自组织映射神经网络用于动态电压稳定分析的新方法

介绍了一种利用人工神经网络(ANN)进行动态电压稳定分析的新方法。这种多层自组织网络(SHNN)综合利用了自组织映射网络(文中使用Kohonen网络)和多层感知机网络（MLP）。Kohonen网络把输入样本按运行条件的相似性进行聚类,从而使MLP网络的性能得到提高。使用2个SHNN模型,一个用于判定电力系统是否处于动态稳定,另一个预测动态稳定系统的PQ节点的电压幅值。通过动态模拟得到训练样本。最后对WSCC 9节点系统和New England 39节点系统进行数字仿真,证明了该方法的有效性。     

Performance evaluation of dynamic load models for voltage stability analysis

In this paper the first order aggregate dynamic load models for the representation of the induction motor loads have been evaluated from the voltage stability analysis point of view. Two models, the First order Variable Admittance (FVA) model and the Aggregate Nonlinear Recovery (ANR) model have been considered along with the system dynamic equations to obtain the dynamic voltage stability limit of the system. The adequacy of these two models is verified with a third order Detailed Induction Motor (DIM) model for the representation of induction motor loads. The results are presented for all the models for three different test systems. It is shown that the dynamic load models used for the representation of induction motor loads have a tremendous effect on the voltage stability of the system.     

电力负荷动特性实测建模的外推和内插

本文在处理实测数据的基础上介绍了综合负荷动特性建模的一些基本概念和问题；比较了差分方程模型和人工神经元模型在非线性外推和内插上的优劣。     

ANALYSIS OF POWER CONVERTER CONTROL USING NEURAL NETWORK AND RULE-BASED METHODS

ABSTRACT

Current-controlled voltage source inverters offer substantial advantages in improving motor system dynamics for high-performance ac drive systems. The controller switches follow a set of reference current waveforms. Fixed-band hysteresis and sinusoidal-band hysteresis controllers have been studied. The first part of this paper develops neural network and fuzzy logic based current-controlled voltage source inverters. The models and learning techniques have been investigated by simulation. The implementation of neural networks is described and simulation results are presented. In the second part of this paper, the new UPS (uninterruptible power supply) with fuzzy logic compensator is proposed. Proposed fuzzy logic compensator is used to prevent voltage drop from nonlinear load. The total harmonic distortion (THD) of proposed scheme is better than that of conventional deadbeat control method for linear and nonlinear load. In the third part of this paper, the application of fuzzy control to DC-DC converters operating at finite switching frequency is studied. Several control methods currently used for buck, boost and buck/boost converters are compared to the fuzzy converter control. Simulation results for several control methods are presented. The simulations show that the fuzzy control method has better dynamic performance and less steady state error.     

DYNAMIC STABILITY OF PARALLEL CONNECTED SYNCHRONOUS GENERATORS BY THE EIGENVALUE METHOD

ABSTRACT

Parallel operation of synchronous generators is commonly used in limited independent power stations. This paper introduces an approach to the determination of dynamic stability of such electrical power stations. The role and influence of the automatic voltage regulators in improving the quality of the parallel operation is discussed. A state-space representation of a power system including two synchronous generators connected in parallel and supplying loads has been accomplished. The eigenvalues method is applied for the determination of the system dynamic stability. The method presented here has the advantage that it provides a technique for evaluating the dynamic stability limit of interconnected-synchronous generators systems. The stable loading conditions for the limited independent power station can also be found by defining the stable regions of operation. Stable-regions charts have been derived for the cases of a single generator station and a power station that consists of two parallel-connected generators. These charts are drawn for a typical independent power station supplying the electric loads of a gas plant. The comparison of the charts for a single -and two parallel generators has shown that parallel operation increases the stable regions at the same loading conditions. An induction motor load of a comparable size to that of the generating unit is applied. Its influence on the dynamic stability of the system is investigated.     

