Along with the growing integration of renewable energy resources,the new power systems,which are dominated by inverter-based resources(IBRs),are facing critical challenges in both planning and operation stages.The con...Along with the growing integration of renewable energy resources,the new power systems,which are dominated by inverter-based resources(IBRs),are facing critical challenges in both planning and operation stages.The conventionally used system strength metric,short-circuit ratio(SCR),exhibits limitations in assessing connections of new IBRs due to their unique dynamic behaviour and control interactions.In this paper,the definition of system strength is reviewed.The underlying principles of conventional SCR and its variants are then discussed,with their constraints explained.To describe the system strength in a more comprehensive way,this paper further classifies system strength into three categories:quasi-static,small-signal,and large-signal.For each category,relevant metrics are introduced and their relative merits are discussed.Electromagnetic transient simulations are presented to illustrate key insights.展开更多
In this paper,a strength-constrained unit commitment(UC)model incorporating system strength constraints based on the weighted short-circuit ratio(WSCR)is proposed.This model facilitates the comprehensive assessment of...In this paper,a strength-constrained unit commitment(UC)model incorporating system strength constraints based on the weighted short-circuit ratio(WSCR)is proposed.This model facilitates the comprehensive assessment of area-wide system strength in power systems with high inverter-based resource(IBR)penetration,thereby contributing to the mitigation of weak grid issues.Unlike traditional models,this approach considers the interactions among multiple IBRs.The UC problem is initially formulated as a mixed-integer nonlinear programming(MINLP)model,reflecting WSCR and bus impedance matrix modification constraints.To enhance computational tractability,the model is transformed into a mixed-integer linear programming(MILP)form.The effectiveness of the proposed approach is validated through simulations on the IEEE 5-bus,IEEE 39-bus,and a modified Korean power system,demonstrating the ability of the proposed UC model enhancing system strength compared to the conventional methodologies.展开更多
Synchronous generators(SGs)are still making major contributions to the re-stabilization of a power system following voltage/frequency disturbances,attributed to their inherent capability of providing system strength a...Synchronous generators(SGs)are still making major contributions to the re-stabilization of a power system following voltage/frequency disturbances,attributed to their inherent capability of providing system strength and inertia.However,SGs powered by fossil fuels are operating to a lesser extent and scheduled for decommissioning in the National Electricity Market(NEM)of Australia due to the accelerating increase of low bidding priced asynchronous generation of wind and solar,which leads to the reduction and even in some cases,a shortage of system strength and inertia.This paper comprehensively reviews the requirements of system strength and inertia in the NEM from an operational security perspective.Australia is the first country that established the regulation rules of system strength and inertia to accommodate issues of an emerging high penetration level of non-synchronous renewable generation.展开更多
Inverter-based resources(IBRs),such as wind and photovoltaic generation,are characterized by low capacity and extensive distribution,which can exacerbate the weak properties of power systems.Precise identification of ...Inverter-based resources(IBRs),such as wind and photovoltaic generation,are characterized by low capacity and extensive distribution,which can exacerbate the weak properties of power systems.Precise identification of weak system status is essential for ensuring the security and economic efficiency of IBR integration.This paper proposes the index of the multiple renewable short-circuit ratio(MRSCR)and its critical value calculated by the voltage(CMRSCR)to provide a comprehensive assessment of power system strength in the presence of high IBR penetration,enhancing the accuracy and reliability of system strength evaluation.First,we introduce a single-infeed equivalent model of the power system integrating multiple IBRs.We examine the factors associated with system properties that are crucial in the strength assessment process.Subsequently,the MRSCR is derived from this analysis.The MRSCR describes the connection between system strength and voltage variation caused by power fluctuations.This implies that voltage variation caused by IBR power fluctuations is more pronounced under weak grid conditions.Following this,the CMRSCR is proposed to precisely evaluate the stability boundary.The disparity between MRSCR and CMRSCR is utilized to evaluate the stability margin of the power system.Unlike a fixed value,the CMRSCR exhibits higher sensitivity as the system approaches a critical state.These indexes have been implemented in the PSD power tools and power system analysis software package,facilitating engineering calculation and analysis of bulk power systems in China.Finally,simulation results validate the effectiveness of the proposed indexes and the research findings.展开更多
Increase in permeability of renewable energy sources(RESs)leads to the prominent problem of voltage stability in power system,so it is urgent to have a system strength evaluation method with both accuracy and practica...Increase in permeability of renewable energy sources(RESs)leads to the prominent problem of voltage stability in power system,so it is urgent to have a system strength evaluation method with both accuracy and practicability to control its access scale within a reasonable range.Therefore,a hybrid intelligence enhancement method is proposed by combining the advantages of mechanism method and data driven method.First,calculation of critical short circuit ratio(CSCR)is set as the direction of intelligent enhancement by taking the multiple renewable energy station short circuit ratio as the quantitative indicator.Then,the construction process of CSCR dataset is proposed,and a batch simulation program of samples is developed accordingly,which provides a data basis for subsequent research.Finally,a multi-task learning model based on progressive layered extraction is used to simultaneously predict CSCR of each RESs connection point,which significantly reduces evaluation error caused by weak links.Predictive performance and anti-noise performance of the proposed method are verified on the CEPRI-FS-102 bus system,which provides strong technical support for real-time monitoring of system strength.展开更多
