域继电保护研究综述

分析了传统继电保护在保障电网安稳运行时存在的问题,对基于广域信息的继电保护研究涉及的主要内容进行了综述,包括:在线自适应整定、潮流转移识别、基于故障元件识别的广域后备保护.在线整定的目的是根据系统运行方式的变化,调整保护定值至最佳状态.计及的运行方式变化包括:电力设备投退、发电机出力与负荷变化等.潮流转移识别旨在防止传统后备保护的不适当动作引发电网连锁跳闸事故,主要方法有:支路开断前后输电断面的有功潮流比较、相邻支路电流比较.广域后备保护利用电网多点量测信息确定故障元件的具体位置,从根本上克服了传统后备保护整定复杂、可靠性低的问题.主要研究包括:基于传统主保护理论的故障识别算法、广域信息的容错性算法.最后,提出了以基于故障元件识别的广域后备保护为基础,构建面向智能电网的广域继电保护系统,并对其发展方向进行了展望.     

Separable identification of nonlinear aggregate power system loads

An identification algorithm for a power system load model is proposed in this paper. The overall non-convex identification problem is separated into convex and non-convex subproblems, allowing for a global optimum to be found.     

电力系统潮流计算研究现状

电力系统潮流计算是电力系统分析中最基本的一项计算。本文对电力系统潮流计算进行了综述。首先简单回顾了潮流计算的发展历史;接着对当前基于计算机的各种潮流算法的原理及其优缺点,作了简要介绍和比较,并介绍了它们采用的一些特别技术及程序设计技巧;最后简述了当前潮流算法存在的问题及对未来的展望。     

Controllable analog emulator for power system analysis

This paper details the development of a controllable analog emulator for power system analysis. The emulator consists of reconfigurable analog hardware for power system emulation and a digital computer, along with associated software, for configuration, control, calibration and data acquisition. The analog hardware is fully controllable via the software interface. System parameters, initial conditions, integration, faults and contingencies can be created or altered via the software with no changes or manual intervention to the analog hardware. This advance overcomes one of the larger drawbacks of older analog computers, which was the need for manual configuration and calibration. The emulation methodology is presented in this paper as well as power system modeling, both theoretical and in analog hardware. The software interface and control is also presented. To validate the operation of the emulator two examples are shown from a prototype emulator. The first being a steady state power flow solution, the second computes the critical clearing time of a generator fault for transient stability.     

电力系统负荷建模中的小波神经网络新技术

电力系统负荷建模对电力系统规划，运行和控制决策起着关键的作用，讨论了负荷建模的基本方法，以及电力系统负荷建模和参数辨识中的小波神经网络新技术，反映了小波变换在系统负荷建模中的应用前景。     

采用广域测量信号的PSS参数优化设计

为了解决传统的电力系统稳定器PSS(Power System Stabilizer)因局限于反馈本地信号而不能很好地抑制区域模式的问题,针对区域模式装设引入广域测量信号的PSS,针对地区模式装设引入本地信号的PSS。根据参与因子确定PSS装设地点,然后应用遗传算法对其参数进行协调。由于PSS反馈远方信号,设计时考虑了通信延迟的影响。算例表明,提出的方案能够较好地抑制低频振荡。     

Design and allocation of power system stabilizers using the particle swarm optimization technique for an interconnected power system

In this paper, three particle swarm optimization (PSO) based power system stabilizers (PSSs) are developed for three power systems. The system under study here is a power pool consisting of 3 power systems. System I represents the Egyptian power system, system II represents the Jordan and Syrian power systems, and system III for the Libyan power system, which are originally self standing and completely independent systems. As a matter of fact each of them should equipped with its own PSS. For this reason this work is started by designing an optimum power stabilizer for each of them standing alone. After which, the developed PSSs are firstly installed one at a time. Then the three PSSs are installed together in the interconnected power system and their effect on its dynamic performance is studied.As a test for stabilization efficiency, the detailed power system model is subjected to a forced outage of a 600-MW generator, which is the biggest unit in the pool, when it is fully loaded. This outage results in loosing of about 3% of the spinning capacity of system I and about 2% of the spinning capacity of the whole interconnected system. The obtained results show an improvement in the power pool performance accompanied with an improvement in the inter-area oscillation.     

Robust hierarchized controllers using wide area measurements in power systems

In this paper, we present a new method for robust centralized controller design using LMI’s with applications to power systems. This method makes possible to increase the damping rate of the decentralized system (that is, power system with PSS’s). It considers delays added to the signals that travel from the generators to the central controller. The robust hierarchized controller is composed by two control layers: the first one consists on decentralized controllers, that are applied independently to each machine of the system, what guarantees the stability and a minimum damping rate; the second one is composed by a centralized controller, that receives delayed information from all machines of the system, and it sends control signals to all generators. The centralized controller algorithm is robust, once it considers various operative conditions for the power system, and it also permits the choice of the communication delays.     

