Efficient integration of distributed generation for meeting the increased load demand

Distributed generation (DG) can be integrated into distribution systems to meet the increasing load demand while expansion and reinforcement of these systems are faced by economical and environmental difficulties. This paper presents an efficient methodology for integration of DG power into distribution systems, in order to maximize the voltage limit loadability (i.e. the maximum loading which can be supplied by the power distribution system while the voltages at all nodes are kept within the limits). The proposed methodology is based on continuation power flow (CPF). The effectiveness of the presented methodology is demonstrated in a test distribution system that consists of 85 nodes with integration of different penetration levels of DG power. The proposed method yields efficiency in obtaining more benefits from the same amount of DG power, decreasing the losses and improving the voltage profile.     

Advanced voltage control integrated in DMS

The paper deals with distribution network (DN) voltage control from the network operation point of view. The basic voltage control devices, under load and no load tap-changing transformers, are specially stressed. Distributed generators (DGs) and capacitor banks are also discussed. The classical principle of single line voltage drop compensation (LDC) is treated as the base voltage control. The optimal voltage control (OVC), which appeared 15 years ago, was developed to overcome some of LDC shortcomings. After the appearance of OVC, distribution management systems (DMSs) developed intensively and were applied immensely in distribution practice. This opportunity has been taken to integrate the distribution voltage control into DMS. The integration of the voltage control with Power flow, State estimation, Medium- and Short-term load forecast is of special interest for the paper. The high quality integration is provided by application of the same DN Data base and Mathematical model. In this way, the advanced voltage control has been developed. It ultimately overcomes all shortcomings of OVC (and LDC as well). This control is the subject of the paper and its properties are compared with LDC and OVC.     

Positive Effect of Constant Leading Power Factor Operation of PV in Power System

A voltage rise problem in distribution networks has been discussed as the foremost concern with respect to the spread of large numbers of photovoltaic systems. We focus on the latent ability of the present distribution network and photovoltaic systems to find a low‐cost solution to the problem and consider a solution to mitigate the voltage rise using the photovoltaic system's constant leading power factor operation. Previously, based on simulations using an aggregated model of a real distribution network, we proposed that a combination of a photovoltaic system's constant leading power factor operation and LDC makes it possible to maintain the line voltage and LTC tap position adequately. In this paper, additionally, we confirm some effects of the proposed method in an aggregated model of a distribution network and a trunk power system. One of them is that the proposed method reduces the frequency of restricting output power from photovoltaic systems and changing the LTC and SVR tap position, although photovoltaic systems rapidly fluctuate. Another is that the proposed method cannot make a significant impact on a trunk power system in a voltage class exceeding 6.6 kV.     

一种智能配电网三相调压器的模糊控制方法

高渗透率的分布式电源接入配电网,可能引起配电网电压幅值越限及馈线调压器频繁动作的问题。首先分析以线路压降补偿器为基础的调压器控制方法的不足和高渗透率分布式电源的接入引起现有控制方法失效的机理。针对这一问题,提出一种以通信为基础的三相调压器模糊控制方法,并设计一种综合考虑配电网潮流有功和无功功率的模糊控制器来缓解调压器的频繁动作。最后,通过改进的IEEE 13节点算例系统验证了所提方法的适用性和效果。     

Radial MV networks voltage regulation with distribution management system coordinated controller

The connection of a great number of distributed generation (DG) plants may cause a critical voltage regulation problem in actual medium voltage (MV) radial distribution networks. After a synthetic survey of different strategies reported in literature to solve this problem, a proposal for an active management of the distribution system which makes use of an innovative controller that coordinates the on load tap changer (OLTC) action with the regulation of reactive exchanges between DG plants and feeders, is presented.     

A survey on control issues in renewableenergy integration and microgrid

This paper describes the usefulness of renewable energy throughout the world to generate power. Renewable energy adds a remarkable scope in power system. Renewable energy sources act as the prime mover of a microgrid. The Microgrid is a small network of power system with distributed generation (DG) units connected in parallel. The integration challenges of renewable energy sources and the control of microgrid are described in this paper. The varied nature of DG system produces voltage and frequency deviation. The unknown nature of the load produces un-modeled dynamics. This un-modeled dynamic introduces measurable effects on the performance of the microgrid. This paper investigates the performance of the microgrid against different scenarios. The voltage of the microgrid is controlled by using different controllers and their results are also investigated. The performance of controllers is investigated using MATLAB/Simulink SimPowerSystems.     

基于单周期控制的二自由度控制器在交流调压中的应用

研究一种用于电力系统交流调压和稳压的二自由度控制器。控制器由单周期控制和传统PWM反馈控制组合而成,能有效抑制输入扰动和负载扰动对输出电压的影响,实现输出电压的快速自动稳定和无级平滑调节。本文分析了控制器的系统构成,从理论上证明其具有二自由度,采用双通道复位积分方式以减小控制误差,最后通过详细的仿真测试了控制器的性能。     

A LRT Control Method Using Sensor Information in Distribution Systems with a Large Amount of PVs and EVs

It is of prime importance to maintain voltage profile within the proper range in distribution systems with a large amount of photovoltaics and electric vehicles (EVs). In particular, there is a possibility that line drop compensation (LDC) logic, which is utilized for the control of load ratio tap transformer (LRT) does not work properly when reverse power flow is included partially. Hence, in this paper, we have developed a new LRT control method based on the sensor information supposing that some section switchgears with sensors are introduced in the future distribution systems. Specifically, the extreme value of voltage profile is estimated by convergence calculation in the section between the section switchgear with sensor and LRT. Moreover, the voltage at the end node can be estimated by LDC method using sensor information of section switchgear. The proposed method was tested using a distribution system model and its effectiveness was shown.     

