分布式电源接入对小电阻接地系统零序电流保护影响的机理分析

从本质上研究了分布式电源接入对小电阻接地系统零序电流保护的影响,并结合数值仿真进行验证。此外,在满足继电保护可靠动作的前提下,分析了配电网允许分布式电源侧的接入最大短路容量与并网位置、并网变压器中性点接地阻抗的关系。结果表明:分布式电源接入可能导致保护动作失去选择性、误动或拒动;在不同并网位置情况下,合理的设置并网变压器中性点接地阻抗值,可以减小分布式电源接入对配电网保护带来的影响,从而可增加允许分布式电源侧的接入最大短路容量。     

浅析DG并网对配电网电流保护的影响

分布式电源(Distributed Generation,DG)与大电网的结合被当今世界众多能源专家认为是21世纪电力行业需不断研究的方向,这是一种既能并网又可以解列运行的发电方式。本文概述了DG并网后对配电网的影响,以含DG的简单配电网为例,用MATLAB仿真定量研究DG并网对配电网电流保护的影响。结果表明,该影响与DG容量及安装位置有关。     

分布式电源接入对配电网电压偏差影响的研究

近年来,为了实现能源的就地开发与利用,减少远距离输电的损耗,分布式电源(Distributed Generator,DG)大力发展。分布式电源并入配电网后,使配电网由单电源网络转化为多电源网络,功率流动方向因此改变,进而影响电压稳定性。本文首先分析了DG接入对电压偏差的影响机理,进而在PSCAD软件中搭建含DG的35/0.4kV配电系统模型,改变DG的容量和位置进行仿真研究,最后结合多个仿真结果,得出DG接入对配网电压偏差的影响规律。     

分布式发电对继电保护的影响

分布式发电的接入使馈电线路的潮流分布和短路电流的大小、方向和分布发生改变,原来继电保护的整定、配合不再适用,针对传统电流型继电保护、基于智能自动化电器以及基于馈线终端单元(FTU)的自动化保护方案,分析DG对配电网保护及自动化的影响,进行有益的探讨。     

分布式电源对配电网继电保护影响的分析

以前的配电网在当初设计时,设备容量是严格按照系统安全性、运行容量与负荷来选择的,不可能考虑到现在大规模接入分布式电源的问题。所以,当分布式电源接入配电网后,会对配电网的设计、电气参数,规划以及运行,电网设备等很多地方带来影响,比如提高了线路正常运行的电压能力;使区域负荷变化的预测难度增加;导致传统的保护设备失效,要求电力公司对此进行改造等。本文将在简要介绍配电网保护的基础上,分析分布式电源对配电网故障电流的影响,然后分析故障时分布式电源对配电网保护的影响。     

解析风电场对电网继电保护的影响

随着风电场机组容量的逐年加大,大规模的风电接入对电力系统的电能质量产生了极大的影响,由于风能具有不可控制性和随机性,当风能增大时向系统提供的短路电流也越大,所以风电场对电网继电保护的影响很重要。本文从风电场对电网继电保护的影响角度进行分析论证,对风电场的保护作用进行分析。     

分布式新能源接入电网的集群优化控制策略研究

该文研究了分布式电源接入交直流混合微电网群的优化规划方法,提出2层优化规划数学模型,分别涵盖区域节点集群划分和分布式电源容量配置协同规划。上层规划模型使用节点耦合度和有功平衡度综合指标,以完成区域节点的集群划分和混合微电网群的构建任务。下层规划模型以投资成本、运行维护成本和购售电成本最小为目标函数,求解各微电网群中分布式电源的接入容量。同时,考虑系统的稳定性和可靠性,约束条件包括系统总节点数约束、节点电压偏差约束、分布式电源出力约束、群间交互功率约束和供电可靠性约束等。通过这些优化规划方法可以有效地优化微电网群的配置,提高电力系统的可靠性和经济性。     

浅析主变差动保护TA接线方法

电力系统中容量在6．3MVA以上的变压器,其主保护一般都装设差动保护。本文以Yd11联接组别的两圈变三相电力变压器为例,通过分析其差动保护的原理、特点、高低压侧差动电流互感器电流的相位差、电流互感器极性等问题,提出了两种Yd11两圈变差动保护电流互感器的具体接线方法。     

一种改进的新型桥式固态限流器的研究

随着电网容量的不断扩大，短路电流限制技术已成为故障保护的一个研究热点。提出的新型桥式电路是在原有桥式拓扑结构上进行了改进，并提出了新的控制策略。详细介绍了新型桥式限流器的基本工作原理及特点，给出了基于Matlab/Simulink软件的仿真分析和基于天津大学动模实验室的实验结果。仿真与实验结果证明了所提出新型拓扑与控制策略的正确性。     

光蓄互补系统接入对配电网供电可靠性的影响

光蓄互补系统接入对配网的供电可靠性有较大影响.首先,介绍了典型系统的负荷曲线和光伏出力曲线特点,以及储能运行策略、配网供电可靠性评估指标和评估方法;然后,讨论了不同出力光伏系统、不同容量储能和光蓄互补系统接入对负荷曲线和配网供电可靠性的影响.最后,比较并分析了光伏、储能和光蓄互补系统对配电网供电可靠性的不同影响.研究结果可为光蓄互补系统的容量优化配置提供参考.     

