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Zero-sequence Circulating Current Reduction for Three-phase Three-level Modular Photovoltaic Grid-connected Systems 被引量:16
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作者 ZHANG Xing SHAO Zhangping WANG Fusheng LIU Ping REN Kangle 《中国电机工程学报》 EI CSCD 北大核心 2013年第9期I0003-I0003,共1页
针对共享正、负母线和交流母线的三相三电平模块化光伏并网系统的零序环流问题,建立三电平模块化系统零序环流的等效模型,并根据激励源的不同将零序环流分成3类,提出一种共享正、负母线和中线的并联方案来抑制I类零序环流,及一种基于改... 针对共享正、负母线和交流母线的三相三电平模块化光伏并网系统的零序环流问题,建立三电平模块化系统零序环流的等效模型,并根据激励源的不同将零序环流分成3类,提出一种共享正、负母线和中线的并联方案来抑制I类零序环流,及一种基于改进型LCL滤波器的并联方案来抑制II、III类零序环流的高频分量,和采用零序环流控制器来抑制II、III类零序环流的低频分量。最后,通过10 kW的三相三电平模块化光伏并网系统的仿真和实验,证明了零序环流模型分析和抑制方法的正确性。 展开更多
关键词 光伏系统 光伏并网 循环电流 模块化 三相 零序 逆变器并联 闭合回路
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Current Circulation and Water Renewal Time in the Enclosed Marine Area of Pagasitikos Basin, Greece
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作者 George Bousbouras Panagiotis Angelidis 《Computational Water, Energy, and Environmental Engineering》 2024年第3期113-132,共20页
Greece boasts an impressive closed coastline stretching across 13,676 km, making it the largest in the Mediterranean basin and one of the largest in the world. Given the significant human activities that take place in... Greece boasts an impressive closed coastline stretching across 13,676 km, making it the largest in the Mediterranean basin and one of the largest in the world. Given the significant human activities that take place in coastal areas, understanding the behavior of the sea environment becomes crucial. In this study, we delve into the generation and movement of marine currents as well as the retention time and water age within the waters of Pagasitikos Sea inlet, Greece, through numerical simulation of hydrodynamic characteristics. The main examined points of the understudy region are the area of the port of Volos, the Trikeri channel where the ingress and egress of water from the Gulf takes place and the exchange of seawater through circulation of the Pagasitikos Gulf with the North Evian Gulf. In order to evaluate the results, they were compared with real field measurements and with simulation on a laboratory dummy of the same area. The computational simulation was performed with the ELCOM 2.2 numerical modeling tool and the AEM3D latest version and the main factors simulated are the tide, the consequence that Coriolis force, boundary conditions, the topography and bottom geometry of the bay and the actual meteorological conditions of a whole year. 展开更多
关键词 Fluid Dynamics Simulation current circulation Pagasitikos Basin ELCOM
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Single-phase-to-ground fault protection based on zero-sequence current ratio coefficient for low-resistance grounding distribution network 被引量:4
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作者 Jianrui Li Yongli Li +1 位作者 Yonghuan Wang Jinzhao Song 《Global Energy Interconnection》 EI CAS CSCD 2021年第6期564-575,共12页
Definite-time zero-sequence over-current protection is presently used in systems whose neutral point is grounded by a low resistance(low-resistance grounding systems).These systems frequently malfunction owing to thei... Definite-time zero-sequence over-current protection is presently used in systems whose neutral point is grounded by a low resistance(low-resistance grounding systems).These systems frequently malfunction owing to their high settings of the action value when a high-impedance grounding fault occurs.In this study,the relationship between the zero-sequence currents of each feeder and the neutral branch was analyzed.Then,a grounding protection method was proposed on the basis of the zero-sequence current ratio coefficient.It is defined as the ratio of the zero-sequence current of the feeder to that of the neutral branch.Nonetheless,both zero-sequence voltage and zero-sequence current are affected by the transition resistance,The influence of transition resistance can be eliminated by calculating this coefficient.Therefore,a method based on the zero-sequence current ratio coefficient was proposed considering the significant difference between the faulty feeder and healthy feeder.Furthermore,unbalanced current can be prevented by setting the starting current.PSCAD simulation results reveal that the proposed method shows high reliability and sensitivity when a high-resistance grounding fault occurs. 展开更多
