Research on the longitudinal protection of a through-type cophase traction direct power supply system based on the empirical wavelet transform

This paper proposes a longitudinal protection scheme utilizing empirical wavelet transform(EWT)for a through-type cophase traction direct power supply system,where both sides of a traction network line exhibit a distinctive boundary structure.This approach capitalizes on the boundary’s capacity to attenuate the high-frequency component of fault signals,resulting in a variation in the high-frequency transient energy ratio when faults occur inside or outside the line.During internal line faults,the high-frequency transient energy at the checkpoints located at both ends surpasses that of its neighboring lines.Conversely,for faults external to the line,the energy is lower compared to adjacent lines.EWT is employed to decompose the collected fault current signals,allowing access to the high-frequency transient energy.The longitudinal protection for the traction network line is established based on disparities between both ends of the traction network line and the high-frequency transient energy on either side of the boundary.Moreover,simulation verification through experimental results demonstrates the effectiveness of the proposed protection scheme across various initial fault angles,distances to faults,and fault transition resistances.

Assessment on Fault Diagnosis and State Evaluation of New Power Grid:AReview

1 Introduction The proposal of the concept of“New Power System”aims to illustrate the transform direction of the traditional power system,acting as the development core of the future new power grid.To achieve this,the proposed strategic targets of“carbon neutralization and carbon peaking”must be implemented and insisted[1].The core feature of the new power system is that renewable energy plays a leading role and becomes the main source of energy supply,meanwhile,the goal of green energy utilization has also been put forward on the agenda.Green energy utilization includes two aspects,one is the exploitation and promotion of various green energy technologies,and the other is the digitalization of energy management.Under this trend,stochastic and fluctuating energy sources such as wind power and photovoltaic power replace deterministic controllable power sources such as thermal power,bringing challenges to power grid regulation and dispatching,as well as flexible operation.The large-scale integration of renewable energy and increasingly high proportion of power electronic equipment tend to bring about fundamental changes in the operation characteristics,safety control,and production mode of the power system.

Classification and rating of disintegrated dolomite strata for slope stability analysis

Although disintegrated dolomite,widely distributed across the globe,has conventionally been a focus of research in underground engineering,the issue of slope stability issues in disintegrated dolomite strata is gaining increasing prominence.This is primarily due to their unique properties,including low strength and loose structure.Current methods for evaluating slope stability,such as basic quality(BQ)and slope stability probability classification(SSPC),do not adequately account for the poor integrity and structural fragmentation characteristic of disintegrated dolomite.To address this challenge,an analysis of the applicability of the limit equilibrium method(LEM),BQ,and SSPC methods was conducted on eight disintegrated dolomite slopes located in Baoshan,Southwest China.However,conflicting results were obtained.Therefore,this paper introduces a novel method,SMRDDS,to provide rapid and accurate assessment of disintegrated dolomite slope stability.This method incorporates parameters such as disintegrated grade,joint state,groundwater conditions,and excavation methods.The findings reveal that six slopes exhibit stability,while two are considered partially unstable.Notably,the proposed method demonstrates a closer match with the actual conditions and is more time-efficient compared with the BQ and SSPC methods.However,due to the limited research on disintegrated dolomite slopes,the results of the SMRDDS method tend to be conservative as a safety precaution.In conclusion,the SMRDDS method can quickly evaluate the current situation of disintegrated dolomite slopes in the field.This contributes significantly to disaster risk reduction for disintegrated dolomite slopes.

Key Issues for Modelling, Operation, Management and Diagnosis of Lithium Batteries: Current States and Prospects

1 Introduction.With the continuous growth of the global population,the energy demand continues to increase.However,due to the dominance of fossil fuels in global energy and fossil fuels are non-renewable,it has led to the global energy crisis[1].Besides,the use of fossil fuels will generate a mass of air pollutants(e.g.,carbon dioxide,sulfur dioxide,etc.),which will cause serious environmental pollution,climate change[2],etc.To resolve the aforementioned issues,countries around the world have implemented a variety of measures hoping to fundamentally adjust the global energy structure and achieve sustainable development.Thereinto,“Paris Agreement”reached in 2015 under the framework of“United Nations Framework Convention on Climate Change”aims to control the increase in the average temperature of the globe to within 2°C below preindustrial levels,and thereafter to peak global greenhouse gas emissions as soon as possible,continuously decreasing thereafter[3].United Kingdom plans to reduce the average exhaust emissions of“new cars”to approximately 50–70 g/km by 20230,which is roughly half of what it is now[4].In addition,China proposed a plan at“United Nations General Assembly”in 2020 to peak carbon dioxide emissions by 2030 and strive to achieve carbon neutrality by 2060.It is a fact that the whole world is committed to changing the current energy structure,protecting the Earth’s ecology,and achieving global sustainable development[5].

