Enhancement of islanding-detection of distributed generation systems via wavelet transform-based approaches

In this paper, a wavelet transform-based approach is proposed to detect the occurrence of islanding events in distributed generation systems. Thanks to time–frequency localization capabilities exhibited by wavelet transform, the approach embedded with this transform technique has grasped the appearance of the islanding event in a highly effective manner. Moreover, for those regions which are in need of a better visualization, the proposed approach would serve as an efficient aid such that the mains power disconnection can be better distinguished. To validate the feasibility of this approach, the method has been validated through several scenarios. Test results supported the effectiveness of the method for the application considered.     

Distributed simulation for power system analysis including shipboard systems

Power systems are distributed in nature. Often they can be divided into sections or groups and treated separately. Terrestrial power systems are divided into separate utilities and are controlled by different regional transmission organization (RTO). Each RTO has detailed data for the area under its control, but only limited data and boundary measurements of the external network. Additionally, shipboard power systems may be divided into sections where local information is kept but not distributed to other parts of the system. Thus, performing a comprehensive power system analysis in such a case is challenging. Also, simulating a large-scale power system with detailed modeling of the components causes a heavy computational burden.     

Intelligent islanding detection of a synchronous distributed generation using governor signal clustering

Detection of intentional and unintentional islanding of distributed generation units is one of the major protection issues of the distribution networks. Regarding the safety and reliable operation of a modern distribution network, an expert diagnosis apparatus is required to distinguish network cut off from variety of normal occurrences. Automatic load-frequency controller (ALFC) is an indispensable component of the synchronous generators. Simulation results show that input signal of the governor includes somewhat singular characteristics for each possible phenomenon or disturbance. Therefore, a new method based on Self-Organizing Map (SOM) neural network is proposed using input signal to the governor to cluster various occurrences into islanding and non-islanding categories. Simulation results presented in this paper shows that the input signal of the governor employed by a SOM can cluster a majority of occurrences of the system and distinguishes the islanding phenomenon with high confidence.     

分布式发电系统的孤岛检测方法研究

通过对孤岛效应和检测盲区的分析,以分布式发电系统中基于逆变器侧的各种检测方法为主,按照其检测思路,从被动检测和主动检测两个方面进行分类归纳.对各种检测方法的检测原理、优缺点以及一些检测方法的改进方案进行综合评述,根据具体的功率的匹配程度和电能质量等要求,来选择将适合的检测方法相结合,充分发挥各自检测方法的优点,才能达到...     

Feasibility of adaptive intentional islanding operation of electric utility systems with distributed generation

As the process of deregulation of the electric utility industry proceeds, the importance of power quality is increasing. A fundamental aspect of power quality is the continuity of power supply that is the absence of momentary, temporary and sustained power interruptions. In this paper a network reconfiguration strategy is proposed which allows the distribution network to separate into a certain number of autonomous islands, supplied by local distributed generation, in case of permanent fault within the grid. Intentional islanding of portions of the grid is automatically carried out with an adaptive network reconfiguration depending upon the local generation/load state at the time of outage.     

A new artificial neural network based method for islanding detection of distributed generators

This paper presents an artificial neural network (ANN) based method for islanding detection of distributed synchronous generators. The proposed method takes advantage of ANN as pattern classifiers. It is capable of identifying the islanding condition based on samples of the voltage waveform measured at the distributed generator terminals only, which is an important advantage over other ANN-based anti-islanding methods. Moreover, the proposed method is robust against false operation. In order to create a training data set for the ANN, a data selection procedure has been proposed, so that the ANN could be trained more effectively, which has contributed positively to the good performance of the method. The concept of the time-performance region has been introduced to assess the method performance, as well as the non-detection zones. A detailed discussion about the data sampling rate to feed the proposed method has also been conducted, so that the computational burden can be faced as an important factor to assess its performance.     

Integrating distributed generation into electric power systems: A review of drivers,challenges and opportunities

It is now more than a decade since distributed generation (DG) began to excite major interest amongst electric power system planners and operators, energy policy makers and regulators as well as developers. This paper presents an overview of the key issues concerning the integration of distributed generation into electric power systems that are of most interest today. The main drivers behind the focus on DG integration, especially of the renewable type, in many countries around the world are discussed. A synopsis of the main challenges that must be overcome in the process is presented. Particular emphasis is placed on the need to move away from the fit and forget approach of connecting DG to electric power systems to a policy of integrating DG into power system planning and operation through active management of distribution networks and application of other novel concepts. The paper also analyses the repercussions in transmission system operation and expansion that result from the connection of large amounts of DG of different energy conversion systems focusing on issues related with impacts in steady state operation, contingency analysis, protection coordination as well as dynamic behaviour analysis. A discussion on the possibility of provision of ancillary services by DG is also included. Some results from studies performed in the interconnected Portuguese transmission system are presented and discussed. Some of the opportunities that could be exploited in support of the integration and hence greater penetration of DG into electric power systems are also explored.     