关键词 Low-resistance grounding system High-impedance grounding fault Grounding protection zero-sequence current ratio coefficient
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Inhibition characteristics of circulating current in parallel inverter driving system of mine hoist 被引量:3
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作者 Kuanfang He Yong Wang Dongming Xiao 《International Journal of Coal Science & Technology》 EI 2016年第1期68-76,共9页
This research investigated the outputting circulation current inhibition characteristic which are controlled by the instantaneous feedback voltage in inverter parallel driving of the mine hoist. We established a trans... This research investigated the outputting circulation current inhibition characteristic which are controlled by the instantaneous feedback voltage in inverter parallel driving of the mine hoist. We established a transfer function of the parallel inverters controlled by the close-loop adjustment of instantaneous voltage feedback. The influence of the parameters of the close-loop feedback circuit to the inhibition effects to the outputting circulation current is observed. After analyzing the circulating current inhibition characteristics, the proportion integration (PI) controller is introduced into the close-loop adjustment by instantaneous voltage feedback. The characteristics equation is gained to determine the PI parameters by drawing the Bode plots. The inhibition effects of the proposed controller are examined by the established simulation model of parallel inverter system. The harmonic distortion rate at the outputting voltage frequency value of 4, 10, 20, 41 and 50 Hz, are all lower than 2.32 % by the instantaneous outputting voltage feedback. 展开更多
关键词 Mine hoist Parallel inverters circulating current Inhibition characteristic - Close-loop adjustment
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Hybrid Predictive Control with Simple Linear Control Based Circulating Current Suppression for Modular Multilevel Converters 被引量:5
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作者 Yuanxiang Sun Zhen Li Zhenbin Zhang 《CES Transactions on Electrical Machines and Systems》 CSCD 2019年第4期335-341,共7页
The modular multilevel converter(MMC)has become a promising topology for widespread power converter applications.However,an evident circulating current flowing between the phases will increase system losses and compli... The modular multilevel converter(MMC)has become a promising topology for widespread power converter applications.However,an evident circulating current flowing between the phases will increase system losses and complicate the heatsink design.This paper proposes a novel hybrid model predictive control method for MMCs.This method utilizes an indirect structure MPC and a sorting algorithm to implement current tracking and capacitor voltages balancing,considerably resulting in reduced calculation burden.In addition,different from the conventional MPC solutions,we add a simple proportional-integral(PI)controller to suppress circulating current through modifying the submodule(SM)inserted number,which is parallel to the MPC loop.This hybrid control solution combines both advantages of MPC and linear control,evidently resulting in improved performance of circulating current.Finally,the MATLAB/Simulink results of an 11-level MMC system verify the effectiveness of the proposed solution. 展开更多
关键词 circulating current suppression hybrid predictive control linear control modular multilevel converters.