Maximum Power Point Tracking Technology for PV Systems: Current Status and Perspectives

Maximum power point tracking(MPPT)technology plays a key role in improving the energy conversion efficiency of photovoltaic(PV)systems,especially when multiple local maximum power points(LMPPs)occur under partial shading conditions(PSC).It is necessary to modify the operating point efficiently and accurately with the help of MPPT technology to maximize the collected power.Even though a lot of research has been carried out and impressive progress achieved for MPPT technology,it still faces some challenges and dilemmas.Firstly,the mathematical model established for PV cells is not precise enough.Second,the existing algorithms are often optimized for specific conditions and lack comprehensive adaptability to the actual operating environment.Besides,a single algorithm may not be able to give full play to its advantages.In the end,the selection criteria for choosing the suitable MPPT algorithm/converter combination to achieve better performance in a given scenario is very limited.Therefore,this paper systematically discusses the current research status and challenges faced by PV MPPT technology around the three aspects of MPPT models,algorithms,and hardware implementation.Through in-depth thinking and discussion,it also puts forward positive perspectives on future development,and five forward-looking solutions to improve the performance of PV systems MPPT are suggested.

State-of-the-art review of MPPT techniques for hybrid PV-TEG systems:modeling,methodologies,and perspectives

The development of alternative renewable energy technologies is crucial for alleviating climate change and promoting energy transformation.Of the currently available technologies,solar energy has promising application prospects owing to its merits of being clean,safe,and sustainable.Solar energy is converted into electricity through photovoltaic(PV)cells;however,the overall conversion efficiency of PV modules is relatively low,and most of the captured solar energy is dissipated in the form of heat.This not only reduces the power generation efficiency of solar cells but may also have a negative impact on the electrical parameters of PV modules and the service life of PV cells.To overcome the shortcomings,an efficient approach involves combining a PV cell with a thermoelectric generator(TEG)to form hybrid PV-TEG systems,which simultaneously improve the energy conversion efficiency of the PV system by reducing the operating temperature of the PV modules and increasing the power output by utilizing the waste heat generated from the PV system to generate electricity via the TEGs.Based on a thorough examination of the literature,this study comprehensively reviews 14 maximum power point tracking(MPPT)algorithms currently applied to hybrid PV-TEG systems and classifies them into five major categories for further discussion,namely conventional,mathematics-based,metaheuristic,artificial intelligence,and other algorithms.This review aims to inspire advanced ideas and research on MPPT algorithms for hybrid PV-TEG systems.

Protection of Zero-Sequence Power Variation in Mountain Wind Farm Collector Lines Based on Multi-Mode Grounding

The arc-suppression coil(ASC)in parallel low resistance(LR)multi-mode grounding is adopted in the mountain wind farm to cope with the phenomenon that is misoperation or refusal of zero-sequence protection in LR grounding wind farm.If the fault disappears before LR is put into the system,it is judged as an instantaneous fault;while the fault does not disappear after LR is put into the system,it is judged as a permanent fault;the single-phase grounding fault(SLG)protection criterion based on zerosequence power variation is proposed to identify the instantaneous-permanent fault.Firstly,the distribution characteristic of zero-sequence voltage(ZSV)and zero-sequence current(ZSC)are analyzed after SLGfault occurs in multi-mode grounding.Then,according to the characteristics that zero-sequence power variation of non-fault collector line is small,while the zero-sequence power variation of fault collector line can reflect the active power component of fault resistance,the protection criterion based on zero-sequence power variation is constructed.The theoretical analysis and simulation results show that the protection criterion can distinguish the property of fault only by using the single terminal information,which has high reliability.

Quantitative description of infrared radiation characteristics of preflawed sandstone during fracturing process

Previous studies show that infrared radiation temperature(IRT)abnormalities are always accompanied by the crack development in rocks under external loads.In this context,experiments were conducted on preflawed sandstone to investigate the infrared radiation characteristics during failure process.Two indicators were defined herein,i.e.coefficient of variation of IRT(CVIRT)and skewness of IRT(SIRT).The regression analysis shows that the IRT probability distributions during loading process fit the Gaussian model.The variations in the CVIRT are characterized by four stages:primary stage,steady stage,accelerating stage and post-peak stage.Besides,the variations in the SIRT are divided into three stages:primary stage,steady stage and failure and post-peak stage.The precursor point for preflawed rock failure is identified based on the CVIRTetime curve,with average precursor point of 83%of the peak stress.Compared with other IRT indicators,the proposed two IRT indicators have higher sensitivity to IRT abnormalities during failure process.Furthermore,the connection between the IRT indicators and the rock fracturing was investigated to interpret the IRT indicator abnormalities.Based on the Verhulst inverse function,a new quantitative model was presented to describe the primary stage,steady stage and accelerating stage of the CVIRTetime curve.The results obtained in this study can provide early-warning information for rock failure prediction.

