In recent years,the large-scale integration of re-newable energy sources represented by wind power and the widespread application of power electronic devices in power systems have led to the emergence of multi-frequen...In recent years,the large-scale integration of re-newable energy sources represented by wind power and the widespread application of power electronic devices in power systems have led to the emergence of multi-frequency oscillation problems covering multiple frequency segments,which seriously threaten system stability and restrict the accommodation of renewable energy.The oscillation problems related to renewable energy integration have become one of the most popular topics in the field of wind power integration and power system stability research.It has received extensive attention from both academia and industries with many promising research results achieved to date.This paper first analyzes several typical multi-frequency oscillation events caused by large-scale wind power integration in domestic and foreign projects,then studies the multi-frequency oscillation problems,including wind turbine’s shafting torsional oscillation,sub/super-synchronous oscillation and high frequency resonance.The state of the art is systematically summarized from the aspects of oscillation mechanism,analysis methods and mitigation measures,and the future research directions are explored.展开更多
The coordinated control of multiple-sources including wind,photovoltaic(PV)and storage brings new challenges to traditional dispatch and control technologies.This paper firstly introduces a framework of wind,PV and st...The coordinated control of multiple-sources including wind,photovoltaic(PV)and storage brings new challenges to traditional dispatch and control technologies.This paper firstly introduces a framework of wind,PV and storage co-generation monitoring system.Then,key technologies of co-generation monitoring system including day-ahead optimal dispatching,active power coordinated control and reactive power and voltage control are proposed.The framework and the techniques described in this paper have been applied in the National Wind,Photovoltaic,Storage and Transmission Demonstration Project of China,and their validity have been tested and verified.展开更多
The sharp increase of the amount of Internet Chinese text data has significantly prolonged the processing time of classification on these data.In order to solve this problem,this paper proposes and implements a parall...The sharp increase of the amount of Internet Chinese text data has significantly prolonged the processing time of classification on these data.In order to solve this problem,this paper proposes and implements a parallel naive Bayes algorithm(PNBA)for Chinese text classification based on Spark,a parallel memory computing platform for big data.This algorithm has implemented parallel operation throughout the entire training and prediction process of naive Bayes classifier mainly by adopting the programming model of resilient distributed datasets(RDD).For comparison,a PNBA based on Hadoop is also implemented.The test results show that in the same computing environment and for the same text sets,the Spark PNBA is obviously superior to the Hadoop PNBA in terms of key indicators such as speedup ratio and scalability.Therefore,Spark-based parallel algorithms can better meet the requirement of large-scale Chinese text data mining.展开更多
This paper aims at putting forward viewpoints regarding the use of stability technology to prevent and control cascading outages by examining recent blackout events.Based on the inquiry reports of the 2011 SouthwestAm...This paper aims at putting forward viewpoints regarding the use of stability technology to prevent and control cascading outages by examining recent blackout events.Based on the inquiry reports of the 2011 SouthwestAmerica blackout and the 2012 India power blackouts,event evolution features are first summarized from a stability perspective.Then a comparative analysis is conducted so as to propose suggestions of effective measures,either preventive or emergency,which could have avoided the blackouts.It is shown that applications of several mature technologies can create opportunities of preventing or interrupting the cascading development.These include offline dynamic simulation,online stability analysis and preventive control,real-time situational awareness and automatic emergency control.Further R&D directions are given to address the challenges of modern power systems as well.They cover system fault identification criterion of protection and control devices,verification of adaptability of control effect to system operating conditions,real-time operational management of emergency control measures and improvement of simulation accuracy.展开更多
Enterocutaneous fistulas(ECFs) are great challenges during the open abdomen. The loss of digestive juice, water-electrolyte imbalance and malnutrition are intractable issues during management of ECF. Techniques such a...Enterocutaneous fistulas(ECFs) are great challenges during the open abdomen. The loss of digestive juice, water-electrolyte imbalance and malnutrition are intractable issues during management of ECF. Techniques such as "fistula patch" and vacuumassisted closure therapy have been applied to prevent contamination of open abdominal wounds by intestinal fistula drainage. However, failures are encountered due to high-output fistula and anatomical complexity. Here, we report 3 D-printed patient-personalized fistula stent for ECF treatment based on 3 D reconstruction of the fistula image. Subsequent follow-up demonstrated that this stent was well-implanted and effective to reduce the volume of enteric fistula effluent.展开更多
