Grid-Forming(GFM)converters are prone to fault-induced overcurrent and power angle instability during grid fault-induced voltage sags.To address this,this paper develops a multi-loop coordinated fault ridethrough(FRT)...Grid-Forming(GFM)converters are prone to fault-induced overcurrent and power angle instability during grid fault-induced voltage sags.To address this,this paper develops a multi-loop coordinated fault ridethrough(FRT)control strategy based on a power outer loop and voltage-current inner loops,aiming to enhance the stability and current-limiting capability of GFM converters during grid fault conditions.During voltage sags,the GFM converter’s voltage source behavior is maintained by dynamically adjusting the reactive power reference to provide voltage support,thereby effectively suppressing the steady-state component of the fault current.To address the active power imbalance induced by voltage sags,a dynamic active power reference correction method based on apparent power is designed to mitigate power angle oscillations and limit transient current.Moreover,an adaptive virtual impedance loop is implemented to enhance dynamic transient current-limiting performance during the fault initiation phase.This approach improves the responsiveness of the inner loop and ensures safe system operation under various fault severities.Under asymmetric fault conditions,a negative-sequence reactive current compensation strategy is incorporated to further suppress negative-sequence voltage and improve voltage symmetry.The proposed control scheme enables coordinated operation of multiple control objectives,including voltage support,current suppression,and power angle stability,across different fault scenarios.Finally,MATLAB/Simulink simulation results validate the effectiveness of the proposed strategy,showcasing its superior performance in current limiting and power angle stability,thereby significantly enhancing the system’s fault ride-through capability.展开更多
This article presents the physics for determining an appropriate helicon plasma source for the linear experimental advanced device(LEAD)through tripartite mutual verification encompassing theoretical analysis,code sim...This article presents the physics for determining an appropriate helicon plasma source for the linear experimental advanced device(LEAD)through tripartite mutual verification encompassing theoretical analysis,code simulation,and experimental validation.Using the HELIC code,plasma excitation processes were simulated with three antenna configurations:m=1 half-helix,m=1 Boswell,and m=0 single-loop helicon antennas,and complemented by theoretical analysis.Key parameters including plasma impedance(R_(p))and energy deposition profiles along radial(P_(r))and axial(P_(z))directions were comparatively analyzed,revealing significantly enhanced R_(p),P_(r),and P_(z) values for the loop antenna configuration as compared with other configurations.Wave propagation equation solutions predicted a primary plasma generation layer at the antenna center;numerical simulations identified an additional plasma formation region at the antenna boundary,indicative of edge Landau damping effects.Interestingly,stronger axial magnetic fields do not necessarily result in higher plasma densities,especially for m=0 antenna configurations.Experimental validation conducted with an m=0 multi-loop plasma source confirmed these findings.Both theoretical analyses and experimental studies on large-volume plasma generation utilizing this innovative source elucidated the underlying mechanisms responsible for the remarkable low mode transition threshold of 150-watt input power and demonstrated significantly enhanced plasma confinement properties.展开更多
An integrated method for identifying the propagation of multi-loop process oscillations and their source location is proposed in this paper. Oscillatory process loop variables are automatically selected based on the c...An integrated method for identifying the propagation of multi-loop process oscillations and their source location is proposed in this paper. Oscillatory process loop variables are automatically selected based on the component-related ratio index and a mixing matrix, both of which are obtained in data preprocessing by spectral independent component analysis. The complex causality among oscillatory process variables is then revealed by Granger causality test and is visualized in the form of causality diagram. The simplification of causal connectivity in the diagram is performed according to the understanding of process knowledge and the final simplest causality diagram, which represents the main oscillation propagation paths, is achieved by the automated cutting-off thresh-old search, with which less significant causality pathways are filtered out. The source of the oscillation disturbance can be identified intuitively through the final causality diagram. Both simulated and real plant data tests are presented to demonstrate the effectiveness and feasibility of the proposed method.展开更多
