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LVRT During-fault-stage Equilibrium Point is Unnecessary for Renewable Grid-tied systems

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LVRT During-fault-stage Equilibrium Point is Unnecessary for...

Power system and Green Energy Conference (PSGEC)

作者： Yayao Zhang Min Cheng Meng Zhan Jiawei Yu Yihua Zhu Mingkang Wu State Key Laboratory of Advanced Electromagnetic Engineering and Technology School of Electrical and Electronic Engineering Huazhong University of Science and Technology Wuhan China Yunnan Power Grid China State Key Laboratory of HVDC Electric Power Research Institute China Southern Power Grid China National Energy Power Grid Technology R&D Centre Electric Power Research Institute China Southern Power Grid China Guangdong Provincial Key Laboratory of Intelligent Operation and Control for New Energy Power System Electric Power Research Institute China Southern Power Grid China

ISBN: (数字)9798350365573

ISBN: (纸本)9798350365580

Transient synchronous stability of renewable grid- tied systems is of paramount importance. Most of previous studies focused on the grid-tied converter in the low voltage ride through (LVRT) during-fault stage and performed stability analysis based on the belief that if the system has (or has no) a stable equilibrium point in the during-fault stage, the system will be stable (or unstable). Therefore, it has been broadly accepted that the existence and/or stability of equilibrium point in the during-fault stage is necessary. However, the whole LVRT contains four different stages and the during-fault stage is only one among them. The transient synchronous stability of whole system should be determined by the initial state in the late post-fault stage and the attraction basin of its equilibrium point. The late post-fault stage is essential for stability and all four stages are important. Clearly treating the during-fault stage as the whole LVRT stages makes the nonlinear switched dynamics problem be greatly simplified and, certainly, is incomplete. In order to clarify this point, this paper analyzes the influence of existence (or nonexistence) of equilibrium point in the during-fault stage on the transient synchronous stability of permanent magnet synchronous generator grid-tied system. We can find that the existence of an equilibrium point in the during-fault stage is only a sufficient condition, rather than a necessary condition. The theoretical analysis is also verified in the hardware-in-the-loop experiment Therefore, a large number of previous studies and results on the transient synchronous stability of renewable grid-tied systems are incomplete and questionable.

关键词： Sufficient conditions Stability criteria Switches Voltage Power system stability Synchronous generators Permanent magnets Nonlinear dynamical systems Transient analysis Magnetic switching

Biomechanical Finite Element Methods Study of a Novel Internal Fixation system for Lumbar Spondylolysis

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SSRN 2025年

作者： Li, Jingyuan Du, Chengfei Wang, Yulei Du, Di Liang, Jinlong Shao, Nengqi Feng, Fanzhe Xu, Wenhao Xu, Yongqing Cui, Yi Center for Joint Surgery Intelligent Manufacturing and Rehabilitation Engineering Center The First Affiliated Hospital of Army Medical University Chongqing400038 China Chongqing Municipal Science and Technology Bureau Key Laboratory of Precision Medicine in Joint Surgery Chongqing400038 China Chongqing Municipal Education Commission Key Laboratory of Joint Biology Chongqing400038 China Tianjin Key Laboratory for Advanced Mechatronic System Design and Intelligent Control School of mechanical engineering Tianjin University of Technology Tianjin300384 China Department of Orthopaedic Surgery 920th Hospital of Joint Logistics Support Force Kunming650032 China Department of Orthopaedic Surgery 920th Hospital of Joint Logistics Support Force No. 212 of Da-Guan Road Xishan District Kunming650032 China

ObjectiveThis study aimed to verify the biomechanical efficacy of a novel internal fixation system for repairing lumbar spondylolysis (LS). Additionally, the changes in the mechanical performance of the novel internal fixation device during compression were *** healthy 25-year-old male volunteer was recruited for lumbar spine CT data acquisition to construct and validate a nonlinear finite element model of the L4-S1 spinal segment (A). Based on this, models were established for L5 spondylolysis (B), traditional internal fixation (C), and the pressurization process of the novel LS repair device fixation (D→E→F). For these six models, we constrained the lower surface of the S1 vertebral body while applying an axial compression force of 500 N and a moment load of 7.5 N·m on the upper surface of the L4 vertebral body to simulate six motions of the lumbar spine. The performance of each finite element model was evaluated by comparing the range of motion (ROM), maximum displacement, and maximum pressure experienced by the lumbar spine under different motion *** with Model C, Models D, E, and F exhibited a reduced ROM and maximum displacement (1%-38.5%, 12.8%-63.6%, and 32.8%-80.2%) compared with Model C during six different motions. Notably, compared with Model C, the novel internal fixation models consistently demonstrated a decreasing trend in the maximum stress on the intervertebral discs (IVD) and an increasing trend in the maximum stress on the articular cartilage and maximum stress and displacement of the bone graft. Moreover, the novel internal fixation model displayed larger ranges of evenly distributed stresses on the isthmus and reduced maximum stress on the internal fixation device across all six motions, with improved stiffness effects during the pressurization process of the novel internal fixation system (D→E→F).ConclusionsAccording to several mechanical comparisons, the novel internal fixation system had better biomechan