Time-Domain Protection for Transmission Lines Connected to Wind Power Plant based on Model Matching and Hausdorff Distance

The system impedance instability,high-order harmonics,and frequency offset are main fault characteristics of wind power system.Moreover,the measurement angle of faulty phase is affected by rotation speed frequency component,which causes traditional directional protections based on angle comparison between voltage and current to operate incorrectly.In this paper,a time-domain protection for connected to wind power plant based on model matching is proposed,which compares the calculated current and the measured current to identify internal faults and external faults.Under external faults,the calculated current and measured current waveform are quite similar because the protected transmission lines is equivalent to a lumped parameter model and the model itself is not damaged.However,the similarity of calculated current and measured current is quite low,due to destroyed integrity of model under internal faults.Additionally,Hausdorff distance is introduced to obtain the similarity of the calculated current and measured current.Since the proposed protection scheme is applied in time domain,it is independent from current frequency offsets of wind energy system,high-order harmonics,and system impedance variations.Comprehensive case studies are undertaken through Power Systems Computer Aided Design(PSCAD),while simulation results verify the accuracy and efficiency of the proposed approach in fault identification.

Adaptive Fractional-Order PID Control for VSC-HVDC Systems via Cooperative Beetle Antennae Search with Offshore Wind Integration

Since the voltage source converter based high voltage direct current(VSC-HVDC)systems owns the features of nonlinearity,strong coupling and multivariable,the classical proportional integral(PI)control is hard to obtain content control effect.Hence,a new perturbation observer based fractional-order PID(PoFoPID)control strategy is designed in this paper for(VSC-HVDC)systems with offshore wind integration,which can efficiently boost the robustness and control performance of entire system.Particularly,it employs a fractional-order PID(FoPID)fra-mework for the sake of compensating the perturbation estimate,which dramatically boost the dynamical responds of the closed-loop system,and the cooperative beetle antennae search(CBAS)algorithm is adopted to quickly and effi-ciently search its best control parameters.Besides,CBAS algorithm is able to efficiently escape a local optimum because of a suitable trade-off between global exploration and local exploitation can be realized.At last,comprehensive case studies are carried out,namely,active and reactive power tracking,5-cycle line-line-line-ground(LLLG)fault,and offshore wind farm integration.Simulation results validate superiorities and effectiveness of PoFoPID control in com-parison of that of PID control and feedback linearization sliding-mode control(FLSMC),respectively.

Classification and Summarization of Solar Irradiance and Power Forecasting Methods:A Thorough Review

Solar forecasting is of great importance for ensuring safe and stable operations of the power system with increased solar power integration,thus numerous models have been presented and reviewed to predict solar irradiance and power forecasting in the past decade.Nevertheless,few studies take into account the temporal and spatial resolutions along with specific characteristics of the models.Therefore,this paper aims to demonstrate a comprehensive and systematic review to further solve these problems.First,five classifications and seven pre-processing methods of solar forecasting data are systematically reviewed,which are significant in improving forecasting accuracy.Then,various methods utilized in solar irradiance and power forecasting are thoroughly summarized and discussed,in which 128 algorithms are elaborated in tables in the light of input variables,temporal resolution,spatial resolution,forecast variables,metrics,and characteristics for a more fair and comprehensive comparison.Moreover,they are categorized into four groups,namely,statistical,physical,hybrid,and others with relevant application conditions and features.Meanwhile,six categories,along with 30 evaluation criteria,are summarized to clarify the major purposes/applicability of the different methods.The prominent merit of this study is that a total of seven perspectives and trends for further research in solar forecasting are identified,which aim to help readers more effectively utilize these approaches for future in-depth research.

