Organic thermoelectric materials are not only used in low-grade waste heat recovery but also have frontier applications in sensors,wearable self-powered devices,biomaterials,and smart materials with the development of...Organic thermoelectric materials are not only used in low-grade waste heat recovery but also have frontier applications in sensors,wearable self-powered devices,biomaterials,and smart materials with the development of flexible electronics.However,investigation on the thermoelectric performance of single-walled carbon nanotubes(SWCNTs)comparable to that of conducting polymers and their composites with SWCNTs has been rarely attempted,and there were few reports on SWCNTs alone as organic thermoelectric materials.Certainly,SWCNTs possess high Young’s modulus,high thermal stability,flexibility,lightweight,easily controllable doping level,and facile p-n transition,while the mechanism of molecular doping of SWCNTs remains to be well understood.Here,facile solution processing achieved the enhancement of p-type and n-type thermoelectric performance of SWCNTs.Small-molecular-weight polyethylene glycol treatment improved electrical conductivity and the Seebeck coefficient of SWCNTs(p-SWCNTs)simultaneously,with the power factor of 303.17±46.25μW·m^(-1)·K^(-2).Small amount of polyethylenimine doping made the Seebeck coefficient of SWCNTs(n-SWCNTs)turn negative and rendered great air stability of n-SWCNTs.The electrical conductivity and power factor of n-SWCNTs reached 1,702.56±164.13 S·cm^(-1)and 418.49±46.30μW·m^(-1)·K^(-2)at 298 K,respectively.The power factor of n-SWCNTs got even higher at 319.5 K in vacuo,reaching a high value of 643.35μW·m^(-1)·K^(-2).Finally,mechanism study in this work provided inspiration and guidance for the application of these types of dopants in the performance improvement of SWCNTs.展开更多
In this paper, by using a matrix technique, a dynamic model of high power factor induction motor with floating winding in parallel connection with capacitors is established. Then, the starting performance of this mot...In this paper, by using a matrix technique, a dynamic model of high power factor induction motor with floating winding in parallel connection with capacitors is established. Then, the starting performance of this motor is analyzed by computer simulation. By comparison of the tested and computed results, which are in good agreement, the dynamic model and simulative method are verified.展开更多
A new type of high power LED drivers is proposed by adopting an improved two-stages non-isolated configuration. In order to improve power factor and achieve accurate average current control under universal input volta...A new type of high power LED drivers is proposed by adopting an improved two-stages non-isolated configuration. In order to improve power factor and achieve accurate average current control under universal input voltages ranging from 100 Vrms to 240 Vrms, the power factor correction and average current mode control methods operating in continuous current conduction mode are designed and implemented. With the LUMILEDS emitter type LEDs, a laboratory prototype is built and measured. And from the measured results, it could be concluded that the proposed driver has many better performances such as high power factor, low current harmonic, accurate average current control and switch protection.展开更多
The development process of high-voltage electric power equipment maintenance was introduced. It is pointed out that the trend of high-voltage electric power equipment maintenance is so called condition-based maintenan...The development process of high-voltage electric power equipment maintenance was introduced. It is pointed out that the trend of high-voltage electric power equipment maintenance is so called condition-based maintenance. With the development of computer technology and sensors, on-line monitoring of high-voltage electric power equipment has developed rapidly. By introducing the main principle of Schering bridge to measure tanδ, the way of on-line monitoring of high-voltage electric power equipment was explained. Difference methods of on-line monitoring of insulation parameters for 35 kV substation were discussed. Finally, the shortcomings as well as its tendency of on-line monitoring were analyzed.展开更多
