微电网系统中多种逆变器的并联组网控制策略

采用氢燃料蓄电池单体的串并联组成的电池模块作为储能系统中的主要储能装置,多种逆变器连接在同一条公共线上.在微电网处于孤岛运行模式时,考虑到储能单元的逆变器间环流的存在、不同设备控制器的不同工作特性、低通滤波器存在的影响,提出新的下垂控制理论.利用逆变器模拟同步发电机的频率调节特性,保证负荷发生变化时微电网频率的稳定性;利用静止无功补偿器SVC补偿系统无功,以保障系统电压的稳定,进而实现多种逆变器的组网运行.利用PSCAD仿真软件进行仿真,验证对所建立的模型采取的一系列控制策略的有效性和正确性.     

微电网主从控制建模仿真

考虑到微电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Droop控制可实现负荷功率变化时不同分布式电源间变化功率的共享,而电压/频率(V/f)控制和Droop控制均可在微电网孤岛运行时为微电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.根据不同电源特性针对性地采用不同控制技术组合,并对微电网孤岛运行模式和并网运行模式之间切换的运行特性进行分析,获得了微电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以及PQ-Droop综合控制策略的正确性和有效性.     

带储能系统的小型风力异步发电机稳压稳频控制

针对小型风力异步发电机机端特性的不稳定,提出了带储能系统的异步发电机稳压稳频控制方法。在直流侧并联铅酸蓄电池系统进行储能,通过控制整流器实现直流侧有功和无功的双向流动。该控制方法包括电压外环和频率内环两个控制环,电压和频率控制器都采用的是PI控制器,用改进的锁相环法实时检测系统的频率变化。为了验证控制方法的有效性,进行了MATLAB/Simulink控制系统仿真和实验。结果表明:采用带储能系统的稳压稳频控制可以提高异步发电机的机端特性,改善独立供电系统的电能质量。     

风光储微电网运行特性仿真分析

为研究含风力发电、太阳能光伏发电和储能系统三种类型微源组成的微电网的运行特性,在MATALB软件平台上,建立了基于主从控制的风光储微电网联合仿真模型.以蓄电池储能系统为主控电源,在微电网并网运行时,所有微源都采用P/Q控制;微电网离网运行时,蓄电池储能系统采用V/f控制,支撑微电网频率和电压.然后对微电网并网运行、离网运行及并离网切换过程进行仿真.仿真结果表明:微电网在并网、离网运行模式下能安全、可靠运行,在运行模式切换过程时能平滑过渡.     

基于MPC的多源孤岛微电网协调控制

含有多种分布式电源(DG)的微电网在孤岛运行时,DG出力的随机性以及负荷的波动性对系统的安全稳定运行带来了巨大挑战。针对含有柴油发电机、光伏发电单元和储能单元的孤岛微电网,提出了各分布式电源的协调控制策略,光伏发电单元采用最大功率跟踪控制以最大限度利用太阳能,储能单元与柴油发电机协调控制以提高系统运行的稳定性。采用模型预测控制策略(MPC)实现并网逆变器的内环电流控制,避免了繁琐的PI参数整定以及PWM调制器的使用,提高了控制器的动静态性能。仿真结果验证了所提控制策略的有效性与可行性。     

孤岛微网模糊PI下垂控制仿真研究

处于孤岛运行的微电网,通常采用下垂控制方式对其输出电压幅值和频率进行控制.而传统下垂控制策略在微网负荷波动情况下,存在电压幅值和频率难以稳定的问题,提出一种基于模糊PI控制的改进下垂控制策略.该策略引入模糊PI控制,通过采集电压幅值和频率的变化,经模糊推理来实时调整下垂系数,减小了负荷功率波动对系统的影响,提高了微电网的稳定性.通过在Matlab/Simulink中建模仿真,验证了该控制策略的可行性.     