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GENERATOR VIBRATION FAULT DIAGNOSIS METHOD BASED ON ROTOR VIBRATION AND STATOR WINDING PARALLEL BRANCHES CIRCULATING CURRENT CHARACTERISTICS 被引量:2
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作者 Wan Shuting Li Heming +1 位作者 Li Yonggang Tang Guiji 《Chinese Journal of Mechanical Engineering》 SCIE EI CAS CSCD 2005年第4期592-596,共5页
Rotor vibration characteristics are first analyzed, which are that the rotor vibration of fundamental frequency will increase due to rotor winding inter-turn short circuit fault, air-gap dynamic eccentricity fault, or... Rotor vibration characteristics are first analyzed, which are that the rotor vibration of fundamental frequency will increase due to rotor winding inter-turn short circuit fault, air-gap dynamic eccentricity fault, or imbalance fault, and the vibration of the second frequency will increase when the air-gap static eccentricity fault occurs. Next, the characteristics of the stator winding parallel branches circulating current are analyzed, which are that the second harmonics circulating current will increase when the rotor winding inter-turn short circuit fault occurs, and the fundamental circulating current will increase when the air-gap eccentricity fault occurs, neither being strongly affected by the imbalance fault. Considering the differences of the rotor vibration and circulating current characteristics caused by different rotor faults, a method of generator vibration fault diagnosis, based on rotor vibration and circulating current characteristics, is developed. Finally, the rotor vibration and circulating current of a type SDF-9 generator is measured in the laboratory to verify the theoretical analysis presented above. 展开更多
关键词 Generator Fault diagnosis Rotor vibration characteristic Stator winding parallel branches circulating current
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Zero-sequence Current Suppressing Strategy for Dual Three-phase Permanent Magnet Synchronous Machines Connected with Single Neutral Point 被引量:2
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作者 Zongwang Li Yuxuan Du +2 位作者 Jinghua Ji Tao Tao Wenxiang Zhao 《CES Transactions on Electrical Machines and Systems》 CSCD 2022年第4期465-472,共8页
Dual three-phase permanent-magnet synchronous machines(DTP-PMSM)connected with a single neutral point provide a loop for zero-sequence current(ZSC).This paper proposes a novel space vector pulse width modulation(SVPWM... Dual three-phase permanent-magnet synchronous machines(DTP-PMSM)connected with a single neutral point provide a loop for zero-sequence current(ZSC).This paper proposes a novel space vector pulse width modulation(SVPWM)strategy to suppress the ZSC.Five vectors are selected as basic voltage vectors in one switching period.The fundamental and harmonic planes and the zero-sequence plane are taken into consideration to synthesis the reference voltage vector.To suppress the ZSC,a non-zero zero-sequence voltage(ZSV)is generated to compensate the third harmonic back-EMF.Rather than triangular carrier modulation,the sawtooth carrier modulation strategy is used to generate asymmetric PWM signals.The modulation range is investigated to explore the variation of modulation range caused by considering the zero-sequence plane.With the proposed method,the ZSC can be considerably reduced.The simulated and experimental results are presented to validate the effectiveness of the proposed modulation strategy. 展开更多
关键词 zero-sequence current a single neutral point dual three-phase permanent-magnet synchronous machine third harmonic back-EMF
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The Circulating Current Analysis and Parameter Design of Interphase-Reactor of HT-7U Toroidal Power Supply
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作者 许留伟 刘小宁 《Plasma Science and Technology》 SCIE EI CAS CSCD 2003年第2期1703-1708,共6页