EFFECT OF LOAD MODELING ON STEADY STATE VOLTAGE STABILITY

ABSTRACT

This paper discusses the importance of load modeling in power systems for voltage stability studies. The steady-state voltage stability analysis is carried out using the available continuation power flow. Different types of load models - constant power; constant current; constant impedance; and composite load, which is a combination of the first three models, are considered. The composite load model is obtained using the LOADSYN software, where the load dependency on voltage is considered. The concept of load connectivity is defined and the confusion about the critical point with respect to PV curves is clarified. It is shown that for nonlinear loads, the critical point is not at the tip of the PV curve.     

Verification and expansion of a method of transient analysis of voltage collapse based on the induction motor load model

Voltage instability is now under intensive study in Japan, and some dynamic methods for analyzing voltage collapse have already been presented. However, the suitability of load models used in the methods and the generality of the results have not been verified. In this paper, useful voltage collapse data acquired in real power systems are presented. The measured data are compared with the result of dynamic digital simulation to verify the suitability of an induction motor load model. In the latter half of this paper, dynamic simulations of voltage collapse with consideration of generator dynamics are carried out. An interconnected power model system with 10 nodes is analyzed. The generality of basic characteristics concerning voltage collapse which have already been obtained without considering generator dynamics is verified by such simulations.     

On influence of load modelling for undervoltage load sheddingstudies

This paper explores the influence of load models on decisions of undervoltage load shedding in power systems. A controlled load rejection can be used as an emergency countermeasure to avoid widespread blackout when system voltages are unstable. In this paper, dynamic simulations of a small power system using both static and dynamic load models are presented. When using a static load model, the system includes an explicit model of a transformer with load tap changer. The aim is to demonstrate how different load models influence the analysis and calculation of the amount of load needed to be shed to stabilise the system voltage     

用人工神经元网络和最小二乘法估计负荷模型的比较

该文分别采用现代辨识技术之一的递推最小二乘法和人工神经元网络(ANN)误差反向传播算 法(BP算法)估计2000年四川电网某一变电站的负荷模型，结果表明人工神经元网络模型 能更好地反映负荷的非线性特性。     

Optimal scheduling of electrical power in energy-deficient scenarios using artificial neural network and Bootstrap aggregating

In a developing country like Pakistan, where the electrical power demand is more than the generated power, maintaining the power system stability is a big challenge. In such cases it becomes, thus, essential to shed just the right amount of load to keep a power system stable. This paper presents a case study of Pakistan’s power system where the generated power, the load demand, frequency deviation and the load shed during a 24-h duration have been provided. The data have been analyzed using two techniques; the conventional artificial neural network (ANN) by implementing feed forward back propagation model and the Bootstrap aggregating or bagging algorithm. The simulation results reveal the superiority of the Bootstrap aggregating algorithm over a conventional ANN technique using feed forward back propagation model.     

Tuning a static var compensator controller over a wide range of load models using an artificial neural network

A novel approach using an artificial neural network (ANN) for tuning a static var compensator (SVC) controller over a wide range of load models is presented in this paper. To enhance power system damping over a wide range of load models, it is desirable to adapt the SVC controller gain in real time based on load models. To do this, online measurements of load parameters which are representative of load models are chosen as the input signals to the neural network. The output of the neural network is the desired gain of the SVC controller. The neural network, once trained by a set of input-output patterns in the training set, can yield a proper SVC controller gain under any load model. Simulation results show that the tuning gain of a SVC controller using the ANN approach can provide better damping of the power system over a wide range of load models than the fixed-gain controller.     

