Load Shedding Application within a Microgrid to Assure Its Dynamic Performance during Its Transition to the Islanded Mode of Operation

This article presents the simulation results and analysis related to the response of the generators within a microgrid towards an accidental overload condition that will require some load shedding action. A microgrid overload can occur due to various reasons ranging from poor load schedule, inadequate switching of circuits within the microgrid, outage of one or more generators inside the microgrid, illegal load connections by some low voltage consumers, etc. It was observed that among the main factors that determine the survival of the microgrid during its transition from the grid connected mode to the islanded mode of operation are the size and type of the load connected (passive or dynamic load) as well as the length of time during which the unexpected load is connected. Models of a speed and voltage regulators of a diesel generator, and important for coping with the overload conditions are provided in the paper. The novelty of the work lies in the load shedding simulation and analysis of the specific generators studied herein, regarding that in many countries the microgrid technology is seen as an important alternative towards the ever increasing load demand and also to assist the system during periods of blackout.

Large-Scale Distributed Photovoltaic Power Dispatching and Operation Management Review

Distributed photovoltaic power (PV) is the main development model of distributed generation. It is necessary to research on dispatching and operation management with large-scale distributed PV connected. This paper analyzes development status, technical requirement and dispatching and operation management situation of distributed PV in Germany and China. Then introduce the preparation of distributed PV dispatching and operation management criterion. Through summarizing the experiences and lessons of large-scale distributed PV development in Germany, it gives advice to the development of distributed PV dispatching and operation management in China.

RDG System in Remote Areas with Utility or Local Feed Topology and Operation Strategy

In remote regions with availability of wind energy, a RDG （renewable distributed generation） system is an advantageous alternative to increase the provision of electrical supply. Usually, these systems are structured on the basis of a connection to an existing weak grid. When the grid is out of service, the system may operate in islanding mode, if the RDG configuration allows it, continuing the provision of energy with standard voltage and frequency values. Facing the latter situation, a wind-diesel/gas generation system is proposed, with a conversion and control strategies based on a variable speed wind turbine employing a DFIG （doubly fed induction generator）, a SC （ultracapacitor） storage system and a SG （synchronous generator） driven by a diesel/gas engine.

Reliability Evaluation and Improvement of Islanded Microgrid Considering Operation Failures of Power Electronic Equipment

With the high integration of power electronic technologies in microgrids,the reliability assessment considering power electronic devices has become a hot topic.However,so far no research has considered the impact of the operation failure probability of power electronic equipment on the overall reliability of the microgrid.This paper aims to construct a holistic operation failure rate model of power electronic systems based on the overall reliability assessment of islanded microgrid with high penetration of renewable energy sources(RESs).In addition,to improve the reliability of islanded microgrid,the conventional battery energy storage system(BESS)is replaced by the hybrid energy storage system(HESS).Based on the proposed model,the operation failure models for the power electronic modules in microgrid are built and tested,and then the sensitivity analysis is performed for exploring the influence of various factors on the reliability of the microgrid.

Optical and SAR image registration based on improved nonsubsampled wavelet transform for sea islands

Homologous feature point extraction is a key problem in the optical and synthetic aperture radar （SAR） image registration for islands. A new feature point extraction method using a threshold shrink operator and non-subsampled wavelet transform （TSO-NSWT） for optical and SAR image registration was proposed. Moreover, the matching for this proposed feature was different from the traditional feature matching strategies and was performed using a similarity measure computed from neighborhood circles in low-frequency bands. Then, a number of reliably matched couples with even distributions were obtained, which assured the accuracy of the registration. Application of the proposed algorithm to SPOT-5 （multi-spectral） and YG-1 （SAR） images showed that a large number of accurately matched couples could be identified. Additionally, both of the root mean square error （RMSE） patterns of the registration parameters computed based on the TSO-NSWT algorithm and traditional NSWT algorithm were analyzed and compared, which further demonstrated the effectiveness of the proposed algorithm. The algorithm can supply the crucial step for island image registration and island recognition.

