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Impedance Analysis of Grid Forming Control Based Modular Multilevel Converters

Journal of Modern Power Systems and Clean Energy 2023年第3期11卷 967-979页

作者： Rongcai Pan Guangfu Tang Shan Liu Zhiyuan He China Electric Power Research Institute Beijing 100192China State Grid Smart Grid Research Institute Beijing 102209China

Grid-forming control(GFC)is promising for power electronics based power systems with high renewable energy penetration.Naturally,the impedance modeling for GFC is necessary and has gained significant attention recently.However,most of the impedance analyses for GFC are based on a twolevel converter(TLC)rather than a modular multilevel converter(MMC).MMC differs from TLC with respect to its dominant multi-frequency response.It is necessary to analyze the impedance of GFC-based MMC owing to its superiority in highvoltage direct current(HVDC)transmission to interlink two weak AC systems with high renewable energy penetration.As the main contribution,this paper presents the AC-and DC-side impedance analyses for the GFC-based MMC with both power and DC voltage control using the harmonic transfer function(HTF),and compares the impedances of GFC-based MMC and TLC.It is inferred that although the impedance is mainly influenced within 200 Hz,the instability still could occur owing to negative resistance triggered by relatively larger parameters.The difference in AC-side impedance with power and DC voltage control is not apparent with proper parameters,while the DC-side impedance differs significantly.The generalized Nyquist criterion is necessary for AC-side stability owing to the relatively large coupling terms under GFC.Moreover,the coupling between AC-and DC-side impedances is noneligible,especially considering the DC-side resonance around the system resonant peak.The effects of parameters,system strength,and virtual impedance on the impedance shaping are analyzed and verified through simulations.

关键词： Sequence impedance modular multilevel converter(MMC) grid-forming control(GFC) harmonic transfer function generalized Nyquist criterion

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Impedance Analysis Considering Unstable Subsystem Poles for MMC-HVDC-based Wind Farm Integration System

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CSEE Journal of Power and Energy Systems 2022年第2期8卷 634-639页

作者： Ke Ji Hui Pang Shan Liu Guangfu Tang China Electric Power Research Institute Beijing100192China Global Energy Interconnection Research Institute Beijing 102211China

Employing the AC/DC impedance analysis method,extensive research has been conducted on issues pertaining to harmonic resonance observed in wind farm-connected MMCHVDC systems over the past 5 years.In general,this method divides the studied system into two subsystems at AC and DC sections.Subsequently,the impedance produced by these subsystems can be used to determine the system stability by implementing Nyquist criterion or generalized Nyquist stability criterion.However,the existing impedance analysis methods usually assume the subsystems to be stable and disregard certain special cases with potentially unstable subsystems,where the unstable poles of these subsystems must be evaluated before applying Nyquist criterion.In view of this consideration,a simplified method for identifying unstable subsystem poles is presented in this paper.Hence,the shortcoming of existing impedance analyses is rectified by considering the unstable subsystem poles.The proposed method and the stability analyses are validated by the electromagnetic transient simulation performed in PSCAD/EMTDC.

关键词： AC/DC side impedance method harmonic resonance MMC-HVDC small-signal stability wind farm

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Reprogramming of hormone-mediated antiviral responses in plants by viruses:A molecular tug of war on the salicylic acid-mediated immunity

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Molecular Plant 2023年第10期16卷 1493-1495页

作者： Faisal Islam Shan Liu Huan Chen Jian Chen International Genome Center Jiangsu UniversityZhenjiang 212013China Joint Center for Single Cell Biology School of Agriculture and BiologyShanghai Jiao Tong University800 Dongchuan RoadShanghai 200240China

Plants are consistently exposed to pathogens throughout theirlife cycle and have developed sophisticated and effective regulatory mechanisms to protect themselves against infections.Viruses,as obligate pathogens,can trigger numerous pathological changes and cause systemic damages that impact all aspects of plant life through encoded viral proteins,conceptuallyconsidered as"effectors."