关键词： Axial compression

Tailoring the Anomalous Hall Effect in Van Der Waals Ferromagnet Fe3gete2

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SSRN 2024年

作者： Wu, Kaile Wang, Qin Wang, Junshan Jiang, Jiaolin Zhao, Tian Zhao, Dong Han, Dan Quan, Zhiyong Ma, Zongmin Wang, Haomin Sang, Shengbo Ge, Yang Shanxi Key Laboratory of Micro Nano Sensors & Artificial Intelligence Perception College of Electronic Information and Optical Engineering Taiyuan University of Technology Taiyuan030024 China Key Lab of Advanced Transducers and Intelligent Control System The Ministry of Education Taiyuan University of Technology Taiyuan030024 China College of Materials Science and Engineering Taiyuan University of Technology Taiyuan030024 China Key Laboratory of Magnetic Molecules and Magnetic Information Materials of Ministry of Education School of Chemistry and Materials Science Shanxi Normal University Taiyuan030031 China State Key Laboratory of Dynamic Measurement Technology North University of China Shanxi Taiyuan030051 China School of Semiconductor and Physics North University of China Shanxi Taiyuan030051 China State Key Laboratory of Functional Materials for Informatics Shanghai Institute of Microsystem and Information Technology Chinese Academy of Sciences Shanghai200050 China Shanxi Research Institute of 6D Artificial Intelligence Biomedical Science Taiyuan030024 China

Two-dimensional van der Waals magnetic materials have shown fascinating natural ferromagnetic properties at the atomic level, which has great potential in fields of low power spintronics, quantum computing and optical communication. Herein, the ferromagnetism and magnetic anisotropy of bulk Fe3GeTe2 (FGT) were investigated, and the testing results indicate a pronounced vertical magnetic anisotropy below the Curie temperature (Tc=165 K) of FGT. In addition, the anomalous Hall effect of FGT nanoflakes was studied at various temperatures and thicknesses by standard Hall bar device in detail. The results show the anomalous Hall resistance (0.764 Ω at 20 K decreased to 0.332 Ω at 140 K) and the obvious rectangular magnetic hysteresis rings below Tc (165 K). Furthermore, we calculated the carrier concentration (2.5×1022 cm-3 at 20K) and mobility (13.3 cm2/(v·s) at 20K) under large magnetic field (-6 T~6 T). Particularly, we demonstrated that the strong tailoring ability of the anomalous Hall effect for FGT-based magnetoelectric transport devices comes form the regulation of magnetic moment by sample thickness and magnetic field angle. The above experimental results verify that FGT is expected to be a prime candidate material for ultrathin 2D spintronic devices to the next generation. © 2024, The Authors. All rights reserved.

关键词： Germanium alloys

Nonlinear Modeling and Sensitivity Performance Analysis of a Novel Tapered Beam-Based Micro-Gyroscope

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SSRN 2022年

作者： Zhang, Kunpeng Xie, Jianwei Hao, Shuying Feng, Jingjing Tianjin Key Laboratory for Advanced Mechatronic System Design and Intelligent Control School of Mechanical Engineering Tianjin University of Technology Tianjin300384 China National Demonstration Center for Experimental Mechanical and Electrical Engineering Education Tianjin University of Technology Tianjin300384 China

In this paper, we investigate a class of tapered beam micro-gyroscope with electrostatically driven and consider the effects of electrostatic force nonlinearity and fringing field. The governing equations of system are derived by Euler angular transformation and Hamilton principle. The ordinary differential equations with fourth-order variable coefficient are solved by the Adomian decomposition method (ADM). Influence of parameters such as shape factors and DC voltage on static deflection, pull-in voltage and natural frequency of tapered beam micro-gyroscope are investigated. Galerkin discretization is performed on the governing equations of the tapered beam micro-gyroscope. The frequency-response equation of the system is deduced and solved by applying the method of multi-scale (MMS). We obtained the influence regular of DC voltage and fringing field effect on the frequency-response curves. Finally, performance of the tapered beam micro-gyroscope is analyzed in terms of bandwidth, sensitivity, and calibration curve nonlinearity under different shape factors. In static analysis, the pull-in voltage of system gradually decreases with the increase of the shape factors of tapered beam micro-gyroscope, and it will be further reduced by considering the fringing field effect. In the dynamic analysis, the maximum amplitude of motion in the drive and sense directions increases significantly with the shape factors of the tapered beam. Softening characteristics caused by the nonlinearity of the electrostatic force are enhanced. Compared with straight beam micro-gyroscope, the tapered beam micro-gyroscope has the higher amplitude of motion and pronounced nonlinear characteristics. Due to the nonlinearity, the frequency-response curves in the drive direction shifts to the left. The amplitude of motion in the drive direction has a high response over a wide frequency band. By controlling the DC voltage, the natural frequency of the sense mode is matched with the nonlinear natural