基于源-荷-储的直流微电网系统协调控制

针对孤岛下独立运行的直流微电网,为了更好的维持系统功率的供需平衡,快速平抑母线电压的波动。利用超级电容和蓄电池的互补特性设计混合储能系统,在下垂控制的基础上,通过增加二次补偿装置抑制负荷功率波动,从而实现直流微电网的精准控制,将系统划分成多个模式运行,通过利用所提的控制策略对各个模块进行联动控制,实现系统平滑的在多个运行模式下切换。完成直流微电网的源-荷-储协调优化控制。最后对其在MATLAB/Simulink上进行仿真实验,验证控制策略的有效性和可行性。     

基于改进虚拟同步机的风储微网综合控制

微电网中负荷变化与风电等分布式电源出力不确定性给整个微网稳定带来很大困难。针对风电出力波动问题,采用虚拟同步发电机控制结合深度强化学习对电池储能系统输出进行控制：首先搭建包含风电、电池储能、负荷、外部电网的微网模型,其次利用深度确定策略梯度算法对虚拟调速器进行设计,结合奖励函数通过反复学习训练生成调速器实现对虚拟同步发电机的改进。最后,在Matlab/Simulink软件中搭建对应的仿真模型,与下垂控制、传统虚拟同步发电机控制进行对比,仿真验证了并网到离网切换场景与孤岛运行场景下,所提出的控制方法对微网频率与电压有良好的稳定效果,可以实现对负荷有功功率与无功功率的快速追踪。     

基于电池储能和可控负荷的孤岛型海岛微电网频率协调控制策略

针对以风电和波浪能发电为主电源的孤岛型海岛微电网,提出一种基于电池储能和可控负荷的孤岛型海岛微电网频率协调控制策略。储能元件采用改进的下垂控制实现类似于电力系统一次调频的有差调频,根据其荷电状态及最大充放电功率,动态调整下垂控制运行点以及下垂控制系数,既能将微网频率偏差控制在合理范围内,又能防止电池储能系统过充过放;利用海水淡化负荷的可控性,将频率偏差引入其转速控制环,实现类似于电力系统二次调频的无差调频。在Matlab/Simulink下搭建了孤岛型海岛微电网的仿真模型,并对不同运行场景进行了仿真验证。结果表明,基于电池储能和可控负荷的孤岛型海岛微电网频率协调控制策略可以有效地分配系统功率差额,维持海岛微电网的频率稳定。     

计及储能调节的时滞互联电力系统频率控制

针对互联电力系统中源荷不确定以及通信延时导致系统频率偏差过大的问题,提出了计及储能调节的两域时滞电力系统频率控制策略.建立了含汽轮发电机、风机和储能等设备的两区域时滞互联电网模型,根据区域控制偏差(ACE)所在的区间对储能装置和汽轮发电机的调频任务进行分工.利用改进粒子群(MPSO)算法优化比例积分微分(PID)负荷频率控制器实现二次调频,提升了一定时滞区间内负荷频率控制(LFC)系统的频率稳定性.对储能装置设计分数阶PID(FOPID)控制器,调节其输出功率以平滑源荷波动,提高了储能系统的辅助调频性能,进一步控制互联电力系统的频率偏差.在MATLAB/Simulink平台对不同工况进行对比分析,验证了所提频率控制策略的有效性.     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that     

On the Thermodynamic Limit for Responses to Static Electromagnetic Fields

For molecular systems,the quantum-mechanical treatment of their responses to static electromagnetic fields usually employs a scalar-potential treatment of the electric field and a vector-potential treatment of the magnetic field.Although the potential for each field separately is associated with the choice of an(unphysical)origin,the precise choice of the origin for the electrostatic field has little consequences for the results.This is different for the     

An affordable accurate evaluation of the binding conformations predicted by molecular docking studies in bio-system

Franck-Condon factors bridge the gap between theoretical modeling and experimental observations for molecular electronic spectroscopy and electron transfer.Under the displaced harmonic oscillator approximation,multidimensional Franck-Condon factors are decomposed into a product of many one-dimensional(1D)Franck-Condon(FC)factors,and each 1D-FC factor is associated with one Huang-Rhys factor that determines the leading contribution of     

Call for Papers

<正>"The Journal of Shanghai Normal University:Mathematics"is published by Shanghai Normal University as regular issues of The Journal of Shanghai Normal University each year from 2014 in English.The editors-in-chief of the issues are professors Yuhao Cong and Maoan Han.The Journal of Shanghai Normal University was started in 1958 with     

Journal of Donghua University ( English Edition) Contents of Volume 31

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