This paper presents the results from laboratory experiments and theoretical analysis to investigate the development of scour around submarine pipeline under steady current conditions. Experiments show that the scour p...This paper presents the results from laboratory experiments and theoretical analysis to investigate the development of scour around submarine pipeline under steady current conditions. Experiments show that the scour process takes place in two stages: the initial rapid scour and the subsequent gradual scour development stage. An empirical formula for calculating the equilibrium scour depth(the maximum scour depth) is developed by using the regression method. This formula together with the maximum entropy theory can be applied to establish a formula to predict the scour process for given water depth, diameter of pipeline and flow velocity. Good agreement between the predicted and measured scour depth is obtained.展开更多
Direct current（DC） and radio frequency（RF） performances of InP-based high electron mobility transistors（HEMTs）are investigated by Sentaurus TCAD. The physical models including hydrodynamic transport model, Shock...Direct current（DC） and radio frequency（RF） performances of InP-based high electron mobility transistors（HEMTs）are investigated by Sentaurus TCAD. The physical models including hydrodynamic transport model, Shockley–Read–Hall recombination, Auger recombination, radiative recombination, density gradient model and high field-dependent mobility are used to characterize the devices. The simulated results and measured results about DC and RF performances are compared, showing that they are well matched. However, the slight differences in channel current and pinch-off voltage may be accounted for by the surface defects resulting from oxidized InAlAs material in the gate-recess region. Moreover,the simulated frequency characteristics can be extrapolated beyond the test equipment limitation of 40 GHz, which gives a more accurate maximum oscillation frequency( f;) of 385 GHz.展开更多
在光储孤岛直流微电网中,需要最大化利用光伏发电,通常对光伏系统采用最大功率点跟踪(maximum power point tracking, MPPT)技术。但传统的MPPT控制速度慢、精度低,特别是在局部阴影情形下极易陷入局部最优解。基于此,首先提出一种将布...在光储孤岛直流微电网中,需要最大化利用光伏发电,通常对光伏系统采用最大功率点跟踪(maximum power point tracking, MPPT)技术。但传统的MPPT控制速度慢、精度低,特别是在局部阴影情形下极易陷入局部最优解。基于此,首先提出一种将布谷鸟搜索算法与电导增量法相结合的混合MPPT控制。利用布谷鸟搜索算法快速全局寻优,再使用电导增量法精确定位,实现快速而准确地跟踪最大功率点。储能单元是光储直流微电网的重要组成部分,其输出电流均分、荷电状态(stateof charge, SoC)均衡和直流母线电压稳定是主要控制目标。但电流均分受线路电阻差异的影响,进而影响SoC均衡和直流母线电压稳定,于是设计一种新的电压电流双环控制策略以实现上述目标。该策略在电压外环采用母线电压作为反馈值,在电流内环中设计了基于一致性算法的控制策略,将SoC与指数函数结合并引入加速因子,使得在充放电过程中实现SoC的快速均衡。所提控制策略既不需要下垂控制,也无需二次补偿控制,减轻了通信负担。最后在Matlab/Simulink中搭建直流微电网系统模型,验证所设计新的混合MPPT控制和电压电流双环控制策略的有效性。展开更多
电力需求的增长和系统容量的提升对输配电电缆的传输容量和运行可靠性提出了更高的要求,有效利用高压直流(high voltage direct current,HVDC)电缆线路的动态增容潜力对于实现电力资源优化配置具有重要意义。通过有限元分析(finite elem...电力需求的增长和系统容量的提升对输配电电缆的传输容量和运行可靠性提出了更高的要求,有效利用高压直流(high voltage direct current,HVDC)电缆线路的动态增容潜力对于实现电力资源优化配置具有重要意义。通过有限元分析(finite element analysis,FEA)方法建立了不同敷设环境中高压直流电缆线路的暂态热场及电场模型,仿真分析了电缆在多种典型动态负荷下的温度分布及绝缘电场特性,研究发现:相比于架空及土壤直埋敷设,隧道敷设的HVDC电缆系统热响应时间常数达到数百小时,因此具有更好的动态增容能力。论文以隧道中敷设为例,通过相应FEA模型反演计算了不同初始负荷与应急时长下直流电缆的允许最大过负荷电流,给出了针对HVDC电缆线路短时动态增容能力的评估方法,并对直流电缆线路动态增容过程中的暂态电热特性进行了分析。结果表明:初始负荷率高,应急持续时间长,绝缘电导率温度敏感性强的高压XLPE直流电缆在动态增容过程中场强变化幅度大,应予以特别关注;初始负荷率不超过50%的隧道敷设双极直流电缆线路,单级可在1.5倍额定电流下安全运行2 h。该结果可为工程中HVDC电缆线路动态增容与优化调度提供理论指导。展开更多
为满足通信基站直流48 V供电需求,提出一种基于光伏与储能融合架构的供电系统,构建光伏阵列-升压变换-储能并网-智能控制的分布式路径,涵盖直流/直流(Direct Current/Direct Current,DC/DC)拓扑优化、最大功率点跟踪(Maximum Power Poin...为满足通信基站直流48 V供电需求,提出一种基于光伏与储能融合架构的供电系统,构建光伏阵列-升压变换-储能并网-智能控制的分布式路径,涵盖直流/直流(Direct Current/Direct Current,DC/DC)拓扑优化、最大功率点跟踪(Maximum Power Point Tracking,MPPT)算法、电磁兼容以及远程运维。实地部署测试结果表明,该系统在电压稳定性、动态响应、能效控制及自恢复能力等方面优于传统供电方案,在5G场景下具有高可行性与高适配性。展开更多
基金financially supported by the National Nature Science Foundation of China (Grant No. 51279189)
文摘This paper presents the results from laboratory experiments and theoretical analysis to investigate the development of scour around submarine pipeline under steady current conditions. Experiments show that the scour process takes place in two stages: the initial rapid scour and the subsequent gradual scour development stage. An empirical formula for calculating the equilibrium scour depth(the maximum scour depth) is developed by using the regression method. This formula together with the maximum entropy theory can be applied to establish a formula to predict the scour process for given water depth, diameter of pipeline and flow velocity. Good agreement between the predicted and measured scour depth is obtained.