New Islanding Detection Method with Better Performance in Presence of Non-resistive Load

Islanding detection is a mandatory component in grid-connected photovoltaic （PV） inverters. It is also a key issue in the photovoltaic agriculture. In this work, an overview on the islanding effect in grid-connected PV power systems was provided. Various islanding detection methods were introduced and their strength and weakness were dicussed. An improved islanding detection method was proposed based on active frequency drift （AFD）. The new method tolerated capacitive and inductive loads, because its perturbation signal was not offset by the non-resistive load. The new method through simulation in MATLAB/Simulink was evaluated and the advantages of the new method were demonstrated.

Vector Shift Method for Islanding Detection Based on Simulation Test

Vector shift(VS)is one of the typical methods used for islanding detection in distributed generations.This paper investigates the impact of both the active power imbalance and load variation on VS method.The investigation was conducted via simulation test in the power system dynamic simulation laboratory of Shandong University.The results show that it will take longer time for the VS relay to detect islanding state with the decrease of active power imbalance.In some cases,the vector shift angle is smaller than the setting and VS method would not be able to detect islanding state.In addition,the performance of VS method is impacted by the load variation in normal operation in which the distributed generator is operated in parallel with the main grid.The simulation results show that VS method would cause nuisance tripping if the load changes sharply. It can be summarized that VS method would be unable to reliably discriminate islanding state and normal system disturbances in some cases.

Y-V vascular pedicle elongation technique in island flap transplantation

Objective To introduce a new technique for vascular pedicle elongation in island flap transplantation, and evaluate its clinical results. Methods From February 1994 to October 2001,16 cases were treated with island flap transplantation with Y-V vascular pedicle elongation technique. There were 10 males and 6 females with the age ranging from 19 to 45 years (average 26. 8 years). The locations of the primary injury were as follows: the fingers in 6 cases, the great toe in 2 cases, the other toes in 2 cases, the knee joint in 3 cases and the proximal tibia in 1 case. The flaps vascularized by a branch of "Y" pattern bifurcation were used. Both branches of "Y" shaped vascular pedicle arising form the same main vessel trink were dissected, then the main vessel trunk was severed at the division of the branches, the arc of "Y" bifurcations was then turned into "V" pattern, the length of pedicle was significantly elongated than the original pedicle. Results The operative procedures were smooth in the patients,

极端条件下多源配电网主动孤岛研究综述与展望

高比例分布式电源接入后的故障配电网,具备主动恢复与自治能力,有利于提升电力系统适应气候变化和灾害风险管理的水平,顺应配电网技术的发展方向。当前,配电网主动孤岛自恢复和稳定运行的研究受到广泛关注。首先,概述多源配电网主动孤岛的内涵,以及多源配电网孤岛与微电网孤岛的区别,分析归纳配电网主动孤岛在分布式电源高比例接入下稳定运行存在的关键问题。其次,从主动孤岛划分、孤岛自组网波动平抑控制以及组网完成后主动孤岛小干扰稳定控制3个方面阐述国内外研究现状,并进行总结。最后,基于电力物联网、高电力电子化下的小干扰抑制以及能源互联网背景下的主动孤岛方案,对多源配电网主动孤岛的发展前景进行展望和总结。

孤岛运行与拓扑重构相互协调的故障配电网韧性提升策略

极端灾害引起的不同程度停电事件向电力系统应对故障的恢复能力发起了挑战,各类型分布式电源和联络开关的参与为故障后配电网供电可靠性的提高带来可能,同时为提升配电网在面临极端灾害场景下的韧性带来可能。为此,提出了一种孤岛重构故障恢复策略,采用混合整数二阶锥规划,利用孤岛运行与拓扑重构的协调运行策略进行关键负荷的恢复,并提出了故障恢复后的配电网韧性综合评价指标,通过“抵抗阶段–恢复阶段–韧性评估”3方面对韧性进行量化评价。最后,以改进的IEEE 33节点配电系统为例,验证了协调策略对配电网故障恢复的有效性,同时验证了所提出的韧性评价指标对于故障配电网恢复后韧性评价的有效性。

