Dear Editor,This letter proposes a convex optimization-based model predictive control(MPC)autonomous guidance method for the Mars ascent vehicle(MAV).We use the modified chebyshev-picard iteration(MCPI)to solve optimi...Dear Editor,This letter proposes a convex optimization-based model predictive control(MPC)autonomous guidance method for the Mars ascent vehicle(MAV).We use the modified chebyshev-picard iteration(MCPI)to solve optimization sub-problems within the MPC framework,eliminating the dynamic constraints in solving the optimal control problem and enhancing the convergence performance of the algorithm.Moreover,this method can repeatedly perform trajectory optimization calculations at a high frequency,achieving timely correction of the optimal control command.Numerical simulations demonstrate that the method can satisfy the requirements of rapid computation and reliability for the MAV system when considering uncertainties and perturbations.展开更多
This paper investigates the problem of Spacecraft Formation-Containment Flying Control(SFCFC)when the desired translational velocity is time-varying.In SFCFC problem,there are multiple leader spacecraft and multiple f...This paper investigates the problem of Spacecraft Formation-Containment Flying Control(SFCFC)when the desired translational velocity is time-varying.In SFCFC problem,there are multiple leader spacecraft and multiple follower spacecraft and SFCFC can be divided into leader spacecraft’s formation control and follower spacecraft’s containment control.First,under the condition that only a part of leader spacecraft can have access to the desired time-varying translational velocity,a velocity estimator is designed for each leader spacecraft.Secondly,based on the estimated translational velocity,a distributed formation control algorithm is designed for leader spacecraft to achieve the desired formation and move with the desired translational velocity simultaneously.Then,to ensure all follower spacecraft converge to the convex hull formed by the leader spacecraft,a distributed containment control algorithm is designed for follower spacecraft.Moreover,to reduce the dependence of the designed control algorithms on the graph information and increase system robustness,the control gains are changing adaptively and the parametric uncertainties are handled,respectively.Finally,simulation results are provided to illustrate the effectiveness of the theoretical results.展开更多
An algorithm based on the marginalized particle filters （MPF） is given in details in this paper to solve the spacecraft attitude estimation problem： attitude and gyro bias estimation using the biased gyro and vecto...An algorithm based on the marginalized particle filters （MPF） is given in details in this paper to solve the spacecraft attitude estimation problem： attitude and gyro bias estimation using the biased gyro and vector observations. In this algorithm, by marginalizing out the state appearing linearly in the spacecraft model, the Kalman filter is associated with each particle in order to reduce the size of the state space and computational burden. The distribution of attitude vector is approximated by a set of particles and estimated using particle filter, while the estimation of gyro bias is obtained for each one of the attitude particles by applying the Kalman filter. The efficiency of this modified MPF estimator is verified through numerical simulation of a fully actuated rigid body. For comparison, unscented Kalman filter （UKF） is also used to gauge the performance of MPE The results presented in this paper clearly derfionstrate that the MPF is superior to UKF in coping with the nonlinear model.展开更多
Non-contact debris removal methods are fuel-efficient in a single operation compared to contact-based strategies as spacecraft don’t need to match debris velocity.To comprehensively analyze this scheme,maneuvering sc...Non-contact debris removal methods are fuel-efficient in a single operation compared to contact-based strategies as spacecraft don’t need to match debris velocity.To comprehensively analyze this scheme,maneuvering schemes for maximum debris removal with minimum fuel consumption,including task assignment,sequence planning,and trajectory planning,must be formulated.The coupling between variables’dimensions and optimization results in task assignment poses challenges,as debris removal is repetitive and uncertain,leading to a vast search space.This paper proposes a novel Greedy Randomized Adaptive Search Procedure with Large Neighborhood and Crossover Mechanisms(GRASP-LNCM)to address this problem.The hybrid dynamic iteration mechanism improves computational efficiency and enhances the optimality of results.The model innovatively considers unsuccessful single removal by using a quantitative method to assess removal percentage.In addition,to improve the efficiency of sequence and trajectory planning,a Suboptimal Search Algorithm(SSA)based on the Lambert property and accelerated Multi-Revolution Lambert Problem(MRLP)solving strategy is established.Finally,a real Iridium-33 debris removal mission is studied.The simulation demonstrates that the proposed algorithm achieves state-of-the-art performance in several typical scenarios.Compared to the contact-based scheme,the new one is simpler,saving more fuel under certain conditions.展开更多
