Development of equipment models for fast distribution three‐phase unbalanced load flow calculation

This paper presents distribution system equipment models for fast distribution three‐phase unbalanced load flow calculation. Recently, the number of distributed generators introduced into distribution systems has been increasing and detailed system analysis using load flow calculation has been eagerly awaited. Moreover, since many distribution system loads are composed of single phase loads, three‐phase unbalanced load flow calculation is required for the distribution system analysis. Although the fast distribution three‐phase unbalanced load flow calculation has been developed, equipment models considering interconnection of distributed generators have not as yet been developed in Japan. This paper develops practical equipment models such as various distributed generators, voltage control equipment, and loads for fast three‐phase unbalanced load flow calculation in distribution systems. The feasibility of the developed models is verified and demonstrated on practical distribution system models with promising results. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 142(3): 8–19, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10106     

Optimal allocation of wind turbine generator in active distribution network

Nowadays, more and more wind turbine generators (WTGs ) are being integrated into power systems. In this paper, an optimal WTG allocation model with the objective of minimizing the annual cost is proposed. The model can take into account the time‐sequential correlation between the wind speed and load demand, as well as four kinds of active management measures, i.e. regulating the on‐load tap changer of the transformer, curtailing the output power of WTG , regulating the power factor of WTG , and managing the demand side. The time‐sequential correlation is handled by the joint probability distribution method. A hybrid solving strategy combining the fuzzy adaptive particle swarm optimization algorithm and primal‐dual interior point method is developed to get the optimal solutions. Case studies carried out on the IEEE 33‐bus active distribution network verify the feasibility of the developed model and the high efficiency of the proposed solving strategy. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

不对称电力系统相序混合建模与三相潮流算法

由于参数不对称元件和不平衡负荷的存在,电力系统中可能出现三相不对称运行的情况。为此,文中提出一种新的不对称电力系统三相潮流计算方法。该方法采用相序混合建模方法对电网建模,并采用分解协调方式实现全网三相潮流的求解。所述方法兼具相分量法的灵活性和对称分量法的计算高效性,适用于输电网和中高压配电网三相潮流分析和故障计算。针对...     

A self adaptive hybrid differential evolution algorithm for phase balancing of unbalanced distribution system

Electrical power distribution systems are critical links between the utility and customer. In general, power distribution systems have unbalanced feeders due to the unbalanced loading. The devices that dependent on balanced three phase supply are affected by the unbalanced feeders. This necessitates the balancing of feeders. Phase swapping, the process of changing the loads amongst phases, has been practiced for feeder phase balancing. The primary objective of phase balancing is to balance the loads with the phases subject to constraints such as load flow equations, capacity and voltage constraints, while maintaining the radial structure. In this paper, a Self adaptive Hybrid Differential Evolution (SaHDE) technique has been employed to solve the phase balancing problem. The effectiveness of the proposed method is demonstrated through modified IEEE 34 node and IEEE 123 node distribution systems.     

A new current balancer in single‐phase three‐wire secondary distribution feeders using the correlation coefficients

This paper proposes a new current balancer in single‐phase three‐wire secondary distribution systems using the correlation coefficients. The components of the load currents correlative to the primary side voltage waveform, which correspond to the active currents, are detected in each feeder, then the nonactive and unbalanced‐active components are compensated on the source side. The balanced currents with unity power factor are obtained in each feeder. The basic principle of the proposed method is discussed in detail, and then confirmed by digital computer simulation. A prototype experimental system is constructed and tested. Experimental results demonstrate that the balanced source currents with unity power factor are obtained in spite of unbalanced load currents. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 169(1): 50–58, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20843     

Fast computation and stable convergence technique for unbalanced load flow calculation in large‐scale systems

This paper presents a new method of unbalanced load flow calculation to improve complexity by the method of advanced symmetrical coordinates. Usually, the electric power system has been calculated only by the positive phase sequence component on the assumption that three‐phase transmission lines and loads are balanced. However, many ultrahigh‐voltage transmission lines are not transposed, and therefore mutual inductances cause negative sequence currents in the trunk transmission system. Negative sequence currents cause heating of generators and transformers, and therefore the three‐phase sequence component should be calculated accurately. We examined the fast computation and good convergence performance of unbalanced load flow calculation by models of three‐phase transmission lines, transformers, and loads. The proposed method is not the phase coordinate system but the method of symmetrical coordinates. This technique decreases numerical complexity by the use of a simplified Jacobian matrix. The convergence performance of this method is inferior to that of the usual Newton–Raphson method. As a consequence, the problem of poor convergence performance is alleviated by a technique for the newly developed deceleration Newton method. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 174(1): 17–24, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21034     

配电网电能质量控制方法研究

针对１０／０．４ｋＶ配电网的运行特点及其运行中存在的问题,提出了一种通过迭加电势来消除中性线电流或使中性电流减小到某值,并控制低压网中电压水平以满足低压用记的电压要求,同时迭加电流提供非线性负荷所需的非正弦电流,以满足谐波电流不向上级电网扩散,并能保证本级电网谐波指标的方法,用以实现纸压配电网的电能质量控制与改善。给出了针对典型算例的模拟计算结果及初步结论。     

