Accurate initial soil conditions play a crucial role in simulating soil hydrothermal and surface energy fluxes in land surface process modeling.This study emphasized the influence of the initial soil temperature(ST)an...Accurate initial soil conditions play a crucial role in simulating soil hydrothermal and surface energy fluxes in land surface process modeling.This study emphasized the influence of the initial soil temperature(ST)and soil moisture(SM)conditions on a land surface energy and water simulation in the permafrost region in the Tibetan Plateau(TP)using the Community Land Model version 5.0(CLM5.0).The results indicate that the default initial schemes for ST and SM in CLM5.0 were simplistic,and inaccurately represented the soil characteristics of permafrost in the TP which led to underestimating ST during the freezing period while overestimating ST and underestimating SLW during the thawing period at the XDT site.Applying the long-term spin-up method to obtain initial soil conditions has only led to limited improvement in simulating soil hydrothermal and surface energy fluxes.The modified initial soil schemes proposed in this study comprehensively incorporate the characteristics of permafrost,which coexists with soil liquid water(SLW),and soil ice(SI)when the ST is below freezing temperature,effectively enhancing the accuracy of the simulated soil hydrothermal and surface energy fluxes.Consequently,the modified initial soil schemes greatly improved upon the results achieved through the long-term spin-up method.Three modified initial soil schemes experiments resulted in a 64%,88%,and 77%reduction in the average mean bias error(MBE)of ST,and a 13%,21%,and 19%reduction in the average root-mean-square error(RMSE)of SLW compared to the default simulation results.Also,the average MBE of net radiation was reduced by 7%,22%,and 21%.展开更多
As one of the five components of Earth's climatic system,the cryosphere has been undergoing rapid shrinking due to global warming.Studies on the formation,evolution,distribution and dynamics of cryospheric compone...As one of the five components of Earth's climatic system,the cryosphere has been undergoing rapid shrinking due to global warming.Studies on the formation,evolution,distribution and dynamics of cryospheric components and their interactions with the human system are of increasing importance to society.In recent decades,the mass loss of glaciers,including the Greenland and Antarctic ice sheets,has accelerated.The extent of sea ice and snow cover has been shrinking,and permafrost has been degrading.The main sustainable development goals in cryospheric regions have been impacted.The shrinking of the cryosphere results in sea-level rise,which is currently affecting,or is soon expected to affect,17 coastal megacities and some small island countries.In East Asia,South Asia and North America,climate anomalies are closely related to the extent of Arctic sea ice and snow cover in the Northern Hemisphere.Increasing freshwater melting from the ice sheets and sea ice may be one reason for the slowdown in Atlantic meridional overturning circulation in the Arctic and Southern Oceans.The foundations of ports and infrastructure in the circum-Arctic permafrost regions suffer from the consequences of permafrost degradation.In high plateaus and mountainous regions,the cryosphere's shrinking has led to fluctuations in river runoff,caused water shortages and increased flooding risks in certain areas.These changes in cryospheric components have shown significant heterogeneity at different temporal and spatial scales.Our results suggest that the quantitative evaluation of future changes in the cryosphere still needs to be improved by enhancing existing observations and model simulations.Theoretical and methodological innovations are required to strengthen social economies'resilience to the impact of cryospheric change.展开更多
The surface energy budget is closely related to freeze-thaw processes and is also a key issue for land surface process research in permafrost regions.In this study,in situ data collected from 2005 to 2015 at the Tangg...The surface energy budget is closely related to freeze-thaw processes and is also a key issue for land surface process research in permafrost regions.In this study,in situ data collected from 2005 to 2015 at the Tanggula site were used to analyze surface energy regimes,the interaction between surface energy budget and freeze-thaw processes.The results confirmed that surface energy flux in the permafrost region of the Qinghai-Tibetan Plateau exhibited obvious seasonal variations.Annual average net radiation(R_(n))for 2010 was 86.5 W m^(-2),with the largest being in July and smallest in November.Surface soil heat flux(G_(0))was positive during warm seasons but negative in cold seasons with annual average value of 2.7 W m^(-2).Variations in R_(n) and G_(0) were closely related to freeze-thaw processes.Sensible heat flux(H)was the main energy budget component during cold seasons,whereas latent heat flux(LE)dominated surface energy distribution in warm seasons.Freeze-thaw processes,snow cover,precipitation,and surface conditions were important influence factors for surface energy flux.Albedo was strongly dependent on soil moisture content and ground surface state,increasing significantly when land surface was covered with deep snow,and exhibited negative correlation with surface soil moisture content.Energy variation was significantly related to active layer thaw depth.Soil heat balance coefficient K was>1 during the investigation time period,indicating the permafrost in the Tanggula area tended to degrade.展开更多
