The absolute stability of a class of indirect control systems was studied by applying the theory of Hermitian quadratic form and Jordan normal form. The algebraic formal criteria for the absolute stability are establi...The absolute stability of a class of indirect control systems was studied by applying the theory of Hermitian quadratic form and Jordan normal form. The algebraic formal criteria for the absolute stability are established, and these results are new and useful.展开更多
In this paper, a linear programming method is proposed to solve model predictive control for a class of hybrid systems. Firstly, using the （max, ＋） algebra, a typical subclass of hybrid systems called max-plus-line...In this paper, a linear programming method is proposed to solve model predictive control for a class of hybrid systems. Firstly, using the （max, ＋） algebra, a typical subclass of hybrid systems called max-plus-linear （MPL） systems is obtained. And then, model predictive control （MPC） framework is extended to MPL systems. In general, the nonlinear optimization approach or extended linear complementarity problem （ELCP） were applied to solve the MPL-MPC optimization problem. A new optimization method based on canonical forms for max-min-plus-scaling （MMPS） functions （using the operations maximization, minimization, addition and scalar multiplication） with linear constraints on the inputs is presented. The proposed approach consists in solving several linear programming problems and is more efficient than nonlinear optimization. The validity of the algorithm is illustrated by an example.展开更多
Tube thinning control without wrinkling occurring is a key problem urgently to be solved for improving the forming qualities in numerical control （NC） bending processes of large-diameter Al-alloy thin-walled tubes ...Tube thinning control without wrinkling occurring is a key problem urgently to be solved for improving the forming qualities in numerical control （NC） bending processes of large-diameter Al-alloy thin-walled tubes （AATTs）. It may be a way solving this problem to exert axial compression loads （ACL） on the tube end in the bending. Thus, this article establishes a three-dimensional （3D） elastic-plastic explicit finite element （FE） model for the bending under ACL and has its reliability verified. Through a multi-index orthogonal experiment design, a combination of process parameters, each expressed by a proper range, for this FE model is derived to overcome the compression instability on tube ends. By combining the FE model with a wrinkling energy prediction model, an in-depth study is conducted on the forming characteristics of large-diameter AATTs with small bending radii and it can be concluded that （1） The larger the tube diameters and the smaller the bending radii, the larger the induced tangent tension stress zones on tube intrados, by which the tube maximum tangent compression stress zones will be partitioned in the bending processes; thus, the smaller the ACL roles in decreasing thinning degrees and the larger the compression instability possibilities on tube ends. （2） The tube wrinkling possibilities under ACL are larger than without ACL acting in the earlier forming periods, and smaller in the later ones. （3） For the tubes with a size factor less than 80, the ACL roles in decreasing thinning degrees are stronger than in increasing wrinkling possibilities.展开更多
随着新型电力系统有功-频率耦合特性逐渐复杂化,传统单一储能并网调频策略给电力系统一次调频带来巨大压力,多类型储能组合参与一次调频模式及储能协同控制下的电网频率特性亟需研究。该文分别研究基于下垂控制的电化学储能与基于虚拟...随着新型电力系统有功-频率耦合特性逐渐复杂化,传统单一储能并网调频策略给电力系统一次调频带来巨大压力,多类型储能组合参与一次调频模式及储能协同控制下的电网频率特性亟需研究。该文分别研究基于下垂控制的电化学储能与基于虚拟同步机控制的飞轮储能的频率响应机理,在多类型储能参与电力系统一次调频时利用低通滤波环节对频率变化率信号进行处理,达到储能协调控制效果;接着,将多类型储能协调控制模型与包含新能源与传统火电的电力系统相结合,建立电力系统频率响应(system frequency response,SFR)模型,利用该模型量化分析储能相关参数对系统频率变化率和稳态频率偏差的影响,并进行参数灵敏度分析;最后,在Matlab/Simulink上搭建模型,验证多类型储能相关调频参数对系统频率特性的影响。研究证明,新型电力系统调频单元考虑多类型储能协调控制能够提升电力系统频率稳定性。展开更多
The distributed leader-following consensus for nonlinear multi-agent systems in strict-feedback forms is investigated under directed topology. Firstly, each follower node is modeled by an integrator incorporating with...The distributed leader-following consensus for nonlinear multi-agent systems in strict-feedback forms is investigated under directed topology. Firstly, each follower node is modeled by an integrator incorporating with nonlinear dynamics. The leader node is modeled as an autonomous nonlinear system which sends its information to one or more followers. Then, a simple and novel distributed protocol is proposed based only on the state feedback, under which the states of the followers ultimately synchronize to the leader. By using Lyapunov stability theorem and matrix theory, it is proved that the distributed leader-following consensus of nonlinear multi-agent systems with strict-feedback form is guaranteed by Lipschitz continuous control laws. Finally, some numerical simulations are provided to show the effectiveness of the developed method.展开更多
电压源型变流器的暂态同步稳定问题是一种典型的非线性问题,在多机系统中更是表现出复杂的高阶特性与交互耦合特性。为明确多控制模式变流器异构系统的交互耦合特性与暂态失稳机理,以跟网型变流器(grid-following voltage source conver...电压源型变流器的暂态同步稳定问题是一种典型的非线性问题,在多机系统中更是表现出复杂的高阶特性与交互耦合特性。为明确多控制模式变流器异构系统的交互耦合特性与暂态失稳机理,以跟网型变流器(grid-following voltage source converter,GFL-VSC)、构网型变流器(grid-forming voltage source converter,GFM-VSC)双机混合并网系统为研究对象,首先采用相量分析法建立了适用于暂态稳定分析的混合并联系统的数学模型,揭示了变流器之间交互耦合作用的产生机理。然后,通过引入三维曲面和等高线提出了一种可视化的稳定性分析方法,直观描绘了系统的平衡关系,并揭示了GFM-VSC有功功率参考值、无功功率控制回路以及GFL-VSC电流参考值对系统暂态同步稳定性的影响。结果表明,GFM-VSC无功功率控制的引入会恶化系统的平衡关系。在电网故障时,可以通过减小GFL-VSC有功电流注入并适当增大其无功电流注入,或减小GFM-VSC有功功率参考值来改善系统的稳定性。最后,利用硬件在环测试验证了理论分析的正确性。展开更多