In order to simultaneously attack a target with impact angle constraint in threedimensional(3-D) space, a novel distributed cooperative guidance law for multiple missiles under directed communication topologies is pro...In order to simultaneously attack a target with impact angle constraint in threedimensional(3-D) space, a novel distributed cooperative guidance law for multiple missiles under directed communication topologies is proposed without radial velocity measurements. First, based on missiles-target 3-D relative motion equations, the multiple missiles cooperative guidance model with impact angle constraint is constructed. Then, in Line-of-Sight(LOS) direction, based on multiagent system cooperative control theory, one guidance law with directed topologies is designed with strict proof, which can guarantee finite time consensus of multiple missiles' impact times. Next, in elevation direction and azimuth direction of LOS, based on homogeneous system stability theory and integral sliding mode control theory, two guidance laws are proposed respectively with strict proof, which can guarantee LOS angles converge to desired values and LOS angular rates converge to zero in finite time. Finally, the effectiveness of the designed cooperative guidance law is demonstrated through simulation results.展开更多
This study presents an improved data-driven Model-Free Adaptive Control(MFAC)strategy for attitude stabilization of a partially constrained combined spacecraft with external disturbances and input saturation. First, a...This study presents an improved data-driven Model-Free Adaptive Control(MFAC)strategy for attitude stabilization of a partially constrained combined spacecraft with external disturbances and input saturation. First, a novel dynamic linearization data model for the partially constrained combined spacecraft with external disturbances is established. The generalized disturbances composed of external disturbances and dynamic linearization errors are then reconstructed by a Discrete Extended State Observer(DESO). With the dynamic linearization data model and reconstructed information, a DESO-MFAC strategy for the combined spacecraft is proposed based only on input and output data. Next, the input saturation is overcome by introducing an antiwindup compensator. Finally, numerical simulations are carried out to demonstrate the effectiveness and feasibility of the proposed controller when the dynamic properties of the partially constrained combined spacecraft are completely unknown.展开更多
Based on the idea of backstepping design, distributedcoordinated tracking problems under directed topology are discussedfor multiple Euler-Lagrange （EL） systems. The dynamicleader case is considered. First, with the...Based on the idea of backstepping design, distributedcoordinated tracking problems under directed topology are discussedfor multiple Euler-Lagrange （EL） systems. The dynamicleader case is considered. First, with the parameter-linearity property,a distributed coordinated adaptive control scheme is proposedfor EL systems in the presence of parametric uncertainties.Then, subject to nonlinear uncertainties and external disturbances,an improved adaptive control algorithm is developed by usingneural-network （NN） approximation of nonlinear functions. Bothproposed algorithms can make tracking errors for each followerultimately bounded. The closed-loop systems are investigated byusing the combination of graph theory, Lyapunov theory, and BarbalatLemma. Numerical examples and comparisons with othermethods are provided to show the effectiveness of the proposedcontrol strategies.展开更多
In this paper, by using quaternion models, the problem of attitude control is investigated for a class of flexible satellites. Two control laws are presented for the considered flexible satellite models to guarantee c...In this paper, by using quaternion models, the problem of attitude control is investigated for a class of flexible satellites. Two control laws are presented for the considered flexible satellite models to guarantee convergence of the closed-loop systems without using angular velocity measurement. One is in the form of a partial state feedback for the case where the modal variable is available, and the other is in the form of an observer-based partial state feedback for the case where the modal variable cannot be measured. Finally, an example is employed to illustrate the effectiveness of the proposed control laws.展开更多