A Critical Review of Active Distribution Network Reconfiguration:Concepts,Development,and Perspectives

In recent years,the large-scale grid connection of various distributed power sources has made the planning and operation of distribution grids increasingly complex.Consequently,a large number of active distribution network reconfiguration techniques have emerged to reduce system losses,improve system safety,and enhance power quality via switching switches to change the system topology while ensuring the radial structure of the network.While scholars have previously reviewed these methods,they all have obvious shortcomings,such as a lack of systematic integration of methods,vague classification,lack of constructive suggestions for future study,etc.Therefore,this paper attempts to provide a comprehensive and profound review of 52 methods and applications of active distribution network reconfiguration through systematic method classification and enumeration.Specifically,these methods are classified into five categories,i.e.,traditional methods,mathematical methods,meta-heuristic algorithms,machine learning methods,and hybrid methods.A thorough comparison of the various methods is also scored in terms of their practicality,complexity,number of switching actions,performance improvement,advantages,and disadvantages.Finally,four summaries and four future research prospects are presented.In summary,this paper aims to provide an up-to-date and well-rounded manual for subsequent researchers and scholars engaged in related fields.

Key Optimization Issues for Renewable Energy Systems under Carbon-Peaking and Carbon Neutrality Targets:Current States and Perspectives

1 Introduction The United States,Japan,Canada,the European Union,and other developed countries and regions have all formulated climate strategies and pledged to achieve net-zero CO_(2) emissions by 2050.China,meanwhile,has announced through the“carbon-peaking and carbon neutrality targets”in September 2020 that it aims to achieve“peak carbon use”by 2030 and“carbon neutrality”by 2060[1].According to statistical data from the International Energy Agency(IEA),Fig.1 illustrates the carbon intensity of electricity generation in various regions in the Announced Pledge Scenario(APS)from 2010 to 2040[2].One can easily observe that each region aims to accomplish a sharp decrease in the carbon intensity of electricity generation after 2020.

Recent Advances in Fault Diagnosis Techniques for Photovoltaic Systems:a Critical Review

If a failure in the components of a photovoltaic(PV)system,such as PV module,controller,inverter,load,cable,etc.goes undetected and uncorrected,it can seriously affect the efficiency,safety,and reliability of the entire PV power plant.In addition,fires can occur if specific faults,such as arc,ground,and line-to-line faults remain unresolved.Therefore,PV system(PVS)fault diagnoses are crucial for PV power plant reliability,efficiency,and safety.Many fault diagnosis methods and techniques for PVS components have been developed.In addition,with the development of PV devices,more advanced and intelligent diagnostic technologies are continuously being researched and developed.However,a systematic and thorough analysis,summary,and conclusion are still urgently required.Thus,this paper introduces the types,causes,and impacts of PVS faults,and reviews and discusses the methods proposed in the literature for PVS fault diagnosis,and in particular,failures in PV arrays.Special attention is paid to the optimization direction of various fault diagnosis methods under different priorities,and their limitations,feasibility,complexity,and cost-effectiveness.Finally,challenges and suggestions are put forward for future research.

A critical survey of technologies of large offshore wind farm integration: summary, advances, and perspectives

Offshore wind farms(OWFs)have received widespread attention for their abundant unexploited wind energy poten-tial and convenient locations conditions.They are rapidly developing towards having large capacity and being located further away from shore.It is thus necessary to explore effective power transmission technologies to connect large OWFs to onshore grids.At present,three types of power transmission technologies have been proposed for large OWF integration.They are:high voltage alternating current(HVAC)transmission,high voltage direct current(HVDC)transmission,and low-frequency alternating current(LFAC)or fractional frequency alternating current transmission.This work undertakes a comprehensive review of grid connection technologies for large OWF integration.Compared with previous reviews,a more exhaustive summary is provided to elaborate HVAC,LFAC,and five HVDC topologies,consisting of line-commutated converter HVDC,voltage source converter HVDC,hybrid-HVDC,diode rectifier-based HVDC,and all DC transmission systems.The fault ride-through technologies of the grid connection schemes are also presented in detail to provide research references and guidelines for researchers.In addition,a comprehensive evalu-ation of the seven grid connection technologies for large OWFs is proposed based on eight specific indicators.Finally,eight conclusions and six perspectives are outlined for future research in integrating large OWFs.

