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Transient performance comparison of grid-forming converters with different FRT control strategies

《能源前沿（英文）》 2023年第17卷第2期页码 239-250 doi: 10.1007/s11708-022-0856-2

摘要： Grid-forming converters (GFMs) are faced with the threat of transient inrush current and synchronization instability issues when subjected to grid faults. Instead of disconnecting from the grid unintentionally, GFMs are required to have fault ride through (FRT) capability to maintain safe and stable operation in grid-connected mode during grid fault periods. In recent studies, different FRT control strategies with distinguishing features and that are feasible for different operation conditions have been proposed for GFMs. To determine their application scope, an intuitive comparison of the transient performance of different FRT control strategies is presented in this paper. First, three typical FRT control strategies (virtual impedance, current limiters, and mode-switching control) are introduced and transient mathematical models are established. A detailed comparison analysis on transient inrush current and transient synchronization stability is then presented. The results will be useful for guiding the selection and design of FRT control strategies. Finally, simulation results based on PSCAD/EMTDC are considered to verify the correctness of the theoretical analysis.

关键词： grid-forming converters (GFMs) fault ride through (FRT) transient stability transient inrush current transient modeling

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A comprehensive review of wind power based power system frequency regulation

《能源前沿（英文）》 2023年第17卷第5期页码 611-634 doi: 10.1007/s11708-023-0876-6

摘要： Wind power (WP) is considered as one of the main renewable energy sources (RESs) for future low-carbon and high-cost-efficient power system. However, its low inertia characteristic may threaten the system frequency stability of the power system with a high penetration of WP generation. Thus, the capability of WP participating in the system frequency regulation has become a research hotspot. In this paper, the impact of WP on power system frequency stability is initially presented. In addition, various existing control strategies of WP participating in frequency regulation are reviewed from the wind turbine (WT) level to the wind farm (WF) level, and their performances are compared in terms of operating principles and practical applications. The pros and cons of each control strategy are also discussed. Moreover, the WP combing with energy storage system (ESS) for system frequency regulation is explored. Furthermore, the prospects, future challenges, and solutions of WP participating in power system frequency regulation are summarized.

关键词： frequency regulation strategies wind turbine generators grid-forming control model predictive control energy storage system

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Modeling and control of photovoltaic energy conversion connected to the grid

Rebei NAJET, Ben Ghanem BELGACEM, Hasnaoui OTHMAN

《能源前沿（英文）》 2012年第6卷第1期页码 35-46 doi: 10.1007/s11708-012-0169-y

摘要： This paper presents modeling and control of a photovoltaic generator (PVG) connected to the grid. The parameters of the PVG have been identified in previous work (series and parallel resistance, reverse saturation current and thermal voltage) using Newton-Raphston and the gradient algorithm. The electrical energy from a PVG is transferred to the grid via two static converters (DC/DC and DC/AC). The objective of the proposed control strategy is to maximize energy captured from the PVG. The adapted control law for extracting maximum power from the PVG is based on the incremental conductance algorithm. The developed algorithm has the capability of searching the maximum photovoltaic power under variable irradiation and temperature. To control the DC/AC inverter, an intelligent system based on two structures is constructed: a current source control structure and a voltage source control structure. The system has been validated by numerical simulation using data obtained from the PVG installed in the laboratory research (INSAT, Tunisia).

关键词： photovoltaic generator (PVG) maximum power point tracker grid-connected static converters

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联网型直流微电网并联双向变流器分层控制 Article

Hui-yong HU, Yong-gang PENG, Yang-hong XIA, Xiao-ming WANG, Wei WEI, Miao YU

《信息与电子工程前沿（英文）》 2017年第18卷第12期页码 2046-2057 doi: 10.1631/FITEE.1601497

摘要：直流微电网通过多个双向变流器并联连接到交流电网，其控制方法直接影响到直流电网的性能。目前的研究工作主要集中在交流、直流及混合微电网的分层控制，而较少关注直流微电网互联的双向变流器的分层控制。本文提出一种直流微电网联网双向变流器的分层控制方法。为抑制交流测零序环流并实现电压控制的反馈线性化，采用d-q-0控制策略来控制内环电流并采用直流电压平方实现外环电压控制。在一次控制阶段采用直流电压下垂控制来实现直流电流的分担，直流电压下垂控制会产生直流电压偏差。接着分析了直流电压偏差和电流分担误差之间的关系。为同时消除直流电压偏差和电流分担误差，在二次控制中采用了下垂斜率调节和电压平移。三次控制中通过多双向变流器的精确有功和无功控制实现直流微网的经济运行。本文提出的直流微网多并联双向变流器分层控制方法可以实现微网内可控/不可控分布式电源的协调。通过Matlab/Simulink仿真验证了算法的有效性，结果表明该算法能满足实际应用需求。