The output feedback control for spacecraft attitude tracking system is investigated in this study. It is assumed that angular velocity measurements are not available for feedback control.A technique named adding power...The output feedback control for spacecraft attitude tracking system is investigated in this study. It is assumed that angular velocity measurements are not available for feedback control.A technique named adding power integrator(API) is adopted to estimate the pseudo-angular-velocity. Then we design a finite-time attitude control law, which only utilizes the relative attitude information. The stability analyses of the feedback system are proved as well, which shows the attitude tracking errors will converge into a region of zero even the external disturbances exist. The simulation results illustrate the high precision and robust attitude control performance of the proposed control strategy.展开更多
Focusing on the non-concave trajectory constraint,a sliding-mode-based nonsingular feedback fast fixed-time three-dimensional terminal guidance of rotor unmanned aerial vehicle landing,planetary landing and spacecraft...Focusing on the non-concave trajectory constraint,a sliding-mode-based nonsingular feedback fast fixed-time three-dimensional terminal guidance of rotor unmanned aerial vehicle landing,planetary landing and spacecraft rendezvous and docking terminal phase with external disturbance is investigated in this paper.Firstly,a fixed-time observer based on real-time differentiator is developed to compensate for the external disturbance,whose estimation error can converge to zero after a time independent of the initial state.Then,a sliding surface ensuring fixed-time convergence is presented.This sliding surface can guarantee that the vehicle achieves a non-concave trajectory,which is better for avoiding collision and maintaining the visibility of the landing site or docking port.Next,the nonsingular guidance ensuring the fixed-time convergence of the sliding surface is proposed,which is continuous and chatter free.At last,three numerical simulations of Mars landing are performed to validate the effectiveness and correctness of the designed scheme.展开更多
Traditional landers typically encounter difficulties achieving stable landings because of the weak gravity and complex terrain of small celestial bodies.A multi-node lander with flexible connections can improve the st...Traditional landers typically encounter difficulties achieving stable landings because of the weak gravity and complex terrain of small celestial bodies.A multi-node lander with flexible connections can improve the stability of a small celestial body landing.However,this also poses new challenges,particularly for landing guidance in hazardous terrain.To address this problem,an equivalent simplified dynamic model of a multi-node flexible lander is first constructed,and its flat output is determined.Subsequently,a trajectoryplanning method combining the flow and vector fields is designed to avoid collision,and the parameters of the vector field are optimized online according to the dynamic and obstacle constraints during the descent process to obtain a more suitable trajectory.Finally,the effectiveness of the proposed trajectory-planning method is verified through comparative simulations of landing and obstacle avoidance from the hover point to the landing area.This study offers new prospects for upcoming small celestial body landing missions in complex terrains.展开更多
In recent years,with the rapid development of unmanned systems technology,unmanned aerial vehicle(UAV)swarm formation flying has gained considerable attention[1,2].Among formation control methods,distributed architect...In recent years,with the rapid development of unmanned systems technology,unmanned aerial vehicle(UAV)swarm formation flying has gained considerable attention[1,2].Among formation control methods,distributed architectures enable the swarm to maintain the shape despite individual UAV failures or communication disruptions,thus demonstrating greater robustness.Moreover,distributed control eliminates reliance on centralized information,yielding a more balanced communication structure across the network[3].展开更多
Small bodies have the characteristics of noncooperative,irregular gravity,and complex terrain on the surface,which cause difficulties in successful landing for conventional landers.In this paper,a multinode flexible l...Small bodies have the characteristics of noncooperative,irregular gravity,and complex terrain on the surface,which cause difficulties in successful landing for conventional landers.In this paper,a multinode flexible lander is put forward to address the problem.The dynamics of this new lander are constructed based on the port-Hamilton framework.The trajectory-tracking formation controller for the lander is designed in a passive way.The proposed dynamics and controller are further validated through numerical simulations.This research presents a fresh concept that holds inspiration for future design involving small-body landers.展开更多