A novel method for optimal DG units capacity and location in Microgrids

Distributed generation (DG) has an overall positive impact on Microgrids. These DGs are usually located close to the load centers which lead to some benefits such as; system power loss and energy cost reduction; voltage profile and stability improvement; environmental friendliness, postponement system upgrading and reliability enhancement. In this paper, a novel combined method based on Genetic Algorithm (GA) and Intelligent Water Drops (IWD) is proposed to find location and capacity of DG in Microgrids for optimizing some objective functions. The objectives are minimizing network power losses, improving voltage regulation and increasing the voltage stability within the framework of system operation and security constraints in Microgrids. In this paper, DG units are modeled as generators that are able to inject just active power to network. The Intelligent Water Drops (IWD) algorithm is a new swarm-based optimization algorithm inspired by observing natural water drops that flow in rivers. A detailed performance analysis is carried out on 69-bus and 33-bus Microgrids to demonstrate the effectiveness of the proposed methodology.     

Optimal location and sizing of real power DG units to improve the voltage stability in the distribution system using ABC algorithm united with chaos

The introduction of a Distributed Generation (DG) unit in the distribution system improves the voltage profile and reduces the system losses. Optimal placement and sizing of DG units play a major role in reducing system losses and in improving voltage profile and voltage stability. This paper presents in determination of optimal location and sizing of DG units using multi objective performance index (MOPI) for enhancing the voltage stability of the radial distribution system. The different technical issues are combined using weighting coefficients and solved under various operating constraints using a Chaotic Artificial Bee Colony (CABC) algorithm. In this paper, real power DG units and constant power load model and other voltage dependent load models such as industrial, residential, and commercial are considered. The effectiveness of the proposed algorithm is validated by testing it on a 38-node and 69-node radial distribution system.     

Optimal placement and sizing of distributed generators based on a novel MPSI index

The Objective: This paper presents a method to identify the optimal location and size of DGs based on the power stability index and particle swarm optimization (PSO) algorithm.Materials and methods: First, a novel maximum power stability index (MPSI) is derived from the well-established theorem of maximum power transfer. The MPSI is utilized as an objective function to determine the optimal DG locations. Next, a PSO-based model with randomized load is developed to optimize DG sizing in view of the system’s real power losses.Results and Conclusion: Lastly, a IEEE 30-bus test system is employed in the simulation. The performance of proposed MPSI index are comparable with other voltage stability indices. The DG optimization model considering voltage stability and loss minimization provides better results compared to that obtained using only loss minimization approach.     

Methods of determining introduction limits of dispersed generation systems in a distribution system

Recently, there has been growing interest in utilizing DGS (dispersed generation systems) to integrate various generation resources and to meet changing electricity demand. In the long term, as much more introduction of both small- and large-capacity DGSs into the distribution system is expected, complete integration of this new technology into the utility system will bring about changes of design strategy and structural makeup of the system. Thus, a study is necessary to determine the introduction limit of DGS into the traditional distribution system without any facility change. In this paper, the authors propose methods of determining the introduction limits of DGS from the viewpoint of voltage regulation in distribution systems using LRT (load-ratio control transformer) and LDC (line drop compensator) as the control scheme. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 120(4): 48–58, 1997     

Optimal placement of DG in radial distribution systems based on new voltage stability index under load growth

This paper presents a comparison of Novel Power Loss Sensitivity, Power Stability Index (PSI), and proposed voltage stability index (VSI) methods for optimal location and sizing of distributed generation (DG) in radial distribution network. The main contribution of the paper is: (i) optimal placement of DGs based on Novel Power Loss Sensitivity and PSI methods, (ii) proposed voltage stability index method for optimal DG placement, (iii) comparison of sensitivity methods for DG location and their size calculations, (iv) optimal placement of DG in the presence of load growth, (v) impact of DG placement at combined load power factor, (vii) impact of DG on voltage stability margin improvement. Voltage profile, the real and reactive powers intake by the grid, real and reactive power flow patterns, cost of energy losses, savings in cost of energy loss and cost of power obtained from DGs are determined. The results show the importance of installing the suitable size of DG at the suitable location. The results are obtained with all sensitivity based methods on the IEEE 12-bus, modified 12-bus, 69-bus and 85-bus test systems.     

