Existing research on the measurement of the valuation effect mainly follows the residual method proposed by Lane and Milesi-Ferretti(2001).This cannot be used to perform structural decomposition.We propose an aggregat...Existing research on the measurement of the valuation effect mainly follows the residual method proposed by Lane and Milesi-Ferretti(2001).This cannot be used to perform structural decomposition.We propose an aggregation approach rather than the residual method to measure structurally the investment flow and valuation effect of China's external assets.The results indicate that the valuation effect of China's external assets has been highly volatile and it was negative during the pandemic period.The structural decomposition shows that portfolio investment and direct investment made the main contributions to the valuation effect.The impact of exchange rates on the valuation effect has generally been higher than that of asset price in terms of direct investment and total external assets but the opposite has been true for portfolio investment.China's outward investments are currently more inclined to Asian countries and a few European countries but inflows to China still mainly come from developed countries.展开更多
Severe disturbances in a power network can cause the system frequency to exceed the safe operating range.As the last defensive line for system emergency control,under frequency load shedding(UFLS)is an important metho...Severe disturbances in a power network can cause the system frequency to exceed the safe operating range.As the last defensive line for system emergency control,under frequency load shedding(UFLS)is an important method for preventing a wide range of frequency excursions.This paper proposes a hierarchical UFLS scheme of“centralized real-time decision-making and decentralized real-time control”for inter-connected systems.The centralized decision-layer of the scheme takes into account the importance of the load based on the equivalent transformation of kinetic energy(KE)and potential energy(PE)in the transient energy function(TEF),while the load PE is used to determine the load shedding amount(LSA)allocation in different loads after faults in real-time.At the same time,the influence of inertia loss is considered in the calculation of unbalanced power,and the decentralized control center is used to implement the one-stage UFLS process to compensate for the unbalanced power.Simulations are carried out on the modified New England 10-generator 39-bus system and 197-bus system in China to verify the performance of the proposed scheme.The results show that,compared with other LSA allocation indicators,the proposed alloca-tion indicators can achieve better fnadir and td.At the same time,compared with other multi-stage UFLS schemes,the proposed scheme can obtain the maximum fnadir with a smaller LSA in scenarios with high renewable energy sources(RES)penetration.展开更多
An optimal configuration method of a multi-energy microgrid system based on the deep joint generation of sourceload-temperature scenarios is proposed to improve the multienergy complementation and the reliability of e...An optimal configuration method of a multi-energy microgrid system based on the deep joint generation of sourceload-temperature scenarios is proposed to improve the multienergy complementation and the reliability of energy supply in extreme scenarios.First,based on the historical meteorological data,the typical meteorological clusters and extreme temperature types are obtained.Then,to reflect the uncertainty of energy consumption and renewable energy output in different weather types,a deep joint generation model using a radiation-electric load-temperature scenario based on a denoising variational autoencoder is established for each weather module.At the same time,to cover the potential high energy consumption scenarios with extreme temperatures,the extreme scenarios with fewer data samples are expanded.Then,the scenarios are reduced by clustering analysis.The normal days of different typical scenarios and extreme temperature scenarios are determined,and the cooling and heating loads are determined by temperature.Finally,the optimal configuration of a multi-energy microgrid system is carried out.Experiments show that the optimal configuration based on the extreme scenarios and typical scenarios can improve the power supply reliability of the system.The proposed method can accurately capture the complementary potential of energy sources.And the economy of the system configuration is improved by 14.56%.展开更多
Due to the slow dynamic power-regulation characteristics of the electrolyser(EL),a novel integrated three-port DC/DC converter topology based on a phase-shifted full-bridge converter and dual active-bridge converter i...Due to the slow dynamic power-regulation characteristics of the electrolyser(EL),a novel integrated three-port DC/DC converter topology based on a phase-shifted full-bridge converter and dual active-bridge converter is proposed in this paper.Especially,the proposed converter can achieve a fast auxiliary response to the EL.This topology has the features of single-stage conversion,high system integration and compatibility with multiple operation modes.The operational principles and a hybrid modulation scheme of the proposed converter are analysed in detail.In addition,the power-transmission characteristics of each port and the soft-switching range are researched.On these bases,six operation modes suitable for a hydrogen energy-storage system are designed.The simulation and a 2-kW scaled-down experimental prototype are established to verify the feasibility and effectiveness of the proposed topology in different operation modes.展开更多