关键词： programming cycle immunity

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An assessment of the subduction rate in the CMIP6 historical experiment

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Acta Oceanologica Sinica 2023年第1期42卷 44-60页

作者： Shan Liu Xueyi Jing Xingrong Chen Huijun Wang National Marine Environmental Forecasting Center Ministry of Natural ResourcesBeijing100081China National Supercomputing Center in Wuxi Wuxi214315China Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters Nanjing University of Information Science&TechnologyNanjing210044China Nansen-Zhu International Research Center Institute of Atmospheric PhysicsChinese Academy of SciencesBeijing100029China

Subduction process is a dynamical bridge for the exchanges of heat between the atmosphere and subsurface ocean water,which is regarded as a central proxy for the ocean climate studies.Given its key indicator in climate signals,it is of importance to examine the ability of a model to simulate the global subduction rate before investigating the climate dynamics.In this paper,we evaluated the ability of 21 climate models from Coupled Model Intercomparison Project Phase 6(CMIP6)in simulating the subduction rate.In general,the simulation ability of the models to the subduction climatology is better than that to the long-term variation trend.Based on the comprehensive analysis of climatology distribution and long-term trend of the subduction rate,GISS-E2-1-G performs better in reproducing the subduction rate climatology and IPSL-CM6A-LR can simulate positive long-term trend for both the global mean subduction rate and the lateral induction term in the Antarctic Circumpolar Current(ACC)region.However,it is still challenging to capture both the distribution characteristics of the subduction climatology and the long-term temporal trend for the 21 CMIP6 models.In addition,the model results demonstrate that,the ACC area is the major region contributing to the long-term trend of the global mean subduction rate.The analysis in this paper indicates that the poor simulation ability of reproducing the long-term trend of global mean subduction rate might be attributed to the ocean dynamics,for example,the zonal velocity at the bottom mixed layer and zonal gradient of mixed layer depth.

关键词： subduction rate CMIP6 climatology long-term trend

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Stability Comparison Between Grid-forming and Grid-following Based Wind Farms Integrated MMC-HVDC

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Journal of Modern Power Systems and Clean Energy 2023年第4期11卷 1341-1355页

作者： Rongcai Pan Dong liu Shan Liu Jie Yang Longze Kou Guangfu Tang China Electric Power Research Institute Beijing 100192Chinaand he is also with the State Key Laboratory of Advanced Power Transmission Technology and Beijing Key Laboratory of DC Grid Technology&SimulationBeijing 102209China State Key Laboratory of Advanced Power Transmission Technology and Beijing Key Laboratory of DC Grid Technology&Simulation Beijing 102209China

Grid-forming(GFM)control based high-voltage DC(HVDC)systems and renewable energy sources(RESs)provide support for enhancing the stability of power systems.However,the interaction and coordination of frequency support between the GFM-based modular multilevel converter based HVDC(MMC-HVDC)and grid-following(GFL)based RESs or GFM-based RESs have not been fully investigated,which are examined in this study.First,the detailed AC-and DC-side impedances of GFM-based MMC-HVDC are analyzed.The impedance characteristics of GFL-and GFM-based wind turbines are next analyzed.Then,the influences of GFL-and GFM-based wind farms(WFs)on the DC-and AC-side stabilities of WF-integrated MMC-HVDC systems are compared and evaluated.The results show that the GFM-based wind turbine performs better than the GFL-based wind turbine.Accordingly,to support a receiving-end AC system,the corresponding frequency supporting strategies are proposed based on the GFM control for WF-integrated MMC-HVDC systems.The GFM-based WF outperforms the GFL-based WF in terms of stability and response time.Simulations in PSCAD/EMTDC demonstrate the DC-and AC-side stability issues and seamless grid support from the RESs,i.e.,WFs,to the receiving-end AC system.