Laser forming is a flexible metal forming process without a die. At present, for this innovative process no exclusive equipment is commercially available. In this paper, some improving measures including temperature m...Laser forming is a flexible metal forming process without a die. At present, for this innovative process no exclusive equipment is commercially available. In this paper, some improving measures including temperature monitoring system, shape monitoring system, cooling system and rotary segment have been proposed on the basis of the general NC laser machine in order to meet the special requirements for laser forming of metals. The improved laser machine may be conveniently used to control dynamically and record the whole laser forming process of metals.展开更多
The construction of the three-dimensionally shaped pylons higher than 400 m requires a very high technological degree. It is known that the application of the tapered slip form method for the erection of the concrete ...The construction of the three-dimensionally shaped pylons higher than 400 m requires a very high technological degree. It is known that the application of the tapered slip form method for the erection of the concrete pylon of long-span cable bridges offers the advantage of being significantly faster than applying the auto-climbing system (ACS) form method. Therefore, this study presents the development of an innovative slip form system for pylons with tapered cross-section. Surface wave inspection system is applied for the determination of slip-up time, wireless hydraulic control system is applied for auto rising, GPS system is used to manage the pylon configuration, and lightweight GFRP (Grass Fiber Reinforced Plastic) panels are applied in the slip form system. Small-scale tests were conducted three times to validate the performance of the developed core technologies, and full-scale tests were conducted twice to validate and verify the developed innovative slip form. The full-scale tapered concrete pylons have hollow shafts and a height of 10 m. The sectional dimensions are varied according to the construction height. The experimental constructions of the tapered pylons using the innovative slip form were conducted successfully. This system is the world’s first application of GFRP slip form panel.展开更多
文摘The absolute stability of a class of indirect control systems was studied by applying the theory of Hermitian quadratic form and Jordan normal form. The algebraic formal criteria for the absolute stability are established, and these results are new and useful.
基金This work was supported by the National Science Foundation of China (No. 60474051)the program for New Century Excellent Talents in University of China (NCET).
文摘In this paper, a linear programming method is proposed to solve model predictive control for a class of hybrid systems. Firstly, using the （max, ＋） algebra, a typical subclass of hybrid systems called max-plus-linear （MPL） systems is obtained. And then, model predictive control （MPC） framework is extended to MPL systems. In general, the nonlinear optimization approach or extended linear complementarity problem （ELCP） were applied to solve the MPL-MPC optimization problem. A new optimization method based on canonical forms for max-min-plus-scaling （MMPS） functions （using the operations maximization, minimization, addition and scalar multiplication） with linear constraints on the inputs is presented. The proposed approach consists in solving several linear programming problems and is more efficient than nonlinear optimization. The validity of the algorithm is illustrated by an example.
基金National Natural Science Foundation of China (59975076, 50175092)National Science Fund of China for Distinguished Young Scholars (50225518)
文摘Tube thinning control without wrinkling occurring is a key problem urgently to be solved for improving the forming qualities in numerical control （NC） bending processes of large-diameter Al-alloy thin-walled tubes （AATTs）. It may be a way solving this problem to exert axial compression loads （ACL） on the tube end in the bending. Thus, this article establishes a three-dimensional （3D） elastic-plastic explicit finite element （FE） model for the bending under ACL and has its reliability verified. Through a multi-index orthogonal experiment design, a combination of process parameters, each expressed by a proper range, for this FE model is derived to overcome the compression instability on tube ends. By combining the FE model with a wrinkling energy prediction model, an in-depth study is conducted on the forming characteristics of large-diameter AATTs with small bending radii and it can be concluded that （1） The larger the tube diameters and the smaller the bending radii, the larger the induced tangent tension stress zones on tube intrados, by which the tube maximum tangent compression stress zones will be partitioned in the bending processes; thus, the smaller the ACL roles in decreasing thinning degrees and the larger the compression instability possibilities on tube ends. （2） The tube wrinkling possibilities under ACL are larger than without ACL acting in the earlier forming periods, and smaller in the later ones. （3） For the tubes with a size factor less than 80, the ACL roles in decreasing thinning degrees are stronger than in increasing wrinkling possibilities.
