Reliability Assessment of a Cyber Physical Microgrid System in Island Mode

As cyber physical systems,microgrids(MGs),with distributed generations and energy management systems,can improve the reliability of power supply for customers in MGs.To quantify the reliability of isolated MGs,a cyber-physical assessment model is proposed.In this model,the circuit breakers and distributed energy resources are treated as the coupling elements between the cyber system and physical system,where the circuit breakers are uniquely modelled by using the Markov process theory based on the indirect interdependencies between cyber physical elements.For the cyber system,the reliability model of communication networks is formulated based on the link connectivity evaluation method.For the physical system,a system state generating method is presented to account for the optimal operation strategy,which considers the influence of the optimization strategy on the failure consequence analysis.With the proposed cyber and physical reliability models,the sequential Monte Carlo(SMC)simulation method is adopted to assess the reliability of islanded MGs.Simulations are carried out on a test system,and results verify the feasibility and effectiveness of proposed assessment method.Furthermore,one application of the proposed method is on the parameter setting of the cyber system,in terms of enhancing MGs reliability.

Overvoltage Condition Assessment of a Microgrid Due to Faults Occurring in the Islanded Mode of Operation

This paper presents the results of the simulations and their respective analyses corresponding to the power frequency overvoltages resulting from various fault types occurring inside a microgrid. During the islanded mode of operation, the analysed microgrid can be simultaneously fed by a diesel generator, a 1 MW wind power turbine, a small solar system and a 1 MW hydroelectric scheme. The operating voltage of the microgrid is 2.4 kV. During a fault in the system, the overvoltages normally occur in two remarkable instants. The first one occurs at the beginning of the fault itself. The second one occurs at the instant when the fault is cleared. The major concern here is the overvoltage during the fault period. Due to the travelling wave effect along cables and overhead lines composing the microgrid system, these overvoltages can be amplified, thus jeopardizing the insulation level of the microgrid transmission system and related equipment. Much of the work available now is dedicated to overvoltages present in high-voltage systems leaving a gap for the study and behaviour on low voltage microgrid systems. The overvoltage stress is characterized by the maximum low-frequency, short-duration (crest value) of the overvoltage. Both cables and overhead lines that constitute the microgrid transmission system are characterized by their R-L-C parameters. The simulations of the microgrid system are conducted using the ATP program. According to the international ANSI and IEEE standards, the minimum BIL (Basic Impulse Insulation Level) and BSL (Basic Impulse Switching Level) for the 2.4 kV voltage level are 20 kV and 10 kV, respectively;thus, care should be taken so that the healthy phases upon which commonly appear such overvoltages are not exceeded in their insulation level.

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.

适应并离网模式切换的DFIG电磁暂态仿真建模

目前,常用的商业仿真软件中的双馈式感应发电机(double-fed Induction Generator,DFIG)模型通常不支持离网运行模式,难以实现风力发电系统由离网到并网的全过程电磁暂态仿真,对电力系统仿真分析工作带来极大不便。研究适应并离网模式切换的DFIG电磁暂态仿真建模方法。基于模块化思想分别对风力机、异步电机、变流器以及断路器进行建模,在系统组装形成DFIG风力发电系统电磁暂态仿真模型。提出了适应并离网模式切换的DFIG受控源等效电路模型和离散时间域实现方法,通过设计状态变量矩阵元素的截取和扩充算法实现了模型在并离网模式下的无缝衔接。在MATLAB/Simulink中搭建DFIG发电系统模型对所提方法和模型进行验证,仿真结果表明,所提建模方法能够很好地支持DFIG离网运行模式,实现DFIG由离网到并网的全过程电磁暂态仿真。

2022年8月四川盆地持续性极端高温特征及不同模式预报误差分析

本文基于2022年8月四川盆地104站逐时温度、降水数据和1971—2021年历史同期数据,及EC、CMA-GFS、CMA-MESO模式的2 m气温预报等数据,运用统计学相关方法分析了此次极端高温过程的特征及预报误差。结果表明:①2022年8月四川盆地极端高温过程范围大、强度强、持续时间长,有87.5%站最高气温超过该站历史同期极值,且高温最强盛时段较历史同期明显推后。②2022年8月最高气温分布为东高西低,最高气温与历史同期极值差分布则相反,其中最高气温随站点海拔增大而减小,而极值差则随站点海拔先增大再减小。另外,受热岛效应影响,极值差大值站点主要集中在龙泉山脉附近。③高温期间,最高、最低气温平均值高、距平大,且累计降水量和雨日数也明显低于历史同期。④相较而言,EC模式的预报优势主要在盆地低海拔地区。而CMA-MESO模式在盆地周边陡峭地形区域的平均绝对误差则更小。另外,EC模式预报的最高气温峰值出现时间更接近于实况,而CMA-MESO模式预报高温持续日数更接近实况。

