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A Staged Strategy for MMC Offshore Converter Station Under Asymmetric AC Fault

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A Staged Strategy for MMC Offshore Converter Station Under A...

IEEE Conference on Energy Internet and Energy System Integration (EI2)

作者： Fangyuan Li Longze Kou Jiapei Zhou Jie Hao State Key Laboratory of Advanced Power Transmission Technology Beijing Key Laboratory of DC Grid Technology & Simulation State Grid Smart Grid Research Institute CO. LTD. Beijing China State Grid Shanxi Electric Power Company electric power Science Research Institute Shanxi China

At present, offshore wind power has become an important development direction for wind power generation. Offshore wind farms often use high-voltage direct current transmission technology with modular multi-level voltage source converters (MMC-HVDC) to transmit electricity to the grid. However, the fault response characteristics of offshore wind farms through the MMC-HVDC transmission system are different from those through AC transmission way. Therefore, it is significant that studying the fault ride through (FRT) technology of offshore wind farms through the MMC-HVDC grid connection system for practical engineering. An electromagnetic transient simulation model for an offshore wind farm composed of a direct drive permanent magnet synchronous generator (D-PMSG) connected to the grid is established through MMC-HVDC transmission technology. The mechanism and suppression strategy of overvoltage generation in the transmission network are provided during the fault clearance and recovery phase of the offshore wind farm HVDC transmission system under AC asymmetric faults. A two-stage improved control strategy for MMC-HVDC offshore converter station in response to asymmetric faults has been proposed, which is beneficial for the joint system to quickly recover from the post fault system voltage and suppress the overvoltage risk during the fault clearing phase. Finally, the proposed strategy is validated based on a domestic ± 500kV project in China, demonstrating its effectiveness.

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High-temperature tensile failure mechanism of RTM-made composite T-joints

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Defence technology 2025年

作者： Zhang, Yujin Obara, Evance Wang, Shuai Zhu, Longyu Li, Weidong Lin, Shiyun Han, Zhilin Luo, Chuyang Center for Civil Aviation Composites Donghua University Shanghai201620 China Composite Center AVIC Manufacturing Technology Institute National Key Laboratory of Advanced Composites Beijing101300 China School of Aeronautics Chongqing Jiaotong University Chongqing400074 China College of Physics Donghua University Shanghai201620 China

This paper focuses on the high-temperature tensile failure mechanism of RTM (resin transfer moulding)-made symmetric and asymmetric composite T-joints. The failure modes as well as the load-displacement curves of symmetric (three specimens) and asymmetric (three specimens) composite T-joints were determined by tensile tests at room and high temperatures. Progressive damage models (PDMs) of symmetric and asymmetric composite T-joints at room and high temperatures were established based on mixed criteria, and the result predicted from the aforementioned PDMs were compared with experimental data. The predicted initial and final failure loads and failure modes are in good agreement with the experimental results. The failure mechanisms of composite T-joints at different temperatures were investigated by scanning electron microscopy. The results reveal that while the failure mode of asymmetric T-joints at high temperatures resembles that at room temperature, there is a difference in the failure modes of symmetric T-joints. The ultimate failure load of symmetric and asymmetric T-joints at elevated temperatures increases and reduces by 18.4% and 4.97%, albeit with a more discrete distribution. This work is expected to provide us with more knowledge about the usability of composite T-joints in elevated temperature environments. © 2025 China Ordnance Society

关键词： Tensile testing

Overvoltage Suppression Strategy Based on Active Control of Current for Half-Wave Commutated Modular Multilevel Converters

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Overvoltage Suppression Strategy Based on Active Control of ...

IEEE International Conference on Power and Energy Systems (ICPES)

作者： Bao Liu Yunfei Xu Guoliang Zhao Nan Fu Chen Jia State Key Laboratory of Advanced Power Transmission Technology China Electric Power Research Institute Beijing China State Key Laboratory of Control and Simulation of Power System and Generation Equipment Tsinghua University Beijing China Electric Power Research Institute of State Grid Liaoning Electric Power Co. Ltd. Shenyang China

ISBN: (数字)9798350391329

ISBN: (纸本)9798350391336

Flexible low-frequency AC transmission technology combines the advantages of 50 Hz AC transmission and DC transmission, and has good application scenarios. High voltage and large capacity AC/AC converters are the core equipment of flexible low-frequency AC transmission systems. The proposal of half-wave commutated modular multilevel converters effectively reduces the number of components and improves system economy. In view of this, this paper proposes an overvoltage suppression strategy for active control of inductor current, which effectively reduces the overvoltage level during commutation. The article first introduces the sparse topology and mathematical model of the half-wave commutated modular multilevel converters. Secondly, the mechanism of overvoltage generation is analyzed. Then, overvoltage suppression strategies are proposed. Finally, a PSCAD simulation model is built to verify the effectiveness and feasibility of the proposed method through simulation.