One experiment was conducted, through tensile tests of Albazzia and Eucalypt roots culled from the fields. The other experiment was conducted, by testing anti-drawing strength of these root systems in the Albazzia and...One experiment was conducted, through tensile tests of Albazzia and Eucalypt roots culled from the fields. The other experiment was conducted, by testing anti-drawing strength of these root systems in the Albazzia and Eucalypt lands. These two experiments had an aim to give insights into the maximum tensile strength and anti-drawing strength of the root systems. Results indicated that the maximum tensile strength of root system is in an exponential relation with the diameter of root system while the maximum tensile strength is positively correlative with the diameter of root system. Anti-drawing force of root system together with root diameter, length, and soil bulk density are folded into a regression equation in an attempt to figure out the static friction coefficient between root system and its ambient soil.展开更多
Coronary artery calcium data and reporting system(CAC-DRS)is a recently introduced standardized reporting system for calcium scoring on computed tomography.CAC-DRS provides four risk categories(0,1,2 and 3)along with ...Coronary artery calcium data and reporting system(CAC-DRS)is a recently introduced standardized reporting system for calcium scoring on computed tomography.CAC-DRS provides four risk categories(0,1,2 and 3)along with treatment recommendations for each category.As with any other new reporting platform,CAC-DRS has both advantages and disadvantages.Improved communication,better clarity of details,organized management recommendations and utility in future research and education are the major strengths of CAC-DRS.It has many limitations such as questionable need for a new system,few missing components,use of a less accurate visual method and treatment suggestions based on expert opinion instead of clinical trials.In this contemporary review,we discuss the new reporting system CAC-DRS,its application,strengths and limitations and conclude with some remarks for the future.展开更多
Efficient and accurate strength analysis of bolted connections is essential in analyzing the integral thermal protection system（ITPS） of hypersonic vehicles, since the system bears severe loads and structural failur...Efficient and accurate strength analysis of bolted connections is essential in analyzing the integral thermal protection system（ITPS） of hypersonic vehicles, since the system bears severe loads and structural failures usually occur at the connections. Investigations of composite mechanical properties used in ITPS are still in progress as the architecture of the composites is complex. A new method is proposed in this paper for strength analysis of bolted connections by investigating the elastic behavior and failure strength of three-dimensional C/C orthogonal composites used in ITPS. In this method a multi-scale finite element method incorporating the global–local method is established to ensure high efficiency in macro-scale and precision in meso-scale in analysis.Simulation results reveal that predictions of material properties show reasonable accuracy compared with test results. And the multi-scale method can analyze the strength of connections efficiently and accurately.展开更多
A novel flocking control approach is proposed for multi-agent systems by integrating the variables of velocities, motion directions, and positions of agents. A received signal strength indicator （RSSI） is applied as...A novel flocking control approach is proposed for multi-agent systems by integrating the variables of velocities, motion directions, and positions of agents. A received signal strength indicator （RSSI） is applied as a variable to estimate the inter-distance between agents. A key parameter that contains the local information of agents is defined, and a multi-variable controller is proposed based on the parameter. For the position control of agents, the RSSI is introduced to substitute the distance as a control variable in the systems. The advantages of RSSI include that the relative distance between every two agents can be adjusted through the communication quality under different environments, and it can shun the shortage of the limit of sensors. Simulation studies demonstrate the effectiveness of the proposed control approach.展开更多
It is known that structural stiffness and strength distributions have an important role in the seismic response of buildings. The effect of using different code-specified lateral load patterns on the seismic performan...It is known that structural stiffness and strength distributions have an important role in the seismic response of buildings. The effect of using different code-specified lateral load patterns on the seismic performance of fixed-base buildings has been investigated by researchers during the past two decades. However, no investigation has yet been carried out for the case of soil-structure systems. In the present study, through intensive parametric analyses of 21,600 linear and nonlinear MDOF systems and considering five different shear strength and stiffness distribution patterns, including three code-specified patterns as well as uniform and concentric patterns subjected to a group of earthquakes recorded on alluvium and soft soils, the effect of structural characteristics distribution on the strength demand and ductility reduction factor of MDOF fixed-base and soil-structure systems are parametrically investigated. The results of this study show that depending on the level of inelasticity, soil flexibility and number of degrees-of-freedoms (DOFs), structural characteristics distribution can significantly affect the strength demand and ductility reduction factor of MDOF systems. It is also found that at high levels of inelasticity, the ductility reduction factor of low-rise MDOF soil-structure systems could be significantly less than that of fixed-base structures and the reduction is less pronounced as the number of stories increases.展开更多
文摘Along with the growing integration of renewable energy resources,the new power systems,which are dominated by inverter-based resources(IBRs),are facing critical challenges in both planning and operation stages.The conventionally used system strength metric,short-circuit ratio(SCR),exhibits limitations in assessing connections of new IBRs due to their unique dynamic behaviour and control interactions.In this paper,the definition of system strength is reviewed.The underlying principles of conventional SCR and its variants are then discussed,with their constraints explained.To describe the system strength in a more comprehensive way,this paper further classifies system strength into three categories:quasi-static,small-signal,and large-signal.For each category,relevant metrics are introduced and their relative merits are discussed.Electromagnetic transient simulations are presented to illustrate key insights.