Based on analysis of construction and operation of micro integrated energy systems(MIES), this paper presents economic optimization for their configuration and sizing. After presenting typical models for MIES, a resid...Based on analysis of construction and operation of micro integrated energy systems(MIES), this paper presents economic optimization for their configuration and sizing. After presenting typical models for MIES, a residential community MIES is developed by analyzing residential direct energy consumption within a general design procedure. Integrating with available current technologies and local resources, the systematic design considers a prime mover, fed by natural gas, with wind power, photovoltaic generation, and two storage devices serving thermal energy and power to satisfy cooling, heating and electricity demands. Control strategies for MIES also arepresented in this study. Multi-objective formulas are obtained by analyzing annual cost and dumped renewable energy to achieve optimal coordination of energy supply and demand. According to historical load data and the probability distribution of distributed generation output,clustering methods based on K-means and discretization methods are employed to obtain typical scenarios representative of uncertainties. The modified non-dominated sorting genetic algorithm is applied to find the Pareto frontier of the constructed multi-objective formulas. In addition, aiming to explore the Pareto frontier, the dumped energy cost ratio is defined to check the energy balance in different MIES designs and provide decision support for the investors. Finally, simulations and comparision show the appropriateness of the developed model and the applicability of the adopted optimization algorithm.展开更多
With the construction of smart grid,lots of renewable energy resources such as wind and solar are deployed in power system.It might make the power system load varied complex than before which will bring difficulties i...With the construction of smart grid,lots of renewable energy resources such as wind and solar are deployed in power system.It might make the power system load varied complex than before which will bring difficulties in short-term load forecasting area.To overcome this issue,this paper proposes a new short-term load forecasting framework based on big data technologies.First,a cluster analysis is performed to classify daily load patterns for individual loads using smart meter data.Next,an association analysis is used to determine critical influential factors.This is followed by the application of a decision tree to establish classification rules.Then,appropriate forecasting models are chosen for different load patterns.Finally,the forecasted total system load is obtained through an aggregation of an individual load’s forecasting results.Case studies using real load data show that the proposed new framework can guarantee the accuracy of short-term load forecasting within required limits.展开更多
The integrated energy system(IES)is an important energy supply method for mitigating the energy crisis.A station-and-network–coordinated planning method for the IES,which considers the integrated demand responses(IDR...The integrated energy system(IES)is an important energy supply method for mitigating the energy crisis.A station-and-network–coordinated planning method for the IES,which considers the integrated demand responses(IDRs)of flexible loads,electric vehicles,and energy storage is proposed in this work.First,based on load substitution at the user side,an energy-station model considering the IDR is established.Then,based on the characteristics of the energy network,a collaborative planning model is established for the energy station and energy network of the IES,considering the comprehensive system investment,operation and maintenance,and clean energy shortage penalty costs,to minimize the total cost.This can help optimize the locations of the power lines and natural gas pipelines and the capacities of the equipment in an energy station.Finally,simulations are performed to demonstrate that the proposed planning method can help delay or reduce the construction of new lines and energy-station equipment,thereby reducing the investment required and improving the planning economics of the IES.展开更多
Cyber threats are serious concerns for power systems.For example,hackers may attack power control systems via interconnected enterprise networks.This paper proposes a risk assessment framework to enhance the resilienc...Cyber threats are serious concerns for power systems.For example,hackers may attack power control systems via interconnected enterprise networks.This paper proposes a risk assessment framework to enhance the resilience of power systems against cyber attacks.The duality element relative fuzzy evaluation method is employed to evaluate identified security vulnerabilities within cyber systems of power systems quantitatively.The attack graph is used to identify possible intrusion scenarios that exploit multiple vulnerabilities.An intrusion response system(IRS)is developed to monitor the impact of intrusion scenarios on power system dynamics in real time.IRS calculates the conditional Lyapunov exponents(CLEs)on line based on the phasor measurement unit data.Power system stability is predicted through the values of CLEs.Control actions based on CLEs will be suggested if power system instability is likely to happen.A generic wind farm control system is used for case study.The effectiveness of IRS is illustrated with the IEEE 39 bus system model.展开更多
Renewable energy based distributed generation(DG) has the potential to reach high penetration levels in the residential region. However, its integration at the demand side will cause rapid power fluctuations of the ti...Renewable energy based distributed generation(DG) has the potential to reach high penetration levels in the residential region. However, its integration at the demand side will cause rapid power fluctuations of the tieline in the residential region. The traditional generators are generally difficult to manage rapid power fluctuations due to their insufficient efficiency requirements and low responding speed. With an effective control strategy, the demand side resources(DSRs) including DGs, electric vehicles and thermostatically-controlled loads at thedemand side, are able to serve as the energy storage system to smooth the load fluctuations. However, it is a challenge to properly model different types of DSRs. To solve this problem, a unified state model is first developed to describe the characteristics of different DSRs. Then a load curve smoothing strategy is proposed to offset the load fluctuations of the tie-line of the residential region, where a control matrix deduced from the unified state model is introduced to manage the power outputs of different DSRs,considering the response order and the comfort levels.Finally, a residential region with households is used to validate the load curve smoothing strategy based on the unified state model, and the results show that the power fluctuation rate of the tie-line is significantly decreased.Meanwhile, comparative study results are shown to demonstrate the advantages of the unified state model based load curve smoothing strategy.展开更多
