Dear Editor,This letter investigates the grid-forming control for power converters.Recently,grid-forming control based on matching of synchronous machines was suggested by using continuous measurements.In the present ...Dear Editor,This letter investigates the grid-forming control for power converters.Recently,grid-forming control based on matching of synchronous machines was suggested by using continuous measurements.In the present letter,we suggest a digital implementation using artificial delays where the controller employs the discrete-time measurements only.展开更多
Effects of process parameters on microstructure and mechanical properties of the AM50A magnesium alloy components formed by double control forming （DCF） were investigated via a four-factor and four-level orthogonal ...Effects of process parameters on microstructure and mechanical properties of the AM50A magnesium alloy components formed by double control forming （DCF） were investigated via a four-factor and four-level orthogonal experiment. The variable curves of DCF showed that the forging procedure was started in the following 35 ms after the injection procedure was completed. It was confirmed that the high-speed filling and high-pressure densifying were combined together in the DCF process. Better surface quality and higher mechanical properties were achieved in the components formed by DCF as compared to die casting （DC） due to the refined and uniform microstructure with a few defects or without defects. Injection speed affected more effectively the yield strength （YS）, ultimate tensile strength （UTS） and elongation as compared to pouring temperature, die temperature and forging force. But the pouring temperature had a more significant effect on hardness as compared to injection speed, die temperature and forging force. Pouring temperature of 675 ＆#176;C, injection speed of 2.7 m/s and forging force of 4000 kN except for die temperature were the optimal parameters for obtaining the highest YS, UTS, elongation and Vickers hardness. Die temperatures of 205, 195, 195 and 225 ＆#176;C were involved in achieving the highest YS, UTS, elongation and Vickers hardness, respectively. Obvious microporosity and microcracks were found on the fracture surface of the components formed by DC, deteriorating the mechanical properties. However, the tensile fracture morphology of the components formed by DCF was characterized by ductile fracture due to a large number of dimples and no defects, which was beneficial for improving the mechanical properties.展开更多
General nonlinear control systems are studied in this paper with the goal to transform them into the so-called controllability canonteal form via state transformation only. The conditions of transformability are given...General nonlinear control systems are studied in this paper with the goal to transform them into the so-called controllability canonteal form via state transformation only. The conditions of transformability are given for both single input and multiple input cases. Besides, by an algebraic approach the procedure for constructing the state transformation is established. This paper is formulated in the framework of calculus rather than differential geometry approach.展开更多
The aluminum alloy parts used in airbag of car were studied with flow control forming(FCF) method, which was a good way to low forming force and better mechanical properties. The key technology of FCF was the design o...The aluminum alloy parts used in airbag of car were studied with flow control forming(FCF) method, which was a good way to low forming force and better mechanical properties. The key technology of FCF was the design of control chamber to divide metal flow. So, the design method of FCF was analyzed and two type of control chamber were put forward. According to divisional principle, calculation model of forming force and approximate formula were given. Then forming process of aluminum alloy multi-layer cylinder parts was simulated. The effect of friction factor, die radius and punch velocity on metal flow and forming force was obtained. Finally, the experiment was preformed under the direction of theory and finite element(FE) simulation results. And the qualified parts were manufactured. The simulation data and experimental results show that the forming sequence of inner wall and outer wall, and then the force step, can be controlled by adjusting the process parameters. And the FCF technology proposed has very important application value in precision forging.展开更多
This paper proposes a sort of new normal forms consisting of observer form and controllable form for nonlinear systems. The conditions for transforming to these normal forms are given, respectively. These normal forms...This paper proposes a sort of new normal forms consisting of observer form and controllable form for nonlinear systems. The conditions for transforming to these normal forms are given, respectively. These normal forms are used to treat the problems of observer design and linearization. The first part of this paper deals with the observer form, and the second the controllable form.展开更多
The relevant results of thermodynamics simulation test, recrystallization study and FEM numercal simulation are described. A method is also introduced that the controlled hot forming is carried out by adopting the pro...The relevant results of thermodynamics simulation test, recrystallization study and FEM numercal simulation are described. A method is also introduced that the controlled hot forming is carried out by adopting the program of expansion-extrusion compound forming.展开更多
At the present stage, the competitive environment among enterprises in our social market is increasingly fierce, which requires strong practical ability and innovation ability for talents. Experimental teaching, as th...At the present stage, the competitive environment among enterprises in our social market is increasingly fierce, which requires strong practical ability and innovation ability for talents. Experimental teaching, as the main means to cultivate talents' problem-solving ability, practical ability and creative ability, should be reformed and innovated in time so as to improve the efficiency and quality of experimental teaching for material forming and control engineering major. Based on this, this paper mainly analyzes the importance of experimental teaching of material forming and control engineering in colleges and universities, and puts forward some methods of exploration and construction of experimental teaching for reference.展开更多