Impact analysis of static voltage assessment based on three‐phase probabilistic load flow with correlated wind power

Impact analysis based on the three‐phase probabilistic load flow (PLF ) algorithm is proposed in this paper to evaluate the effect on static voltage of an unbalanced power system. Correlations between adjacent wind power resources are considered. An improved cumulants method with correlated variables is proposed and applied to the unbalanced system. Cornish–Fisher expansion is used to obtain the cumulative distribution function of bus voltage and line flow. The impacts for wind turbines , which include rated capacity, power factor, and correlation on PLF, are studied, and the relations of the means and standard deviations between three‐phase unbalanced and balanced systems are analyzed. A 25‐bus and a 33‐bus system are studied as examples to show the effectiveness of proposed method, and results of cumulants method are compared with those of Monte Carlo simulations. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

基于连续潮流的配电网供电能力评估

随着非全相运行的分布式电源大量接入配电网,配电网固有的三相不平衡特征更加突出,传统配电网供电能力评估因忽略配电网三相不平衡特征导致结果不准确。为了准确分析三相不平衡特征对配电网最大供电能力评估的影响,建立了以配电网供电负荷参数最大为目标函数,考虑了支路热约束和节点电压等状态变量和分布式电源的有功和无功功率等控制变量的含分布式电源三相不平衡配电网供电能力评估模型。选择电压跌落情况最严重的相作为连续参数,确保预测-校正过程的的连续潮流法求解的结果更加精确。最后,采用拓展的IEEE33节点配电系统进行仿真验证,表明文中所提的模型和求解方法是有效的。     

Unbalanced power flow calculation of a power system containing a variable‐speed generator

There are some factors that render a power system network unbalanced: UHV transmission lines in which three‐phase transmission lines are not transposed, an unbalanced transformer, unbalanced load as well as sustained unbalanced faults. On the other hand, the number of variable‐speed generators used in pumping‐up power stations has recently been increasing in Japan. This paper presents a new means of calculating unbalanced power flow of a power system which contains variable‐speed pumping‐up generators. This new technique is based on the phase coordinate method, because a power system which has elements of unsymmetrical impedance can easily be analyzed by using it. In this paper, phase coordinate models of the variable‐speed generator and its secondary exciting circuit, composed of a GTO converter/inverter, are analyzed first. Procedures of power flow calculation of unbalanced power systems follow. © 2000 Scripta Technica, Electr Eng Jpn, 134(3): 34–43, 2001     

Application of unified voltage analysis for high‐ and low‐voltage distribution systems by power flow calculation using indication method between nodes

It has been noted that the voltage of connection points rises according to the reverse power flow when grid‐connected photovoltaic systems are concentrated in distribution systems in residential areas. When this happens, the photovoltaic system may control the power generation output to maintain a suitable voltage for the connection point. Designing a demand area power system aiming at free access to a distributed power supply for energy‐effective practical use requires a precise understanding of this problem. When analyzing photovoltaic systems mainly connected to low‐voltage systems, we looked for a method of analysis in which the high‐voltage systems and the low‐voltage single‐phase three‐wire systems are unified. This report concerns use of the indication method between nodes using power flow calculation, for the purpose of developing a technique of analyzing unified high‐voltage systems and low‐voltage single‐phase three‐wire systems. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 147(3): 49–62, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10255     

Applying control scheme function of PV inverter for minimizing voltage fluctuation and imbalance with consideration of maximum PV generation

At present, connections of photovoltaic (PV) systems to low‐voltage (LV) distribution systems are growing rapidly because of the compliance with government policies, drop in the prices of PV technologies, and environmental awareness. Unfortunately, the high penetration of solar PV systems, which suffers from the intermittence of sunlight, leads to voltage fluctuation and voltage imbalance, thereby deteriorating the power quality. To cope with this problem, this paper proposes a control strategy of the PV inverter to improve the limiting and balancing of voltage profiles in an unbalanced, three‐phase, four‐wire LV distribution system. The control strategy is based on the real power limitation and the reactive power adjustment through a control scheme function that is embedded in all PV inverters for supporting high penetration of PV systems. However, real power limitation leads to less utilization of solar energy. Then, the concern on PV generation (real power) regarding voltage fluctuation and imbalance is optimally analyzed by multi‐objective particle swarm optimization. The optimal solution of the control scheme function is numerically demonstrated in a modified 29‐node LV distribution system. © 2017 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

An improved fault analysis algorithm for unbalanced multi-phasepower distribution systems