基于有功功率修正的MMC串联结构微电网相间功率平衡控制策略

针对孤岛不平衡负载下模块化多电平变换器(MMC)串联结构微电网系统中微源输出功率波动,引起的相间功率不平衡及运行不稳定问题,研究了一种基于有功功率修正(Active Power Correction,APC)的相间功率平衡控制策略。基于系统孤岛模式等效电路,对系统输出功率进行了数学建模,并分析了相间功率流动模式。在三相输出电压对称的前提下,根据微源功率及负载功率确定需要修正的功率,设计了环流控制器,对直流环流控制实现相间功率互济。通过仿真验证,该策略能使相间功率自适应动态调节,达到相间功率平衡的目的。

基于化工行业的仪控设备智能化云平台设计与应用

针对化工行业仪控设备运维工作量大,数据呈“信息孤岛”,报警泛滥,数据不能可视化、缺乏集成化管理等问题,以supOS工业互联网平台作为技术底座提出了仪控设备智能化云平台的设计与实现方法,为工业互联网化工行业领域提供了一种创新的解决方案:“工业互联网平台+多个工业APP应用服务”(1+X)模式,即仪控设备的位号管理、报警管理、智能巡检、高频故障统计分析、健康状态可视化等业务应用。通过实际应用表明:该云平台可帮助企业高效和智能地管理仪控设备,降低企业管理成本,提高生产效率。

热核聚变发电厂储能系统运行模式研究

[目的]核聚变作为一种新型核能利用形式,其清洁绿色特性被视为人类未来的“终极能源”,也是我国在能源发展道路上的必经之路。在热核聚变发电厂中,中国聚变工程实验堆(CFETR)聚变反应堆具有一定周期性、脉冲式的输出特性,而汽轮发电机组的运行是稳定、连续的,因此核岛和常规岛之间需配有储能岛以进行储能缓冲;为实现其储能缓冲的功能,储能系统需选择合适的运行模式。[方法]核岛与常规岛耦合运行或解耦运行,对应着储能系统不同的运行模式;文章基于CFETR核岛侧的功率输出特性,从系统配置、设备选型和运行控制等方面对储能系统运行模式的不同方案进行分析和对比。[结果]研究结果表明,核岛与常规岛的解耦运行模式在常规岛发电效率、设备设计技术成熟性和机组运行控制上都更具优势,因此推荐热核聚变发电厂储能系统采用解耦运行模式。[结论]储能系统解耦的运行模式方案大都采用成熟技术,可进行规模化的商业应用,因此可为实现热核聚变发电厂的商业化设计提供支撑。

西安市城市气溶胶污染岛长时间序列特征分析

城市气溶胶污染岛(UAPI)对人体健康、城市热环境、城市气候、大气辐射传输等有重要影响。该研究利用西安市2016—2019年城郊多个站点的PM_(2.5)数据定量化计算UAPI强度,分析PM_(2.5)和UAPI强度的日变化和年变化规律,并使用经验模态分解方法(EMD)对UAPI强度的长时间序列多尺度特征进行分析。结果表明,西安市具有明显的城市气溶胶污染岛效应,UAPI强度大于10μg·m^(-3)的比例达87.63%。在日内变化上,UAPI强度呈现夜晚高、白天低的特点;在年内变化上,呈现冬春高、夏秋低的“U”型分布特征;在年际变化上,2016—2019年UAPI效应呈逐年减弱的变化特征。利用EMD分解可以很好地揭示UAPI强度的多尺度特征,如IMF2、IMF4、IMF6分别体现了UAPI强度以周、月、年为周期的变化特征。对比PM_(2.5)和UAPI强度的时间序列,该方法可以较好地排除跨区域传输污染和大区域二次污染等对UAPI强度的影响。

Identification of the magnetic island structure in the HL-2A tokamak

The identification of the magnetic island structure in the HL-2A tokamak is presented. First, the perturbation current as a source for the perturbation flux can be determined by using Mirnov probe measurements. By superposing the perturbation flux and the equilibrium flux reconnected by equilibrium fitting, the structure and the width of the magnetic islands can be estimated. The method has been used in the HL-2A experiments.

