This paper investigates a control and protection strategy for a four-terminal modular multilevel converter(MMC)based high-voltage direct current(HVDC)system under a converter-side AC fault.Based on the system operatin...This paper investigates a control and protection strategy for a four-terminal modular multilevel converter(MMC)based high-voltage direct current(HVDC)system under a converter-side AC fault.Based on the system operating condition,a control and protection strategy against the fault with normal blocking of the converter is proposed.In practical,applications encountering such a fault,the MMC at the fault side may experience different conditions of blocking failure.The blocking failures may occur on:①the whole converter;②one converter arm;③one sub-module(SM)/several SMs of one converter arm;④other conditions.The phenomenon of the multi-terminal HVDC(MTDC)system following the fault is analyzed under the first three conditions with real-time simulations using the real-time digital simulator(RTDS).Based on the impact of different conditions on the MTDC system,the necessity of utilizing special control and protection is discussed.A special control and protection strategy is proposed for emergency conditions,and its effectiveness is verified by real-time simulation results.展开更多
AIM： To investigate the effect of delayed ethyl pyruvate （EP） delivery on distant organ injury, survival time and serum high mobility group box 1 （HMGB1） levels in rats with experimental severe acute pancreatitis...AIM： To investigate the effect of delayed ethyl pyruvate （EP） delivery on distant organ injury, survival time and serum high mobility group box 1 （HMGB1） levels in rats with experimental severe acute pancreatitis （SAP）. METHODS： A SAP model was induced by retrograde injection of artificial bile into the pancreatic ducts of rats. Animals were divided randomly into three groups （n = 32 in each group）： sham group, SAP group and delayed EP treatment group. The rats in the delayed EP treatment group received EP （30 mg/kg） at 12 h, 18 h and 30 h after induction of SAP. Animals were sacrificed, and samples were obtained at 24 h and 48 h after induction of SAP. Serum HMGB1, aspartate arninotransferase （AST）, alanine arninotransferase （ALT）, blood urea nitrogen （BUN）, and creatinine （Cr） levels were measured. Lung wet-to-dry-weight （W/D） ratios and histological scores were calculated to evaluate lung injury. Additional experiments were performed between SAP and delayed EP treatment groups to study the influence of EP on survival times of SAP rats. RESULTS： Delayed EP treatment significantly reduced serum HMGB1 levels, and protected against liver, renal and lung injury with reduced lung W/D ratios （8.22 ±0.42 vs 9.76 ± 0.45, P 〈 0.01）, pulmonary histological scores （7.1 ± 0.7 vs 8.4 ± 1.1, P 〈 0.01）, serum AST （667 ± 103 vs 1 368 ± 271, P 〈 0.01）, ALT （446 ± 91 vs 653 ± 98, P 〈 0.01） and Cr （1.2 ± 0.3 vs 1.8 ± 0.3, P 〈 0.01） levels. SAP rats had a median survival time of 44 h. Delayed EP treatment significantly prolonged median survival time to 72 h （P 〈 0.01）. CONCLUSION： Delayed EP therapy protects against distant organ injury and prolongs survival time via reduced serum HMGBllevels in rats with experimental SAP. EP may potentially serve as an effective new therapeutic option against the inflammatory response and multiple organ dysfunction syndrome （MODS） in SAP patients.展开更多
Two sets of dehydration-melting with a natural solid amphibolite, collected from North Himalayan structure zone, Tibet, have been carried out in multi-anvil apparatus at 2.0 GPa and 800―1000℃, for 12―200 h. One is ...Two sets of dehydration-melting with a natural solid amphibolite, collected from North Himalayan structure zone, Tibet, have been carried out in multi-anvil apparatus at 2.0 GPa and 800―1000℃, for 12―200 h. One is keeping the pressure at 2.0 GPa and the annealing time of 12 h, changing the temperature (800―1000℃). The other is keeping the pressure at 2.0 GPa and temperature at 850℃, varying the annealing time (12―200 h). The products are inspected with microscope and electron probe. The results indicate that at 2.0 GPa, annealing time of 12 h, garnets, melts and clinopyroxenes occur in amphibolite gradually with increasing temperature and the chemical compositions of melt vary from tonalite to granodiorite, and then to tonalite. However, at 2.0 GPa and 850℃, with the annealing time increasing, the garnets, melts and cli-nopyroxenes also occur in amphibolite gradually and the chemical compositions of melt vary from tonalite to granodiorite. In both cases, melts interconnect with each other when the contents of melt are over the 5 vol.