Occasional irregular initial solidification phenomena,including stickers,deep oscillation marks,depressions,and surface cracks of strand shells in continuous casting molds,are important limitations for developing the ...Occasional irregular initial solidification phenomena,including stickers,deep oscillation marks,depressions,and surface cracks of strand shells in continuous casting molds,are important limitations for developing the high-efficiency continuous casting of steels.The application of mold thermal monitoring(MTM) systems,which use thermocouples to detect and respond to temperature variations in molds,has become an effective method to address irregular initial solidification phenomena.Such systems are widely applied in numerous steel companies for sticker breakout prediction.However,monitoring the surface defects of strands remains immature.Hence,indepth research is necessary to utilize the potential advantages and comprehensive monitoring of MTM systems.This paper summarizes what is included in the irregular initial solidification phenomena and systematically reviews the current state of research on these phenomena by the MTM systems.Furthermore,the influences of mold slag behavior on monitoring these phenomena are analyzed.Finally,the remaining problems of the formation mechanisms and investigations of irregular initial solidification phenomena are discussed,and future research directions are proposed.展开更多
Dynamic temperature monitoring at critical locations of IGBT modules is a key means to improve the reliability of high-power converters.However,most ex-isting thermal model-based methods suffer from temper-ature estim...Dynamic temperature monitoring at critical locations of IGBT modules is a key means to improve the reliability of high-power converters.However,most ex-isting thermal model-based methods suffer from temper-ature estimation errors due to model parameter varia-tions and loss calculation errors.To address this problem,based on the reduced-order thermal model,an H_(∞)ob-server-based robust 3-D thermal monitoring method for IGBT modules is proposed in this paper.Through the optimized design of the observer feedback gain,the thermal model and real-time temperature information are effectively combined,which reduces the temperature estimation error in the worst case.Thus,the proposed method is more robust to model parameter uncertainty and loss error than the conventional temperature ob-servers.Experiment validations of the proposed H_(∞)ob-server and conventional observers are provided.The results demonstrate that the proposed observer achieves the highest temperature estimation accuracy under vari-ous system uncertainties,making it an effective solution for reliable online thermal monitoring of IGBT modules over the whole life cycle.展开更多
Online temperature monitoring of IGBTs is a crucial means to enhance the reliability of high-power converters.In the existing thermal model methods,the junction temperature is derived through the device power loss,whi...Online temperature monitoring of IGBTs is a crucial means to enhance the reliability of high-power converters.In the existing thermal model methods,the junction temperature is derived through the device power loss,which is difficult to obtain accurately in real time.This paper proposes a power loss observer to estimate the real-time power loss accurately.Unlike conventional methods,the proposed method only needs measure the heatsink temperature.Moreover,the proposed technique is robust to disturbances such as wind speed fluctuations,solder aging,and temperature dependence of thermal parameters,which helps to improve the temperature estimation accuracy throughout the full life cycle of IGBT modules.This paper analyzes the proposed method’s mathematical principle,algorithm,and implementation steps,while the loss observer is validated by simulation and experiment.展开更多
Running composite insulators are prone to failure due to their harsh surrounding work environment, which directly affects the safe operation of transmission lines. This paper puts forward the method of using fiber Bra...Running composite insulators are prone to failure due to their harsh surrounding work environment, which directly affects the safe operation of transmission lines. This paper puts forward the method of using fiber Bragg grating(FBG) as the monitors to parameters correlated with thermal and stress of the composite insulators in transmission lines at working status. Firstly, monitoring points are found out by the mechanical test on composite insulator samples. Secondly, based on the monitoring theory, this paper introduces the feasibility design frame of the composite insulator with FBG implanted in the rod and the online monitor system. At last, it describes applications of this monitor system in the field of transmission lines.展开更多