考虑用户侧微能网能量支援的电–气–热耦合系统可靠性评估

微能网是用户侧多能耦合的重要形式,大量微能网接入对供能可靠性影响显著。针对当前多能耦合系统可靠性评估对用户侧微能网运行模式、能量支援方式研究不充分的问题,提出考虑多微能网能量支援的电-气-热耦合系统可靠性评估方法。根据能量的网间支援与多能支援,定义并网运行、不完全孤岛独立运行、不完全孤岛联合运行、完全孤岛独立运行、完全孤岛联合运行5种故障后微能网运行模式;构建计及微能网运行模式的电-气-热耦合系统故障影响分析及可靠性评估框架;采用基于功率圆的静态孤岛划分方法确定微能网孤岛范围和孤岛运行模式,建立适用于各种微能网运行模式的统一孤岛多能负荷动态削减模型。算例分析结果表明,故障后通过用户侧多能耦合和微能网联合优化运行,能够实现电、气、热系统间的多能高效支援和支持更多重要负荷的可靠供能。

Stabilization of tearing mode by current drive

The major disruption limits the operation of present tokamaks. Experimental evidences point out that the growth of tearing modes or the magnetic islands is primarily responsible for the occurrence. Taking the non-inductive current drive effects into account, a set of 3D nonlinear equation is derived. It is shown from simulation that the growth of the magnetic island is suppressed effectively by RF current drive. It is consistent with recent experiments on the HL-1 tokamak in which the plasma is stabilized by an RF current drive.

基于孤岛模式的可再生能源电网分层能量平衡控制方法

为提升区域电网的稳定、安全运行,需充分协调和控制各类可再生能源能量。提出基于孤岛模式的可再生能源电网分层能量平衡控制方法。该方法以多代理系统为核心,控制可再生能源电网分层能量平衡。在确定多代理系统的控制条件后,设计多代理系统的结构;利用Agent平台构建分层能量平衡控制方法,使配电网调度层、电网中央控制层以及源储荷本地控制层之间相互协调,通过蓄电池Agent控制和下垂控制协调和调度能量资源、保证输出功率的合理、平衡分配,控制可再生能源电网分层能量平衡。测试显示方法具备可再生能源设备运行状态计算能力,获取不同设备的运行状态结果;控制效果良好,电压在切投过程中稳定在305 V左右,频率的波动范围在49.5 Hz~50.5 Hz之间;日弃风弃光量均低于17%,净负荷波动功率结果均在0.52 kW以下,满足应用需求。

Modeling of the influences of multiple modulated electron cyclotron current drive on NTMs in rotating plasma

In this work, physical models of neoclassical tearing modes （NTMs） including bootstrap current and multiple modulated electron cyclotron current drive model are applied. Based on the specific physical problems during the suppression of NTMs by driven current, this work compares the efficiency of continuous and modulated driven currents, and simulates the physical processes of multiple modulated driven currents on suppressing rotating magnetic island. It is found that when island rotates along the poloidal direction, the suppression ability of continuous driven current can be massively reduced due to current deposition outside the island separatrix and reverse deposition direction at the X point, which can be avoided by current drive modulation. Multiple current drive has a better suppressing effect than single current drive. This work gives realistic numerical simulations by optimizing the model and parameters based on the experiments, which could provide references for successful suppression of NTMs in future advanced tokamak such as international thermonuclear experimental reactor.

基于改进线性二次调节器的微电网运行模式无缝切换控制策略

微电网的主要特点之一是能够在并网模式和孤岛模式下运行,进行微电网运行模式之间的切换可能导致电压和频率的显著波动,严重时会威胁到整个系统的稳定性。无缝切换控制策略是保证微电网稳定可靠运行的关键,为解决传统无缝切换控制策略易受干扰影响和动态稳定性差的问题,提出了一种基于改进线性二次调节器的微电网运行模式无缝切换控制策略,该策略包括并网-孤岛平滑调节器和孤岛-并网平滑调节器。并网-孤岛平滑调节器通过对传统电压控制环的改进,可以为系统提供更多的阻尼并补偿逆变器输出处的瞬态电压降,从而改善系统动态性能。同时,通过对传统下垂控制策略的改进,可以根据系统有功功率的变化来调整其下垂系数,在受干扰的情况下能够将频率偏差降低到期望的水平。孤岛-并网平滑调节器考虑内部控制回路和PLL动态的情况下,根据并网控制策略下的状态空间模型对传统电流控制回路进行了改进,可以保证PCC两侧电压的同步性和微电网频率的稳定性。最后,对所提出的控制策略进行了小信号分析,同时研究了孤岛检测算法对控制策略的潜在影响,突出了所提策略的鲁棒性,并验证了所提控制策略能够平滑稳定地实现微电网运行模式间的切换。