基金partially supported by Korea Electrotechnology Research Institute(KERI)Primary research program through the National Research Council of Science&Technology(NST)funded by the Ministry of Science and ICT(MSIT)(No.25A01038)partially supported by the National Research Foundation of Korea(NRF)grant funded by the Korea government(MSIT)(No.RS-2024-00218377).
文摘In this paper,a strength-constrained unit commitment(UC)model incorporating system strength constraints based on the weighted short-circuit ratio(WSCR)is proposed.This model facilitates the comprehensive assessment of area-wide system strength in power systems with high inverter-based resource(IBR)penetration,thereby contributing to the mitigation of weak grid issues.Unlike traditional models,this approach considers the interactions among multiple IBRs.The UC problem is initially formulated as a mixed-integer nonlinear programming(MINLP)model,reflecting WSCR and bus impedance matrix modification constraints.To enhance computational tractability,the model is transformed into a mixed-integer linear programming(MILP)form.The effectiveness of the proposed approach is validated through simulations on the IEEE 5-bus,IEEE 39-bus,and a modified Korean power system,demonstrating the ability of the proposed UC model enhancing system strength compared to the conventional methodologies.
文摘Synchronous generators(SGs)are still making major contributions to the re-stabilization of a power system following voltage/frequency disturbances,attributed to their inherent capability of providing system strength and inertia.However,SGs powered by fossil fuels are operating to a lesser extent and scheduled for decommissioning in the National Electricity Market(NEM)of Australia due to the accelerating increase of low bidding priced asynchronous generation of wind and solar,which leads to the reduction and even in some cases,a shortage of system strength and inertia.This paper comprehensively reviews the requirements of system strength and inertia in the NEM from an operational security perspective.Australia is the first country that established the regulation rules of system strength and inertia to accommodate issues of an emerging high penetration level of non-synchronous renewable generation.
基金supported by the National Key R&D Program of China(2021YFB2400800).
文摘Inverter-based resources(IBRs),such as wind and photovoltaic generation,are characterized by low capacity and extensive distribution,which can exacerbate the weak properties of power systems.Precise identification of weak system status is essential for ensuring the security and economic efficiency of IBR integration.This paper proposes the index of the multiple renewable short-circuit ratio(MRSCR)and its critical value calculated by the voltage(CMRSCR)to provide a comprehensive assessment of power system strength in the presence of high IBR penetration,enhancing the accuracy and reliability of system strength evaluation.First,we introduce a single-infeed equivalent model of the power system integrating multiple IBRs.We examine the factors associated with system properties that are crucial in the strength assessment process.Subsequently,the MRSCR is derived from this analysis.The MRSCR describes the connection between system strength and voltage variation caused by power fluctuations.This implies that voltage variation caused by IBR power fluctuations is more pronounced under weak grid conditions.Following this,the CMRSCR is proposed to precisely evaluate the stability boundary.The disparity between MRSCR and CMRSCR is utilized to evaluate the stability margin of the power system.Unlike a fixed value,the CMRSCR exhibits higher sensitivity as the system approaches a critical state.These indexes have been implemented in the PSD power tools and power system analysis software package,facilitating engineering calculation and analysis of bulk power systems in China.Finally,simulation results validate the effectiveness of the proposed indexes and the research findings.