基金supported by the National Natural Science Foundation of China(Grant Nos.61404115 and 61434006)the Postdoctoral Science Foundation of Henan Province,China(Grant No.2014006)the Development Fund for Outstanding Young Teachers of Zhengzhou University(Grant No.1521317004)
文摘Direct current（DC） and radio frequency（RF） performances of InP-based high electron mobility transistors（HEMTs）are investigated by Sentaurus TCAD. The physical models including hydrodynamic transport model, Shockley–Read–Hall recombination, Auger recombination, radiative recombination, density gradient model and high field-dependent mobility are used to characterize the devices. The simulated results and measured results about DC and RF performances are compared, showing that they are well matched. However, the slight differences in channel current and pinch-off voltage may be accounted for by the surface defects resulting from oxidized InAlAs material in the gate-recess region. Moreover,the simulated frequency characteristics can be extrapolated beyond the test equipment limitation of 40 GHz, which gives a more accurate maximum oscillation frequency( f;) of 385 GHz.
文摘在光储孤岛直流微电网中,需要最大化利用光伏发电,通常对光伏系统采用最大功率点跟踪(maximum power point tracking, MPPT)技术。但传统的MPPT控制速度慢、精度低,特别是在局部阴影情形下极易陷入局部最优解。基于此,首先提出一种将布谷鸟搜索算法与电导增量法相结合的混合MPPT控制。利用布谷鸟搜索算法快速全局寻优,再使用电导增量法精确定位,实现快速而准确地跟踪最大功率点。储能单元是光储直流微电网的重要组成部分,其输出电流均分、荷电状态(stateof charge, SoC)均衡和直流母线电压稳定是主要控制目标。但电流均分受线路电阻差异的影响,进而影响SoC均衡和直流母线电压稳定,于是设计一种新的电压电流双环控制策略以实现上述目标。该策略在电压外环采用母线电压作为反馈值,在电流内环中设计了基于一致性算法的控制策略,将SoC与指数函数结合并引入加速因子,使得在充放电过程中实现SoC的快速均衡。所提控制策略既不需要下垂控制,也无需二次补偿控制,减轻了通信负担。最后在Matlab/Simulink中搭建直流微电网系统模型,验证所设计新的混合MPPT控制和电压电流双环控制策略的有效性。
文摘电力需求的增长和系统容量的提升对输配电电缆的传输容量和运行可靠性提出了更高的要求,有效利用高压直流(high voltage direct current,HVDC)电缆线路的动态增容潜力对于实现电力资源优化配置具有重要意义。通过有限元分析(finite element analysis,FEA)方法建立了不同敷设环境中高压直流电缆线路的暂态热场及电场模型,仿真分析了电缆在多种典型动态负荷下的温度分布及绝缘电场特性,研究发现:相比于架空及土壤直埋敷设,隧道敷设的HVDC电缆系统热响应时间常数达到数百小时,因此具有更好的动态增容能力。论文以隧道中敷设为例,通过相应FEA模型反演计算了不同初始负荷与应急时长下直流电缆的允许最大过负荷电流,给出了针对HVDC电缆线路短时动态增容能力的评估方法,并对直流电缆线路动态增容过程中的暂态电热特性进行了分析。结果表明:初始负荷率高,应急持续时间长,绝缘电导率温度敏感性强的高压XLPE直流电缆在动态增容过程中场强变化幅度大,应予以特别关注;初始负荷率不超过50%的隧道敷设双极直流电缆线路,单级可在1.5倍额定电流下安全运行2 h。该结果可为工程中HVDC电缆线路动态增容与优化调度提供理论指导。
文摘为满足通信基站直流48 V供电需求,提出一种基于光伏与储能融合架构的供电系统,构建光伏阵列-升压变换-储能并网-智能控制的分布式路径,涵盖直流/直流(Direct Current/Direct Current,DC/DC)拓扑优化、最大功率点跟踪(Maximum Power Point Tracking,MPPT)算法、电磁兼容以及远程运维。实地部署测试结果表明,该系统在电压稳定性、动态响应、能效控制及自恢复能力等方面优于传统供电方案,在5G场景下具有高可行性与高适配性。