%. the viscosities of the melt produced in amphibolite at temperature higher than 850℃ are on a level with 104 Pa·s. The interconnected melt with such a viscosity may segregate from the source rock and form the magma over reasonable geological time. Therefore, it is believed that at the lower part of the overthickened crust, the tonlitic and grano-dioritic magma may be generated through the dehydration melting of amphibolite.展开更多
为有效评估高重频对抗制导武器的效果,研究干扰频率、波门宽度、编码方式和干扰时机等因素对激光高重频干扰效果的影响,首先,通过深入分析导引头抗干扰关键技术和高重频干扰机理,建立了码型识别模型、波门设置模型和高重频干扰模型;而后...为有效评估高重频对抗制导武器的效果,研究干扰频率、波门宽度、编码方式和干扰时机等因素对激光高重频干扰效果的影响,首先,通过深入分析导引头抗干扰关键技术和高重频干扰机理,建立了码型识别模型、波门设置模型和高重频干扰模型;而后,设计了弹道仿真流程,基于过重力补偿比例制导导弹弹道仿真平台,评估了不同影响因素对高重频干扰效果的影响。仿真结果表明:干扰频率和波门宽度对高重频干扰效果的影响较大,频率越高、波门宽度越大干扰效果越好;LFSR状态码对高重频干扰的抗干扰性能比二间隔码好;且在干扰频率达到100 k Hz时,高重频对波门宽度为20μs的二变间隔码的干扰效率能达到100%,脱靶量达到510.4 m;而干扰时机对干扰效果影响较小。文中的研究成果可为高重频干扰装备研制和战术使用提供一定的参考和依据。展开更多
AIM： To investigate the protective effects of ethyl py- ruvate （EP） on acute-on-chronic liver failure （ACLF） in rats. METHODS： An ACLF model was established in rats, and animals were randomly divided into normal...AIM： To investigate the protective effects of ethyl py- ruvate （EP） on acute-on-chronic liver failure （ACLF） in rats. METHODS： An ACLF model was established in rats, and animals were randomly divided into normal, mod- el and EP treatment groups. The rats in EP treatment group received EP （40 mg/kg） at 3 h, 6 h, 12 h and 24 h after induction of ACLF. Serum endotoxin, high mobility group box-1 （HMGB1）, alanine transaminase （ALT）, tumor necrosis factor-α （TNF-α）, interferon-α （IFN-γ）, interleukin （IL）-10 and IL-18 levels, changes of liver histology and HMGB1 expressions in liver tis- sues were detected at 48 h after induction of ACLF. The effects of EP on the survival of ACLF rats were also observed.RESULTS： Serum levels of endotoxin （0.394 ± 0.066 EU/mL vs 0.086±0.017 EU/mL, P 〈 0.001）, HMGB1 （35.42±10,86 μg/L vs 2.14 ± 0.27 μg/L, P 〈 0.001）, ALT （8415.87 ± 3567.54 IU/L vs 38.64 ± 8.82 IU/L, P 〈 0.001）, TNF-α （190.77 ± 12.34 ng/L vs 124.40 ± 4.12 ng/L, P 〈 0.001）, IFN-γ （715.38 ± 86.03 ng/L vs 398.66 ± 32.91 ng/L, P 〈 0.001）, IL-10 （6.85 ± 0.64 ng/L vs 3.49 ± 0.24 ng/L, P 〈 0.001） and IL-18 （85.19 ±3.49 ng/L vs 55.38 ±1.25 ng/L, P 〈 0.001） were significantly increased, and liver tissues presented se- vere pathological injury in the model group compared with the normal group, Howeverr EP administration significantly improved hepatic histopathology and re- duced the serum levels of endotoxin （0.155±0.045 EU/mL vs 0.394 ± 0.066 EU/mL vs P 〈 0.001） and in- flammatory cytokines （11.13 ± 2.58 μg/L vs 35.42 ± 10.86 μg/L for HMGB1, 3512.86 ± 972.67 IU/L vs 8415.87 ± 3567.54 IU/L for ALT, 128.55 ± 5.76 ng/L vs 190.77 ± 12.34 ng/L for TNF-α 438.16 ± 38.10 ng/L vs 715.38 ± 86.03 ng/L for IFN-γ 3.55 ± 0.36 ng/L vs 6.85 ± 0.64 ng/L for IL-10, and 60.35 ± 1.63 ng/L vs 85.19 ± 3.49 ng/L for IL-18, respectively, P 〈 0.001）, and the levels of HMGB1 in liver tissues re- gardless of treatment time after 展开更多