关键词： Bandwidth

Arbitrarily shaped retro-reflector by optics surface transformation

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Chinese Optics Letters 2020年第10期18卷 58-62页

作者： Fei Sun Yichao Liu Yibiao Yang Zhihui Chen Sailing He Key Laboratory of Advanced Transducers and Intelligent Control System Ministry of Education and Shanxi ProvinceCollege of Physics and OptoelectronicsTaiyuan University of TechnologyTaiyuan 030024China Centre for Optical and Electromagnetic Research State Key Laboratory of Modern Optical InstrumentationNational Engineering Research Center for Optical InstrumentsZhejiang UniversityHangzhou 310058China

A novel way to design arbitrarily shaped retro-reflectors by optics surface transformation is proposed. The entire design process consists of filling an optic-null medium between the input and output surfaces of the retroreflector, on which the points have 180 deg reverse corresponding relations. The retro-reflector can be designed to be very thin(a planar structure) with high efficiency. The effective working angles of our retro-reflector are very large(from-80 deg to +80 deg), which can, in principle, be further extended. Layered metal plates and zero refractive index materials are designed to realize the proposed retro-reflector for a TM polarized beam.

关键词： retro-reflector optics surface transformation

Ultrafast Spin-to-Orbit and Orbit-to-Local-Spin Conversions of Tightly Focused Hybridly Polarized Light Pulses

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arXiv

arXiv 2021年

作者： Zhang, Yanxiang Zhang, Zijing Nie, Zhongquan Department of Physics Harbin Institute of Technology Harbin150001 China Key Lab of Advanced Transducers and Intelligent Control System Ministry of Education and Shanxi Province College of Physics and Optoelectronics Taiyuan University of Technology Taiyuan030024 China

Spin-orbit interaction (SOI) have provided a new viable roadmap for the development of spin-based photonics devices. However, existing strategies to control the SOI focus commonly on tailoring the spatial dimension of light fields yet neglecting the inherent temporal one. Herein, we first present ultrafast temporal effects on both spin-to-orbit and orbit-to-local-spin conversions based on the time-assistant vectorial diffractive theory and the fast Fourier transformation. Such interconversions depend upon whether the incident hybridly vectorial light pulse carries vortex phase or not in a single high numerical aperture geometry. For the case of the absence of vortex phase, we find that it enables orbit angular momentum-carrying transverse component fields, and the resultant orbit angular momentum embedded within focused light fields remains constantly revolving as time elapses, which indicates that the controllable spin-to-orbit conversion occurs. By contrast, it is revealed that hybridly polarized vectorial-vortex light pulses allow access to the locally excited circular polarization at the focus, and this induced local circular polarization is independent of ultrafast varying time, whereas the resulting spin angular momentum density components experience the alternation between the appearance and annihilation over time, thus giving rise to the tunable orbit-to-local-spin conversion. These exotic ultrafast interconversions not only breathe a new life into the area of ultrafast photonics, but refresh our understanding on the paradigm of photonic SOI. Copyright © 2021, The Authors. All rights reserved.

关键词： Circular polarization

controlled formation of GaN nanostructures through contactless photoelectrochemical etching for supercapacitor electrode applications

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International Journal of Electrochemical Science 2025年第8期20卷

作者： Yaya Ge Yihang Fan Yibiao Yang Mingda Zhang Xin Liu Binzhao Cao Yuan Tian Hongming Fei College of Physics and Optoelectronics Taiyuan University of Technology Taiyuan 030024 China Key Lab of Advanced Transducers and Intelligent Control System Ministry of Education and Shanxi Province College of Physics and Optoelectronics Taiyuan University of Technology Taiyuan 030024 China

Nanostructured n-type GaN layers were fabricated using the Contactless photoelectrochemical (PEC) etching method in KOH-based solutions under ultraviolet illumination. By adjusting the KOH concentration, distinct surface morphologies were obtained. Low-concentration KOH solutions led to the formation of nanorods at dislocation sites, whereas high-concentration solutions induced interconnected etch pits. Cathodoluminescence (CL) analysis confirmed a strong correlation between the resulting nanostructures and dislocation sites. The formation mechanisms of different nanostructures were discussed. Electrochemical characterization revealed significantly enhanced performance in etched GaN samples. In particular, the GaN layer treated with 0.02 M KOH and 0.02 M K 2 S 2 O 8 exhibited a 16-fold increase in specific capacitance compared to the pristine GaN layer.