关键词：并联双向变流器；分层控制；直流微电网

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Analysis and control of wind-driven self-excited induction generators connected to the grid through powerconverters

S. Senthil KUMAR, N. KUMARESAN, N. Ammasai GOUNDEN, Namani RAKESH

《能源前沿（英文）》 2012年第6卷第4期页码 403-412 doi: 10.1007/s11708-012-0208-8

摘要： The analysis of the wind-driven self-excited induction generators (SEIGs) connected to the grid through power converters has been developed in this paper. For this analysis, a method of representing the grid power as equivalent load resistance in the steady-state equivalent circuit of SEIG has been formulated. The technique of genetic algorithm (GA) has been adopted for making the analysis of the proposed system simple and straightforward. The control of SEIG is attempted by connecting an uncontrolled diode bridge rectifier (DBR) and a line commutated inverter (LCI) between the generator terminals and three-phase utility grid. A simple control technique for maximum power point tracking (MPPT) in wind energy conversion systems (WECS), in which the firing angle of the LCI alone needs to be controlled by sensing the rotor speed of the generator has been proposed. The effectiveness of the proposed method of MPPT and method of analysis of this wind-driven SEIG-converter system connected to the grid through power converters has been demonstrated by experiments and simulation. These experimental and simulated results confirm the usefulness and successful working of the proposed system and its analysis.

关键词： self-excited induction generator (SEIG) renewable power generation power converters maximum power point tracking (MPPT) steady state analysis power generation systems

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Finite element simulations of sheet metal forming under complex strain paths

CHEN Wei, YANG Jichang, WU Xiaofeng, LU Dun, GUO Weigang

《机械工程前沿（英文）》 2007年第2卷第4期页码 399-403 doi: 10.1007/s11465-007-0069-8

摘要： Fracture is a common defect in sheet metal forming and it is essentially caused by tensile instability. This paper analyzes some experiments and theories for building forming limit diagrams of sheet metal and points out the advantages and disadvantages of current experiments and theories. According to this, a method that integrates the finite element simulation and experiment was used to research the forming limit diagrams of the sheet metal under complex strain paths. Taking the rear hanger that undergoes twice stamping as an example, the strain paths of the dangerous point of the rear hanger is investigated. Finally, the forming method of the rear hanger is confirmed. Results indicate that finite element method (FEM) can achieve the complex strain paths and different strain paths will have great impacts on the result of the sheet metal forming.

关键词： dangerous forming method different hanger forming

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Digital high-efficiency print forming method and device for multi-material casting molds

Zhongde SHAN, Zhi GUO, Dong DU, Feng LIU, Wenjiang LI

《机械工程前沿（英文）》 2020年第15卷第2期页码 328-337 doi: 10.1007/s11465-019-0574-6

摘要： Sand mold 3D printing technology based on the principle of droplet ejection has undergone rapid development in recent years and has elicited increasing attention from engineers and technicians. However, current sand mold 3D printing technology exhibits several problems, such as single-material printing molds, low manufacturing efficiency, and necessary post-process drying and heating for the manufacture of sand molds. This study proposes a novel high-efficiency print forming method and device for multi-material casting molds. The proposed method is specifically related to the integrated forming of two-way coating and printing and the short-flow manufacture of roller compaction and layered heating. These processes can realize the high-efficiency print forming of high-performance sand molds. Experimental results demonstrate that the efficiency of sand mold fabrication can be increased by 200% using the proposed two-way coating and printing method. The integrated forming method for layered heating and roller compaction presented in this study effectively shortens the manufacturing process for 3D-printed sand molds, increases sand mold strength by 63.8%, and reduces resin usage by approximately 30%. The manufacture of multi-material casting molds is demonstrated on typical wheeled cast-iron parts. This research provides theoretical guidance for the engineering application of sand mold 3D printing.