关键词： Multilevel converters Reactive power Bridge circuits Valves Mathematical models Topology Safety Voltage control Inductors PSCAD

A Successive "Conversion-Deposition" Mechanism Achieved by Micro-Crystalline Cu2O Modified Current Collector for Composite Lithium Anode

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SSRN 2022年

作者： Cai, Yifei Qin, Bin Li, Chun Si, Xiaoqing Cao, Jian Zheng, Xiaohang Qiao, Liang Qi, Junlei State Key Laboratory of Advanced Welding and Joining Harbin Institute of Technology Harbin150001 China Key Laboratory of Materials Design and Quantum Simulation College of Science Changchun University Changchun130022 China

Lithium (Li) metal is a promising material for high-energy-density batteries, but it is still plagued by obvious capacity degradation and low average Coulombic efficiency resulting from dendrite Li propagation. One main reason is the electro-mechanic coupled failure of plated Li on the current collector, which contributes to non-dense Li deposition on the anode. Transition metal oxides (TMOs) with a conversion-type mechanism have been used directly as the anode materials for lithium ion batteries, which demonstrated better electro-mechanical stability than metal Li. Herein, a successive ''conversion-deposition'' mechanism is ingeniously developed to restrain the generation of dendritic Li. Specifically, a micro-crystalline Cu2O modified current collector was prepared, in which Li+ are sequentially inserted into Cu2O and deposited in the form of Li metal at successive low potential. A Li-Cu half-cell based on the hybrid mechanism sustains a high Coulombic efficiency of over 99.3% in up to 800 cycles. This work ingeniously inhibits the generation of dendrite Li by incorporating conversion-type materials with deposition-dissolution type metal Li, which contributes to a novel concept for the design of functional current collectors for composite Li anodes. © 2022, The Authors. All rights reserved.

关键词： Copper oxides

Research on simulation Modeling Method of New Distributing Network with Large Scale Distributed Energy Sources

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Research on Simulation Modeling Method of New Distributing N...

International Conference on Power System technology (POWERCON)

作者： Huaiguang Gu Longze Kou Lin Zhu Yuqin Gao Yang Gao Ping Xiong State Key Laboratory of Advanced Transmission Technology Beijing Key Laboratory of DC Power Grid Technology and Simulation State Grid Smart Grid Research Institute Co. LTD. Changping Beijing China State Grid Hubei Electric Power Research Institute Hongshan District Wuhan City Hubei Province China

In this paper, a distribution network model with distributed power supply is built. Firstly, the current situation of new energy power generation under the background of carbon neutralization is introduced in the overview. The models of fans, photovoltaic and hybrid energy storage are established respectively, and the corresponding control methods such as maximum power tracking, constant power control, bus voltage control and so on are described in detail. On this basis, the distribution network modeling of photovoltaic energy storage intermodal transportation is completed; Each simulation model is shown.

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Organic–Inorganic Hybrid Perovskite Scintillator for High-Resolution X-Ray Imaging

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SSRN 2023年

作者： Yan, Weipeng Duan, Baojun Zhu, Zijian Song, Yan Song, Guzhou Ma, Jiming Li, Binkang Liu, Yucheng State Key Laboratory of Intense Pulsed Radiation Simulation and Effect Northwest Institute of Nuclear Technology Xi’an710024 China Key Laboratory of Applied Surface and Colloid Chemistry National Ministry of Education Shaanxi Engineering Lab for Advanced Energy Technology School of Materials Science and Engineering Shaanxi Normal University Xi’an710119 China

Herein, Lithium-doped 2D (PEA)2PbBr4 ((PEA)2PbBr4:Li) perovskite single crystals (SCs) synthesized at room temperature are reported, and their scintillation properties are analyzed and compared with those of LYSO:Ce crystals under X-ray excitation. The (PEA)2PbBr4:Li SCs exhibit a fast time response with two decay times (11 ns (85%) and 38 ns (15%)), and the main fast-decay time is significantly shorter than that of LYSO:Ce (42 ns). The (PEA)2PbBr4:Li SCs exhibit a bright blue emission peaking at 428 nm and a narrow radioluminescence spectrum. Further, the (PEA)2PbBr4:Li SCs exhibit a high light yield (approximately 23 300 photons/MeV). In addition, the (PEA)2PbBr4:Li SCs exhibit better spatial resolution (3.3 lp/mm at modulation transfer function = 0.1) in X-ray imaging. The results demonstrate that the low-cost (PEA)2PbBr4:Li SCs scintillator has enormous potential for medical diagnostic applications. © 2023, The Authors. All rights reserved.