This work was supported by the Headquarter Science and Technology Project of State Grid Corporation of China(Research on the transient protection for AC/DC hybrid grid with high-proportion renewable energy,SGAH0000TKJ...This work was supported by the Headquarter Science and Technology Project of State Grid Corporation of China(Research on the transient protection for AC/DC hybrid grid with high-proportion renewable energy,SGAH0000TKJS1900278).We are very sorry for missing the description of the project funding information.展开更多
By focusing on the problems of speed, reliability, operation and maintenance in the practical application of line protection in conventional and smart substations, we propose system architecture and a technical scheme...By focusing on the problems of speed, reliability, operation and maintenance in the practical application of line protection in conventional and smart substations, we propose system architecture and a technical scheme for in-site(similar in meaning to on-site or near-process) line protection based on vertical integration and outdoor installation. The functions of the single-bay merging unit, relay protection, and intelligent terminal are vertically integrated to reduce the number and types of devices, simplify the configuration, reduce signal transmission, and shorten the protection action time. In addition, this vertically integrated device is applied to provide data acquisition and control execution support for substation-area protection, security and stability of devices, and other substation-area devices. The vital performance outputs are tested and compared. Finally, the experimental results verify that the proposed scheme is feasible and the technology is advanced.展开更多
The distributed capacitance of the line becomes larger as the scale of wind farms,the transmission voltage level,and the transmission distance increase.Hence,the error of the traditional time-domain distance protectio...The distributed capacitance of the line becomes larger as the scale of wind farms,the transmission voltage level,and the transmission distance increase.Hence,the error of the traditional time-domain distance protection scheme based on the R-L model,which ignores the distributed capacitance of the line,becomes unacceptable.Therefore,the error of the time-domain fault location method based on the R-L model,especially the maximum error range,is theoretically analyzed in this paper.On this basis,a novel fault location method based on the RL and Bergeron models is proposed.Then,a fast time-domain distance protection scheme is designed.In the proposed scheme,the error in the fitting calculation is used to construct a weight matrix,and an algorithm for solving the time-domain differential equations is designed to improve the calculation speed and stability.Compared with the traditional frequency-domain distance protection scheme,the proposed scheme is independent of the power supply characteristics;thus,it is suitable for wind farm transmission lines.In addition,compared with the traditional method based on the R-L model,the proposed scheme effectively avoids the negative influence of the distributed capacitance of the line,which significantly improves the operating speed.Different types of faults are simulated by PSCAD/EMTDC to verify the effectiveness and superiority of the proposed scheme.展开更多
Conventional transmission line distance protection approaches are subject to malfunction under reverse fault-induced current transformer(CT) saturation for the typically employed breaker-and-a-half configuration. This...Conventional transmission line distance protection approaches are subject to malfunction under reverse fault-induced current transformer(CT) saturation for the typically employed breaker-and-a-half configuration. This paper addresses this issue by proposing a new distance protection approach that combines the blocking and unblocking criteria of distance protection based on the values of incomplete differential current,operation voltage, and current harmonic content. The proposed approach is verified by theoretical analysis, dynamic simulation testing, and field operation to ensure that the obtained distance protection is reliable and refrains from operating unnecessarily under reverse fault-induced CT saturation in the breaker-and-ahalf configuration. Meanwhile, the proposed approach is demonstrated can operate reliably when forward faults occur or various reverse faults are converted to forward faults.展开更多