Comprehensive summary of solid oxide fuel cell control:a state-of-the-art review

Hydrogen energy is a promising renewable resource for the sustainable development of society.As a key member of the fuel cell(FC)family,the solid oxide fuel cell(SOFC)has attracted a lot of attention because of characteristics such as having various sources as fuel and high energy conversion efficiency,and being pollution-free.SOFC is a highly coupled,nonlinear,and multivariable complex system,and thus it is very important to design an appropriate control strategy for an SOFC system to ensure its safe,reliable,and efficient operation.This paper undertakes a comprehen-sive review and detailed summary of the state-of-the-art control approaches of SOFC.These approaches are divided into eight categories of control:proportional integral differential(PID),adaptive(APC),robust,model predictive(MPC),fuzzy logic(FLC),fault-tolerant(FTC),intelligent and observer-based.The SOFC control approaches are carefully evalu-ated in terms of objective,design,application/scenario,robustness,complexity,and accuracy.Finally,five perspectives are proposed for future research directions.

Optimal PV array reconfiguration under partial shading condition through dynamic leader based collective intelligence

This paper applies the innovative idea of DLCI to PV array reconfiguration under various PSCs to capture the maxi-mum output power of a PV generation system.DLCI is a hybrid algorithm that integrates multiple meta-heuristic algo-rithms.Through the competition and cooperation of the search mechanisms of different metaheuristic algorithms,the local exploration and global development of the algorithm can be effectively improved to avoid power mismatch of the PV system caused by the algorithm falling into a local optimum.A series of discrete operations are performed on DLCI to solve the discrete optimization problem of PV array reconfiguration.Two structures(DLCI-I and DLCI-II)are designed to verify the effect of increasing the number of sub-optimizers on the optimized performance of DLCI by simulation based on 10 cases of PSCs.The simulation shows that the increase of the number of sub-optimizers only gives a relatively small improvement on the DLCI optimization performance.DLCI has a significant effect on the reduction in the number of power peaks caused by PSC.The PV array-based reconstruction system of DLCI-II is reduced by 4.05%,1.88%,1.68%,0.99%and 3.39%,when compared to the secondary optimization algorithms.

EMCO-based Optimal Layout Design of Hybrid Wind-wave Energy Converters Array

Marine renewable energy,combining wave energy converters(WECs)and floating wind turbines(FWTs)into hybrid wave-wind energy converters(HWWECs),garners significant global interest.HWWECs offer potential cost reductions,increased power generation,and enhanced system stability.The absorption power of high wind energy sites is primarily influenced by the complex hydrodynamic interactions among floating bodies,which are closely related to the location and wind-wave environment of high wind energy sites.To delve into the positive interactions among HWWECs,this paper proposes a HWWEC array optimization strategy based on the artificial ecosystem opti-mization-manta ray foraging optimization coordinated optimizer(EMCO).In EMCO,the decomposition operator of artificial ecosystem optimization(AEO)and the flipping-dipper foraging operator of manta ray foraging optimization coordinated(MRFO)cooperate dynamically to effectively balance local exploitation and global exploration.To validate the effectiveness of EMCO,experiments were conducted in scenarios with 3,5,8,and 20 HWWECs,and compared with five typical algorithms.Experimental results demonstrate the existence of multiple optimal solutions for HWWEC arrays.EMCO achieves maximum total absorp-tion power and exhibits good stability.Notably,EMCO en-hances the q-factor values of HWWECs across four scales:1.0478,1.0586,1.0612,and 0.9965,respectively.

Dynamic reconfiguration for TEG systems under heterogeneous temperature distribution via adaptive coordinated seeker

A thermoelectric generation(TEG)system has the weakness of relatively low thermoelectric conversion efficiency caused by heterogeneous temperature distribution(HgTD).Dynamic reconfiguration is an effective technique to improve its overall energy efficiency under HgTD.Nevertheless,numerous combinations of electrical switches make dynamic reconfiguration a complex combinatorial optimization problem.This paper aims to design a novel adaptive coordinated seeker(ACS)based on an optimal configuration strategy for large-scale TEG systems with series-paral-lel connected modules under HgTDs.To properly balance global exploration and local exploitation,ACS is based on'divide-and-conquer'parallel computing,which synthetically coordinates the local searching capability of tabu search(TS)and the global searching capability of a pelican optimization algorithm(POA)during iterations.In addition,an equivalent re-optimization strategy for a reconfiguration solution obtained by meta-heuristic algorithms(MhAs)is proposed to reduce redundant switching actions caused by the randomness of MhAs.Two case studies are carried out to assess the feasibility and superiority of AcS in comparison with the artificial bee colony algorithm,ant colony optimization,genetic algorithm,particle swarm optimization,simulated annealing algorithm,TS,and POA.Simulation results indicate that ACS can realize fast and stable dynamic reconfiguration of a TEG system under HgTDs.In addition,RTLAB platform-based hardware-in-the-loop experiments are carried out to further validate the hardware implemen-tation feasibility.