关键词： Lithium

Mode I Fracture Analysis of Adhesively Bonded Bi-Material Dcb Joints

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SSRN 2023年

作者： Wang, Wandong Zhang, Shijie Chen, Guiyong Zhu, Yangxuan Zhao, Tian School of Civil Aviation Northwestern Polytechnical University Shaanxi Xi’an710072 China Co. Ltd 610000 China Hubei Key Laboratory of Theory and Application of Advanced Material Mechanics School of Science Wuhan University of Technology Wuhan430070 China Beijing Key Laboratory of Lightweight Multi-functional Composite Materials and Structures Institute of Advanced Structure Technology Beijing Institute of Technology Beijing100081 China

There has been a disputation about how to design bi-material double cantilever beam (DCB) joints to measure pure mode I fracture toughness. This paper develops a theoretical frame to calculate the stresses in the adhesive layer and perform the data reduction and mode partitioning for generic bi-material DCB specimens. The theoretical model was validated using experimental data and conventional finite element method. The prediction results substantiate that the strain-based design strategy leads to a pure mode I fracture of the bi-material DCB joints. The proposed theoretical method can promote the application of strain-based criterion for designing the adhesively bonded bi-material DCB joints to appropriately obtain the pure mode I critical fracture toughness. © 2023, The Authors. All rights reserved.

关键词： Adhesives

Unsupervised Deep Learning Method for Single Image Super-Resolution of the Thick Pinhole Imaging System Using Deep Image Prior

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SSRN 2024年

作者： Li, Guoguang Sheng, Liang Duan, Baojun Li, Yang Hei, Dongwei Xing, Qingzi Ministry of Education Beijing100084 China Laboratory for Advanced Radiation Sources and Application Tsinghua University Beijing100084 China Department of Engineering Physics Tsinghua University Beijing100084 China State Key Laboratory of Intense Pulsed Radiation Simulation and Effect Northwest Institute of Nuclear Technology Xi’an710024 China

Thick pinhole imaging system is widely used for diagnosing intense pulsed radiation sources. However, owing to the trade-off among spatial resolution, field of view (FOV) and detection efficiency, the imaging system normally falls short in achieving high-precision spatial diagnosis. In this study, we propose an unsupervised deep learning method for single image super-resolution (SISR) of the thick pinhole imaging system. The point spread function (PSF) of the imaging system is obtained by analytical calculation and Monte Carlo simulation methods, and the mathematical model of the imaging system is established using a linear equation. To solve the ill-posed inverse problem, we adopt randomly initialized deep convolutional neural networks (DCNNs) as an image prior without pre-training, which is named deep image prior (DIP). The results demonstrate that, by utilizing the super-resolution technology to increase the number of pixels in reconstructed images, the proposed DIP algorithm can mitigate the spatial resolution degradation caused by an insufficient spatial sampling frequency of the camera. Compared with the traditional expectation-maximization (EM) algorithm, the proposed DIP algorithm exhibits superior capabilities in recovering high-frequency signals and suppressing ringing artifacts. Furthermore, the robustness of the proposed DIP algorithm under different yields is also verified. © 2024, The Authors. All rights reserved.

关键词： Optical transfer function

Observation of molecular and polymeric nitrogen stuffed NaCl ionic layers

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arXiv

arXiv 2025年

作者： Ning, Ping Tian, Yifan Liu, Guangtao Wang, Hongbo Hu, Qingyang Liu, Hanyu Zhou, Mi Ma, Yanming Key Laboratory of Material Simulation Methods and Software Ministry of Education College of Physics Jilin University Changchun130012 China State Key Laboratory of Superhard Materials College of Physics Jilin University Changchun130012 China Center for High Pressure Science and Technology Advanced Research Beijing100094 China International Center of Future Science Jilin University Changchun130012 China

Sodium chloride (NaCl), a ubiquitous and chemically stable compound, has been considered inert under ambient conditions. Its typical B1 structure is highly isotropic without preferential direction, favoring the growth of a three-dimensional network of strong Na-Cl ionic bonds. Here, we employ first-principles structural searching and synchrotron X-ray diffraction to unravel an unexpected chemical reaction between NaCl and N2 to produce a hybrid salt-NaCl(N2)2, where N2 molecules break the isotropic NaCl structure into two-dimensional layers upon synthesis at 50 GPa. In contrast to the insulating properties of pristine NaCl, the electronic bandgap of the N2-stuffed NaCl narrowed to 1.8 eV, becoming an indirect bandgap semiconductor. Further compression to 130 GPa induced the polymerization of N atoms into zigzag N-chains. Our findings not only demonstrate the possibility of unusual N-chemistry under extreme conditions, but also suggest a feasible approach for the design of layered NaCl frameworks to modulate the polymerization of nitrogen. Copyright © 2025, The Authors. All rights reserved.

关键词： Sodium chloride