文摘随着新型电力系统有功-频率耦合特性逐渐复杂化,传统单一储能并网调频策略给电力系统一次调频带来巨大压力,多类型储能组合参与一次调频模式及储能协同控制下的电网频率特性亟需研究。该文分别研究基于下垂控制的电化学储能与基于虚拟同步机控制的飞轮储能的频率响应机理,在多类型储能参与电力系统一次调频时利用低通滤波环节对频率变化率信号进行处理,达到储能协调控制效果;接着,将多类型储能协调控制模型与包含新能源与传统火电的电力系统相结合,建立电力系统频率响应(system frequency response,SFR)模型,利用该模型量化分析储能相关参数对系统频率变化率和稳态频率偏差的影响,并进行参数灵敏度分析;最后,在Matlab/Simulink上搭建模型,验证多类型储能相关调频参数对系统频率特性的影响。研究证明,新型电力系统调频单元考虑多类型储能协调控制能够提升电力系统频率稳定性。
基金National Natural Science Foundation of China(No.61374024)
文摘The distributed leader-following consensus for nonlinear multi-agent systems in strict-feedback forms is investigated under directed topology. Firstly, each follower node is modeled by an integrator incorporating with nonlinear dynamics. The leader node is modeled as an autonomous nonlinear system which sends its information to one or more followers. Then, a simple and novel distributed protocol is proposed based only on the state feedback, under which the states of the followers ultimately synchronize to the leader. By using Lyapunov stability theorem and matrix theory, it is proved that the distributed leader-following consensus of nonlinear multi-agent systems with strict-feedback form is guaranteed by Lipschitz continuous control laws. Finally, some numerical simulations are provided to show the effectiveness of the developed method.
文摘电压源型变流器的暂态同步稳定问题是一种典型的非线性问题,在多机系统中更是表现出复杂的高阶特性与交互耦合特性。为明确多控制模式变流器异构系统的交互耦合特性与暂态失稳机理,以跟网型变流器(grid-following voltage source converter,GFL-VSC)、构网型变流器(grid-forming voltage source converter,GFM-VSC)双机混合并网系统为研究对象,首先采用相量分析法建立了适用于暂态稳定分析的混合并联系统的数学模型,揭示了变流器之间交互耦合作用的产生机理。然后,通过引入三维曲面和等高线提出了一种可视化的稳定性分析方法,直观描绘了系统的平衡关系,并揭示了GFM-VSC有功功率参考值、无功功率控制回路以及GFL-VSC电流参考值对系统暂态同步稳定性的影响。结果表明,GFM-VSC无功功率控制的引入会恶化系统的平衡关系。在电网故障时,可以通过减小GFL-VSC有功电流注入并适当增大其无功电流注入,或减小GFM-VSC有功功率参考值来改善系统的稳定性。最后,利用硬件在环测试验证了理论分析的正确性。
文摘Laser forming is a flexible metal forming process without a die. At present, for this innovative process no exclusive equipment is commercially available. In this paper, some improving measures including temperature monitoring system, shape monitoring system, cooling system and rotary segment have been proposed on the basis of the general NC laser machine in order to meet the special requirements for laser forming of metals. The improved laser machine may be conveniently used to control dynamically and record the whole laser forming process of metals.
文摘The construction of the three-dimensionally shaped pylons higher than 400 m requires a very high technological degree. It is known that the application of the tapered slip form method for the erection of the concrete pylon of long-span cable bridges offers the advantage of being significantly faster than applying the auto-climbing system (ACS) form method. Therefore, this study presents the development of an innovative slip form system for pylons with tapered cross-section. Surface wave inspection system is applied for the determination of slip-up time, wireless hydraulic control system is applied for auto rising, GPS system is used to manage the pylon configuration, and lightweight GFRP (Grass Fiber Reinforced Plastic) panels are applied in the slip form system. Small-scale tests were conducted three times to validate the performance of the developed core technologies, and full-scale tests were conducted twice to validate and verify the developed innovative slip form. The full-scale tapered concrete pylons have hollow shafts and a height of 10 m. The sectional dimensions are varied according to the construction height. The experimental constructions of the tapered pylons using the innovative slip form were conducted successfully. This system is the world’s first application of GFRP slip form panel.