In confined spaces,conventional ground mobile robots may be unable to reach the target location because of limited maneuvering space or the inability to overcome obstacles.This study presents a ground mobile mechanism...In confined spaces,conventional ground mobile robots may be unable to reach the target location because of limited maneuvering space or the inability to overcome obstacles.This study presents a ground mobile mechanism with a multi-loop reconfigurable trunk(GMMRT)designed to enhance mobility in constrained spaces,such as narrow gaps,ditches,and cross-shaped channels.GMMRT can effectively overcome obstacles in confined spaces through the coordinated motion of its wheels and reconfigurable trunk.Its reconfigurable trunk comprises six limbs and four vertex platforms,forming a versatile,adaptable structure.GMMRT supports two topological structures:wheeled mobility and overall rolling.It features three distinct motion modes:(i)adjusting external dimensions,(ii)performing zero-radius steering,and(iii)overall deformation rolling motion.The kinematic model of GMMRT is established,and its parameters are described using Denavit–Hartenberg parameters.The degrees of freedom under the two topological structures are analyzed on the basis of screw theory.Torque analysis of servo motors is conducted through dynamic analysis.An experimental prototype is designed to validate the three motion modes and servo motor selection,and relevant experiments are performed.Through the development and experimental validation of GMMRT,this work advances mobile robot design for confined spaces and provides a promising approach to overcome the limitations of conventional ground robots.展开更多
In 2005,Gogu,a Frenchman,analyzed 35 different existing formulas for mobility calculation and pointed that the formulas for quick mobility calculation had some limitations and were not general.Therefore,looking for a ...In 2005,Gogu,a Frenchman,analyzed 35 different existing formulas for mobility calculation and pointed that the formulas for quick mobility calculation had some limitations and were not general.Therefore,looking for a general and simple mobility formula is still a hot topic in mechanisms.At the meantime,it is also an important topic to complete the mechanism theory.Gogu proposed a new method that can avoid determining virtual constraints in 2008,but the method is still not general.To solve the problem,this paper defines the new concepts of link-group rank,general-kinematic-pair rank,virtual pair,virtual loop,and virtual-loop rank,and gives a new simple and general formula.Our method converts multi-loop mechanisms into some independent virtual loops,simplifies the problem,avoids calculating virtual constraints,and reduces the calculation difficulty.It is proved that the new formula is simple,general and effective through the mobility analysis of several different kinds of mechanisms.The application of this formula will provide great convenience for general engineers in mobility calculation.展开更多
We construct a class of modules for the twisted multi-loop algebra of type A1 × A1 by applying Wakimoto free bosonic realization. We also discuss the structures and the irreducibility of the Fock space.
文摘Grid-Forming(GFM)converters are prone to fault-induced overcurrent and power angle instability during grid fault-induced voltage sags.To address this,this paper develops a multi-loop coordinated fault ridethrough(FRT)control strategy based on a power outer loop and voltage-current inner loops,aiming to enhance the stability and current-limiting capability of GFM converters during grid fault conditions.During voltage sags,the GFM converter’s voltage source behavior is maintained by dynamically adjusting the reactive power reference to provide voltage support,thereby effectively suppressing the steady-state component of the fault current.To address the active power imbalance induced by voltage sags,a dynamic active power reference correction method based on apparent power is designed to mitigate power angle oscillations and limit transient current.Moreover,an adaptive virtual impedance loop is implemented to enhance dynamic transient current-limiting performance during the fault initiation phase.This approach improves the responsiveness of the inner loop and ensures safe system operation under various fault severities.Under asymmetric fault conditions,a negative-sequence reactive current compensation strategy is incorporated to further suppress negative-sequence voltage and improve voltage symmetry.The proposed control scheme enables coordinated operation of multiple control objectives,including voltage support,current suppression,and power angle stability,across different fault scenarios.Finally,MATLAB/Simulink simulation results validate the effectiveness of the proposed strategy,showcasing its superior performance in current limiting and power angle stability,thereby significantly enhancing the system’s fault ride-through capability.
