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Impedance Modeling and Stability Analysis of a Three-phase Three-level NPC Inverter Connected to the Grid

CSEE Journal of Power and Energy Systems 2020年第2期6卷 270-278页

作者： Bo Zhang Xiong Du Jingbo Zhao Jiapei Zhou Xiaoming Zou State Key Laboratory of Power transmission Equipment&System Security and New technology(Chongqing University) Shapingba DistrictChongqing 400044China Power System technology Center Electric Power Research Institute of State GridJiangsu Electric Power Co.Ltd.Jiangsu 320115China hvdc Simulation Center Department of HVDC technologyGlobal Energy Interconnection Research InstituteBeijing 102209China

The interaction between grid-connected inverters and the grid may cause stability issues,and compromise the reliable operation of the inverters.This study investigates the stability of a three-level neutral point clamped(NPC)inverter connected to the grid using impedance-based methods.Because the impedance model of a three-phase three-level NPC inverter has not yet been reported,this study fills the literature gap by analyzing the influence of three-level DC-side neutral point control on the impedance characteristics.By fully considering the DC bus dynamics and DC voltage control loop,and the current loop and phase-locked loop(PLL),the admittance model of a three-phase three-level NPC inverter is established and verified by simulation.Additionally,in the stability analysis of a threelevel NPC inverter grid-connected system,the frequency coupling introduced by the PLL and DC bus dynamics is included with the help of an established admittance model.The stability of the grid-connected system under different grid short circuit ratios(SCR)and operating power levels is analyzed according to the Nyquist stability criterion.The experimental results revealed that the established impedance model of the three-phase three-level NPC inverter can properly represent the stability of this system.

关键词： Grid-connected inverter neutral point control stability three-level

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Defects and failure types of solid insulation in gas‐insulated switchgear:In situ study and case analysis

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High Voltage 2022年第1期7卷 158-164页

作者： Yunqi Xing Zhiwen Wang Lin Liu Yuan Xu Yang Yang Shan Liu Fusheng Zhou Shun He Chuanyang Li State Key Laboratory of Reliability and Intelligence of Electrical Equipment Hebei University of TechnologyTianjinChina Key Laboratory of Electromagnetic Field and Electrical Apparatus Reliability of Hebei Province Hebei University of TechnologyTianjinChina School of Electric Power South China University of TechnologyGuangzhouChina High Voltage Institute China Electric Power Research InstituteBeijingChina Simpson Querrey Institute Northwestern UniversityEvanstonIllinoisUSA HVDC Transmission Technology Department Globe Energy Interconnection Research InstituteBeijingChina Electric Power Research Institute China Southern Power GridGuangzhouChina High Voltage Institute Yunnan Institute of Electrical ScienceYunnanChina Institute of Material Science University of ConnecticutStorrsConnecticutUSA

The gas‐insulated switchgear(GIS)has been widely used in modern ultra‐high voltage systems.However,once it fails,its fully enclosed feature brings challenges in its diagnosis and maintenance.As the failure rate of GIS due to insulator failure has been increasing in recent years,it is necessary and important to understand the commonly existing defects presented in the insulator.First,the manufacturing process of GIS insulators is intro-duced here.The defect types commonly existing in the insulator are categorised.The failure of GIS due to insulator defects that occurred in recent years are reviewed and discussed.The content in this study is useful for engineers and scientists to study on the GIS solid insulation defects and their failure mechanisms.