In the light of user-side energy power control requirements, a power control strategy for a household-level EPR based on HES droop control is proposed, focusing on the on-grid, off-grid and seamless switching process....In the light of user-side energy power control requirements, a power control strategy for a household-level EPR based on HES droop control is proposed, focusing on the on-grid, off-grid and seamless switching process. The system operating states are divided based on the DC bus voltage information with one converter used as a slack terminal to stabilize the DC bus voltage and the other converters as power terminals. In the on-grid mode, the GCC and the HES are used as the main control unit to achieve on-grid stable operation, whereas in the off-grid mode, the PV, HES and LC are used as the main control unit at different voltages to achieve stable operation of the island network. Finally, a DC MG system based on a household-level EPR is developed using the PSCAD / EMTDC simulation platform and the results show that the control strategy can effectively adjust the output of each subunit and maintain the stability of the DC bus voltage.展开更多
Due to the tight coupling between the cyber and physical sides of a cyber-physical power system(CPPS),the safe and reliable operation of CPPSs is being increasingly impacted by cyber security.This situation poses a ch...Due to the tight coupling between the cyber and physical sides of a cyber-physical power system(CPPS),the safe and reliable operation of CPPSs is being increasingly impacted by cyber security.This situation poses a challenge to traditional security defense systems,which considers the threat from only one side,i.e.,cyber or physical.To cope with cyberattacks,this paper reaches beyond the traditional one-side security defense systems and proposes the concept of cyber-physical coordinated situation awareness and active defense to improve the ability of CPPSs.An example of a regional frequency control system is used to show the validness and potential of this concept.Then,the research framework is presented for studying and implementing this concept.Finally,key technologies for cyber-physical coordinated situation awareness and active defense against cyber-attacks are introduced.展开更多
Hydrogen production from renewable energy sources(RESs)is one of the effective ways to achieve carbon peak and carbon neutralization.In order to ensure the efficient,reliable and stable operation of the DC microgrid(M...Hydrogen production from renewable energy sources(RESs)is one of the effective ways to achieve carbon peak and carbon neutralization.In order to ensure the efficient,reliable and stable operation of the DC microgrid(MG)with an electric-hydrogen hybrid energy storage system(ESS),the operational constraints and static dynamic characteristics of a hydrogen energy storage system(HESS)needs to be fully considered.First,different hydrogen production systems,using water electrolysis are compared,and the modeling method of the electrolyzer is summarized.The operational control architecture of the DC MG with electric-hydrogen is analyzed.Combined with the working characteristics of the alkaline electrolyzer,the influence of hydrogen energy storage access on the operational mode of the DC MG is analyzed.The operational control strategies of the DC MG with electric-hydrogen hybrid ESS are classified and analyzed from four different aspects:static and dynamic characteristics of the hydrogen energy storage system,power distribution of the electric-hydrogen hybrid ESS and the efficiency optimization of hydrogen energy storage.Finally,the advantages of a modular hydrogen production system(HPS)are described,and the technical problems and research directions in the future are discussed.展开更多
Greenhouse gas emission regulation and renewable energy promotion policies have been implemented in many countries.Yet these two kinds of regulation policies have complex interactions between each other,and can either...Greenhouse gas emission regulation and renewable energy promotion policies have been implemented in many countries.Yet these two kinds of regulation policies have complex interactions between each other,and can either enhance or reduce the overall emission reduction efficiency.If not well tuned,these regulation policies may deviate from their original intention and lead to unnecessary social cost.Hence,the policy effectiveness,cost effectiveness,and dynamic efficiency of different policy mixtures between emission trading and renewable energy subsidy are studied based on a novel dynamic simulation platform of power economy and power system.Simulation results show that these two kinds of regulation policy can coexist,but a good coordination between the emission trading and the renewable energy subsidy can achieve better emission reduction outcomes.展开更多
Economic and environmental load dispatch aims to determine the amount of electricity generated from power plants to meet load demand while minimizing fossil fuel costs and air pollution emissions subject to operationa...Economic and environmental load dispatch aims to determine the amount of electricity generated from power plants to meet load demand while minimizing fossil fuel costs and air pollution emissions subject to operational and licensing requirements.These two scheduling problems are commonly formulated with non-smooth cost functions respectively considering various effects and constraints,such as the valve point effect,power balance and ramprate limits.The expected increase in plug-in electric vehicles is likely to see a significant impact on the power system due to high charging power consumption and significant uncertainty in charging times.In this paper,multiple electric vehicle charging profiles are comparatively integrated into a 24-hour load demand in an economic and environment dispatch model.Self-learning teaching-learning based optimization(TLBO)is employed to solve the non-convex non-linear dispatch problems.Numerical results onwell-known benchmark functions,as well as test systems with different scales of generation units show the significance of the new scheduling method.展开更多
For lack of deep research on model, system structure and top-level design, the integrated system concept of energy, information and transportation networks fails to provide effective guidance for transferring the theo...For lack of deep research on model, system structure and top-level design, the integrated system concept of energy, information and transportation networks fails to provide effective guidance for transferring the theory to practice. In this paper, with dispatching of energy flow and information flow as a focus, clean energy of wind power and solar power as carrier, battery charging & swapping station as medium and all kinds of transportation flows as entity, a five-in-one threenetwork integrated system model is built by full use of technologies of Internet of Vehicles(IOV) and Internet of things(IOT) to promote the innovative concept of three-network integration into practice, and provide a reference for future researches.展开更多