能源互联网背景下的微电网能量管理分析

能源互联网背景下,可再生能源并网规模日益扩大。由于可再生能源发电功率具有很强的随机性,电力系统运行中出现了所谓“双侧随机问题”,影响安全稳定运行。如何对各种可再生能源进行经济有效的能量管理,是实现能源互联网的关键技术之一。为实现微电网运行的整体优化,对包含各种分布式电源的微电网,建立以综合发电成本最低、环境效益最好作为优化目标的多目标优化模型。利用遗传算法,进行能量管理的优化研究。以联网运行的含有多种分布式电源的微电网为算例进行仿真计算,仿真结果表明了优化模型及算法的有效性。     

Intelligent energy management control for independent microgrid

This work presents a new adaptive scheme for energy management in an independent microgrid. The proposed energy management system has been developed to manage the utilization of power among the hybrid resources and energy storage system in order to supply the load requirement based on multi-agent system (MAS) concept and predicted renewable powers and load powers. Auto regressive moving average models have been developed for predicting the wind speed, atmospheric temperature, irradiation, and connected loads. The structure proposed in this paper includes renewable sources as primary source and storage system as secondary source. A wind generator and solar PV array system together acts as primary source, which supplies power to the local load most of the time in this energy management strategy. When they fail to meet the load demand, the secondary source present in the system will assist the primary source and help to attain the goal of satisfying load demand without interruption. If the primary source and secondary source together are not able to meet the load demand then load shedding will be executed according to the priority set. Thus the developed MAS algorithm co-ordinates the hybrid system components and achieves energy management among renewable energy sources, storage units, and load under varying environmental conditions and varying loads. STATCOM based compensation has been implemented to balance the reactive power demand and to mitigate the voltage fluctuations and harmonics on the AC bus. The proposed microgrid has been simulated with MAS concept in Matlab/Simulink environment. The results presented in this paper show cases the effectiveness of the proposed energy management controller.     

UK distribution system protection issues

In the light of anticipated changes in the UK distribution system leading towards active networks with high penetration levels of distributed generation (DG), a number of major challenges must be addressed with respect to power system protection. Accordingly, the primary objective of this paper is to raise awareness of the potential bottlenecks that may act to inhibit further integration of renewables and other types of generation in distribution systems because of insufficient protection system provisions. The paper presents a UK industry view, formulated using the outcomes of questionnaires, seminars and other academic-industry exchanges carried out under the auspices of the Department of Trade and Industry (DTI) funded centre for DG and sustainable electrical energy (CDG&SEE), of the present and anticipated future protection system challenges in active distribution networks. A systematic methodology for opinion recording and priority assessment based on a carefully designed questionnaire has been proposed and applied to the distribution system protection domain. The industrial consultation involved all UK distribution network operators (DNOs) and a selection of protection system manufacturers and developers. The results of this exercise provide a unique insight into the key challenges facing the ongoing development of effective power system protection systems for distribution systems including DG. In particular this paper supports the assertion that, in order of decreasing significance, the resolution of loss of mains, islanding and certain protection discrimination issues would facilitate the integration of increased levels of DG.     

Development of hybrid ROCOF and RPV method for anti-islanding protection

ABSTRACT

Distributed generation (DG) must have the capability to quickly and accurately detect islanding operations under various operating conditions. An ideal islanding detection method should be without a non-detection zone (NDZ) and exempt from deteriorating power quality. A novel Anti-islanding protection technology that is a hybrid of rate of change of frequency (ROCOF) and reactive power variation (RPV) is proposed in this paper. The method can differentiate between a DG that falls into the NDZ for ROCOF and one that does not, and the RPV method will be initiated when the DG is within the NDZ. The amplitude of the reactive power variable can be accurately calculated using the proposed method. Thus, the degree of deterioration of power quality and power consumption can be effectively limited. The method has been implemented on a 3 kW DG to prove its feasibility. The experimental results demonstrated that in the proposed method, the DG was able to use the minimal amplitude of RPV to detect islanding in the NDZ. The breaker tripping time under various operating conditions conformed to the criteria specified in IEEE Std. 1547.     

Dynamic equivalencing of distribution networks with dispersed generation using Hankel norm approximation

Nowadays the number of dispersed generators (DGs) is growing rapidly. This change will greatly influence power system dynamics. A distribution network, where DGs are connected to the grid, cannot be considered as passive anymore. Therefore, in the future it will not be possible to use simple equivalents of distribution networks for power system dynamic modelling, as it was done before. At the same time, the whole power system cannot generally be represented in a detailed manner for dynamic studies because of huge system dimension. Therefore special techniques have to be applied for aggregation and order-reduction of distribution networks with DG. A brief review of existing techniques is provided here, and the dynamic reduction using Hankel norm approximation is performed for a 10 kV distribution network, which includes DG of different types.     