The distribution and variations of permafrost in the Xidatan region, the northern permafrost boundary of the Qinghai-Tibet Plateau, were examined and analyzed using ground penetrating radar(GPR), borehole drilling, an...The distribution and variations of permafrost in the Xidatan region, the northern permafrost boundary of the Qinghai-Tibet Plateau, were examined and analyzed using ground penetrating radar(GPR), borehole drilling, and thermal monitoring data. Results from GPR profiles together with borehole verification indicate that the lowest elevation limit of permafrost occurrence is 4369 m above sea level in 2012. Compared to previous studies, the maximal rise of permafrost limit is 28 m from 1975 to 2012. The total area of permafrost in the study region has been decreased by 13.8%. One of the two previously existed permafrost islands has disappeared and second one has reduced by 76% in area during the past ~40 years. In addition, the ground temperature in the Xidatan region has increased from 2012 to 2016, with a mean warming rate of ~0.004℃ a^(-1) and ~0.003℃ a^(-1) at the depths of 6 and 15 m, respectively. The rising of permafrost limit in the Xidatan region is mainly due to globalwarming. However, some non-climatic factors such as hydrologic processes and anthropic disturbances have also induced permafrost degradation. If the air temperature continues to increase, the northern permafrost boundary in the Qinghai-Tibet Plateau may continue rising in the future.展开更多
The photodegradation behaviors of poly（butylene succinate）（PBS） and TiO2/PBS nanocomposite were monitored over a period of six months. Material properties and aging mechanisms were studied and explored by various ...The photodegradation behaviors of poly（butylene succinate）（PBS） and TiO2/PBS nanocomposite were monitored over a period of six months. Material properties and aging mechanisms were studied and explored by various characterizations including 1HNMR, FTIR, XRD, mass spectrum, and TGA. The TiO2/PBS nanocomposite was found to be more thermally stable and mechanically robust than the PBS. During aging, crystal formation and the final crystal structure changed notably. Based on the characterization results, it is proposed that the polymer chains have cleaved at the ester linkage by the dissociation of O–H groups and the conversion of C=O to C–O bonds. It was also believed that polymer chain transfer took place, which resulted in the formation of C=C bonds and O–H groups, and the polyester changed to enol or polyether.展开更多
基金supported by the National Natural Science Foundation of China(No.52274319)。
文摘Occasional irregular initial solidification phenomena,including stickers,deep oscillation marks,depressions,and surface cracks of strand shells in continuous casting molds,are important limitations for developing the high-efficiency continuous casting of steels.The application of mold thermal monitoring(MTM) systems,which use thermocouples to detect and respond to temperature variations in molds,has become an effective method to address irregular initial solidification phenomena.Such systems are widely applied in numerous steel companies for sticker breakout prediction.However,monitoring the surface defects of strands remains immature.Hence,indepth research is necessary to utilize the potential advantages and comprehensive monitoring of MTM systems.This paper summarizes what is included in the irregular initial solidification phenomena and systematically reviews the current state of research on these phenomena by the MTM systems.Furthermore,the influences of mold slag behavior on monitoring these phenomena are analyzed.Finally,the remaining problems of the formation mechanisms and investigations of irregular initial solidification phenomena are discussed,and future research directions are proposed.
基金supported by the National Key Research and Development Program of China(No.2022YFE0138400)Zhejiang Provincial Key R&D Program Project(No.2023C01061).
文摘Dynamic temperature monitoring at critical locations of IGBT modules is a key means to improve the reliability of high-power converters.However,most ex-isting thermal model-based methods suffer from temper-ature estimation errors due to model parameter varia-tions and loss calculation errors.To address this problem,based on the reduced-order thermal model,an H_(∞)ob-server-based robust 3-D thermal monitoring method for IGBT modules is proposed in this paper.Through the optimized design of the observer feedback gain,the thermal model and real-time temperature information are effectively combined,which reduces the temperature estimation error in the worst case.Thus,the proposed method is more robust to model parameter uncertainty and loss error than the conventional temperature ob-servers.Experiment validations of the proposed H_(∞)ob-server and conventional observers are provided.The results demonstrate that the proposed observer achieves the highest temperature estimation accuracy under vari-ous system uncertainties,making it an effective solution for reliable online thermal monitoring of IGBT modules over the whole life cycle.