Salient object detection(SOD)has garnered significant interest because of its pivotal role in numerous computer vision and graphics applications.Deep convolutional neural networks have been widely applied in salient o...Salient object detection(SOD)has garnered significant interest because of its pivotal role in numerous computer vision and graphics applications.Deep convolutional neural networks have been widely applied in salient object detection and have achieved remarkable results in this field.To enhance the network representation ability,a very important means is to increase the depth of the neural network to learn as many hierarchical features as possible.However,the information related to the input image features will be lost with the increase in network depth,and existing models suffer from information distortion caused by interpolation during up-sampling and downsampling.In response to this drawback,this article focuses on the feature level and label level to address this significant challenge.On the one hand,a novel cascaded interaction network with a guidance module named global-local aligned attention(GAA)is designed to reduce the negative impact of interpolation on the feature side.On the other hand,a deep supervision strategy based on edge erosion is proposed to reduce the negative guidance of label interpolation on lateral output.Extensive experiments on five popular datasets demonstrate the superiority of our method.展开更多
An active crowbar protective circuit is an effective and common approach for low voltage ride through(LVRT) of a doubly-fed induction generator(DFIG). The crowbar resistance value and its switching scheme both have cr...An active crowbar protective circuit is an effective and common approach for low voltage ride through(LVRT) of a doubly-fed induction generator(DFIG). The crowbar resistance value and its switching scheme both have crucial effects on safety recovery. The effects encountered are correlative dependence and interplay so that analyzing them from a single factor, as most existing LVRT control methods would do, obtains a partial optimal solution. This paper combines these two factors toanalyze their coordination effects on the LVRT control,and to also investigate whether the global optimal performance of these factors can be achieved. The principles for resistance selection and the schemes for crowbar switching are discussed first. Next, the coupling relationship is ana-lyzed based on statistical sampling simulation data with different resistance values and various switching schemes.The results demonstrate that their coordination has critical influence on rotor peak current, DC-link voltage and reactive power. The optimal coordination will be different according to specific requirements. Hence the global optimal combination could be achieved when all requirements are taken into consideration.展开更多
基金supported by the National Defense Basic Scientific Research Program(JCKY2021603B030)the National Natural Science Foundation of China(62273118,12150008)the Natural Science Foundation of Heilongjiang Province(LH2022F023).
文摘Dear Editor,This letter proposes a convex optimization-based model predictive control(MPC)autonomous guidance method for the Mars ascent vehicle(MAV).We use the modified chebyshev-picard iteration(MCPI)to solve optimization sub-problems within the MPC framework,eliminating the dynamic constraints in solving the optimal control problem and enhancing the convergence performance of the algorithm.Moreover,this method can repeatedly perform trajectory optimization calculations at a high frequency,achieving timely correction of the optimal control command.Numerical simulations demonstrate that the method can satisfy the requirements of rapid computation and reliability for the MAV system when considering uncertainties and perturbations.
基金supported by the National Natural Science Foundation of China(Nos.61876050,61673135,61603114).
文摘This paper investigates the problem of Spacecraft Formation-Containment Flying Control(SFCFC)when the desired translational velocity is time-varying.In SFCFC problem,there are multiple leader spacecraft and multiple follower spacecraft and SFCFC can be divided into leader spacecraft’s formation control and follower spacecraft’s containment control.First,under the condition that only a part of leader spacecraft can have access to the desired time-varying translational velocity,a velocity estimator is designed for each leader spacecraft.Secondly,based on the estimated translational velocity,a distributed formation control algorithm is designed for leader spacecraft to achieve the desired formation and move with the desired translational velocity simultaneously.Then,to ensure all follower spacecraft converge to the convex hull formed by the leader spacecraft,a distributed containment control algorithm is designed for follower spacecraft.Moreover,to reduce the dependence of the designed control algorithms on the graph information and increase system robustness,the control gains are changing adaptively and the parametric uncertainties are handled,respectively.Finally,simulation results are provided to illustrate the effectiveness of the theoretical results.