Stochastic noises have a great adverse effect on the prediction accuracy of electric power load.Modeling online and filtering real-time can effectively improve measurement accuracy.Firstly,pretreating and inspecting s...Stochastic noises have a great adverse effect on the prediction accuracy of electric power load.Modeling online and filtering real-time can effectively improve measurement accuracy.Firstly,pretreating and inspecting statistically the electric power load data is essential to characterize the stochastic noise of electric power load.Then,set order for the time series model by Akaike information criterion(AIC)rule and acquire model coefficients to establish ARMA(2,1)model.Next,test the applicability of the established model.Finally,Kalman filter is adopted to process the electric power load data.Simulation results of total variance demonstrate that stochastic noise is obviously decreased after Kalman filtering based on ARMA(2,1)model.Besides,variance is reduced by two orders,and every coefficient of stochastic noise is reduced by one order.The filter method based on time series model does reduce stochastic noise of electric power load,and increase measurement accuracy.展开更多
Tampering,forgery and theft of the measurement and control messages in a smart grid could cause one breakdown in the power system.However,no security measures are employed for communications in intelligent substations...Tampering,forgery and theft of the measurement and control messages in a smart grid could cause one breakdown in the power system.However,no security measures are employed for communications in intelligent substations.Communication services in an intelligent substation have high demands for real-time performance,which must be considered when deploying security measures.This paper studies the security requirements of communication services in intelligent substations,analyzes the security capabilities and shortages of IEC 62351,and proposes a novel security scheme for intelligent substation communications.This security scheme covers internal and telecontrol communications,in which the real-time performance of each security measure is considered.In this scheme,certificateless public key cryptography(CLPKC)is used to avoid the latency of certificate exchange in certificate-based cryptosystem and the problem of key escrow in identity-based cryptosystem;the security measures of generic object-oriented substation event,sampled measure value and manufacturing message specification in IEC 62351 are improved to meet the real-time requirements of the messages as well as to provide new security features to resist repudiation and replay attacks;and the security at transport layer is modified to fit CLPKC,which implements mutual authentication by exchanging signatures.Furthermore,a deployment of CLPKC in an intelligent substation is presented.We also evaluate the security properties of the scheme and analyze the end-to-end delays of secured services by combining theoretical calculation and simulation in this paper.The results indicate that the proposed scheme meets the requirements of security and real-time performance of communications in intelligent substations.展开更多
BACKGROUND Open abdomen(OA) has been generally accepted for its magnificent superiority and effectiveness in patients with severe trauma, severe intra-abdominal infection, and abdominal compartment syndrome. In the me...BACKGROUND Open abdomen(OA) has been generally accepted for its magnificent superiority and effectiveness in patients with severe trauma, severe intra-abdominal infection, and abdominal compartment syndrome. In the meantime, OA calls for a mass of nursing and the subsequent enteroatomospheric fistula(EAF), which is one of the most common complications of OA therapy, remains a thorny challenge.CASE SUMMARY Our team applied thermoplastic polyurethane as a befitting material for producing a 3 D-printed "fistula stent" in the management of an EAF patient,who was initially admitted to local hospital because of abdominal pain and distension and diagnosed with bowel obstruction. After a series of operations and OA therapy, the patient developed an EAF.CONCLUSION Application of this novel "fistula stent" resulted in a drastic reduction in the amount of lost enteric effluent and greatly accelerated rehabilitation processes.展开更多
Synchronous condensers(SCs)are generally used at the receiving-end stations of ultra-high-voltage direct current(UHVDC)transmission systems due to their strong reactive power support and flexible regulation of reactiv...Synchronous condensers(SCs)are generally used at the receiving-end stations of ultra-high-voltage direct current(UHVDC)transmission systems due to their strong reactive power support and flexible regulation of reactive power according to the interconnected grids operating conditions.In this paper,different starting control schemes of a SC integrated power grid are investigated providing four main contributions:1)The principle of reactive power support of the SC on the interconnected power grid is analytically studied,providing the establishment of mathematical models.2)Four different starting control schemes are developed for the initialization and SC integration,i.e.in Scheme 1,a preset initial falling speed is directly utilized without initialization;in Scheme 2,a black start sequential control approach with a static frequency converter(SFC)is proposed;in Scheme 3,PI/PD/PID controllers are respectively applied for the excitation device at the speed-falling stage;in Scheme 4,a pre-insertion approach of an energy absorption component with R/L/RL is utilized to suppress the surges at the SC integration instant.3)The dynamic behaviors of four different starting schemes at specific operating stages are evaluated.4)The success rate of SC integration is analyzed to evaluate starting control performance.Performance of the SC interconnected system with four different starting control schemes is evaluated in the timedomain simulation environment PSCAD/EMTDC^(TM).The results prove the superiority of the proposed starting control approach in Scheme 4.展开更多
基金This work was supported by the National Natural Science Foundation of China(No.51577174).
