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Intersystem crossing and exciton–defect coupling of spin defects in hexagonal boron nitride

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npj Computational Materials 2021年第1期7卷 537-544页

作者： Tyler JSmart kejun li Junqing Xu Yuan Ping Department of Physics University of CaliforniaSanta CruzCAUSA Lawrence livermore National Laboratory LivermoreCAUSA Department of Chemistry and Biochemistry University of CaliforniaSanta CruzCAUSA

Despite the recognition of two-dimensional(2D)systems as emerging and scalable host materials of single-photon emitters or spin qubits,the uncontrolled,and undetermined chemical nature of these quantum defects has been a roadblock to further *** the design of extrinsic defects can circumvent these persistent issues and provide an ultimate ***,we established a complete theoretical framework to accurately and systematically design quantum defects in wide-bandgap 2D *** this approach,essential static and dynamical properties are equally considered for spin qubit *** particular,many-body interactions such as defect–exciton couplings are vital for describing excited state properties of defects in ultrathin 2D ***,nonradiative processes such as phonon-assisted decay and intersystem crossing rates require careful evaluation,which competes together with radiative *** a thorough screening of defects based on firstprinciples calculations,we identify promising single-photon emitters such as SiVV and spin qubits such as TiVV and MoVV in hexagonal boron *** work provided a complete first-principles theoretical framework for defect design in 2D materials.

关键词： defect hexagonal boron

A fast and high-accurate commutation failure identification method for LCC-HVDC system

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High Voltage 2024年第3期9卷 721-732页

作者： Jing Feng Zhijie liu kejun li Bingkun li Jiachen li liangzi li School of Electrical Engineering Shandong UniversityJinanShandongChina

Commutation failure(CF)is one of the most common issues in line-commuted converter-based high voltage direct current systems(LCC-HVDC),leading to critical power system security and stability *** and rapid identification of CF is crucial to prevent subsequent CF in HVDC ***,the existing CF identi-fication methods are lack of the required accuracy and *** relationship between bridge arm current,commutation voltage,and trigger pulse based on the commutation progress mechanism after the AC fault is analysed in this paper.A novel CF identification method is presented,which utilises the CF identification factor,enabling fast and high-accurate identification without relying on the value of the extinction *** pro-posed method offers a simpler and more efficient implementation in engineering ***,the effectiveness of the proposed method is verified in both the standard In-ternational Council on Large Electric systems HVDC model and the Hardware in Loop test using practical project *** results demonstrate that the proposed method can accurately and fast identify CF.

关键词： system method LCC

Latitude migration of solar activity at high latitudes

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Chinese Science Bulletin 2008年第1期53卷 8-11页

作者： GAO PengXin li kejun li QiXiu National Astronomical Observatories Yunnan Observatory Chinese Academy of Sciences Kunming 650011 China University of Graduate Chinese Academy of Sciences Beijing 100864 China

Utilized here is the Carte Synoptique solar filament archive, namely the catalogue of solar filaments from March 1919 to December 1989, corresponding to solar rotation numbers 876 to 1823 to study latitudinal migration of solar activity at high latitudes. Except the well-known poleward migration of solar activity from middle latitudes to the poles, an equatorward migration is found from the solar poles toward middle latitudes (about 40°) within a normal cycle, which is neglected before, and the time in-terval for the former migration (4.4 years) is about 2.2 years shorter than that for the latter (6.6 years), indicating that the change from one migration to the other takes place around the maximum time of a normal cycle. In the future, a dynamo model should represent the migration from the poles toward middle latitudes of the Sun, besides the migration in "butterfly diagrams" and the "rush to the poles". The traditional extended activity cycle is actually a part of the period of the successive migration from the poles toward the solar equator.