A high efficiency, high power factor, and linear constant current LED driver based on adaptive seg- mented linear architecture is presented. When the input voltage varied, the proposed LED driver automatically switche...A high efficiency, high power factor, and linear constant current LED driver based on adaptive seg- mented linear architecture is presented. When the input voltage varied, the proposed LED driver automatically switched over LED strings according to the segmented LED voltage drop, which increased the LED lighting time. The efficiency and power factor are improved, while the system design is simplified by this control scheme. Without the usage of electrolytic capacitor and magnetic components, the proposed driver possesses advantages of smaller size, longer lifetime and lower cost over others. The proposed driver is implemented in 0.8 μm 5 V/40 V HVCMOS process, which occupies an active area of 820× 920μm2. The measured results show that the average value of the internal reference voltage is 500 4- 7 mV, with a standard deviation of only 4.629 mV, thus LED current can be set accurately. Under 220 V root mean square 50 Hz utility voltage and the number ratio of the three LED strings being 47 ： 17 ： 16, the system can realize a high power factor of 0.974 and power conversion efficiency of 93.4%.展开更多
高铁运行阶段直接产生的CO_(2)排放微乎其微,但因列车运行需要电力牵引,上游发电端带来的碳排放不可忽视。文中综合考虑了发电结构以及不同发电方式的碳排放水平,将高铁运行阶段碳排放因子作为高铁环保程度的评估指标。测算结果表明,201...高铁运行阶段直接产生的CO_(2)排放微乎其微,但因列车运行需要电力牵引,上游发电端带来的碳排放不可忽视。文中综合考虑了发电结构以及不同发电方式的碳排放水平,将高铁运行阶段碳排放因子作为高铁环保程度的评估指标。测算结果表明,2018、2019年我国高铁运行阶段碳排放因子水平为27.19、27.09 g CO_(2)/(人·km)。考虑发电端碳排放的高铁运输方式相较于公路、民航客运仍具有显著的环保优势,但发电结构中火电占比偏高导致我国高铁碳排放因子水平高于法国、德国、日本等发达国家。结合我国未来年发电结构的预测,当各发电方式碳排放水平较现状波动不大时,2030、2050年我国高铁运行阶段碳排放因子水平分别为10.87~14.18、2.83~9.49 g CO_(2)/(人·km),分别比高铁列车运输能力利用率较高的2019年降低了47.66%~59.87%、64.97%~89.55%。煤电碳排放因子下降时将实现高铁碳排放因子的同步下降,故推进煤电低碳化生产,高效应用煤电清洁生产新技术,有望进一步提升高铁低碳优势。研究成果将促进交通运输行业与能源行业相互协作,助推“双碳”战略实施。展开更多
It is very important to predict the coupling between the cavity and the high power input source in the coupler design. In this paper, a time domain method is used to calculate the external quality factor Qext for the ...It is very important to predict the coupling between the cavity and the high power input source in the coupler design. In this paper, a time domain method is used to calculate the external quality factor Qext for the BEPC Ⅱ superconducting cavity. A comparison between simulation results and experimental results is presented. The results of simulation and measurement of Qext have a good agreement within an error of 10%. The geometry parameters related with Qext are also studied.展开更多
基金supported by the National Natural Science Foundation of China(no.51373176).
文摘Organic thermoelectric materials are not only used in low-grade waste heat recovery but also have frontier applications in sensors,wearable self-powered devices,biomaterials,and smart materials with the development of flexible electronics.However,investigation on the thermoelectric performance of single-walled carbon nanotubes(SWCNTs)comparable to that of conducting polymers and their composites with SWCNTs has been rarely attempted,and there were few reports on SWCNTs alone as organic thermoelectric materials.Certainly,SWCNTs possess high Young’s modulus,high thermal stability,flexibility,lightweight,easily controllable doping level,and facile p-n transition,while the mechanism of molecular doping of SWCNTs remains to be well understood.Here,facile solution processing achieved the enhancement of p-type and n-type thermoelectric performance of SWCNTs.Small-molecular-weight polyethylene glycol treatment improved electrical conductivity and the Seebeck coefficient of SWCNTs(p-SWCNTs)simultaneously,with the power factor of 303.17±46.25μW·m^(-1)·K^(-2).Small amount of polyethylenimine doping made the Seebeck coefficient of SWCNTs(n-SWCNTs)turn negative and rendered great air stability of n-SWCNTs.The electrical conductivity and power factor of n-SWCNTs reached 1,702.56±164.13 S·cm^(-1)and 418.49±46.30μW·m^(-1)·K^(-2)at 298 K,respectively.The power factor of n-SWCNTs got even higher at 319.5 K in vacuo,reaching a high value of 643.35μW·m^(-1)·K^(-2).Finally,mechanism study in this work provided inspiration and guidance for the application of these types of dopants in the performance improvement of SWCNTs.