文摘In recent years,the large-scale integration of re-newable energy sources represented by wind power and the widespread application of power electronic devices in power systems have led to the emergence of multi-frequency oscillation problems covering multiple frequency segments,which seriously threaten system stability and restrict the accommodation of renewable energy.The oscillation problems related to renewable energy integration have become one of the most popular topics in the field of wind power integration and power system stability research.It has received extensive attention from both academia and industries with many promising research results achieved to date.This paper first analyzes several typical multi-frequency oscillation events caused by large-scale wind power integration in domestic and foreign projects,then studies the multi-frequency oscillation problems,including wind turbine’s shafting torsional oscillation,sub/super-synchronous oscillation and high frequency resonance.The state of the art is systematically summarized from the aspects of oscillation mechanism,analysis methods and mitigation measures,and the future research directions are explored.
文摘The coordinated control of multiple-sources including wind,photovoltaic(PV)and storage brings new challenges to traditional dispatch and control technologies.This paper firstly introduces a framework of wind,PV and storage co-generation monitoring system.Then,key technologies of co-generation monitoring system including day-ahead optimal dispatching,active power coordinated control and reactive power and voltage control are proposed.The framework and the techniques described in this paper have been applied in the National Wind,Photovoltaic,Storage and Transmission Demonstration Project of China,and their validity have been tested and verified.
基金Project(KC18071)supported by the Application Foundation Research Program of Xuzhou,ChinaProjects(2017YFC0804401,2017YFC0804409)supported by the National Key R&D Program of China
文摘The sharp increase of the amount of Internet Chinese text data has significantly prolonged the processing time of classification on these data.In order to solve this problem,this paper proposes and implements a parallel naive Bayes algorithm(PNBA)for Chinese text classification based on Spark,a parallel memory computing platform for big data.This algorithm has implemented parallel operation throughout the entire training and prediction process of naive Bayes classifier mainly by adopting the programming model of resilient distributed datasets(RDD).For comparison,a PNBA based on Hadoop is also implemented.The test results show that in the same computing environment and for the same text sets,the Spark PNBA is obviously superior to the Hadoop PNBA in terms of key indicators such as speedup ratio and scalability.Therefore,Spark-based parallel algorithms can better meet the requirement of large-scale Chinese text data mining.
基金This work is supported by State Grid Corporation of China(No.SGCC-MPLG003-2012).
文摘This paper aims at putting forward viewpoints regarding the use of stability technology to prevent and control cascading outages by examining recent blackout events.Based on the inquiry reports of the 2011 SouthwestAmerica blackout and the 2012 India power blackouts,event evolution features are first summarized from a stability perspective.Then a comparative analysis is conducted so as to propose suggestions of effective measures,either preventive or emergency,which could have avoided the blackouts.It is shown that applications of several mature technologies can create opportunities of preventing or interrupting the cascading development.These include offline dynamic simulation,online stability analysis and preventive control,real-time situational awareness and automatic emergency control.Further R&D directions are given to address the challenges of modern power systems as well.They cover system fault identification criterion of protection and control devices,verification of adaptability of control effect to system operating conditions,real-time operational management of emergency control measures and improvement of simulation accuracy.
基金Supported by the National Natural Science Foundation of China,No.81571881
文摘Enterocutaneous fistulas(ECFs) are great challenges during the open abdomen. The loss of digestive juice, water-electrolyte imbalance and malnutrition are intractable issues during management of ECF. Techniques such as "fistula patch" and vacuumassisted closure therapy have been applied to prevent contamination of open abdominal wounds by intestinal fistula drainage. However, failures are encountered due to high-output fistula and anatomical complexity. Here, we report 3 D-printed patient-personalized fistula stent for ECF treatment based on 3 D reconstruction of the fistula image. Subsequent follow-up demonstrated that this stent was well-implanted and effective to reduce the volume of enteric fistula effluent.