大规模海上风电柔性直流送出系统(voltage source converter based high voltage direct current,VSC-HVDC)可以通过双端换流站的联动作用调节风电机组功率,提升陆上电网的调频能力。为解决远海风电场输出功率与陆上电网频率耦合性差和...大规模海上风电柔性直流送出系统(voltage source converter based high voltage direct current,VSC-HVDC)可以通过双端换流站的联动作用调节风电机组功率,提升陆上电网的调频能力。为解决远海风电场输出功率与陆上电网频率耦合性差和响应滞后的问题,该文提出一种基于匹配控制的陆海换流站协同调频方法。该策略采用双端对称的匹配控制结构,将陆上电网的频率变化通过VSC-HVDC直流电压耦合传递至海上风电侧,并在风电变流器中结合虚拟同步机技术与自适应变阻尼减载控制,使得各风电机组无需通信即可快速响应陆上电网频率波动,动态提供频率支撑功率。通过MATLAB/Simulink软件建立大容量等值直驱型风电机组经VSC-HVDC并网的仿真模型,在弱电网条件下仿真验证了基于匹配控制的VSC-HVDC与海上风电系统联动调频策略的有效性。展开更多
The plastic cement belongs to a sort of polymer material, the chemical composition is very complex, and the plastic cement work-piece is generally manufactured by die press forming. Aimed at being difficult to control...The plastic cement belongs to a sort of polymer material, the chemical composition is very complex, and the plastic cement work-piece is generally manufactured by die press forming. Aimed at being difficult to control in parameters of forming process, the paper explored the humanoid based intelligence control strategy. In the paper, it made the anatomy in control puzzle resulted in uncertainty such as chemical component of plastic cement etc., summarized up the characteristic of cybernetics in forming process, researched on the humanoid based intelligence control strategy, and constructed the control algorithm of forming process in plastic cement work-piece. Taking the process experiment of temperature and pressure control as an example, it validated the good dynamic and static control quality through simulation of control algorithm constructed in this paper. The experimental results show that the control algorithm explored in this paper is reasonably available.展开更多
In this paper,we study the Noether-form invariance of nonholonomic mechanical controllable systems inphase space.Equations of motion of the controllable mechanical systems in phase space are presented.The definitionan...In this paper,we study the Noether-form invariance of nonholonomic mechanical controllable systems inphase space.Equations of motion of the controllable mechanical systems in phase space are presented.The definitionand the criterion for this system are presented.A new conserved quantity and the Noether conserved quantity deducedfrom the Noether-form invariance are obtained.An example is given to illustrate the application of the results.展开更多
[ Objective] To meet the needs of ＂Prevention and Control of Poultry and Poultry Diseases＂ course in higher vocational colleges in new period. [Method] In order to introduce theoretical knowledge, enhance practical ...[ Objective] To meet the needs of ＂Prevention and Control of Poultry and Poultry Diseases＂ course in higher vocational colleges in new period. [Method] In order to introduce theoretical knowledge, enhance practical ability and train quality, teaching content, teaching methods and practical teaching of the course were explored according to trends of academic development and personnel training. [ Result] The reform of teaching form improved the teaching effect, mobilized the learning enthusiasm and initiative of students, and enhanced their ability to solve practical prob- lems. [ Conclusion] The teaching form of ＂Prevention and Control of Poultry and Poultry Diseases＂ course has been successfully reformed.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
基金supported by the National Natural Science Foundation of China(62403296,62303292,62173218).
文摘Dear Editor,This letter investigates the grid-forming control for power converters.Recently,grid-forming control based on matching of synchronous machines was suggested by using continuous measurements.In the present letter,we suggest a digital implementation using artificial delays where the controller employs the discrete-time measurements only.
基金Project(51075099)supported by the National Natural Science Foundation of ChinaProject(E201038)supported by the Natural Science Foundation of Heilongjiang Province,China+2 种基金Project(HIT.NSRIF.2013007)supported by the Fundamental Research Funds for the Central Universities,ChinaProject(2011RFQXG010)supported by the Harbin City Young Scientists Foundation,ChinaProject(LBH-T1102)supported by Specially Postdoctoral Science Foundation of Heilongjiang Province,China
文摘Effects of process parameters on microstructure and mechanical properties of the AM50A magnesium alloy components formed by double control forming （DCF） were investigated via a four-factor and four-level orthogonal experiment. The variable curves of DCF showed that the forging procedure was started in the following 35 ms after the injection procedure was completed. It was confirmed that the high-speed filling and high-pressure densifying were combined together in the DCF process. Better surface quality and higher mechanical properties were achieved in the components formed by DCF as compared to die casting （DC） due to the refined and uniform microstructure with a few defects or without defects. Injection speed affected more effectively the yield strength （YS）, ultimate tensile strength （UTS） and elongation as compared to pouring temperature, die temperature and forging force. But the pouring temperature had a more significant effect on hardness as compared to injection speed, die temperature and forging force. Pouring temperature of 675 ＆#176;C, injection speed of 2.7 m/s and forging force of 4000 kN except for die temperature were the optimal parameters for obtaining the highest YS, UTS, elongation and Vickers hardness. Die temperatures of 205, 195, 195 and 225 ＆#176;C were involved in achieving the highest YS, UTS, elongation and Vickers hardness, respectively. Obvious microporosity and microcracks were found on the fracture surface of the components formed by DC, deteriorating the mechanical properties. However, the tensile fracture morphology of the components formed by DCF was characterized by ductile fracture due to a large number of dimples and no defects, which was beneficial for improving the mechanical properties.