Decentralized load frequency controller for a multi-area interconnected power system

This paper proposes a control scheme for the load frequency control (LFC) problem of multi-area power systems. These systems are treated as interconnected dynamical systems. In the design of the proposed controller, each local area network is overlapped with states representing the interconnections with the other local area networks in the global system. Then, a decentralized control scheme is developed as function of the local area state variables and those resulting from the overlapped states which represent an approximation of the interconnection variables. The proposed controller guarantees the asymptotic stability of the overall closed loop system.The simulation results indicate that the proposed control scheme works well. In addition, they show that the controlled system is robust to changes in the parameters of the power system and to bounded input disturbances acting on the system. Moreover, the simulation results show that the controlled system behaves well even when there is a maximum limit on the rate of change in power generation.     

Fixed-order controller for reduced-order model for damping of power oscillation in wide area network

The interconnected power systems are complex and stabilizing control design still remains challenging task. The use of wide area monitoring system (WAMS) offers an integrated measurement-based and model-based control, which suits to the operation of large electric power system (EPS), along with online analysis. This paper presents a study on fixed-order controller design for equivalent network of coherent generator in order to stabilize inter-area electromechanical oscillations in the system. Firstly, the coherent generators in each area of large EPS are determined by mutual information theory, which represents the dynamic equivalence. Then network of each area with input–output variables of the selected generator that participates dominantly is reduced to lower size by square-root variant of balanced truncation algorithm. The dynamics and important oscillation modes are verified in equivalent representation of each area. Finally a local controller (decentralized) in each coherent area and a centralized controller between two coherent areas for selected generator are designed by reducing the H^∞ norm of its closed loop transfer function as much as possible. These controllers feed supplementary control signal in addition to one fed by local conventionally tuned PSS. The decentralized controller for selected generator is fed by local bus power or generator’s speed signal. On other hand, the centralized controller uses difference of power flow/speed of generators as input signal to dampen the oscillations between equivalent networks of two areas. The simulation results reveal effective damping of power/speed oscillations achieved by designed controller with respect to conventional PSS implemented. The robustness of controller is verified for heavy and light load operating conditions.     

Study of a major oscillations event in northeastern area of the Iranian power network

Iranian power system encountered major oscillations in January 2008 in the northeastern area with an amplitude of about 120 MW. Since not all the events and variables had been recorded, a scenario to simulate the recorded oscillations and results of studies conducted to reproduce the oscillations by simulation are discussed in the first part. Tuning of supplementary controllers, such as PSSs, on the generating units and the use of reactive power compensators in the long transmission line to enhance stability and eliminate severe oscillations between the north and eastern areas are investigated in the second part. Eigen-value analysis and participation factors are used to appreciate the nature of oscillations and the required PSS settings. The results show that, by using the properly tuned PSSs and accurate compensation of the reactive power, transient stability and damping of oscillations are considerably improved.     

A constrained orthogonal state estimator for external system modeling

Attention is focussed on the application of constrained orthogonal state estimation to external system modeling. Inequality constraints enforce realistic limits on the estimates of External System (ES) variables that otherwise can become off bounds due to the limited ES monitoring capabilities at the Internal System control center. Equality constraints are used to model known zero bus injections in both systems. The use of orthogonal methods is advocated to ensure numerical stability, since the estimator has to handle a larger range of measurement weights than in conventional applications of state estimation. Tests to evaluate the performance of the proposed constrained estimator using three power networks of different sizes are also reported in the paper.     

A comprehensive modeling framework for dynamic and steady-state analysis of voltage droop control strategies in HVDC grids

This paper presents a comprehensive modeling framework to analyze and compare the performance of different voltage droop control characteristics in an HVDC grid. All models are fully derived mathematically, both for dynamic simulations and for steady-state power flow analysis. The main contribution lies in the development of a common modeling and control approach for the different droop-based control schemes that have been presented in the literature. The discussion includes power- and current-based droop control, either in their standard form or combined with a deadband, a constant voltage control or consisting of different slopes. Dynamic simulations show that, when applying a comparable underlying dynamic converter control framework, similar dynamic responses can be expected from the different droop control schemes, while the steady-state voltage deviations and power sharing after a contingency are different. A comparison with results from a full-detailed power flow implementation shows that these voltage deviations and power sharing can accurately be predicted by the derived steady-state power flow models, thereby avoiding the need for time-consuming dynamic simulations.     