离网式风光氢醇一体化系统容量配置运行调度优化及经济性分析

为解决可再生能源消纳及氢能源存储、运输难题,提出一种离网式风光氢醇一体化系统。该系统离网运行,利用风力和光伏发电提供电能;通过蓄电池和储氢罐作为储能和储氢设备,以削峰填谷的方式稳定供应电能和氢能,确保电解槽和甲醇生成设备的稳定连续生产甲醇。以系统总收益最大化为目标构建了风光储氢醇的数学模型,并通过混合整数线性规划算法,结合风光真实数据分析,确定系统最佳设备容量与运行调度。以典型日分析其运行策略及系统能量,最后对所制绿色甲醇经济性分析。结果表明:系统能够根据外界条件的变化,合理切换工作状态,实现系统能量平衡;在满足各项约束条件下,提高了可再生能源利用率,降低了系统制甲醇的平准化成本。此研究为新能源消纳与氢能源利用提出了一条可行技术路线,并可为相关示范项目建设提供指导。

基于PMU的特高压直流输电系统孤岛运行控制方法

受特高压(Ultra-High Voltage,UHV)直流输电系统自身运行特点的影响,孤岛运行阶段的环流难以实现快速维稳,提出基于电源管理单元(Power Management Unit,PMU)的特高压直流输电系统孤岛运行控制方法。考虑输出电压的角度会受电压源换流器(Voltage Sourced Converters,VSC)的影响发生瞬时改变,提出有功-相角下垂控制方法,逆变器通过微型PMU的同步信号,确定派克变换的参考坐标系,将特高压直流输电系统孤岛运行阶段的目标维持频率作为控制基准。以调整特高压直流输电系统中所有分布式发电装置(Distributed Generation,DG)的相角参考值处于一致状态为导向,结合微型PMU测得的公共母线电压相角参数,控制有功补偿量。在测试结果中,环流达到0值后出现的偏离情况程度稳定在10.0 VA以内,并在测试后的0.8 s内达到0稳态。

基于新能源快速调节的孤岛微网弹性恢复策略

针对当前孤岛运行微网面临的备用调节容量不足、负荷投切频繁和供电可靠性较低的问题,提出一种基于新能源快速调节的孤岛微网弹性恢复策略。首先根据新能源的快速功率控制技术,建立风、光电源的可快速调节容量模型。在此基础上,以孤岛负荷恢复价值量最大化为目标,考虑孤岛内电源和负荷的波动性、储能和负荷的调节量,根据电源出力程度和负荷可控量,分析不同电源负荷功率关系下的孤岛备用容量来源。然后,考虑新能源快速功率调节技术,分别制定电源充足、电源不足和极端情况下的孤岛弹性运行控制策略。最后,基于改进的41节点公路微网系统进行仿真验证,结果表明,所提恢复策略在保证负荷恢复价值量的同时,能够预留充足的备用容量,显著提升孤岛微网的运行弹性和供电恢复能力。

爱尔兰岛高比例新能源电力系统运行经验与启示

随着全球能源转型步伐的加快,世界各国电力系统均大力发展以风电和光伏发电为主的新能源。爱尔兰岛电力系统为岛屿独立同步电网,具有新能源渗透率高、与外部电网交互功率小等特点。经过长期摸索与发展,爱尔兰岛高比例新能源电力系统运行水平处于世界前列,其先进经验对我国新型电力系统建设具有重要借鉴意义。介绍了爱尔兰岛电力工业的概况,分析了爱尔兰岛电力系统的运行情况,探究了爱尔兰岛电力公司为保证高比例新能源电力系统安全高效运行采取的措施,最后总结其对我国新型电力系统建设的经验与启示。

Control of hybrid AC/DC microgrid under islanding operational conditions

This paper presents control methods for hybrid AC/DC microgrid under islanding operation condition.The control schemes for AC sub-microgrid and DC sub-microgrid are investigated according to the power sharing requirement and operational reliability.In addition,the key control schemes of interlinking converter with DC-link capacitor or energy storage,which will devote to the proper power sharing between AC and DC sub-microgrids to maintain AC and DC side voltage stable,is reviewed.Combining the specific control methods developed for AC and DC sub-microgrids with interlinking converter,the whole hybrid AC/DC microgrid can manage the power flow transferred between sub-microgrids for improving on the operational quality and efficiency.