关键词： (GIS) insulation solid

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Research on blade tip clearance cavitation and turbulent kinetic energy characteristics of axial flow pump based on the partially-averaged Navier-Stokes model

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Journal of Hydrodynamics 2024年第1期36卷 184-201页

作者： Xiao-qi Jia Shuai-kang Zhang Zu-chao Zhu Key Laboratory of Fluid transmission technology of Zhejiang Province Zhejiang Sci-Tech UniversityHangzhou310018China

To reveal the cavitation forms of tip leakage vortex(TLV)of the axial flow pump and the flow mechanism of the flow field,this research adopts the partially-averaged Navier-Stokes(PANS)model to simulate the cavitation values of an axial flow pump,followed by experimental validation.The experimental result shows that compared with the shear stress transport(SST)k-ωmodel,the PANS model significantly reduces the eddy viscosity of the flow field to make the vortex structure clearer and allow the turbulence scale to be more robustly analyzed.The cavitation area within the axial flow pump mainly comprises of TLV cavitation,clearance cavitation and tip leakage flows combined effect of triangular cloud cavitation formed.The formation and development of cavitation are accompanied by the formation and evolution of vortex,and variations in vortex structure also generate and promote the development of cavitation.In addition,an in-depth analysis of the relationship between the turbulent kinetic energy(TKE)transport equation and cavitation patterns was also conducted,finding that the regions with relatively high TKE are mainly distributed around gas/liquid boundaries with serious cavitation and evident gas-liquid change.This phenomenon is mainly attributed to the combined effect of the pressure action term,stress diffusion term and TKE production term.

关键词： Cavitation axial flow pump tip leakage vortex(TLV) partially-averaged Navier-Stokes(PANS)model turbulent kinetic energy(TKE)

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Slip in Couette flow with pressure gradient:Theoretical and experimental investigation of hydrodynamic characteristics considering slip effect

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Journal of Hydrodynamics 2020年第1期32卷 107-115页

作者： Xin Zhao Chao Wei Shi-hua Yuan Science and technology on Vehicle transmission Laborator Bejing Institute of TechnologyBeijing 10081China

A new slip velocity model based on molecular potential theory and macro-force analysis,which is applied in Couette flow with pressure gradient,is built up.The model is validated by later being introduced in hydrodynamic system to predict film distribution,which shows a good agreement with experimental data obtained from multi-beam intensity-based tests with Fe and Cu ball materials under accurate controlled temperature,load and different wall velocities.Results show that the slip length for Fe case is ignorable so it seems like no slip,but for Cu case,the slip length is large to make 20%discrepancy with no slip simulation and also behaves shear-dependently.Moreover,during the experimental cases when both Fe and Cu ball velocities rise from-133 mm/s to 1330 mm/s,the slip velocity changes its direction with entrainment velocity and thus contributes to first enhance and then diminish the hydrodynamic film,but due to slip length on Cu case varying largely than that on Fe case,the film from Cu case and from Fe case has a clear cross-point between uh=80 mm/s and uh=220 m m/s(ub is the ball speed).The results above support strongly that Cu surface will lead to stronger slip than Fe case because of its smaller solid-liquid interaction,and obviously slip will influence hydrodynamic characteristics prominently.

关键词： Slip Couette flow with pressure gradient hydrodynamic characteristic

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Grinding Characteristics of MoS_(2)-Coated Brazed CBN Grinding Wheels in Dry Grinding of Titanium Alloy

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Chinese Journal of Mechanical Engineering 2023年第4期36卷 43-55页

作者： Junshuai Zhao Biao Zhao Wenfeng Ding Bangfu Wu Ming Han Jiuhua Xu Guoliang Liu National Key Laboratory of Science and technology on Helicopter transmission Nanjing University of Aeronautics and AstronauticsNanjing 210016China AECC Zhongchuan transmission Machinery Co. LtdChangsha 410200China