Oxalicine B(1)is an a-pyrone meroterpenoid with a unique bispirocyclic ring system derived from Penicillium oxalicum.The biosynthetic pathway of 15-deoxyoxalicine B(4)was preliminarily reported in Penicillium canescen...Oxalicine B(1)is an a-pyrone meroterpenoid with a unique bispirocyclic ring system derived from Penicillium oxalicum.The biosynthetic pathway of 15-deoxyoxalicine B(4)was preliminarily reported in Penicillium canescens,however,the genetic base and biochemical characterization of tailoring reactions for oxalicine B(1)has remained enigmatic.In this study,we characterized three oxygenases from the metabolic pathway of oxalicine B(1),including a cytochrome P450 hydroxylase OxaL,a hydroxylating Fe(II)/a-KG-dependent dioxygenase OxaK,and a multifunctional cytochrome P450 OxaB.Intriguingly,OxaK can catalyze various multicyclic intermediates or shunt products of oxalicines with impressive substrate promiscuity.OxaB was further proven via biochemical assays to have the ability to convert 15-hydroxdecaturin A(3)to 1 with a spiro-lactone core skeleton through oxidative rearrangement.We also solved the mystery of OxaL that controls C-15 hydroxylation.Chemical investigation of the wild-type strain and deletants enabled us to identify 10 metabolites including three new compounds,and the isolated compounds displayed potent anti-influenza A virus bioactivities exhibiting IC50values in the range of 4.0-19.9μmol/L.Our studies have allowed us to propose a late-stage biosynthetic pathway for oxalicine B(1)and create downstream derivatizations of oxalicines by employing enzymatic strategies.展开更多
In this paper, a data-driven stochastic subspace identification(SSI-DATA) technique is proposed as an advanced stochastic system identification(SSI) to extract the inter-area oscillation modes of a power system from w...In this paper, a data-driven stochastic subspace identification(SSI-DATA) technique is proposed as an advanced stochastic system identification(SSI) to extract the inter-area oscillation modes of a power system from wide-area measurements. For accurate and robust extraction of the modes’ parameters(frequency, damping and mode shape), SSI has already been verified as an effective identification algorithm for output-only modal analysis.The new feature of the proposed SSI-DATA applied to inter-area oscillation modal identification lies in its ability to select the eigenvalue automatically. The effectiveness of the proposed scheme has been fully studied and verified,first using transient stability data generated from the IEEE16-generator 5-area test system, and then using recorded data from an actual event using a Chinese wide-area measurement system(WAMS) in 2004. The results from the simulated and recorded measurements have validated the reliability and applicability of the SSI-DATA technique in power system low frequency oscillation analysis.展开更多
Wind curtailment/hydrogen production/fuel cell vehicle system(WCHPFCVS)is the use of curtailment to electrolyze water to produce hydrogen,which then provides energy for hydrogen fuel cell vehicles.In this paper,a tech...Wind curtailment/hydrogen production/fuel cell vehicle system(WCHPFCVS)is the use of curtailment to electrolyze water to produce hydrogen,which then provides energy for hydrogen fuel cell vehicles.In this paper,a techno-economic analysis of WCHPFCVS is proposed using the HOMER software.Large-scale wind power penetration is expected to lead to serious wind curtailment,and therefore,the hydrogen fuel cell vehicle will play an important role in future renewable energy storage,energy internet sharing,and electric transport areas.A system model of wind curtailment/hydrogen production/fuel cell vehicle is presented and analyzed using HOMER software to optimize the capacity and cost of the system.An annual revenue and profit of the system is then calculated and analyzed for energy conservation,emissions reduction,and environmental benefits.A technoeconomical evaluation of the system when cost of producing hydrogen and hydrogen load(fuel cell vehicle quantities)changes is also presented,taking into consideration the future progress of the technology and its market development.Techno-economic analysis of WCHPFCVS is shown as an effective method through a case study using actual data of curtailment from a wind farm in Jilin province in northeast China.展开更多
In this article,we attempt to document a technical overview on modern miniature unmanned rotorcraft systems.We first give a brief review on the historical development of the rotorcraft unmanned aerial vehicles(UAVs),a...In this article,we attempt to document a technical overview on modern miniature unmanned rotorcraft systems.We first give a brief review on the historical development of the rotorcraft unmanned aerial vehicles(UAVs),and then move on to present a fairly detailed and general overview on the hardware configuration,software integration,aerodynamic modeling and automatic flight control system involved in constructing the unmanned system.The applications of the emerging technology in the military and civilian domains are also highlighted.展开更多