关键词： multi-material casting mold 3D printing efficient print forming method

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Near-field radiative thermoelectric energy converters: a review

Eric TERVO, Elham BAGHERISERESHKI, Zhuomin ZHANG

《能源前沿（英文）》 2018年第12卷第1期页码 5-21 doi: 10.1007/s11708-017-0517-z

摘要： Radiative thermoelectric energy converters, which include thermophotovoltaic cells, thermoradiative cells, electroluminescent refrigerators, and negative electroluminescent refrigerators, are semiconductor p-n devices that either generate electricity or extract heat from a cold body while exchanging thermal radiation with their surroundings. If this exchange occurs at micro or nanoscale distances, power densities can be greatly enhanced and near-field radiation effects may improve performance. This review covers the fundamentals of near-field thermal radiation, photon entropy, and nonequilibrium effects in semiconductor diodes that underpin device operation. The development and state of the art of these near-field converters are discussed in detail, and remaining challenges and opportunities for progress are identified.

关键词： energy conversion systems luminescent refrigeration near-field radiation thermophotovoltaic thermoradiative cell

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Formation mechanism and modeling of surface waviness in incremental sheet forming

《机械工程前沿（英文）》 2022年第17卷第2期 doi: 10.1007/s11465-022-0679-1

摘要： Improving and controlling surface quality has always been a challenge for incremental sheet forming (ISF), whereas the generation mechanism of waviness surface is still unknown, which impedes the widely application of ISF in the industrial field. In this paper, the formation mechanism and the prediction of waviness are both investigated through experiments, numerical simulation, and theoretical analysis. Based on a verified finite element model, the waviness topography is predicted numerically for the first time, and its generation is attributed to the residual bending deformation through deformation history analysis. For more efficient engineering application, a theoretical model for waviness height is proposed based on the generation mechanism, using a modified strain function considering deformation modes. This work is favorable for the perfection of formation mechanism and control of surface quality in ISF.

关键词： surface waviness incremental sheet forming numerical simulation formation mechanism deformation history

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FEM-based strain analysis study for multilayer sheet forming process

Rongjing ZHANG,Lihui LANG,Rizwan ZAFAR

《机械工程前沿（英文）》 2015年第10卷第4期页码 373-379 doi: 10.1007/s11465-015-0371-9

摘要：

Fiber metal laminates have many advantages over traditional laminates (e.g., any type of fiber and resin material can be placed anywhere between the metallic layers without risk of failure of the composite fabric sheets). Furthermore, the process requirements to strictly control the temperature and punch force in fiber metal laminates are also less stringent than those in traditional laminates. To further explore the novel method, this study conducts a finite element method-based (FEM-based) strain analysis on multilayer blanks by using the 3A method. Different forming modes such as wrinkling and fracture are discussed by using experimental and numerical studies. Hydroforming is used for multilayer forming. The Barlat 2000 yield criteria and DYNAFORM/LS-DYNA are used for the simulations. Optimal process parameters are determined on the basis of fixed die-binder gap and variable cavity pressure. The results of this study will enhance the knowledge on the mechanics of multilayer structures formed by using the 3A method and expand its commercial applications.

关键词： finite element method (FEM) strain analysis multilayer sheet forming

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Hybrid forming mechanism of patternless casting and laser cladding

Zhongde SHAN, Fuzhen SUN, Yang LIU

《机械工程前沿（英文）》 2019年第14卷第4期页码 393-401 doi: 10.1007/s11465-019-0550-1

摘要： In accordance with the requirement of manufacturing dies quickly and economically, a hybrid forming method of stamping dies for automobile panels is proposed. The method combines digital patternless casting and high-power laser cladding. An experimental study is conducted on the hybrid forming process and its trial production and application in the manufacturing of stamping dies for typical panels. Results prove that the laser cladding layer exceeds HRC60 (Rockwell hardness) and thus meets the production efficiency requirement of automobile dies. The rate of defects is well controlled. Compared with traditional technology, this technology has remarkable advantages and advancement.