基于Elman神经网络的甘肃电网负荷预测模型

为提高甘肃电网负荷预测精度,提出了一种基于神经网络的负荷预测方法。针对甘肃电力系统负荷数据的非线性和动态特性,在多层前向BP网络中引入特殊关联层,形成有“记忆”能力的Elman神经网络,从而可以映射系统的非线性和动态特性。在网络训练算法中,采用自适应学习速率动量梯度下降反向传播算法,显著提高了网络的训练速率,有效地抑制了网络陷入局部极小点。文中分别采用El-man神经网络与BP神经网络建立模型,对甘肃电网实际历史数据进行仿真预测,经分析比较,证明前者具有收敛速度快、预测精度高的特点。这表明利用Elman回归神经网络建模对甘肃电网负荷进行预测是可行的,能有效提高负荷预测精度,在负荷预测领域有着较好的应用前景。     

Optimal integration of DGs into radialdistribution network in the presence ofplug-in electric vehicles to minimize dailyactive power losses and to improve thevoltage profile of the system using bioinspiredoptimization algorithms

Purpose: The increase in plug-in electric vehicles (PEVs) is likely to see a noteworthy impact on the distribution system due to high electric power consumption during charging and uncertainty in charging behavior. To address this problem, the present work mainly focuses on optimal integration of distributed generators (DG) into radial distribution systems in the presence of PEV loads with their charging behavior under daily load pattern including load models by considering the daily (24 h) power loss and voltage improvement of the system as objectives for better system performance. Design/methodology/approach: To achieve the desired outcomes, an efficient weighted factor multi-objective function is modeled. Particle Swarm Optimization (PSO) and Butterfly Optimization (BO) algorithms are selected and implemented to minimize the objectives of the system. A repetitive backward-forward sweep-based load flow has been introduced to calculate the daily power loss and bus voltages of the radial distribution system. The simulations are carried out using MATLAB software. Findings: The simulation outcomes reveal that the proposed approach definitely improved the system performance in all aspects. Among PSO and BO, BO is comparatively successful in achieving the desired objectives. Originality/value: The main contribution of this paper is the formulation of the multi-objective function that can address daily active power loss and voltage deviation under 24-h load pattern including grouping of residential, industrial and commercial loads. Introduction of repetitive backward-forward sweep-based load flow and the modeling of PEV load with two different charging scenarios.     

ANN modeling for design of a matched low noise pHEMT amplifier for mobile application

For high quality performance, future efficient wireless communication systems require a Broadband Amplifier in the frequency range under consideration. When such an amplifier is plugged into the measuring path it would enable the system to perceive even the weakest of signals. To achieve this, a new Scattering-parameter model that is valid for a wide frequency range has been developed for microwave analysis of a pseudomorphic high electron mobility transistors (pHEMT). The developed neural network model is used for designing a pHEMT power amplifier. The calculated S-parameters, gain and minimum noise figure from the artificial neural networks (ANN) model are the parameters used to design the low noise pHEMT power amplifier. The various gains so obtained from the S-parameters have been plotted with the frequency and it was found to yield a close fit to the simulated model. Neural network training has been done using Levenberg-Marqaurdt back propagation algorithm implemented in ANN toolbox of MATLAB software. All the results have been compared with the experimental data that showed a close agreement and validated our model. The calculated S-parameters, gain and minimum noise figure from the ANN model are the parameters used to design a stabilized and matched LNA.     

Dynamic behavior of a single-phase self-excited induction generator using a three-phase machine feeding single-phase dynamic load

This paper is motivated to analyze the transient behavior of a single-phase self-excited induction generator (SEIG) using a three-phase machine due to switching of single-phase dynamic load like induction motors. The generator consists of a three-phase star connected induction machine excited with three-capacitors and a single-phase induction motor (IM) load. The developed dynamic models of the SEIG and the motor are based on stationary reference frame d–q axes theory incorporating the effect of cross-saturation in the magnetic circuit of the machine and the equations of excitation capacitors are described by three-phase abc model. The system suffers from heavy transients during switching of induction motor and becomes unstable. These problems may be due to resonance caused by series capacitors and the inductive motor load. The use of damping resistors across one series capacitor is proposed to damp out the starting transients for the stable operation. The motor can be started up successfully using the damping resistor. The variation of the damping resistance with the increase in load on the motor after successful starting to maintain constant terminal voltage has been presented. The eigenvalue technique is also employed to examine the transient conditions in the studied SEIG-IM system. The simulated and experimental results are presented for both the unsuccessful and successful starting of the motor. These results are in close agreement with each other, which show the effectiveness of the approach.     