An ambient modal framework for inertia estimation using synchrophasor data is proposed in this letter.Specifically,an analytical formulation is developed for the estimation of inertia based on the frequency and dampin...An ambient modal framework for inertia estimation using synchrophasor data is proposed in this letter.Specifically,an analytical formulation is developed for the estimation of inertia based on the frequency and damping ratio modes extracted from ambient data.An advantage of the proposed framework is that it can rely on synchronized ambient data under non-disturbed conditions for online estimation and tracking of inertia.Ultimately,numerical simulation studies and physical experiments demonstrate the feasibility of the proposed approach.展开更多
Because of the rapid growth of new energy and the accompanying considerable uncertainty in the power market,the demand for flexibility in a power sys-tem has risen sharply.In the meantime,the market structure of auxil...Because of the rapid growth of new energy and the accompanying considerable uncertainty in the power market,the demand for flexibility in a power sys-tem has risen sharply.In the meantime,the market structure of auxiliary services has changed,resulting in market participants(MPs)benefiting less than expected from providing flexible services.To encourage MPs to provide flexibility,this study proposes a dynamic design framework for an auxiliary service compensation mech-anism.To evaluate the proposed framework,a case study is conducted,examining a peak-shaving service in Liao-ning province in northeast China.First,the operational status and limitations of the typical product,the peak-shaving service,in China’s flexibility auxiliary ser-vices market are analyzed.Then,taking into consideration the time value of the flexible products provided by the MPs,a dynamic mechanism for hierarchical compensation of flexibility auxiliary service costs is proposed,and a mathematical model aimed at optimizing the MPs’comprehensive income is constructed.The results show that,compared with the existing traditional mechanism,the proposed method can effectively guarantee fair remu-neration for the flexibility provider,while easing the tense supply-demand relationship in the flexibility market.展开更多
基金The authors appreciate the insightful comments and suggestions of editors and two anonymous reviewers.Guowei Cai thanks the National Natural Science Foundation of China(No.72073147)the National Social Science Major Project(No.22&ZD058)the Ministry of Education Humanities and Social Sciences Planning Foundation Project of China(No.19YJA790001)for their financial support.
文摘Existing research on the measurement of the valuation effect mainly follows the residual method proposed by Lane and Milesi-Ferretti(2001).This cannot be used to perform structural decomposition.We propose an aggregation approach rather than the residual method to measure structurally the investment flow and valuation effect of China's external assets.The results indicate that the valuation effect of China's external assets has been highly volatile and it was negative during the pandemic period.The structural decomposition shows that portfolio investment and direct investment made the main contributions to the valuation effect.The impact of exchange rates on the valuation effect has generally been higher than that of asset price in terms of direct investment and total external assets but the opposite has been true for portfolio investment.China's outward investments are currently more inclined to Asian countries and a few European countries but inflows to China still mainly come from developed countries.
基金supported in part by the National Key R&D Program of China“Response-driven intelligent enhanced analysis and control for bulk power system stability”under Grant 2021YFB2400800.
文摘Severe disturbances in a power network can cause the system frequency to exceed the safe operating range.As the last defensive line for system emergency control,under frequency load shedding(UFLS)is an important method for preventing a wide range of frequency excursions.This paper proposes a hierarchical UFLS scheme of“centralized real-time decision-making and decentralized real-time control”for inter-connected systems.The centralized decision-layer of the scheme takes into account the importance of the load based on the equivalent transformation of kinetic energy(KE)and potential energy(PE)in the transient energy function(TEF),while the load PE is used to determine the load shedding amount(LSA)allocation in different loads after faults in real-time.At the same time,the influence of inertia loss is considered in the calculation of unbalanced power,and the decentralized control center is used to implement the one-stage UFLS process to compensate for the unbalanced power.Simulations are carried out on the modified New England 10-generator 39-bus system and 197-bus system in China to verify the performance of the proposed scheme.The results show that,compared with other LSA allocation indicators,the proposed alloca-tion indicators can achieve better fnadir and td.At the same time,compared with other multi-stage UFLS schemes,the proposed scheme can obtain the maximum fnadir with a smaller LSA in scenarios with high renewable energy sources(RES)penetration.