This paper analyzes the circulating current which is produced by HT-7Usuperconducting toroidal power supply-two sets of two-reverse-star converter with aninterphase-reactor in parallel running on the basis of the outp... This paper analyzes the circulating current which is produced by HT-7Usuperconducting toroidal power supply-two sets of two-reverse-star converter with aninterphase-reactor in parallel running on the basis of the output voltage mathematical equation ofthree-phase semi-wave converter circuit. A new idea of omitting interphase-reactor between twoconverters is proposed, and the parameter design of interphase-reactor of HT-7 toroidal power supplyis presented. Simulated results demonstrate the validity of this new project. 展开更多
关键词 circulating current interphase-reactor two-reverse-star converter
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Improved Ladder Wave Modulation of Circulating Current Suppressing Control Strategy of MMC
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作者 Pinggang Song Yunfeng Li Lina Wang 《Energy and Power Engineering》 2013年第4期1176-1181,共6页
This paper partitions the arm current of MMC into uncontrollable current and controllable current. The former is determined by the load that can’t be controlled by taking any control strategy. The later caused by the... This paper partitions the arm current of MMC into uncontrollable current and controllable current. The former is determined by the load that can’t be controlled by taking any control strategy. The later caused by the unbalanced total inserted voltage of three arms can be controlled by some improved algorithms. The conclusion based on the researching the essence of circulating current is reached that change the number of the inserted sub-modules in each phase can suppress the circulating current. Combined with the improved ladder wave modulation, a novel circulating current suppression strategy particularly for the inverter station is developed. The improved strategy can adapt to load changes and reduce the circulating current and output voltage THD of MMC ac terminals greatly without increasing any peripheral circuits. Finally, the simulation model of 100 submodules in each phase is constructed in MATLAB and the simulation results verify the correctness and effectiveness of the modified control algorithm. 展开更多
关键词 Modular MULTILEVEL Converter High Voltage Direct current Transmission circulating current Module CHANGING Selection Algorithm Double Frequency NEGATIVE Component
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Zero-Sequence Current Suppression Strategy for Open-End Winding Permanent Magnet Synchronous Motor Based on Model Predictive Control
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作者 LIU Huashan LI Jie YAO Fei 《Journal of Donghua University(English Edition)》 EI CAS 2020年第4期286-292,共7页
Compared with the traditional three-phase star connection winding,the open-end winding permanent magnet synchronous motor(OW-PMSM)system with a common direct current(DC)bus has a zero-sequence circuit,which makes the ... Compared with the traditional three-phase star connection winding,the open-end winding permanent magnet synchronous motor(OW-PMSM)system with a common direct current(DC)bus has a zero-sequence circuit,which makes the common-mode voltage and the back electromotive force(EMF)harmonic generated by the inverters produce the zero-sequence current in the zero-sequence circuit,and the zero-sequence current has great influence on the operation efficiency and stability of the motor control system.A zero-sequence current suppression strategy is presented based on model predictive current control for OW-PMSM.Through the mathematical model of OW-PMSM to establish the predictive model and the zero-sequence circuit model,the common-mode voltage under different voltage vector combinations is fully considered during vector selection and action time calculation.Then zero-sequence loop constraints are established,so as to suppress the zero-sequence current.In the end,the control strategy proposed in this paper is verified by simulation experiments. 展开更多
关键词 open-end winding permanent magnet synchronous motor(OW-PMSM) zero-sequence current HARMONIC model predictive current control common-mode voltage
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Distributed On-line Monitoring System for Sheath Circulating Current of Cross-linked Power Cables