A generalized power flow analysis for distribution systems with high penetration of distributed generation

In this paper, the element incidence matrix has been extended to develop a comprehensive three-phase distribution system power flow program for radial topology. Three-phase overhead or underground primary feeders and double-phase or single-phase line sections near the end of the feeder laterals have been considered. Unbalanced loads with different types including constant power, constant current and constant impedance are modeled at the system buses. Substation voltage regulator (SVR) consisting of three single phase units connected in wye or two single-phase units connected in open delta are modeled to satisfy the desired voltage level along the feeder. The mathematical model of distributed generation (DG) connected as PQ and PV buses are integrated into the power flow program to simulate the penetration of DGs in the distribution systems. The proposed method has been tested and compared with different IEEE test feeders result. The developed algorithm has been used to study the impact of both SVR and high penetration of DG on voltage profile and system power losses.     

Optimization of biomass fuelled systems for distributed power generation using Particle Swarm Optimization

With sufficient territory and abundant biomass resources Spain appears to have suitable conditions to develop biomass utilization technologies. As an important decentralized power technology, biomass gasification and power generation has a potential market in making use of biomass wastes. This paper addresses biomass fuelled generation of electricity in the specific aspect of finding the best location and the supply area of the electric generation plant for three alternative technologies (gas motor, gas turbine and fuel cell-microturbine hybrid power cycle), taking into account the variables involved in the problem, such as the local distribution of biomass resources, transportation costs, distance to existing electric lines, etc. For each technology, not only optimal location and supply area of the biomass plant, but also net present value and generated electric power are determined by an own binary variant of Particle Swarm Optimization (PSO). According to the values derived from the optimization algorithm, the most profitable technology can be chosen. Computer simulations show the good performance of the proposed binary PSO algorithm to optimize biomass fuelled systems for distributed power generation.     

Direct power control of three-phase VSIs for the minimization of common-mode emissions in distributed generation systems

This paper presents two new direct power control (DPC) strategies of three-phase grid connected VSIs for distributed generation, devised for the minimization of common-mode emissions. These strategies have been called DPC-EMC 1 (electro magnetically compatible) and DPC-EMC 2. Both of them reduce the common-mode emissions of the VSI by using either even or odd voltage vectors in each of the six sectors in which the grid voltage lies, without using any null vector. DPC-EMC 2 outperforms DPC-EMC 1 in terms ripple of the active and reactive power waveforms. These approaches permit the common-mode emissions to be reduced in comparison with the classic DPC algorithm, at the expense of an increase of the harmonic content of the injected current waveform which can be further corrected by a proper power line filter. An experimental comparison among the classic DPC, DPC-EMC 1 and DPC-EMC 2 is presented in terms of dynamic performance, harmonic content of the injected current and harmonic content of the common-mode voltage.     

Disturbance detection in grid-connected distributed generation system using wavelet and S-transform

In this paper, wavelet transform and S-transform based approach is proposed for islanding detection and disturbance due to load rejection in distributed generation (DG) based hybrid system. The two types of distributed generation technology: inverter based and rotating machine based, that consists of photovoltaic, fuel cell and wind systems are considered in hybrid system configuration. The negative sequence voltage signal is analyzed through wavelet transform and S-transform for islanding detection of these resources from the grid. The above two approaches are also used in study of voltage profile at point of common coupling (PCC) with a non-linear load connected. The study for different scenarios in operation of DG system is presented in the form of time-frequency analysis. The energy content and standard deviation (STD) of S-transform contour and wavelet transform signal is also reported for both islanding detection and disturbance due to load rejection.     

Market-based multiagent system for reconfiguration of shipboard power systems

On ships, the electric shipboard power system (SPS) supplies electrical power to critical functions such as navigation, communication, emergency systems, and in the case of warships, weapon systems. During ship operation, some parts of the SPS may become unavailable due to damage, fault, or maintenance. For the survivability and reliability of ships, it is desired to make the SPS highly reconfigurable. This paper presents a market-based multiagent system (MAS) for the reconfiguration of radial SPS. Radial SPSs are found on majority of ships. In the proposed MAS, each agent only communicates with its neighbor agents to make the system work in a fully decentralized manner. The MAS is implemented using Java Agent Development Framework (JADE), which is fully implemented in Java and compliant with Foundation of Intelligent Physical Agents (FIPA). An SPS with two generators and four loads is used for testing the proposed MAS. The results show the proposed MAS can successfully reconfigure a radial SPS.     

Energy losses in a distribution line with distributed generation based on stochastic power flow

This paper proposes a methodology for stochastic power flow in a distribution line with dispersed photovoltaic (PV) penetration. Both load and PV generation are stochastic processes. The methodology uses a probabilistic model for load demand based on measured data and an extensive stochastic modeling of PV units’ power production based on historical meteorological data and commercial available PV panels. Annual power flow simulations are performed to evaluate loss reduction resulting for different penetration levels and siting strategies of PV into an urban radial distribution feeder. Finally, a cost index for the losses is defined taking into account System Marginal Price data. Results may be of interest for dimensioning, siting and cost allocation in distribution systems with dispersed generation.     