基金supported by the Science and Technology Project of State Grid Corporation of China(No.52467K150007)
文摘Based on analysis of construction and operation of micro integrated energy systems(MIES), this paper presents economic optimization for their configuration and sizing. After presenting typical models for MIES, a residential community MIES is developed by analyzing residential direct energy consumption within a general design procedure. Integrating with available current technologies and local resources, the systematic design considers a prime mover, fed by natural gas, with wind power, photovoltaic generation, and two storage devices serving thermal energy and power to satisfy cooling, heating and electricity demands. Control strategies for MIES also arepresented in this study. Multi-objective formulas are obtained by analyzing annual cost and dumped renewable energy to achieve optimal coordination of energy supply and demand. According to historical load data and the probability distribution of distributed generation output,clustering methods based on K-means and discretization methods are employed to obtain typical scenarios representative of uncertainties. The modified non-dominated sorting genetic algorithm is applied to find the Pareto frontier of the constructed multi-objective formulas. In addition, aiming to explore the Pareto frontier, the dumped energy cost ratio is defined to check the energy balance in different MIES designs and provide decision support for the investors. Finally, simulations and comparision show the appropriateness of the developed model and the applicability of the adopted optimization algorithm.
文摘With the construction of smart grid,lots of renewable energy resources such as wind and solar are deployed in power system.It might make the power system load varied complex than before which will bring difficulties in short-term load forecasting area.To overcome this issue,this paper proposes a new short-term load forecasting framework based on big data technologies.First,a cluster analysis is performed to classify daily load patterns for individual loads using smart meter data.Next,an association analysis is used to determine critical influential factors.This is followed by the application of a decision tree to establish classification rules.Then,appropriate forecasting models are chosen for different load patterns.Finally,the forecasted total system load is obtained through an aggregation of an individual load’s forecasting results.Case studies using real load data show that the proposed new framework can guarantee the accuracy of short-term load forecasting within required limits.
基金supported in part by the National Key R&D Program of China(2018YFB0905000)the Science and Technology Project of the State Grid Corporation of China(SGTJDK00DWJS1800232)
文摘The integrated energy system(IES)is an important energy supply method for mitigating the energy crisis.A station-and-network–coordinated planning method for the IES,which considers the integrated demand responses(IDRs)of flexible loads,electric vehicles,and energy storage is proposed in this work.First,based on load substitution at the user side,an energy-station model considering the IDR is established.Then,based on the characteristics of the energy network,a collaborative planning model is established for the energy station and energy network of the IES,considering the comprehensive system investment,operation and maintenance,and clean energy shortage penalty costs,to minimize the total cost.This can help optimize the locations of the power lines and natural gas pipelines and the capacities of the equipment in an energy station.Finally,simulations are performed to demonstrate that the proposed planning method can help delay or reduce the construction of new lines and energy-station equipment,thereby reducing the investment required and improving the planning economics of the IES.
文摘Cyber threats are serious concerns for power systems.For example,hackers may attack power control systems via interconnected enterprise networks.This paper proposes a risk assessment framework to enhance the resilience of power systems against cyber attacks.The duality element relative fuzzy evaluation method is employed to evaluate identified security vulnerabilities within cyber systems of power systems quantitatively.The attack graph is used to identify possible intrusion scenarios that exploit multiple vulnerabilities.An intrusion response system(IRS)is developed to monitor the impact of intrusion scenarios on power system dynamics in real time.IRS calculates the conditional Lyapunov exponents(CLEs)on line based on the phasor measurement unit data.Power system stability is predicted through the values of CLEs.Control actions based on CLEs will be suggested if power system instability is likely to happen.A generic wind farm control system is used for case study.The effectiveness of IRS is illustrated with the IEEE 39 bus system model.
基金supported by National High Technology Research and Development Program of China(863Program)(No.2015AA050403)National Natural Science Foundation of China(No.51677124,No.51607033,No.51607034)Research and Demonstration on Combined Optimal Operation and Testing Technology for New Distributed Energy,Energy Storage and Active Load of State Grid Corporation of China
文摘Renewable energy based distributed generation(DG) has the potential to reach high penetration levels in the residential region. However, its integration at the demand side will cause rapid power fluctuations of the tieline in the residential region. The traditional generators are generally difficult to manage rapid power fluctuations due to their insufficient efficiency requirements and low responding speed. With an effective control strategy, the demand side resources(DSRs) including DGs, electric vehicles and thermostatically-controlled loads at thedemand side, are able to serve as the energy storage system to smooth the load fluctuations. However, it is a challenge to properly model different types of DSRs. To solve this problem, a unified state model is first developed to describe the characteristics of different DSRs. Then a load curve smoothing strategy is proposed to offset the load fluctuations of the tie-line of the residential region, where a control matrix deduced from the unified state model is introduced to manage the power outputs of different DSRs,considering the response order and the comfort levels.Finally, a residential region with households is used to validate the load curve smoothing strategy based on the unified state model, and the results show that the power fluctuation rate of the tie-line is significantly decreased.Meanwhile, comparative study results are shown to demonstrate the advantages of the unified state model based load curve smoothing strategy.
基金National Key R&D Program of China(2018YFB0905000)Science and Technology Project of State Grid Corporation of China(SGTJDK00DWJS1800232).