关键词： Renewable energy source(RES) modular multilevel converter(MMC) wind farm grid-forming(GFM) highvoltage direct current

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Multiobjective economic model predictive control using utopia-tracking for the wet flue gas desulphurization system

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Chinese Journal of Chemical Engineering 2023年第2期54卷 343-352页

作者： Shan Liu Wenqi Zhong Xi Chen Li Sun Lukuan Yang Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education School of Energy and EnvironmentSoutheast UniversityNanjing 210096China

Efficient control of the desulphurization system is challenging in maximizing the economic objective while reducing the SO_(2) emission concentration. The conventional optimization method is generally based on a hierarchical structure in which the upper optimization layer calculates the steady-state results and the lower control layer is responsible to drive the process to the target point. However, the conventional hierarchical structure does not take the economic performance of the dynamic tracking process into account. To this end, multi-objective economic model predictive control(MOEMPC) is introduced in this paper, which unifies the optimization and control layers in a single stage. The objective functions are formulated in terms of a dynamic horizon and to balance the stability and economic performance. In the MOEMPC scheme, economic performance and SO_(2) emission performance are guaranteed by tracking a set of utopia points during dynamic transitions. The terminal penalty function and stabilizing constraint conditions are designed to ensure the stability of the system. Finally, an optimized control method for the stable operation of the complex desulfurization system has been established. Simulation results demonstrate that MOEMPC is superior over another control strategy in terms of economic performance and emission reduction, especially when the desulphurization system suffers from frequent flue gas disturbances.

关键词： Desulphurization system Economics Economic model predictive control Flue gas Optimization Utopia point

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Uncertainty and disturbance estimator-based model predictive control for wet flue gas desulphurization system

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Chinese Journal of Chemical Engineering 2024年第3期67卷 182-194页

作者： Shan Liu Wenqi Zhong Li Sun Xi Chen Rafal Madonski School of Energy and Environment Key Laboratory of Energy Thermal Conversion and Control of Ministry of EducationSoutheast UniversityNanjing 210096China Faculty of Automatic Control Electronics and Computer ScienceSilesian University of TechnologyGliwise 44-100Poland

Wet flue gas desulphurization technology is widely used in the industrial process for its capability of efficient pollution removal.The desulphurization control system,however,is subjected to complex reaction mechanisms and severe disturbances,which make for it difficult to achieve certain practically relevant control goals including emission and economic performances as well as system robustness.To address these challenges,a new robust control scheme based on uncertainty and disturbance estimator(UDE)and model predictive control(MPC)is proposed in this paper.The UDE is used to estimate and dynamically compensate acting disturbances,whereas MPC is deployed for optimal feedback regulation of the resultant dynamics.By viewing the system nonlinearities and unknown dynamics as disturbances,the proposed control framework allows to locally treat the considered nonlinear plant as a linear one.The obtained simulation results confirm that the utilization of UDE makes the tracking error negligibly small,even in the presence of unmodeled dynamics.In the conducted comparison study,the introduced control scheme outperforms both the standard MPC and PID(proportional-integral-derivative)control strategies in terms of transient performance and robustness.Furthermore,the results reveal that a lowpass-filter time constant has a significant effect on the robustness and the convergence range of the tracking error.

关键词： Desulphurization system Disturbance rejection Model predictive control Uncertainty and disturbance estimator Nonlinear system

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In vitro investigation of HBV clinical isolates from Chinese patients reveals that genotype C isolates possess higher infectivity than genotype B isolates

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Virologica Sinica 2022年第3期37卷 398-407页

作者： Tingting liu Anlei liu Yong liu shan Cen Quan Zhang Department of Transfusion Medicine Nanjing Drum Tower HospitalThe Affiliated Hospital of Nanjing University Medical SchoolNanjing210008China Department of Emergency Medicine Peking Union Medical College HospitalChinese Academy of Medical ScienceBeijing100730China Department of Laboratory Medicine Nanjing Drum Tower Hospital and Jiangsu Key Laboratory for Molecular MedicineThe Affiliated Hospital of Nanjing University Medical SchoolNanjing210008China Institute of Medicinal Biotechnology Chinese Academy of Medical ScienceBeijing100050China Department of Infectious Diseases Nanjing Drum Tower HospitalThe Affiliated Hospital of Nanjing University Medical SchoolNanjing210008China

