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.

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.

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.

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.

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。

孤网模式下水电机组智能鲁棒控制

针对孤网模式下水电机组PID控制策略鲁棒性差的缺点,设计了适用于非线性水轮机调节系统(hydraulic turbine regulating system,HTRS)的基于状态动态测量、反馈线性化和改进黏菌算法(improved slime mold algorithm,ISMA)的智能鲁棒控制器(intelligentrobustcontroller,IRC),以实现对水电站全工况实时最优控制。首先,充分考虑水轮机非线性、随动系统限速环节和高阶发电机特性,构建非线性、复杂HTRS数值仿真模型,并引入系统跟踪偏差的积分,推导出了孤网模式下考虑系统跟踪偏差的HTRS高阶状态空间方程模型。然后,结合高阶状态空间方程和H∞控制实现了HTRS鲁棒控制。进一步,基于ISMA对H∞控制器参数进行智能寻优。最后,结合某电站真实数据构建非线性、复杂HTRS仿真平台,验证了所提控制策略对系统参数和工况的敏感性、频率扰动下的强鲁棒性。

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。

并联改进VSG功率环流的分析与抑制策略研究

为了抑制孤岛模式下光伏微电网逆变器之间由于输电线路阻抗差异所引起的环流问题,文章提出了一种用于多逆变器并联系统的改进的虚拟同步发电机(Virtual Synchronous Generator,VSG)控制策略。首先,基于传统的VSG控制框图,通过引入线路功率反馈环节,使每台逆变器分别抵消其输电线路上的功率损耗,以提高有功、无功功率均分精度,并降低输出电压跌落,改善电能质量;然后,通过引入同步控制器,减小逆变器并联瞬间的电流冲击,降低多逆变器并联系统之间的瞬时环流;最后,通过仿真与实验验证了所提控制策略的有效性。

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。

基于马尔可夫蒙特卡罗算法的孤岛模式混合储能微网下垂平坦控制方法

孤岛状况是造成混合储能微网下垂的主要因素,为使混合储能微网正常运行,提出基于马尔可夫蒙特卡罗算法的孤岛模式混合储能微网下垂平坦控制方法。使用马尔可夫蒙特卡罗算法对缺失光伏数据进行填补。依据填补后的微网光伏数据计算微网自身荷电状态,并依据该荷电状态数值建立混合储能微网超级电容和蓄电池功率控制模型,实现孤岛模式混合储能微网下垂平坦控制。结果表明:所提方法填补光伏数据时的效率高于0.99,具备良好的下垂平坦控制能力。采用所提方法可对孤岛模式混合储能微网下垂进行良好控制,可有效保证混合储能微网的平稳运行,具有一定应用价值。

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。

微网综合控制与分析

考虑到微网内分布式电源和负荷所具有的分散性,根据分布式电源的类型以及与储能装置的不同组合方式,采用不同的控制策略分别进行了相应控制器的设计。基于下垂特性的电压/频率(V/f)控制实现了负荷功率变化时不同分布式电源间变化功率的共享,且在微网孤岛运行时能为微网系统提供频率支撑;PQ控制可根据实际运行情况实现分布式电源有功和无功功率的指定控制。通过对微网孤岛运行模式和联网运行模式之间切换、孤岛模式下切/增负荷以及微网内某一电源功率变化3种情况下的运行特性进行分析,获得了微网中相应分布式电源的功率、电压、电流及系统频率的变化规律,证明了PQ-V/f综合控制策略的正确性和有效性。

孤岛模式下的微网优化运行策略

微网的灵活、高效、经济、环保以及能源多样等优势使微网与传统大电网的运行管理方式有所不同。研究了微网在孤岛运行模式下,考虑分布式电源的发电成本、环境成本以及微网的设备维护成本,在满足微网运行约束条件的基础上,优化微网内不同分布式电源和储能系统的功率输出,使系统的总运行成本最小。分析并建立了含有风力发电系统、微汽轮机、燃料电池、柴油发电机和蓄电池的微网优化运行模型,在对风电功率和敏感性负荷预测的基础上,采用遗传算法求解该模型,并通过算例验证了方法的可行性。

基于风光荷功率曲线的有源配电网动态孤岛划分方法

分布式电源大量融入配电网后,基于分布式电源孤岛运行成为配电网故障处理的一种重要方式,其中孤岛划分是实现分布式电源孤岛运行的关键。文中从孤岛控制方式以及多时间段有功平衡这两个角度对有源配电网孤岛划分问题进行了研究。介绍了孤岛控制方式研究情况,综合考虑了分布式电源出力间歇性和负荷需求波动性,建立了基于风光荷功率曲线的孤岛风险评估模型;提出了多时段动态孤岛划分方法,该方法实现了恢复负荷最大化,同时也考虑了孤岛内控制方式,为实现工程化奠定基础。对一典型含风光储配电网算例进行了仿真,仿真结果表明了所述动态孤岛划分方法的可行性和有效性。

舟山多端柔性直流输电控制保护系统

对多端柔性直流输电控制及保护系统的分层设计及其功能配置进行了描述。介绍了多端柔性直流输电系统中多站之间的协调控制功能,即当直流电压控制站失去直流电压控制功能后,通过设计的基于站间通信和直流电压偏差检测的自适应策略,可以实现其余功率站的直流电压无偏差接管。介绍了工程采用的快速负序控制、直流侧主动充电以及在线联网转孤岛运行等控制功能设计。最后给出的部分现场试验结果证明了多端柔性直流输电控制保护系统可以很好地满足舟山五端柔性直流输电工程的需求。

逆变器并联的自适应滑模全局鲁棒电压控制方法

针对孤岛微电网非线性负载产生的谐波电流扰动和逆变器滤波参数摄动,使得经典的比例–积分–微分电压控制器难以实现对逆变器满足精度的控制,文中设计一种自适应滑模全局鲁棒电压控制器。该控制器对逆变系统负载电流扰动和滤波参数摄动采取自适应预测,使得控制系统具备全局鲁棒性。另外,负载电流扰动的自适应预测,在保证控制系统稳定性前提下,能够实时调节输入电压控制信号的切换增益,从而限制了输出电压的抖振。仿真和实验结果表明:该策略降低了逆变系统输出电压的抖振、谐波畸变率、稳态跟踪误差以及并联逆变器之间的环流,提高了逆变系统输出电压的动态调节能力及抵御滤波参数摄动的能力。