关键词： patternless casting laser cladding hybrid forming rapid tooling

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Highlight yield forming and innovative technologies in tropical crops

Wenquan WANG

《农业科学与工程前沿（英文）》 2016年第3卷第4期页码 283-284 doi: 10.15302/J-FASE-2016128

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Properties and effect of forming sewage sludge into lightweight ceramics

Min YUE, Qinyan YUE, Yuanfeng QI, Baoyu GAO, Hui YU

《环境科学与工程前沿（英文）》 2012年第6卷第1期页码 117-124 doi: 10.1007/s11783-010-0220-3

摘要： In this work we investigated the chemical, thermal and toxic properties of dried sewage sludge (DSS), the preparation and properties of lightweight sludge ceramic (LSC) and the mechanisms of action of the organic and inorganic foaming agents (OFAs and IFAs). The chemical components and thermal properties of the raw materials were studied by Energy Dispersive X-ray Detection (EDX) and Thermogravimetric Analysis and Differential Scanning Calorimetry (DSC/TGA). The mineral phases of the raw materials and the formed ceramics were determined by X-ray Diffraction (XRD). The leaching characteristics of heavy metals were investigated with Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). Different ratios of DSS and clay were mixed and pressed into raw pellets. After drying and preheating treatment, the raw pellets were sintered at 1150°C for 10 min. The physical properties of LSC (50 wt% DSS added) were tested. The results showed that when the addition of DSS was above 50 wt%, LSC began to shrink, and a maximum density occurred. The environmental safety of LSC was satisfactory. XRD showed that some new mineral phases formed in the LSC. Observation of the microstructure by Scanning Electron Microscope (SEM) indicated that the body of LSC was porous.

关键词： sludge foaming agents ceramics preheating process

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Optimal placement of PMUs for the smart grid implementation in Indian power grid—A case study

Pathirikkat GOPAKUMAR, G. Surya CHANDRA, M. Jaya Bharata REDDY, Dusmata Kumar MOHANTA

《能源前沿（英文）》 2013年第7卷第3期页码 358-372 doi: 10.1007/s11708-013-0257-7

摘要： Efficient utilization of energy resources is essential for a developing country like India. The concept of smart grid (SG) can provide a highly reliable power system with optimized utilization of available resources. The present Indian power grid requires revolutionary changes to meet the growing demands and to make the grid smarter and reliable. One of the important requirements for SG is the instantaneous monitoring of the voltage, current and power flows at all buses in the grid. The traditional monitoring system cannot satisfy this requirement since they are based on nonlinear power flow equations. Synchro-phasor-measurement devices like phasor measurement units (PMUs) can measure the phasor values of voltages at installed buses. Consequently, the currents passing through all branches connected to that bus can be computed. Since the voltage phasor values at the neighboring buses of a bus containing the PMU can be estimated using Ohm’s law, it is redundant to install PMUs at all the buses in a power grid for its complete observability. This paper proposes the optimal geographical locations for the PMUs in southern region Indian power grid for the implementation of SG, using Integer Linear Programming. The proposed optimal geographical locations for PMU placement can be a stepping stone for the implementation of SG in India.

关键词： phasor measurement units (PMUs) smart grid (SG) southern region Indian power grid (SRIPG) integer linear programming (ILP)

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Optimal redundant placement of PMUs in Indian power grid — northern, eastern and north-eastern regions

Pathirikkat GOPAKUMAR, G. Surya CHANDRA, M. Jaya Bharata REDDY, Dusmata Kumar MOHANTA

《能源前沿（英文）》 2013年第7卷第4期页码 413-428 doi: 10.1007/s11708-013-0274-6

摘要： Effective utilization of renewable energy sources and efficient management of electric energy are essential for any developing countries like India. This can be envisioned through the implementation of concepts of smart grid (SG). One of the key requisites for SG implementation is that the grid should be completely observable. Renovation of conventional Indian power grid to a SG necessitates incorporation of the phasor measurement units (PMUs) in the present power grid measurement and monitoring system. Since the cost of PMU is high and any bus containing a PMU makes the neighboring connected buses observable, optimal placement of PMUs is very important for complete observability of the grid. This paper proposes optimal redundant geographical locations in the northern, eastern and north-eastern regions of Indian power grid for PMU placement. The PMUs installed in these geographical locations will make the grid completely observable and maintain the observability under the conditions of failure of some PMUs or branch outages. Integer linear programming has been used for finding the optimal PMU locations. The results proposed in this paper can be a stepping stone for revamping the Indian power grid to a SG ensuring complete observability during different contingency conditions.

关键词： phasor measurement unit (PMU) smart grid (SG) Indian power grid northern region Indian power grid (NRIPG) eastern region Indian power grid (ERIPG) north-eastern region Indian power grid (NERIPG) redundancy integer linear programing (ILP)