文摘Increase in permeability of renewable energy sources(RESs)leads to the prominent problem of voltage stability in power system,so it is urgent to have a system strength evaluation method with both accuracy and practicability to control its access scale within a reasonable range.Therefore,a hybrid intelligence enhancement method is proposed by combining the advantages of mechanism method and data driven method.First,calculation of critical short circuit ratio(CSCR)is set as the direction of intelligent enhancement by taking the multiple renewable energy station short circuit ratio as the quantitative indicator.Then,the construction process of CSCR dataset is proposed,and a batch simulation program of samples is developed accordingly,which provides a data basis for subsequent research.Finally,a multi-task learning model based on progressive layered extraction is used to simultaneously predict CSCR of each RESs connection point,which significantly reduces evaluation error caused by weak links.Predictive performance and anti-noise performance of the proposed method are verified on the CEPRI-FS-102 bus system,which provides strong technical support for real-time monitoring of system strength.
文摘One experiment was conducted, through tensile tests of Albazzia and Eucalypt roots culled from the fields. The other experiment was conducted, by testing anti-drawing strength of these root systems in the Albazzia and Eucalypt lands. These two experiments had an aim to give insights into the maximum tensile strength and anti-drawing strength of the root systems. Results indicated that the maximum tensile strength of root system is in an exponential relation with the diameter of root system while the maximum tensile strength is positively correlative with the diameter of root system. Anti-drawing force of root system together with root diameter, length, and soil bulk density are folded into a regression equation in an attempt to figure out the static friction coefficient between root system and its ambient soil.
文摘Coronary artery calcium data and reporting system(CAC-DRS)is a recently introduced standardized reporting system for calcium scoring on computed tomography.CAC-DRS provides four risk categories(0,1,2 and 3)along with treatment recommendations for each category.As with any other new reporting platform,CAC-DRS has both advantages and disadvantages.Improved communication,better clarity of details,organized management recommendations and utility in future research and education are the major strengths of CAC-DRS.It has many limitations such as questionable need for a new system,few missing components,use of a less accurate visual method and treatment suggestions based on expert opinion instead of clinical trials.In this contemporary review,we discuss the new reporting system CAC-DRS,its application,strengths and limitations and conclude with some remarks for the future.
基金co-supported by the Priority Academic Program Development of Jiangsu Higher Education Institutionsthe National Natural Science Foundation of China (No. 11302105)
文摘Efficient and accurate strength analysis of bolted connections is essential in analyzing the integral thermal protection system（ITPS） of hypersonic vehicles, since the system bears severe loads and structural failures usually occur at the connections. Investigations of composite mechanical properties used in ITPS are still in progress as the architecture of the composites is complex. A new method is proposed in this paper for strength analysis of bolted connections by investigating the elastic behavior and failure strength of three-dimensional C/C orthogonal composites used in ITPS. In this method a multi-scale finite element method incorporating the global–local method is established to ensure high efficiency in macro-scale and precision in meso-scale in analysis.Simulation results reveal that predictions of material properties show reasonable accuracy compared with test results. And the multi-scale method can analyze the strength of connections efficiently and accurately.
基金supported by the National Basic Research Program of China (973Program) under Grant No. 2010CB731800the National Natural Science Foundation of China under Grant No. 60934003 and 61074065the Key Project for Natural Science Research of Hebei Education Departmentunder Grant No. ZD200908
文摘A novel flocking control approach is proposed for multi-agent systems by integrating the variables of velocities, motion directions, and positions of agents. A received signal strength indicator （RSSI） is applied as a variable to estimate the inter-distance between agents. A key parameter that contains the local information of agents is defined, and a multi-variable controller is proposed based on the parameter. For the position control of agents, the RSSI is introduced to substitute the distance as a control variable in the systems. The advantages of RSSI include that the relative distance between every two agents can be adjusted through the communication quality under different environments, and it can shun the shortage of the limit of sensors. Simulation studies demonstrate the effectiveness of the proposed control approach.
文摘It is known that structural stiffness and strength distributions have an important role in the seismic response of buildings. The effect of using different code-specified lateral load patterns on the seismic performance of fixed-base buildings has been investigated by researchers during the past two decades. However, no investigation has yet been carried out for the case of soil-structure systems. In the present study, through intensive parametric analyses of 21,600 linear and nonlinear MDOF systems and considering five different shear strength and stiffness distribution patterns, including three code-specified patterns as well as uniform and concentric patterns subjected to a group of earthquakes recorded on alluvium and soft soils, the effect of structural characteristics distribution on the strength demand and ductility reduction factor of MDOF fixed-base and soil-structure systems are parametrically investigated. The results of this study show that depending on the level of inelasticity, soil flexibility and number of degrees-of-freedoms (DOFs), structural characteristics distribution can significantly affect the strength demand and ductility reduction factor of MDOF systems. It is also found that at high levels of inelasticity, the ductility reduction factor of low-rise MDOF soil-structure systems could be significantly less than that of fixed-base structures and the reduction is less pronounced as the number of stories increases.