基金supported by National Key Research and Development Program of China(2019YFB1505400)Jilin Science and Technology Development Program(20160411003XH)Jilin Industrial Technology Research and Development Program(2019C058-8).
文摘An optimal configuration method of a multi-energy microgrid system based on the deep joint generation of sourceload-temperature scenarios is proposed to improve the multienergy complementation and the reliability of energy supply in extreme scenarios.First,based on the historical meteorological data,the typical meteorological clusters and extreme temperature types are obtained.Then,to reflect the uncertainty of energy consumption and renewable energy output in different weather types,a deep joint generation model using a radiation-electric load-temperature scenario based on a denoising variational autoencoder is established for each weather module.At the same time,to cover the potential high energy consumption scenarios with extreme temperatures,the extreme scenarios with fewer data samples are expanded.Then,the scenarios are reduced by clustering analysis.The normal days of different typical scenarios and extreme temperature scenarios are determined,and the cooling and heating loads are determined by temperature.Finally,the optimal configuration of a multi-energy microgrid system is carried out.Experiments show that the optimal configuration based on the extreme scenarios and typical scenarios can improve the power supply reliability of the system.The proposed method can accurately capture the complementary potential of energy sources.And the economy of the system configuration is improved by 14.56%.
基金supported by the National Key R&D Program of China (no.2018YFB1503100)the National Natural Science Foundation of China (no.51907021).
文摘Due to the slow dynamic power-regulation characteristics of the electrolyser(EL),a novel integrated three-port DC/DC converter topology based on a phase-shifted full-bridge converter and dual active-bridge converter is proposed in this paper.Especially,the proposed converter can achieve a fast auxiliary response to the EL.This topology has the features of single-stage conversion,high system integration and compatibility with multiple operation modes.The operational principles and a hybrid modulation scheme of the proposed converter are analysed in detail.In addition,the power-transmission characteristics of each port and the soft-switching range are researched.On these bases,six operation modes suitable for a hydrogen energy-storage system are designed.The simulation and a 2-kW scaled-down experimental prototype are established to verify the feasibility and effectiveness of the proposed topology in different operation modes.
基金supported by grants from the CAMS Innovation Fund for Medical Sciences(CIFMS)(2019-I2M-1-005 and 2021I2M-1-055)the National Natural Science Foundation of China(No.31872617 and 82073744)the central level,scientific research institutes for basic R&D fund business(3332018097)。
文摘Oxalicine B(1)is an a-pyrone meroterpenoid with a unique bispirocyclic ring system derived from Penicillium oxalicum.The biosynthetic pathway of 15-deoxyoxalicine B(4)was preliminarily reported in Penicillium canescens,however,the genetic base and biochemical characterization of tailoring reactions for oxalicine B(1)has remained enigmatic.In this study,we characterized three oxygenases from the metabolic pathway of oxalicine B(1),including a cytochrome P450 hydroxylase OxaL,a hydroxylating Fe(II)/a-KG-dependent dioxygenase OxaK,and a multifunctional cytochrome P450 OxaB.Intriguingly,OxaK can catalyze various multicyclic intermediates or shunt products of oxalicines with impressive substrate promiscuity.OxaB was further proven via biochemical assays to have the ability to convert 15-hydroxdecaturin A(3)to 1 with a spiro-lactone core skeleton through oxidative rearrangement.We also solved the mystery of OxaL that controls C-15 hydroxylation.Chemical investigation of the wild-type strain and deletants enabled us to identify 10 metabolites including three new compounds,and the isolated compounds displayed potent anti-influenza A virus bioactivities exhibiting IC50values in the range of 4.0-19.9μmol/L.Our studies have allowed us to propose a late-stage biosynthetic pathway for oxalicine B(1)and create downstream derivatizations of oxalicines by employing enzymatic strategies.