关键词：太阳活性太阳周期纬度偏移地球

Identification Method for Single-line-to-ground Faults with line Break Based on Phasor Measurement in Distribution Networks

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Journal of Modern Power Systems and Clean Energy 2023年第3期11卷 907-916页

作者： Yadong liu Zichang li Yingjie Yan Guanghui He Jian Fang kejun li Xiuchen Jiang Institute of Intelligent Power Transmission and Distribution.Shanghai Jiao Tong University Shanghai 201100China Electric Power Test Institute of Guangzhou Power Supply Bureau Co. Ltd.Guangzhou 510420China IEEE

The single-line-to-ground faults with line breaks(SLGFs-LBs)occur more and more frequently in distribution networks and can cause major safety *** is difficult to distinguish the single-line-to-ground faults(SLGFs)in resonant grounding systems and ungrounding systems due to the same electrical characteristics on the source side and uncertain operation conditions of distribution *** paper proposes a method for distinguishing SLGFs-LBs and ***,the source-side and load-side voltage characteristics of SLGFs and SLGFs-LBs are analyzed,and the phase difference between the voltages of the fault phase and non-fault phase on the load side is selected as the identification *** measurement units(PMUs)are selected as measuring ***,the effects of operation conditions and external devices in distribution networks on the proposed method are discussed,and the phase errors caused by them are calculated to correct the identification ***,the field testing and simulation experiments are conducted to verify the effectiveness and robustness of the proposed method.

关键词： Distribution network phase measurement unit single-line-to-ground fault(SLGF) identification method influencing factor

Predictive Current Control for Voltage Source Inverters Considering Dead-Time Effect

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CES Transactions on Electrical Machines and Systems 2020年第1期4卷 35-42页

作者： Yu li Zhenbin Zhang kejun li Pinjia Zhang Feng Gao School of Electrical Engineering Shandong UniversityJinanChina Shandong University China Department of Electrical Engineering Tsinghua University as an Associate ProfessorChina

This paper proposes a new concept of synthesized voltage vector to address dead-time effect issue for Finite Control Set Model Predictive Control(FCS-MPC)*** a voltage source inverter(VSI),dead-time is inevitably inserted between the turn off and turn on instants of power devices to avoid short circuit *** influence of dead-time leads to output voltage vector error of three-phase ***,it will result in computing deviation in cost function,and will deteriorate the performance of the system if not properly dealt *** this paper,the problem is clearly analyzed,and the solution to this issue is proposed by introducing a synthesized voltage *** proposed solution is verified by Hardware-in-the-loop(HiL)test in real time,and results validate the effectiveness of the proposed solution.

关键词： Dead-time model predictive control voltage source inverter.

Situation Projection Based on Multi-time-scale Recursive Dynamic State Estimation

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Situation Projection Based on Multi-time-scale Recursive Dyn...

作者： liangzi li kejun li Kaiqi Sun Zhijie liu Wentao liu School of Electrical Engineering Shandong University

In order to solve the problem of lacking of situation awareness in smart distribution network,this paper proposed a real-time situation projection method for distribution network based on multi-time-scale dynamic state *** on hybrid measurement including micro PMU,a multi-time-scale recursive dynamic state estimation was realized through recursive transformation between state projection and pseudo measurement.A pseudo measurement Correction algorithm is implemented in the proposed state estimation loop to increase the estimation *** the historic states data calculated from the proposed state-measurement recursive dynamic state estimation,a novel real-time situation projection method is proposed in this *** the modelling of partitioned multivariate time series analysis,the proposed situation projection method is achieved by predicting the situation indexes for the distribution network operator in real *** validates the feasibility of the proposed method to improve the situation awareness level in the distribution network.