Once an asymmetrical fault occurs on the AC side of the receiving-end of a high-voltage direct current(HVDC)transmission system,the current reference will be affected by the control regulation on the DC inverter side ...Once an asymmetrical fault occurs on the AC side of the receiving-end of a high-voltage direct current(HVDC)transmission system,the current reference will be affected by the control regulation on the DC inverter side and the commutation voltage asymmetry.In this case,the advance firing angle will fluctuate periodically,causing security threats to the system.If the fault cannot be cleared in time,the effect may be even more serious.However,the traditional proportional-integral(PI)controller cannot effectively suppress the periodic components in the input error signal,which is an important cause of continuous commutation failure.Thus,the system requires more time to recover from the fault.Motivated by this,a selfadaptive auto-disturbance rejection PI controller is proposed in this study.The controller has the advantages of fast response speed and strong anti-interference ability of the auto-disturbance rejection controller.On one hand,it can automatically adjust PI,and the parameters can maintain the system’s adaptive ability.On the other hand,the discretization process satisfies the computer simulation requirements.By applying the proposed controller to a system under constant current control and extinction angle control,the dynamic response speed can be improved and the robust performance of the system can be ensured when dealing with a wide range of perturbations.Finally,simulation results show that the proposed algorithm can effectively suppress the continuous commutation failure of DC transmission systems.展开更多
The surface energy budget over the Qinghai-Tibet Plateau(QTP)and the Arctic significantly influences the climate system with global consequences.The performances of 30 selected Coupled Model Intercomparison Project Ph...The surface energy budget over the Qinghai-Tibet Plateau(QTP)and the Arctic significantly influences the climate system with global consequences.The performances of 30 selected Coupled Model Intercomparison Project Phase 6(CMIP6)models were evaluated based on six sites in the QTP and Arctic.The simulation results for latent heat flux(LE)were more accurate in the QTP,where the correlation coefficient and root mean square error(RMSE)were 0.9 and 30 W m−2,respectively.The results for sensible heat flux(H)were more accurate in the Arctic,the correlation coefficient and RMSE were 0.8 and 24 W m−2,respectively.Furthermore,the multiple models mean results revealed that the surface energy flux had seasonal variation and regional differences over the QTP and the Arctic.In the QTP,H was the lowest in winter,increased in spring,and reached the maximum in summer.However,the transitional changes in spring and autumn were not apparent in the Arctic,mainly due to seasonal net radiation difference between the two places.LE was affected by precipitation and surface soil moisture content.This work is important for understanding land-atmosphere interactions and useful for improving the accuracy of land surface models simulations.展开更多
基金the National Natural Science Foundation of China(Grant No.U20A2081)West Light Foundation of the Chinese Academy of Sciences(Grant No.xbzg-zdsys-202102)the Second Tibetan Plateau Scientific Expedition and Research(STEP)Project(Grant No.2019QZKK0105).
文摘Accurate initial soil conditions play a crucial role in simulating soil hydrothermal and surface energy fluxes in land surface process modeling.This study emphasized the influence of the initial soil temperature(ST)and soil moisture(SM)conditions on a land surface energy and water simulation in the permafrost region in the Tibetan Plateau(TP)using the Community Land Model version 5.0(CLM5.0).The results indicate that the default initial schemes for ST and SM in CLM5.0 were simplistic,and inaccurately represented the soil characteristics of permafrost in the TP which led to underestimating ST during the freezing period while overestimating ST and underestimating SLW during the thawing period at the XDT site.Applying the long-term spin-up method to obtain initial soil conditions has only led to limited improvement in simulating soil hydrothermal and surface energy fluxes.The modified initial soil schemes proposed in this study comprehensively incorporate the characteristics of permafrost,which coexists with soil liquid water(SLW),and soil ice(SI)when the ST is below freezing temperature,effectively enhancing the accuracy of the simulated soil hydrothermal and surface energy fluxes.Consequently,the modified initial soil schemes greatly improved upon the results achieved through the long-term spin-up method.Three modified initial soil schemes experiments resulted in a 64%,88%,and 77%reduction in the average mean bias error(MBE)of ST,and a 13%,21%,and 19%reduction in the average root-mean-square error(RMSE)of SLW compared to the default simulation results.Also,the average MBE of net radiation was reduced by 7%,22%,and 21%.
基金This research was supported by Yunnan University(YJRC3201702)the National Natural Science Foundation of China(Grant Nos.41761144075,41690142,41941015,41771075,41871096,41671057,41801052,41561016,41701061,41861013)the Ministry of Science and Technology(2013FY111400).