基金This work was supported by the Research Fund for the Doctoral Program of Higher Education of China (No. 20050213010)the National High Technology Research and Development Program of China (863 Program) (No. 2004AA735080).
文摘An algorithm based on the marginalized particle filters （MPF） is given in details in this paper to solve the spacecraft attitude estimation problem： attitude and gyro bias estimation using the biased gyro and vector observations. In this algorithm, by marginalizing out the state appearing linearly in the spacecraft model, the Kalman filter is associated with each particle in order to reduce the size of the state space and computational burden. The distribution of attitude vector is approximated by a set of particles and estimated using particle filter, while the estimation of gyro bias is obtained for each one of the attitude particles by applying the Kalman filter. The efficiency of this modified MPF estimator is verified through numerical simulation of a fully actuated rigid body. For comparison, unscented Kalman filter （UKF） is also used to gauge the performance of MPE The results presented in this paper clearly derfionstrate that the MPF is superior to UKF in coping with the nonlinear model.
基金co-supported by the National Natural Science Foundation of China(Nos.U23B6001,62273118,12150008)the Fundamental Research Funds for the Central Universities,China(No.2023FRFK02043)+1 种基金the Natural Science Foundation of Heilongjiang Province,China(No.LH2022F023)China Aerospace Science and Technology Corporation Youth Talent Support Program.
文摘Non-contact debris removal methods are fuel-efficient in a single operation compared to contact-based strategies as spacecraft don’t need to match debris velocity.To comprehensively analyze this scheme,maneuvering schemes for maximum debris removal with minimum fuel consumption,including task assignment,sequence planning,and trajectory planning,must be formulated.The coupling between variables’dimensions and optimization results in task assignment poses challenges,as debris removal is repetitive and uncertain,leading to a vast search space.This paper proposes a novel Greedy Randomized Adaptive Search Procedure with Large Neighborhood and Crossover Mechanisms(GRASP-LNCM)to address this problem.The hybrid dynamic iteration mechanism improves computational efficiency and enhances the optimality of results.The model innovatively considers unsuccessful single removal by using a quantitative method to assess removal percentage.In addition,to improve the efficiency of sequence and trajectory planning,a Suboptimal Search Algorithm(SSA)based on the Lambert property and accelerated Multi-Revolution Lambert Problem(MRLP)solving strategy is established.Finally,a real Iridium-33 debris removal mission is studied.The simulation demonstrates that the proposed algorithm achieves state-of-the-art performance in several typical scenarios.Compared to the contact-based scheme,the new one is simpler,saving more fuel under certain conditions.
基金supported by the National Natural Science Foundation of China(Nos.61603114,61673135)
文摘In order to simultaneously attack a target with impact angle constraint in threedimensional(3-D) space, a novel distributed cooperative guidance law for multiple missiles under directed communication topologies is proposed without radial velocity measurements. First, based on missiles-target 3-D relative motion equations, the multiple missiles cooperative guidance model with impact angle constraint is constructed. Then, in Line-of-Sight(LOS) direction, based on multiagent system cooperative control theory, one guidance law with directed topologies is designed with strict proof, which can guarantee finite time consensus of multiple missiles' impact times. Next, in elevation direction and azimuth direction of LOS, based on homogeneous system stability theory and integral sliding mode control theory, two guidance laws are proposed respectively with strict proof, which can guarantee LOS angles converge to desired values and LOS angular rates converge to zero in finite time. Finally, the effectiveness of the designed cooperative guidance law is demonstrated through simulation results.
基金supported by National Natural Science Foundation of China(Nos.61603114,61673135)the Fundamental Research Funds for the Central Universities of China(No.HIT.NSRIF.201826)
文摘This study presents an improved data-driven Model-Free Adaptive Control(MFAC)strategy for attitude stabilization of a partially constrained combined spacecraft with external disturbances and input saturation. First, a novel dynamic linearization data model for the partially constrained combined spacecraft with external disturbances is established. The generalized disturbances composed of external disturbances and dynamic linearization errors are then reconstructed by a Discrete Extended State Observer(DESO). With the dynamic linearization data model and reconstructed information, a DESO-MFAC strategy for the combined spacecraft is proposed based only on input and output data. Next, the input saturation is overcome by introducing an antiwindup compensator. Finally, numerical simulations are carried out to demonstrate the effectiveness and feasibility of the proposed controller when the dynamic properties of the partially constrained combined spacecraft are completely unknown.