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机械系统开关类元件的混合键合图建模

中南大学学报（自然科学版） 2017年第3期48卷 658-665页

作者：胡均平李科军中南大学机电工程学院湖南长沙410083

针对键合图难以表达机械系统开关类元件的非线性动力学问题,以常见的干摩擦、间隙接触碰撞副和单向不可逆传动为研究对象,通过分析其作用机理,引入开关类量的混合键合图建模方法,运用功率结型结构(简称SPG)概念,提出一种新的开关类元件... 详细信息

针对键合图难以表达机械系统开关类元件的非线性动力学问题,以常见的干摩擦、间隙接触碰撞副和单向不可逆传动为研究对象,通过分析其作用机理,引入开关类量的混合键合图建模方法,运用功率结型结构(简称SPG)概念,提出一种新的开关类元件键合图建模方法和键合图模型。以包含干摩擦、间隙接触碰撞副和单向不可逆传动的机械系统为例,根据开关类元件的键合图模型,结合机械传动的工作原理,建立整个系统的键合图模型,提取其状态方程,并通过仿真计算予以验证。研究结果表明:该模型不仅可以统一表达开关类元件在系统不同工作模式下的动力学特性,而且其因果关系在系统处于任何运动状态时均保持不变;仿真结果验证了建模方法正确、可行。

关键词：机械系统开关类元件混合键合图功率结型结构因果关系

考虑打桩反弹的组合锤头冲击过程的动态特性分析

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中南大学学报（自然科学版） 2017年第2期48卷 348-354页

作者：胡均平李科军中南大学机电工程学院湖南长沙410083

针对打桩过程中桩体容易损坏的现象,提出一种在锤体内腔填充质量块的组合锤头打桩的新型锤击模型。运用键合图理论对锤击系统建模,为模拟打桩反弹时各质量块与垫层接触、分离的非线性特性,引入开关类量的键合图元件功率结型结构(SPJ),... 详细信息

针对打桩过程中桩体容易损坏的现象,提出一种在锤体内腔填充质量块的组合锤头打桩的新型锤击模型。运用键合图理论对锤击系统建模,为模拟打桩反弹时各质量块与垫层接触、分离的非线性特性,引入开关类量的键合图元件功率结型结构(SPJ),采用集中参数搭建锤击系统的键合图模型,据此建立可统一表达系统所有运动状态的数学模型。利用量纲一分析法推导锤击力的数值解,并基于Matlab软件仿真分析填充质量块和垫层参数对锤击力的影响。通过试验验证该模型的准确性。研究结果表明:采用组合锤头时,锤击力波形出现2个峰值,且峰值减小,这不仅可以保护桩体,而且可提高能量传递效率;各参数中,填充质量块和锤垫对锤击性能的影响最大,砧坐垫的影响次之,桩垫的影响最小。该模型可用于锤击系统的参数优化研究及动态特性分析。

关键词：组合锤头键合图反弹锤击力

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旋挖钻机回转制动能量回收系统设计与分析

中南大学学报（自然科学版） 2016年第10期47卷 3386-3393页

作者：胡均平李科军中南大学机电工程学院湖南长沙410083

为利用旋挖钻机在回转阶段的制动能量,提出一种基于二次调节技术和液压蓄能器的能量回收系统。通过分析上车回转的工况特点,运用功率键合图理论建立回转动能回收利用的数学模型。针对系统参数的不确定性及存在的外干扰,设计自适应模糊... 详细信息

为利用旋挖钻机在回转阶段的制动能量,提出一种基于二次调节技术和液压蓄能器的能量回收系统。通过分析上车回转的工况特点,运用功率键合图理论建立回转动能回收利用的数学模型。针对系统参数的不确定性及存在的外干扰,设计自适应模糊滑模控制器对回转速度进行跟踪控制,并利用李雅普诺夫函数证明控制系统的稳定性和收敛性。为对系统进行优化设计,仿真分析液压蓄能器容积、充气压力及回转制动时间这3个主要因素对系统工作性能的影响规律。研究结果表明:所提出的回转系统在制动时能有效地完成能量回收,其中,回转制动时间对系统工作压力和能量回收效率影响最大,而液压蓄能器容积和充气压力对能量回收效率影响较小,但对恒压网络压力波动影响较大。

关键词：旋挖钻机回转动能能量回收二次调节技术自适应模糊控制