孤岛光伏并联逆变器系统的固定时间模糊反步控制策略

针对孤岛光伏并联逆变器系统存在固有的建模不确定性以及动态性能差的问题,提出一种固定时间模糊反步控制策略。首先,将滤波器参数和输出电流作为未知项,建立含有滤波器参数摄动和输出电流扰动的单台逆变器等效数学模型。其次,将固定时间Lyapunov稳定性原理、模糊逻辑控制理论和反步控制理论相结合,利用固定时间模糊反步控制器逼近系统中的未知项,以改善逆变器的输出电压。然后,基于严格的Lyapunov定理证明所提控制策略下的系统是固定时间稳定的,且稳定时间的上界与系统的初始状态无关。最后,通过两台20 kW样机验证了所提控制策略的有效性。

基于子模块电容能量波动的MMILC下垂控制策略

交直流混合配电网中,孤岛模式下互联换流器(interlinking converter,ILC)具有实现配网间功率平衡、维持交流频率和直流电压稳定的作用。模块化多电平互联换流器(modular multilevel interlinking converter,MMILC)作为ILC的拓扑之一,具有谐波特性好、波形质量高、开关损耗低等优势。文中提出一种适用于MMILC的两级式下垂控制策略,首先基于子模块电容能量波动特性建立了适用于MMILC的新型交直流侧统一下垂特性;然后推导得出了MMILC直流侧电压与等效子模块电容电压间的数学关系,使MMILC仍可通过直流电压偏差进行功率调节,同时设置了下垂特性曲线的死区和最低允许运行范围;最后,分别对MMILC在不同负载模式和过载情况下的控制性能进行了仿真。仿真结果表明,所提出的MMILC两级式下垂控制策略可以自动平衡不同负载模式下交直流侧配网的功率偏差,过载情况下可以瞬时闭锁,验证了控制策略的正确性和有效性。

VOCs治理中的活性炭:作用、难题及“绿岛”模式

活性炭吸附是挥发性有机物(VOCs)治理的主流技术之一。本文概括介绍了活性炭在VOCs治理中的作用、应用场景及选用指标,分析了目前活性炭吸附净化VOCs过程中的安全问题及活性炭再生失效难题产生的原因等。此外,重点关注了为解决间歇、零散、小规模排放VOCs治理的活性炭“分散吸附+集中再生”的“绿岛”模式。

基于改进扩展状态观测器的交流孤岛微电网鲁棒性电压滑模控制

针对交流孤岛微电网中系统参数和负荷变化等不确定因素导致的电压不稳定的问题,提出了一种基于改进的扩展状态观测器(MESO)的鲁棒电压滑模控制策略。首先,将系统内部和外部扰动视为集总不确定性,并以此建立孤岛微电网系统的状态空间模型。其次,基于线性扩展状态观测器(ESO)设计了一种改进的扩展状态观测器(MESO),从而通过MESO估计系统的不确定性。最后,提出了一种具有多幂次趋近律的滑模控制器,从而使系统的输出电压能够快速、准确地跟踪参考电压,增强系统的鲁棒性,并通过仿真对比实验验证所提策略的有效性。实验结果表明,所提鲁棒性电压滑模控制策略可有效抵抗系统的内部和外部干扰,能够在不同负载类型下快速跟踪其参考输入电压,使输出电压具有良好的动态调节能力和稳态性能。

Control of Distributed Generation Using Non-Sinusoidal Pulse Width Modulation

The islanded mode is one of the connection modes of the grid distributed generation resources.In this study,a distributed generation resource is connected to linear and nonlinear loads via a three-phase inverter where a control method needing no current sensors or compensator elements is applied to the distribute generation system in the islanded mode.This control method has two main loops in each phase.The first loop controls the voltage control loops that adjust the three-phase point of common coupling,the amplitude of the non-sinusoidal reference waveform and the near-state pulse width modulation(NSPWM)method.The next loop compensates the harmonic compensator loop that calculates the voltage harmonics of the point of common coupling in each phase,and injects them to compensate the non-sinusoidal reference waveforms of each phase.The simulation results in MATLAB/SIMULINK show that this method can generate balanced threephase sinusoidal voltage with an acceptable total harmonic distortion(THD)at the joint connection point.