文摘In the light of user-side energy power control requirements, a power control strategy for a household-level EPR based on HES droop control is proposed, focusing on the on-grid, off-grid and seamless switching process. The system operating states are divided based on the DC bus voltage information with one converter used as a slack terminal to stabilize the DC bus voltage and the other converters as power terminals. In the on-grid mode, the GCC and the HES are used as the main control unit to achieve on-grid stable operation, whereas in the off-grid mode, the PV, HES and LC are used as the main control unit at different voltages to achieve stable operation of the island network. Finally, a DC MG system based on a household-level EPR is developed using the PSCAD / EMTDC simulation platform and the results show that the control strategy can effectively adjust the output of each subunit and maintain the stability of the DC bus voltage.
基金This work was supported in part by the National Key Research and Development Program of China(No.2017YFB0903000)the Science and Technology Project of the State Grid Corporation of China(Basic Theory and Methodology for Analysis and Control of Grid Cyber Physical Systems(Supporting Projects)).
文摘Due to the tight coupling between the cyber and physical sides of a cyber-physical power system(CPPS),the safe and reliable operation of CPPSs is being increasingly impacted by cyber security.This situation poses a challenge to traditional security defense systems,which considers the threat from only one side,i.e.,cyber or physical.To cope with cyberattacks,this paper reaches beyond the traditional one-side security defense systems and proposes the concept of cyber-physical coordinated situation awareness and active defense to improve the ability of CPPSs.An example of a regional frequency control system is used to show the validness and potential of this concept.Then,the research framework is presented for studying and implementing this concept.Finally,key technologies for cyber-physical coordinated situation awareness and active defense against cyber-attacks are introduced.
基金This work was supported by the Major Science and Technology Project in Inner Mongolia Autonomous Region(2021ZD0040).
文摘Hydrogen production from renewable energy sources(RESs)is one of the effective ways to achieve carbon peak and carbon neutralization.In order to ensure the efficient,reliable and stable operation of the DC microgrid(MG)with an electric-hydrogen hybrid energy storage system(ESS),the operational constraints and static dynamic characteristics of a hydrogen energy storage system(HESS)needs to be fully considered.First,different hydrogen production systems,using water electrolysis are compared,and the modeling method of the electrolyzer is summarized.The operational control architecture of the DC MG with electric-hydrogen is analyzed.Combined with the working characteristics of the alkaline electrolyzer,the influence of hydrogen energy storage access on the operational mode of the DC MG is analyzed.The operational control strategies of the DC MG with electric-hydrogen hybrid ESS are classified and analyzed from four different aspects:static and dynamic characteristics of the hydrogen energy storage system,power distribution of the electric-hydrogen hybrid ESS and the efficiency optimization of hydrogen energy storage.Finally,the advantages of a modular hydrogen production system(HPS)are described,and the technical problems and research directions in the future are discussed.
基金This work was jointly supported by the Major Projects on Planning and Operation Control of Large Scale Grid,State Grid Corporation of China(SGCC-MPLG001-2012)State Grid EPRI Project(YS11002)the National Natural Science Foundation of China(91024028).
文摘Greenhouse gas emission regulation and renewable energy promotion policies have been implemented in many countries.Yet these two kinds of regulation policies have complex interactions between each other,and can either enhance or reduce the overall emission reduction efficiency.If not well tuned,these regulation policies may deviate from their original intention and lead to unnecessary social cost.Hence,the policy effectiveness,cost effectiveness,and dynamic efficiency of different policy mixtures between emission trading and renewable energy subsidy are studied based on a novel dynamic simulation platform of power economy and power system.Simulation results show that these two kinds of regulation policy can coexist,but a good coordination between the emission trading and the renewable energy subsidy can achieve better emission reduction outcomes.
基金The authors would also like to thank UK EPSRC under grant EP/L001063/1 and China NSFC under grants 51361130153 and 61273040.
文摘Economic and environmental load dispatch aims to determine the amount of electricity generated from power plants to meet load demand while minimizing fossil fuel costs and air pollution emissions subject to operational and licensing requirements.These two scheduling problems are commonly formulated with non-smooth cost functions respectively considering various effects and constraints,such as the valve point effect,power balance and ramprate limits.The expected increase in plug-in electric vehicles is likely to see a significant impact on the power system due to high charging power consumption and significant uncertainty in charging times.In this paper,multiple electric vehicle charging profiles are comparatively integrated into a 24-hour load demand in an economic and environment dispatch model.Self-learning teaching-learning based optimization(TLBO)is employed to solve the non-convex non-linear dispatch problems.Numerical results onwell-known benchmark functions,as well as test systems with different scales of generation units show the significance of the new scheduling method.
基金supported by National Key Research and Development Program of China(2017YFB0903000)
文摘For lack of deep research on model, system structure and top-level design, the integrated system concept of energy, information and transportation networks fails to provide effective guidance for transferring the theory to practice. In this paper, with dispatching of energy flow and information flow as a focus, clean energy of wind power and solar power as carrier, battery charging & swapping station as medium and all kinds of transportation flows as entity, a five-in-one threenetwork integrated system model is built by full use of technologies of Internet of Vehicles(IOV) and Internet of things(IOT) to promote the innovative concept of three-network integration into practice, and provide a reference for future researches.
