With the implementation of environmental protection, sustainable development and conservation-oriented policies, components and parts of thin-walled welded tubes have gained increasing application in the aircraft and ...With the implementation of environmental protection, sustainable development and conservation-oriented policies, components and parts of thin-walled welded tubes have gained increasing application in the aircraft and automotive industries because of their advantages： easily achieving forming and manufacturing process at low cost and in a short time. The current research on welded tube plastic forming is mainly concentrated on tube internal high-pressure forming, tube bending forming, and tube spinning forming. The focuses are on the material properties and char- acterization of welded tubes, finite element modeling for welded tube forming, and inhomogeneous deformation behavior and the mechanism and rules of deformation coordination in welded tube plastic forming. This paper summarizes the research progress in welded tube plastic forming from these aspects. Finally, with a focus on the urgent demand of the aviation, aerospace and automotive industries for high-strength and light-weight tubes, this paper discusses the development trends and challenges in the theory and technology of welded tube plastic forming in the future. Among them, laser tailor-welded technology will find application in the manufacture of high-strength steel tubes. Tube-end forming technology, such as tube flaring and flanging technology, will expand its appli- cation in welded tubes. Therefore, future studies will focus on the FE modeling regarding how to consider effects of welding on residual stresses, welding distortions and microstructure, the inhomo- geneous deformation and coordination mechanism of the plastic forming process of tailor-welded tubes, and some end-forming processes of welded tubes, and more comprehensive research on the formin~ mechanism and limit of welded tubes.展开更多
To coordinate the protection of PMSG(permanent magnet synchronous generator),collector circuits and outgoing lines,a comprehensive and improved protection method of PMSG based wind farms with LVRT(low voltage ride thr...To coordinate the protection of PMSG(permanent magnet synchronous generator),collector circuits and outgoing lines,a comprehensive and improved protection method of PMSG based wind farms with LVRT(low voltage ride through)capability is proposed.The proposed method includes adding a short time delay to the collector network current protection zone I and a directional protective relaying to the collector network protection,installing grounding transformers and zero sequence current protection,and generator low-voltage protection action improvement.A LVRT scheme consisting of variable resistance dumping circuit,grid side dynamic reactive power control and reactive power compensation control is proposed.The fault characteristics of PMSG based wind farms are analyzed,and a PMSG based wind farm in Dabancheng,Xinjiang,is used as an example to analyze typical wind farm protection configuration,the setting values considering LVRT requirements,and the coordination problems.Finally,an improved wind farm protection coordination methodology is proposed and its validity is verified by simulation.展开更多
基金support from the National Science Fund for Excellent Young Scholars of China(No.51222509)the National Natural Science Foundation of China(No.51175429)+1 种基金the Research Fund of the State Key Laboratory of Solidification Processing(No.97-QZ-2014 and 90-QP-2013)of Chinathe Marie Curie International Research Staff Exchange Scheme(IRSES,Mat Pro Future,No.318968)within the 7th EC Framework Programme(FP7)
文摘With the implementation of environmental protection, sustainable development and conservation-oriented policies, components and parts of thin-walled welded tubes have gained increasing application in the aircraft and automotive industries because of their advantages： easily achieving forming and manufacturing process at low cost and in a short time. The current research on welded tube plastic forming is mainly concentrated on tube internal high-pressure forming, tube bending forming, and tube spinning forming. The focuses are on the material properties and char- acterization of welded tubes, finite element modeling for welded tube forming, and inhomogeneous deformation behavior and the mechanism and rules of deformation coordination in welded tube plastic forming. This paper summarizes the research progress in welded tube plastic forming from these aspects. Finally, with a focus on the urgent demand of the aviation, aerospace and automotive industries for high-strength and light-weight tubes, this paper discusses the development trends and challenges in the theory and technology of welded tube plastic forming in the future. Among them, laser tailor-welded technology will find application in the manufacture of high-strength steel tubes. Tube-end forming technology, such as tube flaring and flanging technology, will expand its appli- cation in welded tubes. Therefore, future studies will focus on the FE modeling regarding how to consider effects of welding on residual stresses, welding distortions and microstructure, the inhomo- geneous deformation and coordination mechanism of the plastic forming process of tailor-welded tubes, and some end-forming processes of welded tubes, and more comprehensive research on the formin~ mechanism and limit of welded tubes.
文摘To coordinate the protection of PMSG(permanent magnet synchronous generator),collector circuits and outgoing lines,a comprehensive and improved protection method of PMSG based wind farms with LVRT(low voltage ride through)capability is proposed.The proposed method includes adding a short time delay to the collector network current protection zone I and a directional protective relaying to the collector network protection,installing grounding transformers and zero sequence current protection,and generator low-voltage protection action improvement.A LVRT scheme consisting of variable resistance dumping circuit,grid side dynamic reactive power control and reactive power compensation control is proposed.The fault characteristics of PMSG based wind farms are analyzed,and a PMSG based wind farm in Dabancheng,Xinjiang,is used as an example to analyze typical wind farm protection configuration,the setting values considering LVRT requirements,and the coordination problems.Finally,an improved wind farm protection coordination methodology is proposed and its validity is verified by simulation.