Insulation performance of high voltage IGBT modules is one of the key attributes in power system applications.However,the existing standards of IGBT devices and research on the evaluation of insulation performance of ...Insulation performance of high voltage IGBT modules is one of the key attributes in power system applications.However,the existing standards of IGBT devices and research on the evaluation of insulation performance of high voltage IGBT modules are insufficient;for example,partial discharge resistance under DC voltage blocking condition is not considered.In this paper,a new test was proposed to allow the measurement of partial discharges in all the components of IGBT modules under DC voltage.The topology of the measuring circuit is arranged in the polarity discrimination way to exclude the interference,and the voltage and discharge current waveforms during the partial discharge process are measured by the wideband time domain measurement technique.According to the proposed test,the discharge phenomenon of the IGBT modules below the rating voltage were detected.A comprehensive waveform analysis on the voltage and discharge current was performed,and the influence of the applied voltage on the waveform parameters was obtained.The waveform parameters are influenced by the applied voltage and insulation structure,which enables the discrimination of the causes of the observed partial discharge in the IGBT module under DC voltage by the waveform analysis technique.Based on the waveform analysis technique,the types and causes of the observed partial discharges were discussed and inferred,and the correctness of the inference was further verified by observation.The proposed test and waveform analysis technique provide the possibility to evaluate and distinguish partial discharges in the high voltage IGBT module under DC voltage,which may be helpful to insulation performance evaluation and insulation defect diagnosis in high voltage IGBT module.展开更多
With the increasing demand of higher travelling speed,a new streamlined high-speed maglev train has been designed to reach a speed of 600 km/h.To better capture the flow field structures around the maglev train,an imp...With the increasing demand of higher travelling speed,a new streamlined high-speed maglev train has been designed to reach a speed of 600 km/h.To better capture the flow field structures around the maglev train,an improved delayed detached eddy simulation(IDDES)is adopted to model the turbulence.Results show that the new maglev train has good aerodynamic load performance such as small drag coefficient contributing to energy conservation.The main frequencies of aerodynamic forces for each car have a scattered distribution.There are two pairs of counter-rotating large vortices in the non-streamlined part of the train that make the boundary layer thicker.Many high-intensity vortices are distributed in the narrow space between skirt plates or train floor and track.In the gap between the train floor and track(except near the tail car nose),the main frequency of vortex shedding remains constant and its strength increases exponentially in the streamwise direction.In the wake,the counter-rotating vortices gradually expand and reproduce some small vortices that move downward.The vortex has quite random and complex frequencydomain distribution characteristics in the wake.The maximum time-averaged velocity of the slipstream occurs near the nose of the head car,based on which,the track-side safety domain is divided.展开更多
基金This work is supported by UK EPSRC and UK National Grid.
文摘This paper investigates a control and protection strategy for a four-terminal modular multilevel converter(MMC)based high-voltage direct current(HVDC)system under a converter-side AC fault.Based on the system operating condition,a control and protection strategy against the fault with normal blocking of the converter is proposed.In practical,applications encountering such a fault,the MMC at the fault side may experience different conditions of blocking failure.The blocking failures may occur on:①the whole converter;②one converter arm;③one sub-module(SM)/several SMs of one converter arm;④other conditions.The phenomenon of the multi-terminal HVDC(MTDC)system following the fault is analyzed under the first three conditions with real-time simulations using the real-time digital simulator(RTDS).Based on the impact of different conditions on the MTDC system,the necessity of utilizing special control and protection is discussed.A special control and protection strategy is proposed for emergency conditions,and its effectiveness is verified by real-time simulation results.
