Dynamic load modelling based on measurements in medium voltage distribution network

The paper presents dynamic load model parameters obtained from measurements on medium voltage (10 kV) bus. Over 100 measurements are performed on secondary side of 110/10 kV transformer during different periods of the day, different days of the week and different seasons of the year. The measured real and reactive power responses to voltage step are used as the input to parameter identification procedure based on curve fitting using least squares method and load model parameters are determined. The results of measurements are statistically analysed and discussed and relationship between model parameters established and quantified. The load model parameters are classified into several groups (year, season, day, time of the day) and 95.5% probability ranges determined for each group. Finally the identified parameters of the dynamic load model are compared with previously published data and simulated load model responses with recorded field measurements.     

An extended Kalman filtering approach for detection and analysis of voltage dips in power systems

This paper proposes a new method based on the use of an extended Kalman filter for the detection and analysis of voltage dips in power systems. The paper describes the model used to enable the most accurate representation of the system and the selection of the parameters to ensure optimal filter performance. The results obtained using this method are presented both for simulated and for real voltage dips and are compared with the results obtained using the rms method proposed in the power quality standards in order to demonstrate the improved performance of this new method in the estimation of the time instant of the beginning and end of a voltage dip as well as in the estimation of the magnitude and phase angle of voltage supply during the event.     

Transmission voltage recovery delayed by stalled air conditionercompressors

Southern California Edison Company (SCE) has experienced delayed voltage recovery following fault clearing on the transmission system. The authors describe these occurrences and document the studies which successfully modeled the voltage recovery process. The studies showed how the stalling of single-phase air conditioner compressors following a power system fault was the root cause of delayed voltage recovery. Tests of air conditioner response to voltage dips are documented. The results of these tests are used to derive the mathematical load models used in voltage recovery studies     

A Method for Determining Nonlinear Inductances of Electrical Equivalent Circuit for Three-Phase Induction Motor

Accurate values of the equivalent circuit parameters of three-phase induction motor are critical for its precise performance evaluation. Motor parameters, mainly the inductances obtained from conventional no-load and blocked rotor tests are constant parameters for all load conditions. However, due to inherent nature of the core material property, i.e., nonlinear B-H curve, the inductances do not remain constant in practical. This work proposes a method comprising simple tests using which all the motor nonlinear inductances can be determined. The motor mathematical model under the test conditions is also developed. The results obtained from equivalent circuit using the nonlinear inductances are validated with experimental results for two different motors and good agreement has been achieved. It is observed that the motor performances calculated using nonlinear inductances matches more closely to experimental results as compared to that using constant inductances.     

东北电网大扰动试验仿真计算中的综合负荷模型及其拟合参数

2004年和2005年分别在东北电网进行了4次金属性三相短路大扰动试验。以上述大扰动试验的实测数据为依据,对试验结果和仿真结果进行了对比研究,并调整了励磁系统的模型和参数,恢复了接入低压网络的小电源供电。通过分析各种负荷模型的适应性,给出了考虑配电网的综合负荷模型的拟合参数。采用上述拟合参数进行仿真实验,验证了该综合负荷模型及其拟合参数的正确性和有效性。     

NUMERICAL SIMULATION OF SYNCHRONOUS GENERATOR ON STEADY STATE

ABSTRACT

In its first part, this paper deals with steady state operation of a synchronous generator knowing its geometry, its magnetic characteristic, its output voltage and the field current. The second part is about the computation of the field current and load angle knowing the load of the synchronous generator, in terms of active power (P), reactive power (Q) and terminal voltage (V).

While the magnetic material characteristic is linear, the machine's equations can be solved analytically for the determination of its operating point. But when it is in a nonlinear area the problem becomes more intricate. In that case numerical modeling is very useful. In this paper we propose a model based on the simultaneous solution of electric and magnetic equations, where the latter are solved using the FEM. To consider the movement, the electric equations are expressed in d-q reference axes. As current and load angle are unknown, one has to add a new nonlinear electric equation to the classical nonlinear magnetic system. In our model the solution is obtained using the Newton-Raphson iterative procedure.

Numerical applications have been done on an EDF (Electricité de France) 1300MW synchronous generator designed by GEC.ALSTHOM. To show the validity of the model different trials have been performed, first without load, then when the machine produces active and reactive power.     