基金supported by the National Natural Science Foundation of China(6130400561174200)the Research Fund for the Doctoral Program of Higher Education of China(20102302110031)
文摘Based on the idea of backstepping design, distributedcoordinated tracking problems under directed topology are discussedfor multiple Euler-Lagrange （EL） systems. The dynamicleader case is considered. First, with the parameter-linearity property,a distributed coordinated adaptive control scheme is proposedfor EL systems in the presence of parametric uncertainties.Then, subject to nonlinear uncertainties and external disturbances,an improved adaptive control algorithm is developed by usingneural-network （NN） approximation of nonlinear functions. Bothproposed algorithms can make tracking errors for each followerultimately bounded. The closed-loop systems are investigated byusing the combination of graph theory, Lyapunov theory, and BarbalatLemma. Numerical examples and comparisons with othermethods are provided to show the effectiveness of the proposedcontrol strategies.
基金co-supported by the Major Program of National Natural Science Foundation of China (Nos.61690210,61690212)Shenzhen Municipal Basic Research Project for Discipline Layout (No.JCYJ20170413112722597)Shenzhen Municipal Project for Basic Research (Nos.JCYJ20170307150952660,JCYJ20170307150227897)
文摘In this paper, by using quaternion models, the problem of attitude control is investigated for a class of flexible satellites. Two control laws are presented for the considered flexible satellite models to guarantee convergence of the closed-loop systems without using angular velocity measurement. One is in the form of a partial state feedback for the case where the modal variable is available, and the other is in the form of an observer-based partial state feedback for the case where the modal variable cannot be measured. Finally, an example is employed to illustrate the effectiveness of the proposed control laws.
基金supported by the National Natural Science Foundation of China(616731356140310361603114)
文摘The output feedback control for spacecraft attitude tracking system is investigated in this study. It is assumed that angular velocity measurements are not available for feedback control.A technique named adding power integrator(API) is adopted to estimate the pseudo-angular-velocity. Then we design a finite-time attitude control law, which only utilizes the relative attitude information. The stability analyses of the feedback system are proved as well, which shows the attitude tracking errors will converge into a region of zero even the external disturbances exist. The simulation results illustrate the high precision and robust attitude control performance of the proposed control strategy.
基金co-supported by the National Defense Basic Scientific Research Project,China(No.JCKY2020903B002)the National Natural Science Foundation of China(Nos.61973100,62273118 and 12150008)。
文摘Focusing on the non-concave trajectory constraint,a sliding-mode-based nonsingular feedback fast fixed-time three-dimensional terminal guidance of rotor unmanned aerial vehicle landing,planetary landing and spacecraft rendezvous and docking terminal phase with external disturbance is investigated in this paper.Firstly,a fixed-time observer based on real-time differentiator is developed to compensate for the external disturbance,whose estimation error can converge to zero after a time independent of the initial state.Then,a sliding surface ensuring fixed-time convergence is presented.This sliding surface can guarantee that the vehicle achieves a non-concave trajectory,which is better for avoiding collision and maintaining the visibility of the landing site or docking port.Next,the nonsingular guidance ensuring the fixed-time convergence of the sliding surface is proposed,which is continuous and chatter free.At last,three numerical simulations of Mars landing are performed to validate the effectiveness and correctness of the designed scheme.
基金the National Key R&D Program(grant number 2019YFA0706500)the National Defense Basic Research Projects(grant number JCKY2021603B030).