As an important green manufacturing process,dry grinding has problems such as high grinding temperature and insufficient cooling capacity.Aiming at the problems of sticking and burns in dry grinding of titanium alloys,grinding performance evaluation of molybdenum disulfide(MoS_(2))solid lubricant coated brazed cubic boron carbide(CBN)grinding wheel(MoS_(2)-coated CBN wheel)in dry grinding titanium alloys was carried out.The lubrication mechanism of MoS_(2)in the grinding process is analyzed,and the MoS_(2)-coated CBN wheel is prepared.The results show that the MoS_(2)solid lubricant can form a lubricating film on the ground surface and reduce the friction coefficient and grinding force.Within the experimental parameters,normal grinding force decreased by 42.5%,and tangential grinding force decreased by 28.1%.MoS_(2)lubricant can effectively improve the heat dissipation effect of titanium alloy grinding arc area.Compared with common CBN grinding wheel,MoS_(2)-coated CBN wheel has lower grinding temperature.When the grinding depth reaches 20μm,the grinding temperature decreased by 30.5%.The wear of CBN grains of grinding wheel were analyzed by mathematical statistical method.MoS_(2)lubricating coating can essentially decrease the wear of grains,reduce the adhesion of titanium alloy chip,prolong the service life of grinding wheel,and help to enhance the surface quality of workpiece.This research provides high-quality and efficient technical support for titanium alloy grinding.

关键词： Titanium alloy Dry grinding MoS_(2)-coated CBN wheel Grinding wheel wear

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Numerical study of gas-solid two-phase flow and erosion in a cavity with a slope

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Particuology 2022年第3期20卷 25-35页

作者： Zhe Lin Xiwang Sun Yi Li Zuchao Zhu Key Laboratory of Fluid transmission technology of Zhejiang Province Zhejiang Sci-Tech UniversityHangzhou 310018China National Provincial Joint Engineering Laboratory for Fluid transmission System technology Zhejiang Sci-Tech UniversityHangzhou 310018China

Gate valve is mainly used to turn on or turn off the pipeline in pneumatic conveying.When the gate valve is fully open,the particles are easy to collide with the cavity rear wall and enter into the cavity,resulting in particles’accumulation in the cavity.The particles in cavity will accumulate between the cavity bottom and the flashboard bottom wall and prevent the gate from turning off normally.Meanwhile,the particles’collision with cavity rear wall will cause serious erosion.Both the particles’accumulation and erosion will cause the poor sealing of the gate valve,further resulting in the leakage of the pipeline system.To reduce the particles’accumulation in cavity and erosion on cavity when the gate valve is fully open,we simplify the gate valve into a cavity structure and study it.We find that adding a slope upstream the cavity can effectively reduce the particles’accumulation in the cavity and the erosion on the cavity rear wall.In this work,Eulerian-Lagrangian method in commercial code(FLUENT)was used to study the gas-solid two-phase flow and erosion characteristics of a cavity with a slope.The particle distribution shows that the particles with Stokes number St=1.3 and St=13 cannot enter the cavity due to the slope,but the particles with St=0.13 enter the cavity following the gas.For St=13,the particles collide with the wall many times in the ideal cavity.Erosion results show that the slope can transfer the erosion on cavity rear wall to the slope and reduce the maximum erosion rate of the wall near the cavity to some degrees.

关键词： Cavity with a slope Gas-solid flow Solid particle erosion Stokes number

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Fast electrothermal coupling calculation method for supporting digital twin construction of electrical equipment

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High Voltage 2023年第2期8卷 390-400页

作者： Xiaosong Zhu Youyuan Wang Ruixiao Meng Shi Long Shaowen Wu State Key Laboratory of Power transmission Equipment and System Security and New technology(Chongqing University) ChongqingChina

The failure of electrical equipment directly or indirectly caused by overheating has become one of the main reasons for equipment accidents.The real-time condition monitoring method of electrical equipment based on digital twin(DT)has received extensive attention and is considered as a technology with great engineering values and excellent application prospects.However,the current calculation of DT mostly relies on the traditional finite element method(CFEM).This method becomes less computationally efficient as the size of the DT increases,especially for electrical equipment with high complexity.It is difficult to meet the requirements real-time calculation in DT.Therefore,starting from the algorithm optimization and parallel architecture,based on the weighted residual method and stabilised conforming nodal integration,a novel discrete method of electrothermal coupling equation is proposed and the data storage structure of the algorithm from the bottom layer is redesigned,and the corresponding GPU and multi-core CPU parallel framework are proposed.Finally,taking the high voltage bushing as an example,the correctness of the method in this paper is verified by the CFEM code and commercial software ABAQUS.Under the same grid and accuracy requirement,the calculation time is shortened by at least five times than ABAQUS.And the method is easy to extend to other types of multi-physics calculations.