广域测量技术在电力系统中的应用研究进展

大规模交直流混合电网的建设和发展,对电力系统稳定和控制在空间广度和时间维度上提出了更高的要求。广域测量系统(Wide Area Measurement System,WAMS)的同步量测数据在空间和时间上满足上述要求,因而研究WAMS技术在电力系统中的应用十分必要。从WAMS的结构和原理出发,总结了近五年来广域测量系统在电力系统动态监测与故障分析、辨识与估计、系统稳定控制和广域保护等方面的研究进展,并详细分析了其中存在的问题。最后展望了广域测量技术需要进一步研究的问题,指出基于WAMS技术构建大规模互联电力系统的广域安全监测及控制系统是一个很有意义的研究方向。     

一种适应大跨度电压变化的综合负荷静态模型

建立合理的综合负荷静态模型对电力系统静态电压稳定性分析具有重要意义．在对感应电动机静态电压特性进行动模实验和仿真分析的基础上,对综合负荷的静态电压特性进行了较深入全面的研究．提出了一种综合负荷静态模型．所提出的模型能合理地描述综合负荷在低电压运行条件下的静态行为,具有全电压范围适应性,对电力系统静态电压稳定性分析具有较大的理论和实用价值．     

A new paradigm for parameter estimation in system modeling

In this paper, we consider a basic problem in system identification, that of estimating the unknown parameters of a given model by using input/output data. Available methods (extended Kalman filtering, unscented Kalman filtering, particle filtering, maximum likelihood, prediction error method, etc.) have been extensively studied in the literature, especially in relation to consistency analysis. Yet, other important aspects, such as computational complexity, have been somewhat overlooked so that, when such methods are used in practical problems, remarkable drawbacks may arise. This is why parameter estimation is often performed using empirical procedures. This paper aims to revisit the issue of setting up an estimator that is able to provide reliable estimates at low computational cost. In contrast to other paradigms, the main idea in the new introduced two‐stage estimation method is to retrieve the estimator through simulation experiments in a training phase. Once training is terminated, the user is provided with an explicitly given estimator that can be used over and over basically with no computational effort. The advantages and drawbacks of the two‐stage approach as well as other traditional paradigms are identified with an illustrative example. A more concrete example of tire parameter estimation is also provided. Copyright © 2012 John Wiley & Sons, Ltd.     

An interpretative structural modeling based network reconfiguration strategy for power systems

The network reconfiguration is an important stage of restoring a power system after a complete blackout or a local outage. Reasonable planning of the network reconfiguration procedure is essential for rapidly restoring the power system concerned. An approach for evaluating the importance of a line is first proposed based on the line contraction concept. Then, the interpretative structural modeling (ISM) is employed to analyze the relationship among the factors having impacts on the network reconfiguration. The security and speediness of restoring generating units are considered with priority, and a method is next proposed to select the generating unit to be restored by maximizing the restoration benefit with both the generation capacity of the restored generating unit and the importance of the line in the restoration path considered. Both the start-up sequence of generating units and the related restoration paths are optimized together in the proposed method, and in this way the shortcomings of separately solving these two issues in the existing methods are avoided. Finally, the New England 10-unit 39-bus power system and the Guangdong power system in South China are employed to demonstrate the basic features of the proposed method.     

电力系统综合负荷建模平台的开发

开发了一个电力系统综合负荷建模软件平台.平台由原始数据库服务器、应用服务器和客户机3个层次构成，实现原始负荷特性数据管理、数据预处理与基于元件的负荷特性综合、模型结构选择与辨识建模以及动特性分类与综合三大功能.运用结构化软件设计思想，各功能模块相互独立;数据库服务器采用SQL Server 2000开发工具，操作界面采用Visual Basic6.0开发环境，功能模块采用Visual Basic6.0和Visual C＋＋6.0实现.平台以湖南电网综合负荷特性的调查统计数据和变电站现场采集的负荷特性数据为基础，实现了基于元件和基于量测2种途径的综合负荷建模，具有功能完善、设计新颖、运行可靠、操作简单、扩展性好的特点，能够方便地建立各典型用户、各用电行业和变电站的综合负荷模型.     

新型功角与相量广域测量系统及其在河南电网中的全面实施

提出一种新型功角测量原理,具有不需专门安装探头、不需停机安装、可在任意时刻启动的特点。在此基础上研发了功角与相量测量单元APMU(Angle&PhaseMeasurementUnit)。对河南电网内全部发电厂安装了APMU,4个500kV枢纽变电所安装了相量测量单元PMU(PhaseMeasure鄄mentUnit),构成系统级的广域测量系统WAMS(WideAreaMeasurementSystem)。介绍了该WAMS的系统结构,实现了功角监视、同步故障录波、引入状态估计的功能。