Hepatitis B virus(HBV)genotype B and C are two major genotypes that are prevalent in Asia and differ in natural history and disease progression.The impact of HBV genotypes on viral replication and protein expression has been explored by the transfection of hepatoma cells with replication-competent HBV DNA,which mimics the later stages of the viral life cycle.However,the influence of HBV genotypes on the early events of viral infection remains undetermined,mainly due to the difficulties in obtaining sufficient infectious viral particles for infection assays.Here,we report that a high-titer HBV inoculum can be generated from the transient transfection-based cell model after optimizing transfection conditions and modifying the HBV-expressing construct.By performing in vitro infection assays using transiently transfected derived viruses,we found that clinical genotype C isolates possessed higher infectivity than genotype B isolates.Moreover,we identified a naturally occurring mutation sL21S in small hepatitis B surface protein,which markedly decreased the infectivity of HBV genotype C isolates,but not that of genotype B isolates.In summary,using infectious viral particles provided by the optimized transient transfection-based cell model,we have been able to investigate a wide range of HBV variants on viral infectivity,which may contribute to our understanding of the reasons for different clinical outcomes in HBV infections and the development of therapeutic drugs targeting the early stages of HBV life cycle.

关键词： Hepatitis B virus(HBV) Genotype B Genotype C Clinical isolates Infectivity sL21S

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Analysis of Operational Characteristics and Equivalent Test Method for IGBTs in MMC

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CSEE Journal of Power and Energy Systems 2023年第4期9卷 1567-1576页

作者： Yixuan Yang Guangfu Tang Shan Liu Gaoyong Wang Zhiyuan He State Key Laboratory of Aiternate Electrical Power System with Renewable Energy Sources North China Electric Power UniversityBeijing 102206China State Grid Smart Grid Research Institute Co. Ltd.Beijing 102209China.

A design methodology and a feasible equivalent circuit are proposed to test the reliability of insulated gate bipolar transistors(IGBT)in actual modular multilevel converter(MMC)conditions,which is impossible for existing IGBT test platforms due to unexplicit equivalent indexes and low reliability of test platforms.Characteristics of IGBT devices are extracted during MMC operation,and turn-off transient and effective current are highlighted as key indexes for the equivalent test.A feasible equivalent timing diagram and a corresponding test circuit are proposed,as well as the circuit's operation concept.The proposed equivalent test method is verified by a back-to-back experiment with twenty-four submodules,and results indicate the proposed method has good equivalence.Between the proposed circuit waveform and the back-to-back experiment waveform,all indexes have errors of less than 5.9%.Furthermore,the proposed circuit components have losses less than 0.7 times those of the device under test,making them reliable and suitable for long-term operation tests for IGBT devices in MMC.Index Terms-Equivalent test,IGBT,MMC,reliability.

关键词： Equivalent test IGBT MMC reliability

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Iterative Learning Control for Flexible Manipulator Using Fourier Basis Function

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International Journal of Automation and computing 2015年第6期12卷 639-647页

作者： Li Zhang Shan Liu College of Control Science and Engineering Zhejiang University

Perfect tracking of the tip position of a flexible-link manipulator(FLM) is unable to be achieved by causal control because it is a typical non-minimum phase system. Combined with non-causal stable inversion, an adaptive iterative learning control scheme based on Fourier basis function is presented for the tip trajectory tracking of FLM performing repetitive tasks. In this method,an iterative identification algorithm is used to construct the Fourier basis function space model of the manipulator, and a pseudoinverse type iterative learning law is designed to approximate the stable inversion of the non-minimum phase system, which guarantees the convergence and robustness of the control system. Simulation results show the performance and effectiveness of the proposed scheme.

关键词： Flexible-link manipulator(FLM) non-minimum phase s

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