基金supported by the National Natural Science Foundation of China(No.51507028)the Hong Kong Polytechnic University under Project G-UA3Z
文摘In this paper, a data-driven stochastic subspace identification(SSI-DATA) technique is proposed as an advanced stochastic system identification(SSI) to extract the inter-area oscillation modes of a power system from wide-area measurements. For accurate and robust extraction of the modes’ parameters(frequency, damping and mode shape), SSI has already been verified as an effective identification algorithm for output-only modal analysis.The new feature of the proposed SSI-DATA applied to inter-area oscillation modal identification lies in its ability to select the eigenvalue automatically. The effectiveness of the proposed scheme has been fully studied and verified,first using transient stability data generated from the IEEE16-generator 5-area test system, and then using recorded data from an actual event using a Chinese wide-area measurement system(WAMS) in 2004. The results from the simulated and recorded measurements have validated the reliability and applicability of the SSI-DATA technique in power system low frequency oscillation analysis.
基金supported in part by the National High Technology Research and Development Program(863 Program)of China(No.2014AA052502)Changjiang Scholars and Innovative Research Team in University(No.IRT1114)+1 种基金National Natural Science Foundation of China(Nos.51177010 and 51377017)Foundation of the Jilin Technology Development Program(Nos.20140203003SF and 20150411008XH).
文摘Wind curtailment/hydrogen production/fuel cell vehicle system(WCHPFCVS)is the use of curtailment to electrolyze water to produce hydrogen,which then provides energy for hydrogen fuel cell vehicles.In this paper,a techno-economic analysis of WCHPFCVS is proposed using the HOMER software.Large-scale wind power penetration is expected to lead to serious wind curtailment,and therefore,the hydrogen fuel cell vehicle will play an important role in future renewable energy storage,energy internet sharing,and electric transport areas.A system model of wind curtailment/hydrogen production/fuel cell vehicle is presented and analyzed using HOMER software to optimize the capacity and cost of the system.An annual revenue and profit of the system is then calculated and analyzed for energy conservation,emissions reduction,and environmental benefits.A technoeconomical evaluation of the system when cost of producing hydrogen and hydrogen load(fuel cell vehicle quantities)changes is also presented,taking into consideration the future progress of the technology and its market development.Techno-economic analysis of WCHPFCVS is shown as an effective method through a case study using actual data of curtailment from a wind farm in Jilin province in northeast China.
文摘In this article,we attempt to document a technical overview on modern miniature unmanned rotorcraft systems.We first give a brief review on the historical development of the rotorcraft unmanned aerial vehicles(UAVs),and then move on to present a fairly detailed and general overview on the hardware configuration,software integration,aerodynamic modeling and automatic flight control system involved in constructing the unmanned system.The applications of the emerging technology in the military and civilian domains are also highlighted.
基金This work was supported in part by the National Science Foundation of China(No.51877032)in part by the State Grid Corporation of China(No.2018GWJLDKY06).
文摘An ambient modal framework for inertia estimation using synchrophasor data is proposed in this letter.Specifically,an analytical formulation is developed for the estimation of inertia based on the frequency and damping ratio modes extracted from ambient data.An advantage of the proposed framework is that it can rely on synchronized ambient data under non-disturbed conditions for online estimation and tracking of inertia.Ultimately,numerical simulation studies and physical experiments demonstrate the feasibility of the proposed approach.
基金supported by the National Key Research and Development Program“Renewable Energy and Thermal Power Coupling Integration and Flexible Operation Control Technology”(No.2019YFB1505400).
文摘Because of the rapid growth of new energy and the accompanying considerable uncertainty in the power market,the demand for flexibility in a power sys-tem has risen sharply.In the meantime,the market structure of auxiliary services has changed,resulting in market participants(MPs)benefiting less than expected from providing flexible services.To encourage MPs to provide flexibility,this study proposes a dynamic design framework for an auxiliary service compensation mech-anism.To evaluate the proposed framework,a case study is conducted,examining a peak-shaving service in Liao-ning province in northeast China.First,the operational status and limitations of the typical product,the peak-shaving service,in China’s flexibility auxiliary ser-vices market are analyzed.Then,taking into consideration the time value of the flexible products provided by the MPs,a dynamic mechanism for hierarchical compensation of flexibility auxiliary service costs is proposed,and a mathematical model aimed at optimizing the MPs’comprehensive income is constructed.The results show that,compared with the existing traditional mechanism,the proposed method can effectively guarantee fair remu-neration for the flexibility provider,while easing the tense supply-demand relationship in the flexibility market.