分散发电对电力系统安全可靠运行的影响研究

分别从线路潮流、网络损耗、电网静态电压稳定性、电能质量以及系统保护等方面,研究分散发电对电力系统运行造成的各种影响.以光伏发电为例,论证分散发电对配电系统总体影响的情况.案例研究表明,适度的分散发电能给电力系统带来诸如减少输电损失、降低生产成本、推迟发电容量、输配电容量投资等方面的好处.     

Modeling and control of distributed generation systems including PEM fuel cell and gas turbine

This paper concentrates on the modeling and control of distributed generation systems including fuel cell and gas turbine. The fuel cell is connected to the power system through a dc/ac converter, which is equipped with both voltage- and power-control loops. The gas turbine is also assumed to be equipped with both voltage-control and generation (or frequency)-control loops. Moreover the gas turbine is modeled using the d–q frame of reference. The interfacing of the gas turbine with the power system is achieved by transforming its equations from the d–q frame of reference to power system frame of reference. A multivariable supplementary fuzzy logic controller is proposed for improving the dynamics of the combined fuel cell and gas turbine system. This fuzzy logic controller is designed using the Matlab Fuzzy Logic Toolbox A distribution test system including a load, a fuel cell and a gas turbine, connected to a power grid is simulated using Matlab/Simulink software package. The dynamics of the combined distributed generation plant are analyzed for the cases of with and without controller. The accuracy of the presented model and the effectiveness of the proposed multivariable supplementary fuzzy controller are deduced from the simulation results.     

含分布式电源的配电网的供电恢复技术研究综述

本文总结了含DG的配电网的供电恢复的国内外研究现状,分别从DG对配电网供电恢复起到的作用、含DG的配电网的网络描述方法以及网络简化方法、含DG的配电网供电恢复的策略、含DG的配电网供电恢复问题的数学建模与优化求解方法、含DG的配电网供电恢复的控制方式以及时变情况下含DG的配电网供电恢复等多个方面进行论述。在概述含DG的配电网的供电恢复的研究现状的基础上,展望了下一步值得继续研究的问题和方向。     

光伏发电系统的PSCAD/EMTDC仿真建模及孤岛检测研究

基于PSCAD/EMTDC仿真平台搭建了并网光伏发电系统模型,分析了并网光伏发电系统的孤岛效应现象。并网逆变器采用最大功率点跟踪(MPPT)-电压控制策略,孤岛效应识别方法采用基于频率-无功电流反馈的孤岛检测方法。通过光伏发电系统输出特性仿真及孤岛检测仿真,验证了所提模型和方法的正确性。     

Optimization of distributed generation systems using a new discrete PSO and OPF

Many methods have been applied to achieve optimal site and size of distributed generation systems. This paper introduces a new hybrid method, which employs discrete particle swarm optimization and optimal power flow to overcome this shortcoming. The main technical constraints are imposed for utilities, which could apply this approach to search the best sites to connect distributed generation systems in a distribution network choosing among a large number of potential combinations. A fair comparison between the proposed algorithm and other methods is performed. For such goal, convergence curves of objective function versus number of iterations are computed. The proposed algorithm reaches a better solution than Genetic Algorithms considering similar number of evaluations.     

Data acquisition,power forecasting and coordinated dispatch of power systems with distributed PV power generation

The integration of photovoltaic (PV) power generation with highly random and intermittent characteristics has posed significant challenges to the safe and economic operations of power systems. This paper establishes an entire operation structure covering PV data acquisition, PV power forecasting, and coordinated dispatch of power systems with large-scale behind-the-meter distributed PV units. The PV data acquisition method provides training data for the power forecasting model, and then the forecasting results serve as the references for developing coordinated dispatch strategies. Real-world systems and numerical studies validate the effectiveness and superiority of the proposed operation structure.     

Reliability centered planning for distributed generation considering wind power volatility

This paper investigates a stochastic planning model to minimize the lifecycle cost of distributed generation (DG) systems under the energy reliability criterion, namely the loss-of-load probability. In particular, our study focuses on the DG system penetrated by renewable wind technology. The optimization is formulated to determine the wind turbine capacity and their placement in the DG system with the intent to minimize the capital, operational and environmental costs. Statistical moments including mean and variance are utilized to characterize the wind power volatility and the load uncertainty. Genetic algorithm combined with heuristic search is used to find the best sitting and sizing of the distributed energy recourses. Our study is among the first attempts in the literature to model and optimize DG system based on continuous probabilistic theory. The moment methods are shown to be effective in characterizing the stochastic behavior of wind power and load dynamics. Case studies are provided to demonstrate the application and performance of the planning method.