文摘As one of the five components of Earth's climatic system,the cryosphere has been undergoing rapid shrinking due to global warming.Studies on the formation,evolution,distribution and dynamics of cryospheric components and their interactions with the human system are of increasing importance to society.In recent decades,the mass loss of glaciers,including the Greenland and Antarctic ice sheets,has accelerated.The extent of sea ice and snow cover has been shrinking,and permafrost has been degrading.The main sustainable development goals in cryospheric regions have been impacted.The shrinking of the cryosphere results in sea-level rise,which is currently affecting,or is soon expected to affect,17 coastal megacities and some small island countries.In East Asia,South Asia and North America,climate anomalies are closely related to the extent of Arctic sea ice and snow cover in the Northern Hemisphere.Increasing freshwater melting from the ice sheets and sea ice may be one reason for the slowdown in Atlantic meridional overturning circulation in the Arctic and Southern Oceans.The foundations of ports and infrastructure in the circum-Arctic permafrost regions suffer from the consequences of permafrost degradation.In high plateaus and mountainous regions,the cryosphere's shrinking has led to fluctuations in river runoff,caused water shortages and increased flooding risks in certain areas.These changes in cryospheric components have shown significant heterogeneity at different temporal and spatial scales.Our results suggest that the quantitative evaluation of future changes in the cryosphere still needs to be improved by enhancing existing observations and model simulations.Theoretical and methodological innovations are required to strengthen social economies'resilience to the impact of cryospheric change.
基金supported by the National Natural Science Foundation of China(Grant Nos.42071093,41671070)the National Key Research and Development Program of China(2020YFA0608500)+1 种基金the State Key Laboratory of Cryospheric Science(SKLCS-ZZ-2020)the National Natural Science Foundation of China(Grant Nos.41941015,42071093,41690142,41771076,41601078,and 41571069)。
文摘The surface energy budget is closely related to freeze-thaw processes and is also a key issue for land surface process research in permafrost regions.In this study,in situ data collected from 2005 to 2015 at the Tanggula site were used to analyze surface energy regimes,the interaction between surface energy budget and freeze-thaw processes.The results confirmed that surface energy flux in the permafrost region of the Qinghai-Tibetan Plateau exhibited obvious seasonal variations.Annual average net radiation(R_(n))for 2010 was 86.5 W m^(-2),with the largest being in July and smallest in November.Surface soil heat flux(G_(0))was positive during warm seasons but negative in cold seasons with annual average value of 2.7 W m^(-2).Variations in R_(n) and G_(0) were closely related to freeze-thaw processes.Sensible heat flux(H)was the main energy budget component during cold seasons,whereas latent heat flux(LE)dominated surface energy distribution in warm seasons.Freeze-thaw processes,snow cover,precipitation,and surface conditions were important influence factors for surface energy flux.Albedo was strongly dependent on soil moisture content and ground surface state,increasing significantly when land surface was covered with deep snow,and exhibited negative correlation with surface soil moisture content.Energy variation was significantly related to active layer thaw depth.Soil heat balance coefficient K was>1 during the investigation time period,indicating the permafrost in the Tanggula area tended to degrade.
文摘This work was supported by the Headquarter Science and Technology Project of State Grid Corporation of China(Research on the transient protection for AC/DC hybrid grid with high-proportion renewable energy,SGAH0000TKJS1900278).We are very sorry for missing the description of the project funding information.
基金supported by the Scientific and Technological Project of SGCC Headquarters (521101180004, Research on Outdoor Installation Protection Scheme and Key Technologies)National Key Research and Development Program of China ( 2016YFB0900600)
文摘By focusing on the problems of speed, reliability, operation and maintenance in the practical application of line protection in conventional and smart substations, we propose system architecture and a technical scheme for in-site(similar in meaning to on-site or near-process) line protection based on vertical integration and outdoor installation. The functions of the single-bay merging unit, relay protection, and intelligent terminal are vertically integrated to reduce the number and types of devices, simplify the configuration, reduce signal transmission, and shorten the protection action time. In addition, this vertically integrated device is applied to provide data acquisition and control execution support for substation-area protection, security and stability of devices, and other substation-area devices. The vital performance outputs are tested and compared. Finally, the experimental results verify that the proposed scheme is feasible and the technology is advanced.
基金supported by the Science and Technology Program of State Grid Corporation of China“Research on the Principle of Fast Protection in Time-frequency Domain with Single-ended Quantities of High-proportion New Energy Grid Lines”(No.5100-202040327A-0-0-00).