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作者 MENG Yong-peng PENG Fa-dong +3 位作者 YAN Li CHEN Xiao-lin CHENG Yong-hong LIU Jing 《高电压技术》 EI CAS CSCD 北大核心 2009年第3期533-538,共6页
关键词 供电系统 电缆 信号采集 在线监测系统
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On the Huanghai (Yellow) Sea circulation:a review by current measurements 被引量:15
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作者 Heung-Jae Lie(Physical Oceanography Dvision, Korea Ocean Research and Development Institute, P.O. Box 29, Ansan, 425 - 600Seoul, Korea) 《Acta Oceanologica Sinica》 SCIE CAS CSCD 1999年第3期355-373,共19页
The Huanghai (Yellow) Sea circulations suggested in the past were constructed mostly based on hydrographic data or simple numerical models, and were not rigorously compered with direct current measurements. Ourpresent... The Huanghai (Yellow) Sea circulations suggested in the past were constructed mostly based on hydrographic data or simple numerical models, and were not rigorously compered with direct current measurements. Ourpresent understanding of the Huanghai Sea circulation is still very poor and superficial. To evaluate our present knowledge about the circulation and to sketch a more realistic circulation pattern, the previous studies on the circulation arebriefly reviewed and directly measured current data collected in the past are revisited. The Huanghai Sea Warm Current and the northeastward extension in summer of the Changjiang diluted water are paid more attention to, which arethe major currents of the basic circulation, and then attempted to sketch the Huanghai Sea circulation by synthesizinghydrography and current data. The Huanghai Sea circulation is not considered to be persistent since the thin water column, less than 100 m, responds quickly and sensitively to external driving forces. Directly measured current data showthat saline water originating from the Kuroshio water turns clockwise around Cheju-do throughout the year and eventually joins the Tsushima Warm Current at the western channel of the Korea Strait. This clockwise current is called theCheju Warm Current. The current data do not support the persistent existence of the Huanghai Sea Warm Current,which has ho believed to supply heat and salt to the Huanghai Sea throughout the year. However, a northward flowis generated intermittently during the weakening phase of cold air outbreaks in winter. The northeast extension of theChangjiang diluted water in summer is evidenced by satellite-tracked surface drifters. 展开更多
关键词 Huanghai Sea circulATION Cheju Warm current
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Numerical Study of the Secondary Circulations in Rip Current Systems 被引量:1
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作者 LI Rui GUAN Changlong 《Journal of Ocean University of China》 SCIE CAS 2015年第1期9-16,共8页
To investigate the mechanism of secondary circulations in rip current systems, and to explore the relationship between wave conditions and secondary circulation intensity, a series of numerical experiments is performe... To investigate the mechanism of secondary circulations in rip current systems, and to explore the relationship between wave conditions and secondary circulation intensity, a series of numerical experiments is performed using coupled nearshore wave model and circulation model. In these experiments, the rip currents and secondary circulations generated above barred beaches with rip channels are simulated. A comparison experiment is conducted to investigate the formation and hydrodynamics of the secondary circulations. Model results indicate that the secondary circulations consist of alongshore flows driven by wave set-up near the shoreline, part of the feeder currents driven by the wave set-up over the bars, and onshore flows at the end of the rip channel driven by wave breaking and convection. The existence of the secondary circulation barely affects the rip current, but narrows and intensifies the feeder currents. Three groups of experiments of varying incident wave conditions are performed to investigate the relationship between wave conditions and secondary circulation intensity. The velocity of the alongshore flow of the secondary circulation is sensitive to the variation of the incident wave height and water depth. It is also found that the alongshore flow intensity is in direct proportion to the alongshore variation of the wave height gradient between the bars and the shoreline. 展开更多
