To investigate the interaction between the tropical Pacific and China seas a variable-grid global ocean circulation model with fine grid covering the area from 20°S to 50°N and from 99° to 150°E is...To investigate the interaction between the tropical Pacific and China seas a variable-grid global ocean circulation model with fine grid covering the area from 20°S to 50°N and from 99° to 150°E is developed. Numerical computation of the annually cyclic circulation fields is performed. The results of the annual mean zonal currents and deep to abyssal western boundary currents in the equatorial Pacific Ocean are reported. The North Equatorial Current,the North Equatorial Countercurrent, the South Equatorial Current and the Equatorial Undercurrent are fairly well simulated. The model well reproduces the northward flowing abyssal western boundary current.From the model results a lower deep western boundary current east of the Bismarck-Solomon-New Hebrides Island chain at depths around 2 000 m has been found. The model results also show that the currents in the equatorial Pacific Ocean have multi-layer structures both in zonal currents and western boundary currents, indicating that the global ocean overturning thermohaline circulation appears of multi-layer pattern.展开更多
随着宽禁带功率半导体器件的广泛使用,更高开关频率的双有源桥(dual active bridge,DAB)变换器带来了更大的开关损耗,对于软开关技术提出更高要求。为了进一步拓展零电压开通(zero-voltage switching,ZVS)范围,文中对ZVS精确模型和传统...随着宽禁带功率半导体器件的广泛使用,更高开关频率的双有源桥(dual active bridge,DAB)变换器带来了更大的开关损耗,对于软开关技术提出更高要求。为了进一步拓展零电压开通(zero-voltage switching,ZVS)范围,文中对ZVS精确模型和传统电感电流全局最优条件方法进行分析,提出一种结合励磁电流运行的移相调制策略,该策略可实现DAB变换器全功率范围内所有开关管的ZVS运行(8-ZVS运行)。在考虑开关管非线性特性和死区时间限制基础上得到更精确的ZVS模型,并推导引入励磁电流的ZVS模型。此外,所提出的控制方案具有无缝模式转换的特点,电感电流的有效值也可以达到准最佳状态。最后,搭建6kW/150kHz的高频DAB变换器样机以验证模型有效性。实验结果表明,该控制算法可以在任意模式和工况下实现8-ZVS运行,从而提升系统在轻载和中载工况下运行效率。展开更多
为提高局部阴影条件下光伏发电的能量利用率,提出一种改进型快速全局最大功率点跟踪(global maximum power point tracking,GMPPT)算法.首先,研究局部阴影条件下光伏阵列的输出特性,并根据光伏阵列输出曲线中膝点与开路电压的关系,将其...为提高局部阴影条件下光伏发电的能量利用率,提出一种改进型快速全局最大功率点跟踪(global maximum power point tracking,GMPPT)算法.首先,研究局部阴影条件下光伏阵列的输出特性,并根据光伏阵列输出曲线中膝点与开路电压的关系,将其划分为恒流区和恒压区;其次,分析传统的最大功率梯形(maximum power trapezium,MPT)算法和以MPT算法为基础的改进型快速GMPPT算法的工作原理,改进型快速GMPPT算法利用电压的动态上、下限来限定搜索区间,并跳过调整时间较长的恒流区,以提高跟踪速度;最后,通过仿真与实验验证算法的有效性.实验结果表明:改进型快速GMPPT算法的最短跟踪时间为4.0 s,扫描电压与能量损失分别为17.34 V和98.19 J;与传统全局扫描算法相比,跟踪时间缩短68.25%,扫描电压降低74.86%,能量损失减少58.19%;与MPT算法相比,跟踪时间缩短68.00%,扫描电压降低75.63%,能量损失减少62.31%.展开更多
基金This study is supported by the National Natural Sci-ence Foundation of China under contract No.40136010the Major State Basic Research Program of China under contract No.G1999043808the Youth Fund of National“863”Project of China under contract No.2002AA639350.
文摘To investigate the interaction between the tropical Pacific and China seas a variable-grid global ocean circulation model with fine grid covering the area from 20°S to 50°N and from 99° to 150°E is developed. Numerical computation of the annually cyclic circulation fields is performed. The results of the annual mean zonal currents and deep to abyssal western boundary currents in the equatorial Pacific Ocean are reported. The North Equatorial Current,the North Equatorial Countercurrent, the South Equatorial Current and the Equatorial Undercurrent are fairly well simulated. The model well reproduces the northward flowing abyssal western boundary current.From the model results a lower deep western boundary current east of the Bismarck-Solomon-New Hebrides Island chain at depths around 2 000 m has been found. The model results also show that the currents in the equatorial Pacific Ocean have multi-layer structures both in zonal currents and western boundary currents, indicating that the global ocean overturning thermohaline circulation appears of multi-layer pattern.
文摘随着宽禁带功率半导体器件的广泛使用,更高开关频率的双有源桥(dual active bridge,DAB)变换器带来了更大的开关损耗,对于软开关技术提出更高要求。为了进一步拓展零电压开通(zero-voltage switching,ZVS)范围,文中对ZVS精确模型和传统电感电流全局最优条件方法进行分析,提出一种结合励磁电流运行的移相调制策略,该策略可实现DAB变换器全功率范围内所有开关管的ZVS运行(8-ZVS运行)。在考虑开关管非线性特性和死区时间限制基础上得到更精确的ZVS模型,并推导引入励磁电流的ZVS模型。此外,所提出的控制方案具有无缝模式转换的特点,电感电流的有效值也可以达到准最佳状态。最后,搭建6kW/150kHz的高频DAB变换器样机以验证模型有效性。实验结果表明,该控制算法可以在任意模式和工况下实现8-ZVS运行,从而提升系统在轻载和中载工况下运行效率。
文摘为提高局部阴影条件下光伏发电的能量利用率,提出一种改进型快速全局最大功率点跟踪(global maximum power point tracking,GMPPT)算法.首先,研究局部阴影条件下光伏阵列的输出特性,并根据光伏阵列输出曲线中膝点与开路电压的关系,将其划分为恒流区和恒压区;其次,分析传统的最大功率梯形(maximum power trapezium,MPT)算法和以MPT算法为基础的改进型快速GMPPT算法的工作原理,改进型快速GMPPT算法利用电压的动态上、下限来限定搜索区间,并跳过调整时间较长的恒流区,以提高跟踪速度;最后,通过仿真与实验验证算法的有效性.实验结果表明:改进型快速GMPPT算法的最短跟踪时间为4.0 s,扫描电压与能量损失分别为17.34 V和98.19 J;与传统全局扫描算法相比,跟踪时间缩短68.25%,扫描电压降低74.86%,能量损失减少58.19%;与MPT算法相比,跟踪时间缩短68.00%,扫描电压降低75.63%,能量损失减少62.31%.