文摘The distributed capacitance of the line becomes larger as the scale of wind farms,the transmission voltage level,and the transmission distance increase.Hence,the error of the traditional time-domain distance protection scheme based on the R-L model,which ignores the distributed capacitance of the line,becomes unacceptable.Therefore,the error of the time-domain fault location method based on the R-L model,especially the maximum error range,is theoretically analyzed in this paper.On this basis,a novel fault location method based on the RL and Bergeron models is proposed.Then,a fast time-domain distance protection scheme is designed.In the proposed scheme,the error in the fitting calculation is used to construct a weight matrix,and an algorithm for solving the time-domain differential equations is designed to improve the calculation speed and stability.Compared with the traditional frequency-domain distance protection scheme,the proposed scheme is independent of the power supply characteristics;thus,it is suitable for wind farm transmission lines.In addition,compared with the traditional method based on the R-L model,the proposed scheme effectively avoids the negative influence of the distributed capacitance of the line,which significantly improves the operating speed.Different types of faults are simulated by PSCAD/EMTDC to verify the effectiveness and superiority of the proposed scheme.
基金supported by Science and Technology Program of State Grid Corporation of China “Research on Fault Coupling Characteristics and New Protection Principle of AC/DC Hybrid Power Grid”。
文摘Conventional transmission line distance protection approaches are subject to malfunction under reverse fault-induced current transformer(CT) saturation for the typically employed breaker-and-a-half configuration. This paper addresses this issue by proposing a new distance protection approach that combines the blocking and unblocking criteria of distance protection based on the values of incomplete differential current,operation voltage, and current harmonic content. The proposed approach is verified by theoretical analysis, dynamic simulation testing, and field operation to ensure that the obtained distance protection is reliable and refrains from operating unnecessarily under reverse fault-induced CT saturation in the breaker-and-ahalf configuration. Meanwhile, the proposed approach is demonstrated can operate reliably when forward faults occur or various reverse faults are converted to forward faults.
基金supported by the Science and Technology Project of State Grid Corporation of China(No.524608170147)
文摘Once an asymmetrical fault occurs on the AC side of the receiving-end of a high-voltage direct current(HVDC)transmission system,the current reference will be affected by the control regulation on the DC inverter side and the commutation voltage asymmetry.In this case,the advance firing angle will fluctuate periodically,causing security threats to the system.If the fault cannot be cleared in time,the effect may be even more serious.However,the traditional proportional-integral(PI)controller cannot effectively suppress the periodic components in the input error signal,which is an important cause of continuous commutation failure.Thus,the system requires more time to recover from the fault.Motivated by this,a selfadaptive auto-disturbance rejection PI controller is proposed in this study.The controller has the advantages of fast response speed and strong anti-interference ability of the auto-disturbance rejection controller.On one hand,it can automatically adjust PI,and the parameters can maintain the system’s adaptive ability.On the other hand,the discretization process satisfies the computer simulation requirements.By applying the proposed controller to a system under constant current control and extinction angle control,the dynamic response speed can be improved and the robust performance of the system can be ensured when dealing with a wide range of perturbations.Finally,simulation results show that the proposed algorithm can effectively suppress the continuous commutation failure of DC transmission systems.
基金supported by the National Key Research and Development Program of China:[Grant Number 2020YFA0608502]the National Natural Science Foundation of China:[Grant Number 42071093]+2 种基金the Natural Science Foundation of Gansu Province:[Grant Number 22JR5RA054]the State Key Laboratory of Cryospheric Science:[Grant Number SKLCS-ZZ-2022]the National Natural Science Foundation of China:[Grant Number 41941015,41671070].
文摘The surface energy budget over the Qinghai-Tibet Plateau(QTP)and the Arctic significantly influences the climate system with global consequences.The performances of 30 selected Coupled Model Intercomparison Project Phase 6(CMIP6)models were evaluated based on six sites in the QTP and Arctic.The simulation results for latent heat flux(LE)were more accurate in the QTP,where the correlation coefficient and root mean square error(RMSE)were 0.9 and 30 W m−2,respectively.The results for sensible heat flux(H)were more accurate in the Arctic,the correlation coefficient and RMSE were 0.8 and 24 W m−2,respectively.Furthermore,the multiple models mean results revealed that the surface energy flux had seasonal variation and regional differences over the QTP and the Arctic.In the QTP,H was the lowest in winter,increased in spring,and reached the maximum in summer.However,the transitional changes in spring and autumn were not apparent in the Arctic,mainly due to seasonal net radiation difference between the two places.LE was affected by precipitation and surface soil moisture content.This work is important for understanding land-atmosphere interactions and useful for improving the accuracy of land surface models simulations.