基于自抗扰控制的直流微电网双向Buck-Boost变换器控制策略研究

为了降低直流微电网母线电压的波动,提出基于自抗扰控制的双向Buck-Boost变换器控制策略。运用直流母线电压外环、直流变换器电感电流内环的控制方法实现直流微电网与储能系统之间的能量双向流动。进一步提出基于扩张状态观测器观测输出总扰动,包括负载电流和母线电压的变化,在负载扰动电流影响系统的直流母线电压最终输出前,主动从外环被控对象的输入信号电感电流或输出信号母线电压中提取扰动信息,然后尽快用控制信号将其消除,从而大大降低其对被控量的影响,以有效抑制暂态直流母线的电压波动和冲击,在母线电压产生波动时能够快速恢复到正常的工作状态。仿真验证表明:储能系统可以通过控制策略实现能量的双向传递,并且当母线产生功率波动和电流冲击时,储能系统可以使直流母线电压稳定,提高了系统的可靠性。     

An implicit discontinuous Galerkin finite element framework for modeling fracture failure of ductile materials undergoing finite plastic deformation

It is a challenge to achieve a complete simulation of fracture failure in ductile materials undergoing large plastic deformation within implicit finite element frameworks due to instability issues. Currently, traditional nodal force or crack surface traction release methods target the direct release of tractions on cracked surfaces within the current time/load step. An abrupt change from a system without cracks to another system with cracks may contribute to the instability issues. Specifically, because of broken meshes, discontinuous Galerkin (DG) methods have an advantage over traditional continuous elements in naturally accommodating crack openings along DG interfaces across elements. To improve the convergence in nonlinear iterations during crack openings, we propose a relaxation scheme for DG formulations to gradually recover the traction‐free condition on cracked surfaces. Furthermore, this DG‐based relaxation scheme for crack openings in finite plastic media has been consistently formulated within the incomplete interior penalty DG framework. Finally, we have demonstrated a good performance of the proposed implicit DG formulation along with the DG relaxation scheme by successfully solving a nuclear fuel rod structural failure problem with multiple hydride crack openings and the Sandia Fracture Challenge benchmark.     

基于高阶DG方法的非定常流场声辐射特性数值模拟研究

随着航空噪声越来越受到关注,计算声传播的算法成为研究热点。高阶间断伽辽金(Discontinuous Galerkin,DG)方法具有高精度、对网格质量要求低、适合自适应和并行计算等优点,可以以较高的效率对声场进行计算。文章运用高阶DG方法对线性化欧拉方程(Linearized Euler Equations, LEE)进行空间离散,并且基于离散后的线性化欧拉方程对带有背景流场的NACA0012翼型和30P30N多段翼型的声场进行数值计算。采用有限体积法计算得出流场信息后,通过插值将流场数据导入声场网格,并运用高阶DG方法进行声场计算。计算结果与参考文献中FW-H(Ffowcs Williams-Hawkings)算法对比一致性较好,验证了高阶DG算法的可行性。     

Analysis on the feasibility of a PV-diesel generator hybrid system without energy storage

A sustainable option in the mandatory use of diesel generator set (DG) is its integration into the solar photo-voltaic system (PV). A major issue, in this integration, is achieving an optimum mix of energy delivered by DG as well as that obtainable from PV. This paper determines the optimum mix of outputs from a PV and the DG on the basis of minimum cost of energy in Rs/kWh. A time step simulation-based methodology is adopted. Results indicate, if 70 % of the annual energy demand is met by DG while remaining 30 % is met by the PV, the cost of energy will be the least at 13.1 Rs/kWh. Sensitivity of the optimum mix is examined in the light of relevant parameters.     

A conservative high‐order discontinuous Galerkin method for the shallow water equations with arbitrary topography

A conservative high‐order Godunov‐type scheme is presented for solving the balance laws of the 1D shallow water equations (SWE). The scheme adopts a finite element Runge–Kutta (RK) discontinuous Galerkin (DG) framework. Based on an overall third‐order accurate formulation, the model is referred to as RKDG3. Treatment of topographic source term is built in the DG approximation. Simplified formulae for initializing bed data at a discrete level are derived by assuming a local linear bed function to ease practical flow simulations. Owing to the adverse effects caused by using an uncontrolled global limiting process in an RKDG3 scheme (RKDG3‐GL), a new conservative RKDG3 scheme with user‐parameter‐free local limiting method (RKDG3‐LL) is designed to gain better accuracy and conservativeness. The advantages of the new RKDG3‐LL model are demonstrated by applying to several steady and transient benchmark flow tests with irregular (either differentiable or non‐differentiable) topography. Copyright © 2010 John Wiley & Sons, Ltd.