关键词： electrical coupling method

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Determination of Slip Length in Couette Flow Based on an Analytical Simulation Incorporating Surface Interaction

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Chinese Physics Letters 2017年第3期34卷 77-81页

作者：赵欣魏超苑士华 Science and technology on Vehicle transmission Laboratory Beijing Institute of TechnologyBeijing 100081

An analytical simulation based on a new model incorporating surface interaction is conducted to study the slip phenomenon in the Couette flow at different scales. The velocity profile is calculated by taking account of the micro-force between molecules and macro-force from the viscous shearing effect, as they contribute to the achieve- ment of the slip length. The calculated results are compared with those obtained from the molecular dynamics simulation, showing an excellent agreement. Further, the effect of the shear rate on the slip is investigated. The results can well predict the fluid flow behaviors on a solid substrate, but has to be proved by experiment.

关键词： MD Determination of Slip Length in Couette Flow Based on an Analytical Simulation Incorporating Surface Interaction

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Design of hydraulic shift mechanism for AMT vehicles based on the collaborative optimization method

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Journal of Beijing Institute of technology 2016年第1期25卷 35-41页

作者：苗成生刘海鸥陈慧岩胡宇辉 Science and technology on Vehicle transmission Laboratory Beijing Institute of Technology

Based on multidisciplinary design optimization（MDO）,a new design method is put forward for hydraulic shift mechanism of heavy-duty vehicle automated manual transmission（AMT）.Taking a shift cylinder for example,the collaborative optimization（CO）method for the design problem of a cylinder is devided into one system level design optimization problem and three subsystem level design optimization problems.The system level is an economic model and the subsystem level is mechanics,kinetics,and a reliability model.Application of the multidisciplinary design optimization software iSIGHT modeling and solving,optimal solution of the shifting cylinder CO model is obtained.According to the optimal solution,oil cylinders are machined out and installed on the gearbox of an AMT system for the bench cycle shift test.The results show that the output force and action speed of the optimized mechanism can meet requirements very well.In addition,the optimized mechanism has a better performance compared to the structure of the traditional design method,which indicates that the CO method can optimize the design of hydraulic transmission.

关键词： hydraulic shifting mechanism collaborative optimization automated manual transmission

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Effect of End Shape on Flow and Heat Transfer Characteristics of Two Parallel Plates

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Journal of Thermal Science 2024年第3期33卷 815-832页

作者： ZHANG Guang HONG Tianxiao WANG Dongrui XIN Jialin TAO Junyu LIN Zhe Key Laboratory of Fluid transmission technology of Zhejiang Province Zhejiang Sci-Tech UniversityHangzhou310018China

Flow around a pair of flat plates is a basic hydrodynamics problem.In this paper,the flow and heat transfer characteristics of two parallel plates with different edge shapes are numerically calculated.Under different inclined angles,the influence of chamfered and rounded structures with different sizes at the end-edge on unsteady flow and heat transfer characteristics of two parallel plates are analyzed.It is found that the instability and unsteadiness of flow decrease with the increase of end-edge size,and the non-uniformity of wake velocity of both rounded and chamfered plates decreases gradually.The non-uniformity of wake temperature increases firstly and then decreases at a small inclined angle,and the amplitude becomes the largest when S_(rou)(S_(cha))=3,while it basically keeps monotonically increasing at a large inclined angle.Moreover,the global heat transfer performance of the flat plate is obviously affected by the end-edge modification,especially the chamfered structure.With the increase of chamfered size,the global Nusselt number basically shows the decreasing trend.This study provides a theoretical basis for the application of plate-shape structure in engineering fields.

关键词： two parallel plates end shape flow characteristic heat transfer numerical simulation

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