基金supported by the National Key Research and Development Program of China(No.2022YFE 0138400)the National Nature Science Foundation of China(No.51925702)Zhejiang Provincial Key R&D Program Project(No.2023C01061).
文摘Online temperature monitoring of IGBTs is a crucial means to enhance the reliability of high-power converters.In the existing thermal model methods,the junction temperature is derived through the device power loss,which is difficult to obtain accurately in real time.This paper proposes a power loss observer to estimate the real-time power loss accurately.Unlike conventional methods,the proposed method only needs measure the heatsink temperature.Moreover,the proposed technique is robust to disturbances such as wind speed fluctuations,solder aging,and temperature dependence of thermal parameters,which helps to improve the temperature estimation accuracy throughout the full life cycle of IGBT modules.This paper analyzes the proposed method’s mathematical principle,algorithm,and implementation steps,while the loss observer is validated by simulation and experiment.
基金supported by National High-tech Research and Development Program of China (863 Program) (2013AA030701)Science and Technology Project of the State Grid Xinjiang Electric Power Corporation (5230DK15009L)
文摘Running composite insulators are prone to failure due to their harsh surrounding work environment, which directly affects the safe operation of transmission lines. This paper puts forward the method of using fiber Bragg grating(FBG) as the monitors to parameters correlated with thermal and stress of the composite insulators in transmission lines at working status. Firstly, monitoring points are found out by the mechanical test on composite insulator samples. Secondly, based on the monitoring theory, this paper introduces the feasibility design frame of the composite insulator with FBG implanted in the rod and the online monitor system. At last, it describes applications of this monitor system in the field of transmission lines.
基金supported by the National Natural Science Foundation of China (Grant no. 41601069) the State Key Program of National Natural Science of China (Grant No. 41730640)the Independent Project of the State Key Laboratory of Frozen Soils Engineering (SKLFSEZT-32 and SKLFSE-ZQ-37)
文摘The distribution and variations of permafrost in the Xidatan region, the northern permafrost boundary of the Qinghai-Tibet Plateau, were examined and analyzed using ground penetrating radar(GPR), borehole drilling, and thermal monitoring data. Results from GPR profiles together with borehole verification indicate that the lowest elevation limit of permafrost occurrence is 4369 m above sea level in 2012. Compared to previous studies, the maximal rise of permafrost limit is 28 m from 1975 to 2012. The total area of permafrost in the study region has been decreased by 13.8%. One of the two previously existed permafrost islands has disappeared and second one has reduced by 76% in area during the past ~40 years. In addition, the ground temperature in the Xidatan region has increased from 2012 to 2016, with a mean warming rate of ~0.004℃ a^(-1) and ~0.003℃ a^(-1) at the depths of 6 and 15 m, respectively. The rising of permafrost limit in the Xidatan region is mainly due to globalwarming. However, some non-climatic factors such as hydrologic processes and anthropic disturbances have also induced permafrost degradation. If the air temperature continues to increase, the northern permafrost boundary in the Qinghai-Tibet Plateau may continue rising in the future.
基金supported by the Natural Science Foundation of Fujian Province(2016J01740)National Natural Science Foundation of China(21473096)+1 种基金State Key Laboratory of Structural Chemistry(20150010)the Guiding Project of Fujian Province(2016Y0073)
文摘The photodegradation behaviors of poly（butylene succinate）（PBS） and TiO2/PBS nanocomposite were monitored over a period of six months. Material properties and aging mechanisms were studied and explored by various characterizations including 1HNMR, FTIR, XRD, mass spectrum, and TGA. The TiO2/PBS nanocomposite was found to be more thermally stable and mechanically robust than the PBS. During aging, crystal formation and the final crystal structure changed notably. Based on the characterization results, it is proposed that the polymer chains have cleaved at the ester linkage by the dissociation of O–H groups and the conversion of C=O to C–O bonds. It was also believed that polymer chain transfer took place, which resulted in the formation of C=C bonds and O–H groups, and the polyester changed to enol or polyether.