基金supported by the National Key Research and Development Program of China(Grant No.2022YFE03100002)the National Natural Science Foundation of China(Grant Nos.12435015 and 12075241)。
文摘This article presents the physics for determining an appropriate helicon plasma source for the linear experimental advanced device(LEAD)through tripartite mutual verification encompassing theoretical analysis,code simulation,and experimental validation.Using the HELIC code,plasma excitation processes were simulated with three antenna configurations:m=1 half-helix,m=1 Boswell,and m=0 single-loop helicon antennas,and complemented by theoretical analysis.Key parameters including plasma impedance(R_(p))and energy deposition profiles along radial(P_(r))and axial(P_(z))directions were comparatively analyzed,revealing significantly enhanced R_(p),P_(r),and P_(z) values for the loop antenna configuration as compared with other configurations.Wave propagation equation solutions predicted a primary plasma generation layer at the antenna center;numerical simulations identified an additional plasma formation region at the antenna boundary,indicative of edge Landau damping effects.Interestingly,stronger axial magnetic fields do not necessarily result in higher plasma densities,especially for m=0 antenna configurations.Experimental validation conducted with an m=0 multi-loop plasma source confirmed these findings.Both theoretical analyses and experimental studies on large-volume plasma generation utilizing this innovative source elucidated the underlying mechanisms responsible for the remarkable low mode transition threshold of 150-watt input power and demonstrated significantly enhanced plasma confinement properties.
基金Supported by the National Natural Science Foundation of China （60974061）.
文摘An integrated method for identifying the propagation of multi-loop process oscillations and their source location is proposed in this paper. Oscillatory process loop variables are automatically selected based on the component-related ratio index and a mixing matrix, both of which are obtained in data preprocessing by spectral independent component analysis. The complex causality among oscillatory process variables is then revealed by Granger causality test and is visualized in the form of causality diagram. The simplification of causal connectivity in the diagram is performed according to the understanding of process knowledge and the final simplest causality diagram, which represents the main oscillation propagation paths, is achieved by the automated cutting-off thresh-old search, with which less significant causality pathways are filtered out. The source of the oscillation disturbance can be identified intuitively through the final causality diagram. Both simulated and real plant data tests are presented to demonstrate the effectiveness and feasibility of the proposed method.
基金supported by the Fundamental Research Funds for the Central Universities,China(Grant No.2024JBZX012).
文摘In confined spaces,conventional ground mobile robots may be unable to reach the target location because of limited maneuvering space or the inability to overcome obstacles.This study presents a ground mobile mechanism with a multi-loop reconfigurable trunk(GMMRT)designed to enhance mobility in constrained spaces,such as narrow gaps,ditches,and cross-shaped channels.GMMRT can effectively overcome obstacles in confined spaces through the coordinated motion of its wheels and reconfigurable trunk.Its reconfigurable trunk comprises six limbs and four vertex platforms,forming a versatile,adaptable structure.GMMRT supports two topological structures:wheeled mobility and overall rolling.It features three distinct motion modes:(i)adjusting external dimensions,(ii)performing zero-radius steering,and(iii)overall deformation rolling motion.The kinematic model of GMMRT is established,and its parameters are described using Denavit–Hartenberg parameters.The degrees of freedom under the two topological structures are analyzed on the basis of screw theory.Torque analysis of servo motors is conducted through dynamic analysis.An experimental prototype is designed to validate the three motion modes and servo motor selection,and relevant experiments are performed.Through the development and experimental validation of GMMRT,this work advances mobile robot design for confined spaces and provides a promising approach to overcome the limitations of conventional ground robots.
文摘In 2005,Gogu,a Frenchman,analyzed 35 different existing formulas for mobility calculation and pointed that the formulas for quick mobility calculation had some limitations and were not general.Therefore,looking for a general and simple mobility formula is still a hot topic in mechanisms.At the meantime,it is also an important topic to complete the mechanism theory.Gogu proposed a new method that can avoid determining virtual constraints in 2008,but the method is still not general.To solve the problem,this paper defines the new concepts of link-group rank,general-kinematic-pair rank,virtual pair,virtual loop,and virtual-loop rank,and gives a new simple and general formula.Our method converts multi-loop mechanisms into some independent virtual loops,simplifies the problem,avoids calculating virtual constraints,and reduces the calculation difficulty.It is proved that the new formula is simple,general and effective through the mobility analysis of several different kinds of mechanisms.The application of this formula will provide great convenience for general engineers in mobility calculation.
文摘We construct a class of modules for the twisted multi-loop algebra of type A1 × A1 by applying Wakimoto free bosonic realization. We also discuss the structures and the irreducibility of the Fock space.