文摘In this paper, by using a matrix technique, a dynamic model of high power factor induction motor with floating winding in parallel connection with capacitors is established. Then, the starting performance of this motor is analyzed by computer simulation. By comparison of the tested and computed results, which are in good agreement, the dynamic model and simulative method are verified.
文摘A new type of high power LED drivers is proposed by adopting an improved two-stages non-isolated configuration. In order to improve power factor and achieve accurate average current control under universal input voltages ranging from 100 Vrms to 240 Vrms, the power factor correction and average current mode control methods operating in continuous current conduction mode are designed and implemented. With the LUMILEDS emitter type LEDs, a laboratory prototype is built and measured. And from the measured results, it could be concluded that the proposed driver has many better performances such as high power factor, low current harmonic, accurate average current control and switch protection.
文摘The development process of high-voltage electric power equipment maintenance was introduced. It is pointed out that the trend of high-voltage electric power equipment maintenance is so called condition-based maintenance. With the development of computer technology and sensors, on-line monitoring of high-voltage electric power equipment has developed rapidly. By introducing the main principle of Schering bridge to measure tanδ, the way of on-line monitoring of high-voltage electric power equipment was explained. Difference methods of on-line monitoring of insulation parameters for 35 kV substation were discussed. Finally, the shortcomings as well as its tendency of on-line monitoring were analyzed.
基金supported by the National Natural Science Foundation of China(Nos.61234002,61322405,61306044,61376033)
文摘A high efficiency, high power factor, and linear constant current LED driver based on adaptive seg- mented linear architecture is presented. When the input voltage varied, the proposed LED driver automatically switched over LED strings according to the segmented LED voltage drop, which increased the LED lighting time. The efficiency and power factor are improved, while the system design is simplified by this control scheme. Without the usage of electrolytic capacitor and magnetic components, the proposed driver possesses advantages of smaller size, longer lifetime and lower cost over others. The proposed driver is implemented in 0.8 μm 5 V/40 V HVCMOS process, which occupies an active area of 820× 920μm2. The measured results show that the average value of the internal reference voltage is 500 4- 7 mV, with a standard deviation of only 4.629 mV, thus LED current can be set accurately. Under 220 V root mean square 50 Hz utility voltage and the number ratio of the three LED strings being 47 ： 17 ： 16, the system can realize a high power factor of 0.974 and power conversion efficiency of 93.4%.
文摘高铁运行阶段直接产生的CO_(2)排放微乎其微,但因列车运行需要电力牵引,上游发电端带来的碳排放不可忽视。文中综合考虑了发电结构以及不同发电方式的碳排放水平,将高铁运行阶段碳排放因子作为高铁环保程度的评估指标。测算结果表明,2018、2019年我国高铁运行阶段碳排放因子水平为27.19、27.09 g CO_(2)/(人·km)。考虑发电端碳排放的高铁运输方式相较于公路、民航客运仍具有显著的环保优势,但发电结构中火电占比偏高导致我国高铁碳排放因子水平高于法国、德国、日本等发达国家。结合我国未来年发电结构的预测,当各发电方式碳排放水平较现状波动不大时,2030、2050年我国高铁运行阶段碳排放因子水平分别为10.87~14.18、2.83~9.49 g CO_(2)/(人·km),分别比高铁列车运输能力利用率较高的2019年降低了47.66%~59.87%、64.97%~89.55%。煤电碳排放因子下降时将实现高铁碳排放因子的同步下降,故推进煤电低碳化生产,高效应用煤电清洁生产新技术,有望进一步提升高铁低碳优势。研究成果将促进交通运输行业与能源行业相互协作,助推“双碳”战略实施。
基金Supported by National Natural Science Foundation of China(k711360503)
文摘It is very important to predict the coupling between the cavity and the high power input source in the coupler design. In this paper, a time domain method is used to calculate the external quality factor Qext for the BEPC Ⅱ superconducting cavity. A comparison between simulation results and experimental results is presented. The results of simulation and measurement of Qext have a good agreement within an error of 10%. The geometry parameters related with Qext are also studied.