基金The National Natural Science Foundation of China, No. 30600593
文摘AIM： To investigate the effect of delayed ethyl pyruvate （EP） delivery on distant organ injury, survival time and serum high mobility group box 1 （HMGB1） levels in rats with experimental severe acute pancreatitis （SAP）. METHODS： A SAP model was induced by retrograde injection of artificial bile into the pancreatic ducts of rats. Animals were divided randomly into three groups （n = 32 in each group）： sham group, SAP group and delayed EP treatment group. The rats in the delayed EP treatment group received EP （30 mg/kg） at 12 h, 18 h and 30 h after induction of SAP. Animals were sacrificed, and samples were obtained at 24 h and 48 h after induction of SAP. Serum HMGB1, aspartate arninotransferase （AST）, alanine arninotransferase （ALT）, blood urea nitrogen （BUN）, and creatinine （Cr） levels were measured. Lung wet-to-dry-weight （W/D） ratios and histological scores were calculated to evaluate lung injury. Additional experiments were performed between SAP and delayed EP treatment groups to study the influence of EP on survival times of SAP rats. RESULTS： Delayed EP treatment significantly reduced serum HMGB1 levels, and protected against liver, renal and lung injury with reduced lung W/D ratios （8.22 ±0.42 vs 9.76 ± 0.45, P 〈 0.01）, pulmonary histological scores （7.1 ± 0.7 vs 8.4 ± 1.1, P 〈 0.01）, serum AST （667 ± 103 vs 1 368 ± 271, P 〈 0.01）, ALT （446 ± 91 vs 653 ± 98, P 〈 0.01） and Cr （1.2 ± 0.3 vs 1.8 ± 0.3, P 〈 0.01） levels. SAP rats had a median survival time of 44 h. Delayed EP treatment significantly prolonged median survival time to 72 h （P 〈 0.01）. CONCLUSION： Delayed EP therapy protects against distant organ injury and prolongs survival time via reduced serum HMGBllevels in rats with experimental SAP. EP may potentially serve as an effective new therapeutic option against the inflammatory response and multiple organ dysfunction syndrome （MODS） in SAP patients.
基金the National Natural Science Foumndation of China(Grant Nos.10299040 , 40103 003) the Knowleige Innovation Program of the Chinese Acacemy of Sciences(Gant No.RJCX2-SW-No.3).
文摘Two sets of dehydration-melting with a natural solid amphibolite, collected from North Himalayan structure zone, Tibet, have been carried out in multi-anvil apparatus at 2.0 GPa and 800―1000℃, for 12―200 h. One is keeping the pressure at 2.0 GPa and the annealing time of 12 h, changing the temperature (800―1000℃). The other is keeping the pressure at 2.0 GPa and temperature at 850℃, varying the annealing time (12―200 h). The products are inspected with microscope and electron probe. The results indicate that at 2.0 GPa, annealing time of 12 h, garnets, melts and clinopyroxenes occur in amphibolite gradually with increasing temperature and the chemical compositions of melt vary from tonalite to granodiorite, and then to tonalite. However, at 2.0 GPa and 850℃, with the annealing time increasing, the garnets, melts and cli-nopyroxenes also occur in amphibolite gradually and the chemical compositions of melt vary from tonalite to granodiorite. In both cases, melts interconnect with each other when the contents of melt are over the 5 vol.%. the viscosities of the melt produced in amphibolite at temperature higher than 850℃ are on a level with 104 Pa·s. The interconnected melt with such a viscosity may segregate from the source rock and form the magma over reasonable geological time. Therefore, it is believed that at the lower part of the overthickened crust, the tonlitic and grano-dioritic magma may be generated through the dehydration melting of amphibolite.
文摘为有效评估高重频对抗制导武器的效果,研究干扰频率、波门宽度、编码方式和干扰时机等因素对激光高重频干扰效果的影响,首先,通过深入分析导引头抗干扰关键技术和高重频干扰机理,建立了码型识别模型、波门设置模型和高重频干扰模型;而后,设计了弹道仿真流程,基于过重力补偿比例制导导弹弹道仿真平台,评估了不同影响因素对高重频干扰效果的影响。仿真结果表明:干扰频率和波门宽度对高重频干扰效果的影响较大,频率越高、波门宽度越大干扰效果越好;LFSR状态码对高重频干扰的抗干扰性能比二间隔码好;且在干扰频率达到100 k Hz时,高重频对波门宽度为20μs的二变间隔码的干扰效率能达到100%,脱靶量达到510.4 m;而干扰时机对干扰效果影响较小。文中的研究成果可为高重频干扰装备研制和战术使用提供一定的参考和依据。
基金Supported by The National Natural Science Foundation of China,No.81071342