新型整流变压器及其滤波系统的运行参数特性分析

新型整流变压器及其滤波系统由网侧、阀侧绕组,独立滤波绕组及与之相连的滤波器组构成,其特殊的滤波支路能够在滤波和无功补偿的同时改善变压器的运行特性。首先推导以谐波抑制因子为表达方式的谐波电流抑制模型以考察谐波传递情况;然后构建网侧绕组电流和负载电流之间的数学关系,藉此研究无功补偿特性,并分析相关的运行参数;之后建立阀侧电压与网侧电压的数学关系,以研究滤波器对阀侧电压的影响。理论分析表明,新型整流变压器及其滤波系统可以有效抑制谐波,降低网侧电流和视在功率,提高网侧功率因数并增加负载电压。实际应用在工业直流供电系统中的新型整流变压器的现场实测结果,验证了理论分析的正确性。该文更全面地揭示了新型整流变压器能改善整流系统的运行特性,所推导的数学模型将为新型整流变压器在降噪节能等方面的进一步研究提供理论依据。     

降低HVDC逆变器无功损耗的非线性附加控制

在逆变侧交流电压下降期间,逆变器对无功消耗的增多会导致电压进一步恶化,甚至崩溃。因此,在传统PI控制的基础上,基于非线性控制中的状态反馈精确线性化方法,设计了用于降低故障期间逆变器无功消耗的非线性附加控制器。仿真结果表明该非线性附加控制器能合理地调节换流器在电压下降期间对无功功率的吸收,以维持逆变侧电压水平,从而提高系统的暂态稳定性。     

Harmonic modeling of linear and nonlinear loads based on Kalman filtering algorithm

Most harmonic nonlinear load modeling techniques developed in the last two decades, assume that the load connected to the load bus has a constant admittance, inductive or capacitive, which depends on the mode of operation of the load (constant R, L, and C). This is not true, since the loads in most cases are nonlinear and they inject harmonics into the system. This paper presents a new application of Kalman filtering (KF) to nonlinear load modeling in the presence or absence of harmonics. The proposed technique uses directly available samples of the load voltage and current to estimate, and track the variation of load parameters. The proposed algorithm can be used directly on-line for harmonics load modeling, as well as, to track the load power active and reactive. The effects of the critical parameters on the behavior of the proposed algorithm are discussed. Results for different simulated examples and practical examples from field measurements are reported in the paper. The conclusion drawn from these examples is that the algorithm is successful in estimating the load parameters.     

传导干扰对电磁继电器工作特性的影响分析

航天电磁继电器的电磁兼容分析技术是军用和航天电子设备的高可靠性、强耐环境的技术基础。以某型号航天电磁继电器为研究对象,建立有限元模型。参照国家标准GB／T17626．29（直流电源输入端口电压暂降、短时中断和电压变化的抗扰度试验）的规定仿真了在电压暂降、短时中断和电压变化三种传导干扰下继电器的动态特性,并且与无干扰情况下的动态特性对比。分析了传导干扰对航天电磁继电器工作的影响,其结论对电磁继电器的设计有一定的指导意义,是研究带有继电器电子设备电磁兼容性的基础。     

基于Larsen推理的电压暂降下工业过程负荷损失率评估方法

明确电压暂降对工业过程的影响程度,是进行暂降损失估计、提供治理方案的前提。考虑了工业过程设备级/过程级的电压暂降耐受能力,提出了一种负荷损失率的评估方法,以量化电压暂降对工业过程造成的危害。首先,为解决过程参数难以获取、精度低的问题,建立了基于物理结构的过程参数等值响应模型。将过程级的非电量过程参数值等效为电压值,以输入电压暂降特征量刻画设备和工业过程的耐受特性。然后,提出了基于Larsen推理的负荷损失率评估方法,以暂降特征量为推理前件、以负荷损失率为推理后件,构建了前件、后件的隶属度函数。实现了基于监测数据的过程负荷损失率的推理评估,减小评估结果对精确信息的依赖性。最后,应用该方法评估海南省某石化企业的电压暂降下负荷损失率,结果表明所提出方法正确且有效。     

Measured and predicted cold load pick up and feeder parameterdetermination using the harmonic model algorithm

This paper presents theory of the “cold load harmonic”, CLHARM, model algorithm for simulation of power feeder currents resulting from both cold load pickup, CLPU, and the “step voltage test”, STEPV. The STEPV method is also presented. Feeder parameters obtained from field STEPV measurement are used to predict CLPU on that feeder using the CLHARM algorithm. STEPV test measurements and actual measured CLPU currents on the same feeder are compared with computer predictions. The CLHARM aggregates feeder thermostatically controlled load to simulate regain of diversity during outage restoration. All feeder weather sensitive load is lumped in CLHARM, using mean parameter values of a simple thermodynamic model. The ultimate objective of this work is experimentally obtained feeder “signatures” for CLPU prediction as a feeder design tool     

UPS逆变器电压控制的Delta调制策略研究

当电流控制的delta调制控制策略应用于UPS逆变器控制时，存在负载变动引起逆变器输出电压幅值不稳定、负载为非线性时逆变器输出电压波形畸变严重等问题。为克服这些不利，该文提出一种电压控制的Delta调制的逆变器闭环控制策略：首先建立了系统控制结构并详细叙述了系统运行原理，然后根据控制结构建立了系统的解析模型，导出了影响系统性能的主要参数。基于离散傅立叶变换和MATLAB仿真，得出并分析了系统主要参数变动影响逆变器性能的各种特性曲线，以指导系统的工程设计。实验结果证明，电压控制的Delta调制逆变器控制策略具有抗扰动能力强、输出电压波形畸变小、实现简单等优点，适合应用于UPS逆变器。     