EFFECTS OF INDUCTION MOTOR LOAD ON DYNAMIC STABILITY OF POWER SYSTEMS

Abstract

A study of the effects of induction motor load on the dynamic stability of power systems is presented in this paper. The power system is modelled as a multivariable system with load dynamics considered in the feedback path. The induction motor is represented by a transfer function matrix relating bus voltage magnitude and frequency to the active power and reactive power of the motor

Multivariable Nyquist criterion and eigenvalue analysis are used to investigate the effects of induction motor dynamics on system stability     

电压稳定分析中异步电动机动态负荷建模探讨

探讨电压稳定分析中异步电动机(IM)负荷的建模问题。分析一般的动态负荷模型(GDLM)不能捕捉IM动态行为的机理。分别以IM的滑差模型和滑差磁链模型为基础，严格地导出了适用于电压稳定分析的简化一阶(SIM)和详细三阶(DIM)动态负荷模型，同时还说明了SIM和DIM模型实质上是对GDLM模型进行了不同程度的改进。对SIM和DIM模型在暂态电压稳定分析和静态电压稳定分析中的适用性进行分析比较，仿真结果表明：SIM和DIM分别以不同的准确度适用于不同场合的电压稳定分析。     

MODELING AND ELIMINATION OF LOAD BUSES IN OPTIMAL POWER FLOW SOLUTIONS

ABSTRACT

This paper presents a method to solve the optimal power flow problem after eliminating load buses from the system. Loads are first modeled and reflected in the admittance matrix and then their respective buses are eliminated. The obtained model is a reduced model of the original system. The admittance matrix is of the same order as the number of voltage-controlled buses in the system. The variables of the reduced model are the voltage-controlled buses voltages, angles and active power generations. Newton Raphson method is used to calculate the variables of the reduced model while minimizing an objective function. Voltages and angles of the original system are then calculated by a direct method. These voltages are required to update load models and to check for voltage and line current violations at the eliminated portions of the network. The simulation is carried out on two systems, IEEE 118 bus test system and a 131 bus actual system. It is shown that solution time is significantly reduced when compared to the conventional optimal power flow Newton Raphson method using the original system.     

A new approach for low voltage ride through capability in DFIG based wind farm

Protection against voltage dips is very important for transient stability in a Doubly Fed Induction Generator (DFIG). Conventional crowbar circuits have been used for protection of DFIGs; however, they may be insufficient in some transient situations. Therefore, the Low Voltage Ride Through (LVRT) capability was enhanced by a Demagnetization Current Controller (DCC) for the purpose of transient analysis. In addition, both stator and rotor circuit electromotive forces were modeled in a DFIG. The performances of the DFIG models with and without the DCC were compared. Modeling was carried out in a MATLAB/SIMULINK environment. A comparison of system behaviors was made between three-phase faults with and without a stator–rotor dynamic. Parameters for the DFIG including output voltage, speed, electrical torque variations and d–q axis rotor–stator current variations in addition to a 34.5 kV bus voltage were examined. It was found that in the DFIG model the system became stable in a short time when using the DCC.     

负荷模型对电力系统动态稳定的影响

随着大区电网的互联,低频振荡在我国电力系统中已成为突出的问题.本文研究电力系统的负荷模型对电力系统动态稳定的影响.通过搭建单机无穷大系统,理论上研究送端负荷分别采用恒功率,恒电流及恒阻抗模型时,分析其与自动电压调节器及电力系统稳定器的相互作用对电力系统动态稳定的影响.通过对一个两区域四机系统的典型实例,利用PSD-BP...