关键词 secondary circulation rip current WAVES radiation stress
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Optimal design of auxiliary-teeth to solve circulation current reduction of permanent magnet linear synchronous motor 被引量:1
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作者 JANG Ki-bong KIM Jee-hyun +1 位作者 AN Ho-jin KIM Gyu-tak 《Journal of Central South University》 SCIE EI CAS 2011年第3期690-696,共7页
A discontinuity of magnetic circuits according to the end effect is generated in the permanent magnet linear synchronous motor (PMLSM). Due to the unbalanced back electro-motive force (EMF) and impedance produced,... A discontinuity of magnetic circuits according to the end effect is generated in the permanent magnet linear synchronous motor (PMLSM). Due to the unbalanced back electro-motive force (EMF) and impedance produced, unbalanced current is generated. The cireulatin8 current, which is caused by a decrease in the thrust, is generated by the unbalanced current. The optimal design of auxiliary-teeth at the end of the mover was carried out to solve the unbalance of phase by using design of experiment (DOE), and compared with the basic model through finite element analysis (FEA). As a result, the auxiliary-teeth model compensates for the decrease of thrust caused by the unbalanced phase. Also, this model is proven to reduce the detent force by the vibration and noise of the PMLSM and copper loss caused by the circulating current. 展开更多
关键词 permanent magnet linear synchronous motor auxiliary-teeth circulation current end effect thrust reduction
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Current-event Play and Circulation of Information in late Ming China
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作者 Nie Lina 《学术界》 CSSCI 北大核心 2018年第4期238-246,共9页
This essay examines current-event plays( shishiju 时事剧) and their social functions in late Ming China. Drawing on awide range or primary sources and built on secondary scholarship on information history,the essay of... This essay examines current-event plays( shishiju 时事剧) and their social functions in late Ming China. Drawing on awide range or primary sources and built on secondary scholarship on information history,the essay offered a complete picture of the booming,features,social functions and the decline of the current-event plays. The essay argues that many current-event plays addressed on credibility,timeliness and easy accessibility,which enabled current-event plays to play an important role in information circulation. This essay further exposes the current-event plays not only opened a forum for public discussion but also influenced public opinions greatly from literate elites to the masses in Ming China. Through analyzing current-event plays in the context of Ming society,this essay expands the realm of studying information history. 展开更多
关键词 学习信息 事件 中国 循环 社会功能 散文 奖学金 接近性
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Interannual variability of eddy kinetic energy in the South China Sea related to two types of winter circulation events
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作者 Wenlian LI Qinyan LIU +2 位作者 Wendong FANG Tingting ZU Haiying CHEN 《Journal of Oceanology and Limnology》 SCIE CAS CSCD 2023年第3期831-851,共21页
Interannual variations of the eddy kinetic energy(EKE)related to two types of winter circulation events(“O”and“U”)were investigated based on the outputs of the Ocean General Circulation Model(OGCM)for the Earth Si... Interannual variations of the eddy kinetic energy(EKE)related to two types of winter circulation events(“O”and“U”)were investigated based on the outputs of the Ocean General Circulation Model(OGCM)for the Earth Simulator(OFES)and the corresponding energetic analyses.Results show that the EKE is strong and extends eastward to offshore the Vietnam coast about 2°,associated with the weaker South China Sea western