文摘AIM： To investigate the protective effects of ethyl py- ruvate （EP） on acute-on-chronic liver failure （ACLF） in rats. METHODS： An ACLF model was established in rats, and animals were randomly divided into normal, mod- el and EP treatment groups. The rats in EP treatment group received EP （40 mg/kg） at 3 h, 6 h, 12 h and 24 h after induction of ACLF. Serum endotoxin, high mobility group box-1 （HMGB1）, alanine transaminase （ALT）, tumor necrosis factor-α （TNF-α）, interferon-α （IFN-γ）, interleukin （IL）-10 and IL-18 levels, changes of liver histology and HMGB1 expressions in liver tis- sues were detected at 48 h after induction of ACLF. The effects of EP on the survival of ACLF rats were also observed.RESULTS： Serum levels of endotoxin （0.394 ± 0.066 EU/mL vs 0.086±0.017 EU/mL, P 〈 0.001）, HMGB1 （35.42±10,86 μg/L vs 2.14 ± 0.27 μg/L, P 〈 0.001）, ALT （8415.87 ± 3567.54 IU/L vs 38.64 ± 8.82 IU/L, P 〈 0.001）, TNF-α （190.77 ± 12.34 ng/L vs 124.40 ± 4.12 ng/L, P 〈 0.001）, IFN-γ （715.38 ± 86.03 ng/L vs 398.66 ± 32.91 ng/L, P 〈 0.001）, IL-10 （6.85 ± 0.64 ng/L vs 3.49 ± 0.24 ng/L, P 〈 0.001） and IL-18 （85.19 ±3.49 ng/L vs 55.38 ±1.25 ng/L, P 〈 0.001） were significantly increased, and liver tissues presented se- vere pathological injury in the model group compared with the normal group, Howeverr EP administration significantly improved hepatic histopathology and re- duced the serum levels of endotoxin （0.155±0.045 EU/mL vs 0.394 ± 0.066 EU/mL vs P 〈 0.001） and in- flammatory cytokines （11.13 ± 2.58 μg/L vs 35.42 ± 10.86 μg/L for HMGB1, 3512.86 ± 972.67 IU/L vs 8415.87 ± 3567.54 IU/L for ALT, 128.55 ± 5.76 ng/L vs 190.77 ± 12.34 ng/L for TNF-α 438.16 ± 38.10 ng/L vs 715.38 ± 86.03 ng/L for IFN-γ 3.55 ± 0.36 ng/L vs 6.85 ± 0.64 ng/L for IL-10, and 60.35 ± 1.63 ng/L vs 85.19 ± 3.49 ng/L for IL-18, respectively, P 〈 0.001）, and the levels of HMGB1 in liver tissues re- gardless of treatment time after
基金This work was supported by the National Natural Science Foundation of China-State Grid Corporation Joint Fund for Smart Grid(No.U1766219)the Fundamental Research Funds for the Central Universities(No.2017XS027).
文摘Insulation performance of high voltage IGBT modules is one of the key attributes in power system applications.However,the existing standards of IGBT devices and research on the evaluation of insulation performance of high voltage IGBT modules are insufficient;for example,partial discharge resistance under DC voltage blocking condition is not considered.In this paper,a new test was proposed to allow the measurement of partial discharges in all the components of IGBT modules under DC voltage.The topology of the measuring circuit is arranged in the polarity discrimination way to exclude the interference,and the voltage and discharge current waveforms during the partial discharge process are measured by the wideband time domain measurement technique.According to the proposed test,the discharge phenomenon of the IGBT modules below the rating voltage were detected.A comprehensive waveform analysis on the voltage and discharge current was performed,and the influence of the applied voltage on the waveform parameters was obtained.The waveform parameters are influenced by the applied voltage and insulation structure,which enables the discrimination of the causes of the observed partial discharge in the IGBT module under DC voltage by the waveform analysis technique.Based on the waveform analysis technique,the types and causes of the observed partial discharges were discussed and inferred,and the correctness of the inference was further verified by observation.The proposed test and waveform analysis technique provide the possibility to evaluate and distinguish partial discharges in the high voltage IGBT module under DC voltage,which may be helpful to insulation performance evaluation and insulation defect diagnosis in high voltage IGBT module.
基金Project supported by the National Natural Science Foundation of China(No.51605397)the National Key R&D Program of China(No.2016YFB1200602-15)the Sichuan Provincial Science and Technology Support Program(No.2019YJ0227),China。
文摘With the increasing demand of higher travelling speed,a new streamlined high-speed maglev train has been designed to reach a speed of 600 km/h.To better capture the flow field structures around the maglev train,an improved delayed detached eddy simulation(IDDES)is adopted to model the turbulence.Results show that the new maglev train has good aerodynamic load performance such as small drag coefficient contributing to energy conservation.The main frequencies of aerodynamic forces for each car have a scattered distribution.There are two pairs of counter-rotating large vortices in the non-streamlined part of the train that make the boundary layer thicker.Many high-intensity vortices are distributed in the narrow space between skirt plates or train floor and track.In the gap between the train floor and track(except near the tail car nose),the main frequency of vortex shedding remains constant and its strength increases exponentially in the streamwise direction.In the wake,the counter-rotating vortices gradually expand and reproduce some small vortices that move downward.The vortex has quite random and complex frequencydomain distribution characteristics in the wake.The maximum time-averaged velocity of the slipstream occurs near the nose of the head car,based on which,the track-side safety domain is divided.
