Solid-state transformer-based smart transformer(ST)can provide the dc connectivity and advanced services to improve the grid performance and to increase the penetration of the power electronics interfaced resources(e....Solid-state transformer-based smart transformer(ST)can provide the dc connectivity and advanced services to improve the grid performance and to increase the penetration of the power electronics interfaced resources(e.g.,distributed generators and electric vehicle charging stations)in modern electricity distribution grids.Since the ST is a new and effective paradigm of the electricity grid evolution to well understand the ST,this paper systematically presents the basic architecture and the typical control schemes of the ST and then the advanced services that ST can provide to improve the electricity grids performances in terms of the power flow control,power quality improvement,active damping and active contribution to improve distribution grid resilience by means of enabling autonomous microgrids operation as well as launching a restoration procedure following a general blackout.展开更多
Bio-inspired micro-air-vehicles(MAVs)usually operate in the atmospheric boundary layer at a low Reynolds number and complex wind conditions including large-scale turbulence,strong shear,and gusts.We develop an open je...Bio-inspired micro-air-vehicles(MAVs)usually operate in the atmospheric boundary layer at a low Reynolds number and complex wind conditions including large-scale turbulence,strong shear,and gusts.We develop an open jet facility(OJF)to meet the requirements of MAV flight experiments at very low speed and high turbulence intensity.Powered by a stage-driven fan,the OJF is capable of generating wind speeds covering 0.1–16.8 m/s,with a velocity ratio of 100:1.The contraction section of the OJF is designed using an adjoint-driven optimization method,resulting in a con-traction ratio of 3:1 and a length-to-diameter ratio of 0.75.A modularized design of the jet nozzle can produce laminar or high-turbulence wind conditions.Flow field calibration results demonstrate that the OJF is capable of producing a high-quality baseline flow with steady airspeed as low as 0.1 m/s,uniform region around 80%of the cross-sectional test area,and turbulence intensity around 0.5%.Equipped with an optimized active grid(AG),the OJF can reproduce controllable,fully-developed turbulent wind conditions with the turbulence intensity up to 24%,energy spectrum satisfying the five-thirds power law,and the uniform region close to 70%of the cross-sectional area of the test section.The turbulence intensity,integral length scale,Kol-mogorov length scale,and mean energy dissipation rate of the generated flow can be adjusted by varying the area of the triangular through-hole in the wings of the AG.展开更多
基金the German Federal Ministry of Education and Research(BMBF)within the Kopernikus Project ENSURE"New ENergy grid StructURes for the German Energiewende"(03SFK1I0-2)。
文摘Solid-state transformer-based smart transformer(ST)can provide the dc connectivity and advanced services to improve the grid performance and to increase the penetration of the power electronics interfaced resources(e.g.,distributed generators and electric vehicle charging stations)in modern electricity distribution grids.Since the ST is a new and effective paradigm of the electricity grid evolution to well understand the ST,this paper systematically presents the basic architecture and the typical control schemes of the ST and then the advanced services that ST can provide to improve the electricity grids performances in terms of the power flow control,power quality improvement,active damping and active contribution to improve distribution grid resilience by means of enabling autonomous microgrids operation as well as launching a restoration procedure following a general blackout.
基金This work has been supported in part by the National Natural Science Foundation of China(Grant Nos.11925201 and 11988102)the National Key R&D Program of China(Grant No.2020YFE0204200)the Xplorer Prize.
文摘Bio-inspired micro-air-vehicles(MAVs)usually operate in the atmospheric boundary layer at a low Reynolds number and complex wind conditions including large-scale turbulence,strong shear,and gusts.We develop an open jet facility(OJF)to meet the requirements of MAV flight experiments at very low speed and high turbulence intensity.Powered by a stage-driven fan,the OJF is capable of generating wind speeds covering 0.1–16.8 m/s,with a velocity ratio of 100:1.The contraction section of the OJF is designed using an adjoint-driven optimization method,resulting in a con-traction ratio of 3:1 and a length-to-diameter ratio of 0.75.A modularized design of the jet nozzle can produce laminar or high-turbulence wind conditions.Flow field calibration results demonstrate that the OJF is capable of producing a high-quality baseline flow with steady airspeed as low as 0.1 m/s,uniform region around 80%of the cross-sectional test area,and turbulence intensity around 0.5%.Equipped with an optimized active grid(AG),the OJF can reproduce controllable,fully-developed turbulent wind conditions with the turbulence intensity up to 24%,energy spectrum satisfying the five-thirds power law,and the uniform region close to 70%of the cross-sectional area of the test section.The turbulence intensity,integral length scale,Kol-mogorov length scale,and mean energy dissipation rate of the generated flow can be adjusted by varying the area of the triangular through-hole in the wings of the AG.