boundary current(SCSwbc)in“O”type years,while the EKE is weak and high value that can be attained is narrowed along the coast,associated with the stronger SCSwbc in“U”type years.The energy budget shows that the wind stress and barotropic/baroclinic instability are important factors to regulate the EKE in“U”and“O”years.For“U”years,under a strong winter monsoon forcing,the SCSwbc strengthen,the directly wind work and barotropic conversion from the mean kinetic energy(MKE)to EKE are weak,thus the EKE decrease corresponding to the baroclinic conversion from the kinetic energy to potential energy.However,the situation is reversed in“O”years.Under the influence of El Niño events,wind stress forces can weaken SCSwbc and enhance EKE in pattern“O”,whereas La Niña events have relatively weaker influences.The barotropic conversion rate in“O”type is nearly eight times of the“U”type.The pressure work and advection term are the main sources to greatly suppress EKE in the SCSwbc region. 展开更多
关键词 two-type winter circulation South China Sea western boundary current energy budget
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海上风电单芯海缆接地环流影响因素分析 被引量:1
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作者 杨玉新 王劲松 +1 位作者 朱永利 李岩 《南方电网技术》 CSCD 北大核心 2024年第3期56-64,共9页
单芯海缆在生产、施工方面相对于三芯海缆更具优势,但是其接地环流异常引起的海缆故障频繁发生。单芯海缆接地环流运行机理及检测策略有待深入研究。建立了基于阻抗矩阵的单芯海缆数学模型,揭示了铠装电阻率、铠装层相对磁导率、接地电... 单芯海缆在生产、施工方面相对于三芯海缆更具优势,但是其接地环流异常引起的海缆故障频繁发生。单芯海缆接地环流运行机理及检测策略有待深入研究。建立了基于阻抗矩阵的单芯海缆数学模型,揭示了铠装电阻率、铠装层相对磁导率、接地电阻、短路电阻等因素对阻抗矩阵内参数和接地环流的影响规律。结合实际工程案例分析了海缆接地环流分配不均的机理,为海缆的运行状态评估及检修提供了参考依据。 展开更多
关键词 单芯海缆 接地环流 阻抗矩阵 PSCAD仿真
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考虑铁心结构的三相变压器励磁涌流和角型绕组环流分析
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作者 柴济民 郑玉平 潘书燕 《电力科学与技术学报》 CAS CSCD 北大核心 2024年第2期91-100,共10页
基于三相组式、五柱式和三柱式铁心结构变压器的磁路特征和运行方程,首先,提出运用星形侧零序电流和电压来拟合角型绕组环流的数值方法,并进一步研究不同铁心结构变压器的角型绕组环流和励磁涌流的特点;然后,进行软件仿真和现场录波以... 基于三相组式、五柱式和三柱式铁心结构变压器的磁路特征和运行方程,首先,提出运用星形侧零序电流和电压来拟合角型绕组环流的数值方法,并进一步研究不同铁心结构变压器的角型绕组环流和励磁涌流的特点;然后,进行软件仿真和现场录波以验证该数值方法的有效性,可判断三相组式和五柱式变压器的各相绕组差流即为对应相的励磁涌流,而三柱式变压器某相的绕组差流并不是对应相的励磁电流;最后,进一步的理论分析与仿真验证表明,在3类铁心结构的变压器从星形侧空载合闸时,星形侧任意两相的线电流之差可以认为是这两相等效磁路的励磁涌流之差。研究结论可以为不同铁心结构三相变压器的励磁涌流识别提供依据。 展开更多
关键词 变压器 励磁涌流 环流 零序分量
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基于磁共振成像三维动脉自旋标记评价经颅交流电刺激对阿尔茨海默病脑灌注的影响
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作者 王涛 闫少珍 +4 位作者 薛寒笑 席晗予 齐志刚 唐毅 卢洁 《中华老年心脑血管病杂志》 CAS 北大核心 2024年第11期1315-1319,共5页
目的 探讨经颅交流电刺激(transcranial alternating current stimulation, tACS)对阿尔茨海默病(Alzheimer's disease, AD)患者脑血流量(cerebral blood flow, CBF)的影响。方法 回顾性分析2019年9月至2022年4月首都医科大学宣武... 目的 探讨经颅交流电刺激(transcranial alternating current stimulation, tACS)对阿尔茨海默病(Alzheimer's disease, AD)患者脑血流量(cerebral blood flow, CBF)的影响。方法 回顾性分析2019年9月至2022年4月首都医科大学宣武医院神经内科记忆门诊及病房诊治的轻度AD患者21例,接受3周tACS治疗,基线(T_(0)期)、完成即刻(T_(1)期)和3个月(T_(2)期)分别进行简易智能状态检查量表(mini-mental state examination, MMSE)评分、听觉词语学习测验(auditory verbal learning test, AVLT)评分和磁共振成像数据采集,CBF图z变换(z-transform CBF,zCBF)减少个体差异,分析tACS治疗前后MMSE、AVLT评分以及脑zCBF、CBF的变化,采用Spearman相关性分析zCBF、CBF与认知功能评分的关系。结果 与T_(0)期比较,AD患者T_(1)期MMSE评分明显增加[22.00(20.00,25.00)分vs 20.00(18.00,21.50)分,P<0.01]。基于体素分析显示,与T_(0)期比较,AD患者T_(1)期双侧额叶及颞叶皮质zCBF明显增加,T_(2)期右侧额叶及颞叶皮质zCBF明显增加(P<0.05)。zCBF增加最明显的脑区位于右侧岛叶。基于感兴趣区分析显示,与T_(0)期比较,AD患者T_(1)期右侧额叶及颞叶皮质zCBF、CBF明显增加,差异有统计学意义(P<0.05)。T_(1)期右侧额叶皮质CBF改变值与AVLT评分延迟再认改变值呈正相关(r=0.617,P=0.005),T_(2)期左侧额叶皮质CBF改变值与MMSE评分改变值呈正相关(r=0.596,P=0.012)。结论 磁共振成像三维动脉自旋标记可客观评价tACS治疗后AD患者CBF变化,为评估tACS疗效提供可靠影像学指标。 展开更多
关键词 阿尔茨海默病 经颅交流电刺激 脑血管循环 磁共振成像
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基于新型VLMZVM的ANPC型三电平并网逆变器环流抑制方法
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作者 杨向真 刘灿 +3 位作者 杜燕 张徐进博 张涛 施永 《太阳能学报》 EI CAS CSCD 北大核心 2024年第6期272-284,共13页
为解决广泛应用在大功率分布式发电系统中的多机有源中点钳位(ANPC)型三电平并网逆变器间的低频零序环流问题,提出一种基于虚拟大矢量的新型十三矢量调制(VLMZVM)策略。通过建立多机ANPC型三电平并网逆变器零序环流模型,分析零序环流产... 为解决广泛应用在大功率分布式发电系统中的多机有源中点钳位(ANPC)型三电平并网逆变器间的低频零序环流问题,提出一种基于虚拟大矢量的新型十三矢量调制(VLMZVM)策略。通过建立多机ANPC型三电平并网逆变器零序环流模型,分析零序环流产生机理和影响因素,通过检测零序环流状态,实时选择虚拟大矢量或实际大矢量合成方法来抑制零序环流,并提出区分奇偶扇区的矢量分配方法快速选择合成矢量。实验结果验证了新型VLMZVM策略能在电流突变、参数不一致、全功率因数范围都具有很好的环流抑制效果。 展开更多
关键词 逆变器 分布式发电 功率因数 虚拟矢量 环流抑制 调制策略
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