The results of an improved method for fault calculations in unbalanced multi-phase power distribution systems containing nonutility generators and large induction motor loads are presented in this paper. The method utilizes a combined time- and frequency-domain analysis approach to produce results that are superior to those obtained in “classical” fault analysis without the large increase in computer time with complete time-domain solutions. Sources and loads can be represented by either classical frequency-domain models or detailed differential equation models. The potentially unbalanced power distribution system is represented by an admittance matrix formed using a linear graph-based application of AC circuit theory. The time-domain differential equation source and load models are interfaced with the frequency-domain distribution system model using time series analyses to estimate equivalent voltage and current phasors from discrete data sets     

A multiphase optimal power flow algorithm for unbalanced distribution systems

This paper describes a new methodology for the optimization of an n-conductor electrical system, in which the phase imbalances, different types of loads, neutral cables, groundings and other inherent characteristics of distribution systems are taken into account. In addition, the methodology is useful for the detailed analysis required for smart grids. A formulation for the optimal power flow of an n-conductor system was developed using a primal–dual interior point method and the n-conductor current injection method in rectangular coordinates. Distribution and transmission systems were analyzed to verify the generality and efficiency of the proposed methodology.     

Optimal siting and sizing of intermittent distributed generators in distribution system

Intermittent distributed generators (IDGs), such as distributed wind turbine generator (WTG) and photovoltaic generator (PVG), have been developing rapidly in recent years. The output power of WTG and PVG highly depends on the wind speed and illumination intensity, respectively. There always exist correlations among the wind speed, illumination intensity, and bus load, which could have significant influence on the determination of siting and sizing of IDGs in distribution system. Given this background, a chance‐constrained‐programming‐based IDGs planning model, which can take into account the correlations, is developed in this paper. Latin hypercube sampling technique and Cholesky decomposition are introduced to handle the correlations. A Monte Carlo simulation‐embedded multi‐population differential evolution algorithm is employed to solve the developed model. Case studies carried out on the Baran & Wu 33‐bus distribution system verify the feasibility of the developed model and effectiveness of the proposed solving methodology. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

配电网三相不平衡补偿装置的研究

为了解决中、低压配电网系统中普遍存在的三相负荷不平衡问题,利用晶闸管控制电抗器和固定电容器组相结合的补偿方式来进行负荷不平衡和无功功率的综合补偿。根据三相不平衡补偿原理,可以由负载的三相线电流获得需要补偿的电纳值;利用分相调节模式,可以提供三相分别控制的、连续平滑变化的等效电纳值,通过调节静止晶闸管的触发角,获得电纳的给定值,达到补偿效果。仿真结果表明,该装置可以对三相不平衡负荷同时实现无功功率补偿和负荷平衡化。     

A new fault location algorithm using direct circuit analysis for distribution systems

The unbalanced nature of distribution systems due to single-phase laterals and loads gives difficulty in the fault location. This paper proposes a new fault location algorithm developed by the direct three-phase circuit analysis for unbalanced distribution systems, which has not been investigated due to high complexity. The proposed algorithm overcomes the limit of the conventional algorithm, which requires the balanced system. It is applicable to any power system, but especially useful for the unbalanced distribution systems. Its effectiveness has been proved through many EMTP simulations.     

三相不平衡与无功功率综合补偿系统的研究

在中低压配电网中 ,三相负荷随机变化 ,产生三相不平衡 ,从而给电网带来了一系列的问题。本文针对三相不平衡负荷的补偿原理进行了深入的研究 ,提出了补偿算法 ,并且设计了无功功率和三相不平衡补偿的综合系统。仿真结果和实际运行表明 ,此方法是有效的。     

Modeling of unbalanced three‐phase driving‐point impedance with application to control of grid‐connected power converters

The dq transformation is widely used in the analysis and control of three‐phase symmetrical and balanced systems. The transformation is the real counterpart of the complex transformations derived from the symmetrical component theory. The widespread distributed generation and dynamically connected unbalanced loads in a three‐phase system inherently create unbalanced voltages to the point of common coupling. The unbalanced voltages will always be transformed as coupled positive‐sequence and negative‐sequence components with double‐frequency ripples that can be removed by some filtering algorithms in the dq frame. However, a technique for modeling unbalanced three‐phase impedance between voltages and currents of same sequences or of opposite sequences is still missing. We propose an effective method for modeling unbalanced three‐phase impedance using a decoupled zero‐sequence impedance and two interacting positive‐sequence and negative‐sequence balanced impedances in the dq frame. The proposed method can decompose a system with unbalanced resistance, inductance, or capacitance into a combination of independent reciprocal bases (IRB). Each IRB basis belongs to one of the positive‐sequence, negative‐sequence, or zero‐sequence system components to facilitate further analysis. The effectiveness of this approach is verified with a case study of an unbalanced load and another case study of an unbalanced voltage compensator in a microgrid application. Copyright © 2015 John Wiley & Sons, Ltd.     

配电网三相潮流计算

针对我国目前配电自动化实施情况和实际配电网中存在负荷严重不对称的特点，提出三相配电网络实时潮流计算方法。并对北京回龙观居民小区配电自动化系统中某10kV配电线路某时刻的实测数据作了实时计算，计算结果表明采用三相潮流计算比常规潮流计算更能反映网络的实际运行状态。