考虑负荷模糊性的最优协调电压控制

现有电压控制中没有考虑预测负荷和实际负荷之间的偏差,电压控制效果难以保证。为此引入负荷模糊数度量负荷偏离不确定性,提出考虑负荷模糊性的长期电压稳定最优协调控制方法。在含有连续离散时间微分代数方程约束和以负荷节点电压偏差与控制成本最小为控制目标的准稳态控制模型的基础上,建立协调电压控制模糊非线性规划模型;然后,根据最大隶属度原则,将模糊非线性规划问题转化为普通非线性规划问题,并基于内点法求解。通过新英格兰10机39节点系统算例仿真验证该模糊优化电压控制方法的有效性和鲁棒性。     

A Microcomputer Based On-Line Identification Approach to Power System Dynamic Load Modelling

An on-line method for the development of power system load models using system identification techniques is presented. The modelling procedure involves the selection of the load model structure as well as the estimation of the load model parameters. A load model structure selection technique based on the model reference error cost function is used and a square root based least squares estimator is developed. The collection of large volumes of data, for later off-line analysis, is avoided by using an online microcomputer system for the acquisition and analysis of perturbed load data. Load tests were carried out for both agricultural and industrial/commercial loads and typical results obtained are also presented in this paper.     

基于节点戴维南等值的静态电压稳定裕度快速求解

提出一种基于节点戴维南等值参数的静态电压稳定裕度的快速计算方法。通过建立戴维南内电势与负荷裕度的二次多项式模型及节点电压与负荷裕度之间的泰勒展开模型,运用电网基态的参数,求取该节点的戴维南等值参数。根据鼻形点所处的边界条件,导出负荷裕度与等值参数之间的内在联系,从而计算出研究节点的最大负荷裕度。不同于连续潮流计算方法和其他电力系统戴维南等值方法,该方法计算简单快速,能给出节点负荷水平,直观明了。应用这种戴维南等效电路方法计算节点负荷水平时,越是靠近电压稳定极限点,其计算结果越准确。IEEE14和IEEE30节点系统计算验证了此方法的正确性和实用性。     

Effects of momentary voltage dips on the operation of induction andsynchronous motors

Simplified stability calculations of induction and synchronous motors on voltage dips are presented. The voltage dip withstand characteristics of induction and synchronous motors rated at the same horsepower and driving the same inertial loads are calculated. The motor characteristics influencing stability are: the type of motor selected (synchronous or induction); the pull-out torque of synchronous motors and the breakdown torque of induction motors; a constant excitation controller or an excitation boost on voltage dips for the synchronous motors; load and motor inertia; and load characteristics. Synchronous motors are not suitable for fast autoclosing or bus transfer, although these can be autoresynchronized. Transient torques and current surges must be considered when induction motors are connected for fast bus transfer. Due to varying power systems, motors and load characteristics, and much interaction between these, an analysis of avoiding a shutdown on voltage dips has to be performed on a case-by-case basis. This may include a computer-based study. The stiffness of the power system in relation to motor loads, the probable type of faults and fault clearance times, and motor protection and controls are some other concerns requiring an analysis in this context     

电力系统负荷建模和算法的研究及进展

为了给研究人员提供负荷建模研究及在电力系统分析中具有的重要意义较全面的认识,分析了现有的负荷建模方法,系统地阐述了负荷模型及算法上的进展,它包括在静态负荷方面通过采用连续动态方法,根据负荷电压的变化实时修正负荷模型参数,在临界状态下通过分段多项式模型描述加以改进;在负荷建模方面分析了负荷动特性描述、负荷时变性、模型参数的分散性、负荷模型无功分析和负荷的非线性、变结构特性方面问题解决的进展。结果表明,通过采用上述解决方法,使得负荷模型的精确性和适应性得到了较大程度的提高,从而满足复杂大电力系统的动态行为和安全稳定分析的要求。     

泉州地区电网电压骤降的分析及建议

电力系统的电压骤降问题值得关注。通过对泉州地区工业用户受电压骤降影响的程度及电压骤降对敏感设备的影响后果的调查,了解一些敏感设备对电压骤降的耐受能力,同时在一变电站的110kV母线上安装监测仪进行电压监测,并对电网进行仿真计算,最后提出了减缓电压骤降的措施,如加强设备维护,减少故障发生的次数;缩短故障清除时间等。文章还提出了建议,如建立完善的电压质量监测网络;在电力规划、设计时就关注电能质量,加强运行方式的研究等。