基金Science and Technology Project of SGCC(SGTJDK00DWJS1600014).
文摘Stochastic noises have a great adverse effect on the prediction accuracy of electric power load.Modeling online and filtering real-time can effectively improve measurement accuracy.Firstly,pretreating and inspecting statistically the electric power load data is essential to characterize the stochastic noise of electric power load.Then,set order for the time series model by Akaike information criterion(AIC)rule and acquire model coefficients to establish ARMA(2,1)model.Next,test the applicability of the established model.Finally,Kalman filter is adopted to process the electric power load data.Simulation results of total variance demonstrate that stochastic noise is obviously decreased after Kalman filtering based on ARMA(2,1)model.Besides,variance is reduced by two orders,and every coefficient of stochastic noise is reduced by one order.The filter method based on time series model does reduce stochastic noise of electric power load,and increase measurement accuracy.
基金supported by the National Key Research and Development Program of China(No.2017YFB0903000)the National Natural Science Foundation of China(No.51377122)the project of State Grid Corporation of China(Research on Cooperative Situation Awareness and Active Defense Method of Cyber Physical Power System for Cyber Attack).
文摘Tampering,forgery and theft of the measurement and control messages in a smart grid could cause one breakdown in the power system.However,no security measures are employed for communications in intelligent substations.Communication services in an intelligent substation have high demands for real-time performance,which must be considered when deploying security measures.This paper studies the security requirements of communication services in intelligent substations,analyzes the security capabilities and shortages of IEC 62351,and proposes a novel security scheme for intelligent substation communications.This security scheme covers internal and telecontrol communications,in which the real-time performance of each security measure is considered.In this scheme,certificateless public key cryptography(CLPKC)is used to avoid the latency of certificate exchange in certificate-based cryptosystem and the problem of key escrow in identity-based cryptosystem;the security measures of generic object-oriented substation event,sampled measure value and manufacturing message specification in IEC 62351 are improved to meet the real-time requirements of the messages as well as to provide new security features to resist repudiation and replay attacks;and the security at transport layer is modified to fit CLPKC,which implements mutual authentication by exchanging signatures.Furthermore,a deployment of CLPKC in an intelligent substation is presented.We also evaluate the security properties of the scheme and analyze the end-to-end delays of secured services by combining theoretical calculation and simulation in this paper.The results indicate that the proposed scheme meets the requirements of security and real-time performance of communications in intelligent substations.
文摘BACKGROUND Open abdomen(OA) has been generally accepted for its magnificent superiority and effectiveness in patients with severe trauma, severe intra-abdominal infection, and abdominal compartment syndrome. In the meantime, OA calls for a mass of nursing and the subsequent enteroatomospheric fistula(EAF), which is one of the most common complications of OA therapy, remains a thorny challenge.CASE SUMMARY Our team applied thermoplastic polyurethane as a befitting material for producing a 3 D-printed "fistula stent" in the management of an EAF patient,who was initially admitted to local hospital because of abdominal pain and distension and diagnosed with bowel obstruction. After a series of operations and OA therapy, the patient developed an EAF.CONCLUSION Application of this novel "fistula stent" resulted in a drastic reduction in the amount of lost enteric effluent and greatly accelerated rehabilitation processes.
基金supported by the National Natural Science Foundation of China under Grant 51807091the Natural Science Foundation of Jiangsu Province BK20180478+2 种基金the China Postdoctoral Science Foundation under Grant 2019M661846the State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources under Grant LAPS20016Engineering and Physical Sciences Research Council under Grant EP/N032888/1.
文摘Synchronous condensers(SCs)are generally used at the receiving-end stations of ultra-high-voltage direct current(UHVDC)transmission systems due to their strong reactive power support and flexible regulation of reactive power according to the interconnected grids operating conditions.In this paper,different starting control schemes of a SC integrated power grid are investigated providing four main contributions:1)The principle of reactive power support of the SC on the interconnected power grid is analytically studied,providing the establishment of mathematical models.2)Four different starting control schemes are developed for the initialization and SC integration,i.e.in Scheme 1,a preset initial falling speed is directly utilized without initialization;in Scheme 2,a black start sequential control approach with a static frequency converter(SFC)is proposed;in Scheme 3,PI/PD/PID controllers are respectively applied for the excitation device at the speed-falling stage;in Scheme 4,a pre-insertion approach of an energy absorption component with R/L/RL is utilized to suppress the surges at the SC integration instant.3)The dynamic behaviors of four different starting schemes at specific operating stages are evaluated.4)The success rate of SC integration is analyzed to evaluate starting control performance.Performance of the SC interconnected system with four different starting control schemes is evaluated in the timedomain simulation environment PSCAD/EMTDC^(TM).The results prove the superiority of the proposed starting control approach in Scheme 4.