考虑移动式储能调度的配电网灾后多源协同孤岛运行策略

针对极端事件导致的配电网大面积停电现象,在路-电耦合背景下,提出一种考虑移动式储能调度的配电网灾后多源协同孤岛运行策略。首先,基于路-电耦合背景下的灾后运行框架,以加权切负荷量最小为目标,同时考虑交通流量的变化对移动式储能调度过程的影响,建立多源协同孤岛运行模型;然后,根据所建模型的特点以及决策需求,基于两阶段优化框架制定孤岛运行决策流程,确保失电孤岛区域与含本地电源区域负荷恢复的协调进行;最后,采用IEEE 33节点配电网与29节点交通路网相耦合的算例进行分析,验证所提策略的有效性。结果表明,所提孤岛运行策略可以充分发挥各电源在配电网灾后恢复时的协同能力,实现了有限电能的最优分配和转移,有效提升了配电网灾后恢复效果。

微电网孤岛运行工况下DT模型自适应迁移方法

微电网在孤岛运行工况变化情况下,会造成数字孪生(DT)模型迁移时无法准确匹配源域模型,从而导致迁移效率偏低等问题。为此,研究提出微电网孤岛运行工况变化场景下的数字孪生模型自适应迁移方法。通过分析微电网在孤岛运行工况下的运行特点,建立数字孪生模型,利用微电网孤岛运行工况的时变性,匹配计算源域模型,并通过缩小不同微电网孤岛运行工况下的源域数据分布差异,实现数字孪生模型的自适应迁移。实验结果表明,电流负载、实际电流等部分特征数据迁移效果较好,且具有较高迁移效率,验证了所提迁移方法可以适应不同微电网孤岛运行工况,具有较好的实用性。

Modeling,Simulation,and Risk Analysis of Battery Energy Storage Systems in New Energy Grid Integration Scenarios

Energy storage batteries can smooth the volatility of renewable energy sources.The operating conditions during power grid integration of renewable energy can affect the performance and failure risk of battery energy storage system(BESS).However,the current modeling of grid-connected BESS is overly simplistic,typically only considering state of charge(SOC)and power constraints.Detailed lithium(Li)-ion battery cell models are computationally intensive and impractical for real-time applications and may not be suitable for power grid operating conditions.Additionally,there is a lack of real-time batteries risk assessment frameworks.To address these issues,in this study,we establish a thermal-electric-performance(TEP)coupling model based on a multitime scale BESS model,incorporating the electrical and thermal characteristics of Li-ion batteries along with their performance degradation to achieve detailed simulation of grid-connected BESS.Additionally,considering the operating characteristics of energy storage batteries and electrical and thermal abuse factors,we developed a battery pack operational riskmodel,which takes into account SOCand charge-discharge rate(Cr),using amodified failure rate to represent the BESS risk.By integrating detailed simulation of energy storage with predictive failure risk analysis,we obtained a detailed model for BESS risk analysis.This model offers a multi-time scale integrated simulation that spans month-level energy storage simulation times,day-level performance degradation,minutescale failure rate,and second-level BESS characteristics.It offers a critical tool for the study of BESS.Finally,the performance and risk of energy storage batteries under three scenarios—microgrid energy storage,wind power smoothing,and power grid failure response—are simulated,achieving a real-time state-dependent operational risk analysis of the BESS.

单相统一电能质量调节器二次纹波补偿及抑制策略

在单相半桥非隔离统一电能质量调节器(UPQC)中,交、直流间瞬时功率不平衡导致直流侧出现二次电压纹波,影响电能质量的补偿效果。该文分别在UPQC并网、离网两种模式下提出二次纹波的补偿及抑制策略。首先,分析UPQC在并网运行条件下直流二次纹波的产生机理及其对电能质量补偿的影响,并提出分别在并、串联侧变换器加入陷波器及特征次谐波控制,以降低网侧电流及串联侧电压谐波。其次,在UPQC离网运行时,为有效抑制直流电压二次纹波,提出一种利用UPQC闲置的串联侧变换器与复用的直流分裂电容构建半桥有源功率解耦电路的方法,控制难度低且无需额外增加解耦电路元件。最后,通过仿真和实验验证了所提方法的可行性。在并网模式中,所提策略减少了74%的电流谐波及42%的电压谐波;在离网模式中,所提策略减少了66.7%直流电压二次纹波。同时,该文所提出的二次纹波的补偿及抑制策略,可优化直流电容参数设计,并进一步减小UPQC体积。