文摘General nonlinear control systems are studied in this paper with the goal to transform them into the so-called controllability canonteal form via state transformation only. The conditions of transformability are given for both single input and multiple input cases. Besides, by an algebraic approach the procedure for constructing the state transformation is established. This paper is formulated in the framework of calculus rather than differential geometry approach.
文摘The aluminum alloy parts used in airbag of car were studied with flow control forming(FCF) method, which was a good way to low forming force and better mechanical properties. The key technology of FCF was the design of control chamber to divide metal flow. So, the design method of FCF was analyzed and two type of control chamber were put forward. According to divisional principle, calculation model of forming force and approximate formula were given. Then forming process of aluminum alloy multi-layer cylinder parts was simulated. The effect of friction factor, die radius and punch velocity on metal flow and forming force was obtained. Finally, the experiment was preformed under the direction of theory and finite element(FE) simulation results. And the qualified parts were manufactured. The simulation data and experimental results show that the forming sequence of inner wall and outer wall, and then the force step, can be controlled by adjusting the process parameters. And the FCF technology proposed has very important application value in precision forging.
基金The project is supported by the National Natural Science Foundation of China.
文摘This paper proposes a sort of new normal forms consisting of observer form and controllable form for nonlinear systems. The conditions for transforming to these normal forms are given, respectively. These normal forms are used to treat the problems of observer design and linearization. The first part of this paper deals with the observer form, and the second the controllable form.
文摘The relevant results of thermodynamics simulation test, recrystallization study and FEM numercal simulation are described. A method is also introduced that the controlled hot forming is carried out by adopting the program of expansion-extrusion compound forming.
文摘At the present stage, the competitive environment among enterprises in our social market is increasingly fierce, which requires strong practical ability and innovation ability for talents. Experimental teaching, as the main means to cultivate talents' problem-solving ability, practical ability and creative ability, should be reformed and innovated in time so as to improve the efficiency and quality of experimental teaching for material forming and control engineering major. Based on this, this paper mainly analyzes the importance of experimental teaching of material forming and control engineering in colleges and universities, and puts forward some methods of exploration and construction of experimental teaching for reference.
文摘大规模海上风电柔性直流送出系统(voltage source converter based high voltage direct current,VSC-HVDC)可以通过双端换流站的联动作用调节风电机组功率,提升陆上电网的调频能力。为解决远海风电场输出功率与陆上电网频率耦合性差和响应滞后的问题,该文提出一种基于匹配控制的陆海换流站协同调频方法。该策略采用双端对称的匹配控制结构,将陆上电网的频率变化通过VSC-HVDC直流电压耦合传递至海上风电侧,并在风电变流器中结合虚拟同步机技术与自适应变阻尼减载控制,使得各风电机组无需通信即可快速响应陆上电网频率波动,动态提供频率支撑功率。通过MATLAB/Simulink软件建立大容量等值直驱型风电机组经VSC-HVDC并网的仿真模型,在弱电网条件下仿真验证了基于匹配控制的VSC-HVDC与海上风电系统联动调频策略的有效性。
文摘The plastic cement belongs to a sort of polymer material, the chemical composition is very complex, and the plastic cement work-piece is generally manufactured by die press forming. Aimed at being difficult to control in parameters of forming process, the paper explored the humanoid based intelligence control strategy. In the paper, it made the anatomy in control puzzle resulted in uncertainty such as chemical component of plastic cement etc., summarized up the characteristic of cybernetics in forming process, researched on the humanoid based intelligence control strategy, and constructed the control algorithm of forming process in plastic cement work-piece. Taking the process experiment of temperature and pressure control as an example, it validated the good dynamic and static control quality through simulation of control algorithm constructed in this paper. The experimental results show that the control algorithm explored in this paper is reasonably available.
基金the Graduate Students' Innovative Foundation of Chinanivcrsity of Petroleum(East China)under Grant No.S2006-31
文摘In this paper,we study the Noether-form invariance of nonholonomic mechanical controllable systems inphase space.Equations of motion of the controllable mechanical systems in phase space are presented.The definitionand the criterion for this system are presented.A new conserved quantity and the Noether conserved quantity deducedfrom the Noether-form invariance are obtained.An example is given to illustrate the application of the results.
基金funded by the Teaching Reform Subject of Jiangxi Educational Department in 2009 (JXJG-09-62-3)
文摘[ Objective] To meet the needs of ＂Prevention and Control of Poultry and Poultry Diseases＂ course in higher vocational colleges in new period. [Method] In order to introduce theoretical knowledge, enhance practical ability and train quality, teaching content, teaching methods and practical teaching of the course were explored according to trends of academic development and personnel training. [ Result] The reform of teaching form improved the teaching effect, mobilized the learning enthusiasm and initiative of students, and enhanced their ability to solve practical prob- lems. [ Conclusion] The teaching form of ＂Prevention and Control of Poultry and Poultry Diseases＂ course has been successfully reformed.
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.