分布式发电接入电网的静态电压稳定特性及影响分析

分布式发电(Distributed Generation,DG)接入电网在缓解环境污染和能源短缺压力的同时,也会给电网的安全运行分析带来新的挑战,特别是DG控制策略的多样性将使电网静态电压稳定问题更加复杂。DG接入电网对静态电压稳定性的影响主要取决于DG的接入容量、控制方式等因素。首先对DG接入线路的复杂外部网络进行等值,推导负荷节点电压与分布式发电渗透率的解析表达式。在此基础上,分析不同DG渗透率下的节点电压以及负荷PV特性,比较DG采用不同无功控制策略对负荷PV特性的影响。最后,将扩展线路电压稳定指标应用于含DG的电网静态电压稳定分析,研究DG采用主动无功控制策略对线路电压稳定指标的影响。     

Effect of load models on assessment of energy losses in distributed generation planning

Distributed Generation (DG) is gaining in significance due to the keen public awareness of the environmental impacts of electric power generation and significant advances in several generation technologies which are much more environmentally friendly (wind power generation, micro-turbines, fuel cells, and photovoltaic) than conventional coal, oil and gas-fired plants. Accurate assessment of energy losses when DG is connected is gaining in significance due to the developments in the electricity market place, such as increasing competition, real time pricing and spot pricing. However, inappropriate modelling can give rise to misleading results. This paper presents an investigation into the effect of load models on the predicted energy losses in DG planning. Following a brief introduction the paper proposes a detailed voltage dependent load model, for DG planning use, which considers three categories of loads: residential, industrial and commercial. The paper proposes a methodology to study the effect of load models on the assessment of energy losses based on time series simulations to take into account both the variations of renewable generation and load demand. A comparative study of energy losses between the use of a traditional constant load model and the voltage dependent load model and at various load levels is carried out using a 38-node example power system. Simulations presented in the paper indicate that the load model to be adopted can significantly affect the results of DG planning.     

Design, installation, and initial operating experience with linedrop compensation at John Day powerhouse

This paper describes design, installation, testing, and initial operating experience with line drop compensation (LDC) at John Day powerhouse. The voltage stability analysis is performed to quantify the system benefit provided by John Day LDC, transient stability studies are performed to determine target levels for LDC settings. The design, which utilizes both reactive current droop compensation and line drop compensation, is described. LDC installation and testing are presented. Operating experience is discussed, and LDC benefit for system disturbances is demonstrated     

考虑风光无功调节的配电网分布式电源双层规划

分布式电源(distributed generation, DG)作为配电网运行优化中关键一环,其合理的调控策略可以有效提高新能源渗透,减少电压波动,并降低网络损耗,因此在规划阶段,应充分考虑DG无功出力,最大限度发挥DG互补能力。本文建立了以经济性和稳定性为目标的含DG控制模型的双层配电网规划模型,在上层中以最小年综合费用为目标对DG位置容量进行决策,下层计算电压偏差最小化时的DG控制策略,使用粒子群算法对该模型进行分层求解,求得年费用和电压波动最优的DG安装位置和容量,并在IEEE 33节点算例中验证了该模型能够有效提高源网协同控制能力,发挥DG调节作用。     

On the appropriate monitoring period for voltage flicker measurement in the presence of distributed generation

Voltage flicker or voltage fluctuations are considered a major power quality problem causing temperature rise, generators and motors overloading and affecting humans through the irritating light flicker. It is expected that the level of voltage flicker will increase due to the increased penetration of distributed generation (DG) in the distribution system. Site monitoring is required to make sure that the level of voltage flicker is within the allowed limit. In order to determine the appropriate monitoring period for voltage flicker measurement while considering DGs, two case studies were considered in the paper; 1 week and 1 day monitoring periods. The results reveal that a monitoring period of 1 week may be very long especially in the presence of DG and it may hide valuable information. On the other hand a 1-day monitoring period is more appropriate in these situations. Therefore it is recommended to use 1-day monitoring period instead of 1 week especially in the presence of DG.     

含分布式电源的三相不平衡配电网潮流计算

根据配电网三相不平衡的实际情况,为准确计算各种分布式电源(distributed generation,DG)并入配电网后的潮流问题,文章基于前推回代法,提出了可处理PV和PQ节点模型DG的三相不平衡潮流算法。按照配电网拓扑结构,利用支路分层技术,加快了潮流计算速度。在处理PV节点模型DG时,将电压正序分量幅值作为电压调节参数,计算电压正序分量幅值和额定电压幅值差,得到PV节点的无功补偿量,将DG由PV节点运行模型转换为PQ节点运行模型。IEEE 34节点系统算例结果验证了该算法的正确性。最后,通过分析DG对电压的调节和无功补偿能力,研究了不同类型DG对配电网电压的影响。     

分布式电源接入城市配电网规则分析

为减轻分布式电源接入对城市配电网产生的负面影响,国内外制定了一些分布式电源并网准则,以保证分布式电源的安全有效接入,但这些并网规则的制定依据并没有明确给出。为此,以天津城区典型的35 kV 高压、10 kV中压和400 V低压配电网为例,计算分析接入分布式电源对城市配电网线路载流量和母线电压的影响,给出分布式电源并网规则中关于接入容量和接入电压等级要求的依据,并讨论分布式电源接入配电网后对电压偏差、频率偏差、谐波及三相不平衡度等方面的电能质量的影响及其要求和依据。