关键词： Contactless photoelectrochemical(PEC) etching KOH concentration Dislocations Nanostructures Specific capacitance

Thermal-Economic Optimization and Working Fluid Selection of Subcritical Organic Rankine system for Low-Temperature Waste Heat Recovery

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SSRN 2022年

作者： Zhang, Chao Li, Yongwang Fu, Wencheng Zhiting, Tong Tianjin Key Laboratory for Advanced Mechatronic System Design and Intelligent Control School of Mechanical Engineering Tianjin University of Technology Tianjin300384 China National Demonstration Center for Experimental Mechanical and Electrical Engineering Education Tianjin University of Technology Tianjin300384 China

In the present study, multi-objective optimization is conducted to search for the best operating condition for a subcritical organic Rankine system with the trade-off between system exergy efficiency and dynamic payback period (PBP). A 150°C wastewater heat source is employed as a typical low-temperature heat source. Five decision variables are considered: turbine inlet temperature and pressure, pinch point temperature differences in evaporator and condenser, and condensing temperature. The multi-objective genetic algorithm combined with the backpropagation neural network method is employed as the optimization approach. In addition, the improved Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS) is developed to gain the optimal Pareto front solution for either working fluid and find the optimal working fluid among the candidates investigated. The results show that working fluid R236fa is the optimal solution, despite the minimum PBP for working fluid R123 and the maximum system exergy efficiency for working fluid R1234ze. Under the optimal working condition for working fluid R236fa, the system exergy efficiency and the PBP are 0.465 and 7.377 years, respectively. © 2022, The Authors. All rights reserved.

关键词： Multiobjective optimization

Towards Energy-Efficiency: Integrating MATD3 Reinforcement Learning Method for Computational Offloading in RIS-Aided UAV-MEC Environments

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IEEE Internet of Things Journal 2025年

作者： Wu, Liangshun Zhang, Cong Zhang, Bin Du, Jianbo Qu, Junsuo Key Laboratory of Embedded System and Service Computing Tongji University Ministry of Education Shanghai201804 China Shanghai Key Laboratory of Trustworthy Computing East China Normal University Shanghai201210 China School of Electronic Information and Electrical Engineering Shanghai Jiao Tong University Shanghai200240 China Xi'an Key Laboratory of Advanced Control and Intelligent Process School of Automation Xi'an University of Posts & Telecommunications Xi'an710061 China Xinjiang University of Political Science and Law Tumushuke832003 China School of Remote Sensing and Information Engineering Wuhan University Wuhan430079 China Department of Computer City University of Hong Kong 999077 Hong Kong School of Communications and Information Engineering Xi'an University of Posts & Telecommunications Xi'an710061 China

With the proliferation of IoT devices, there is an escalating demand for enhanced computing and communication capabilities. Mobile Edge Computing (MEC) addresses this need by relocating computing resources to the network edge, thereby delivering swifter and more efficient services. This paper introduces a computation offloading and energy consumption optimization framework that leverages Reconfigurable intelligent Surfaces (RIS), Unmanned Aerial Vehicles (UAVs), and MEC. The scheme aims to maximize energy efficiency through the optimization of task allocation, RIS phase shifts, and UAV trajectories. By employing the Multi-Agent Twin Delayed Deep Deterministic Policy Gradient (MATD3) reinforcement learning algorithm, the paper further refines UAV trajectories and RIS configurations. The simulation results indicate that the proposed method surpasses the traditional Concave-Convex Procedure (CCCP) algorithm in both UAV trajectory control and RIS configuration, demonstrating quicker convergence and enhanced stability. The method proves to be adaptable to diverse environments and tasks, showcasing notable benefits in RIS-assisted interference suppression, particularly with large RIS, thereby enhancing UAV data reception rates. Additionally, MATD3 exhibits faster and smoother convergence for extended task durations and smaller RIS scenarios. Simulation results reveal that UAVs tend to move closer to RIS, with energy efficiency falling as IoT tasks increase, affirming the proposed algorithm's high energy efficiency and effectiveness. © 2025 IEEE.

关键词： Unmanned aerial vehicles (UAV)