文摘Traditional landers typically encounter difficulties achieving stable landings because of the weak gravity and complex terrain of small celestial bodies.A multi-node lander with flexible connections can improve the stability of a small celestial body landing.However,this also poses new challenges,particularly for landing guidance in hazardous terrain.To address this problem,an equivalent simplified dynamic model of a multi-node flexible lander is first constructed,and its flat output is determined.Subsequently,a trajectoryplanning method combining the flow and vector fields is designed to avoid collision,and the parameters of the vector field are optimized online according to the dynamic and obstacle constraints during the descent process to obtain a more suitable trajectory.Finally,the effectiveness of the proposed trajectory-planning method is verified through comparative simulations of landing and obstacle avoidance from the hover point to the landing area.This study offers new prospects for upcoming small celestial body landing missions in complex terrains.
基金supported by Guangdong Basic and Applied Basic Research Foundation(Grant No.2023B1515120018)Shenzhen Fundamental Research Program(Grant Nos.JCYJ20241202124010014 and GXWD20231129140908002)。
文摘In recent years,with the rapid development of unmanned systems technology,unmanned aerial vehicle(UAV)swarm formation flying has gained considerable attention[1,2].Among formation control methods,distributed architectures enable the swarm to maintain the shape despite individual UAV failures or communication disruptions,thus demonstrating greater robustness.Moreover,distributed control eliminates reliance on centralized information,yielding a more balanced communication structure across the network[3].
基金supported by the National Key R&D Program(grant number 2019YFA0706500)the National Natural Science Foundation of China(grant number 62273118)National defense basic research projects(grant numbers JCKY2021603B030,JCKY2020903B002).
文摘Small bodies have the characteristics of noncooperative,irregular gravity,and complex terrain on the surface,which cause difficulties in successful landing for conventional landers.In this paper,a multinode flexible lander is put forward to address the problem.The dynamics of this new lander are constructed based on the port-Hamilton framework.The trajectory-tracking formation controller for the lander is designed in a passive way.The proposed dynamics and controller are further validated through numerical simulations.This research presents a fresh concept that holds inspiration for future design involving small-body landers.
基金supported in part by Shenzhen Science and Technology Program,China(No.GXWD20231129140908002).
文摘Salient object detection(SOD)has garnered significant interest because of its pivotal role in numerous computer vision and graphics applications.Deep convolutional neural networks have been widely applied in salient object detection and have achieved remarkable results in this field.To enhance the network representation ability,a very important means is to increase the depth of the neural network to learn as many hierarchical features as possible.However,the information related to the input image features will be lost with the increase in network depth,and existing models suffer from information distortion caused by interpolation during up-sampling and downsampling.In response to this drawback,this article focuses on the feature level and label level to address this significant challenge.On the one hand,a novel cascaded interaction network with a guidance module named global-local aligned attention(GAA)is designed to reduce the negative impact of interpolation on the feature side.On the other hand,a deep supervision strategy based on edge erosion is proposed to reduce the negative guidance of label interpolation on lateral output.Extensive experiments on five popular datasets demonstrate the superiority of our method.
基金supported by the National Natural Science Foundation of China (No. 61773137, No. 61403099)the National Natural Science Foundation of Shandong Province (No. 2014BSA10007, No. 2014J14LN92)
文摘An active crowbar protective circuit is an effective and common approach for low voltage ride through(LVRT) of a doubly-fed induction generator(DFIG). The crowbar resistance value and its switching scheme both have crucial effects on safety recovery. The effects encountered are correlative dependence and interplay so that analyzing them from a single factor, as most existing LVRT control methods would do, obtains a partial optimal solution. This paper combines these two factors toanalyze their coordination effects on the LVRT control,and to also investigate whether the global optimal performance of these factors can be achieved. The principles for resistance selection and the schemes for crowbar switching are discussed first. Next, the coupling relationship is ana-lyzed based on statistical sampling simulation data with different resistance values and various switching schemes.The results demonstrate that their coordination has critical influence on rotor peak current, DC-link voltage and reactive power. The optimal coordination will be different according to specific requirements. Hence the global optimal combination could be achieved when all requirements are taken into consideration.
