The fractal dimensions in different topological spaces of polyferric chloride-humic acid （PFC-HA） flocs, formed in flocculating different kinds of humic acids （HA） water at different initial pH （9.0, 7.0, 5.0） a...The fractal dimensions in different topological spaces of polyferric chloride-humic acid （PFC-HA） flocs, formed in flocculating different kinds of humic acids （HA） water at different initial pH （9.0, 7.0, 5.0） and PFC dosages, were calculated by effective densitymaximum diameter, image analysis, and N2 absorption-desorption methods, respectively. The mass fractal dimensions （De） of PFC-HA floes were calculated by bi-logarithm relation of effective density with maximum diameter and Logan empirical equation. The Df value was more than 2.0 at initial pH of 7,0, which was 11% and 13% higher than those at pH 9.0 and 5.0, respecively, indicating the most compact flocs formed in flocculated HA water at initial pH of 7.0. The image analysis for those flocs indicates that after flocculating the HA water at initial pH greater than 7.0 with PFC flocculant, the fractal dimensions of D2 （logA vs. logdL） and D3 （logVsphere vs. logdL） of PFC-HA floes decreased with the increase of PFC dosages, and PFC-HA floes showed a gradually looser structure. At the optimum dosage of PFC, the D2 （logA vs. logdL） values of the flocs show 14%-43% difference with their corresponding Dr, and they even had different tendency with the change of initial pH values. However, the D2 values of the floes formed at three different initial pH in HA solution had a same tendency with the corresponding Df. Based on fractal Frenkel-Halsey-HiU （FHH） adsorption and desorption equations, the pore surface fractal dimensions （Ds） for dried powders of PFC-HA flocs formed in HA water with initial pH 9.0 and 7.0 were all close to 2.9421, and the Ds values of flocs formed at initial pH 5.0 were less than 2.3746. It indicated that the pore surface fractal dimensions of PFC-HA floes dried powder mainly show the irregularity from the mesopore-size distribution and marcopore-size distribution.展开更多
在高电压-大电流的大功率牵引传动系统中,驱动逆变器受到开关损耗和散热条件等的限制,逆变器的最高工作开关频率通常只有几百赫兹。为了提高逆变器的输出性能,通常在中频段采用同步调制策略。针对同步SVPWM,总结了满足半周期奇对称HWS(h...在高电压-大电流的大功率牵引传动系统中,驱动逆变器受到开关损耗和散热条件等的限制,逆变器的最高工作开关频率通常只有几百赫兹。为了提高逆变器的输出性能,通常在中频段采用同步调制策略。针对同步SVPWM,总结了满足半周期奇对称HWS(half-wave odd symmetry)、1/4周期偶对称QWS(quarter-wave even symmetry)和三相对称3PS(quarter-wave even symmetry)的对称性规律,介绍了其中的同步CSVS的脉冲生成规律及发波方式。通过阻感负载下的仿真和实验,对同步CSVS的电流谐波特性进行分析,得到了电流谐波含量随调制比的变化规律以及电流谐波主要集中次数的分布规律,为同步CSVS的应用提供了一定的参考价值。展开更多
基金supported by the National Natural Science Foundation of China (No. 20407004, 50578012, 50178009)the High-Tech Research and Development Program (863) of China (No. 2007AA06Z301)+2 种基金the Fok Ying Tung Education Foundation of National Education Ministry of China (No. 91078)the Beijing Municipal Commission of Education Project, Program for New Cen- tury Excellent Talents in University (No. NCET-06-0120)the Beijing Nova of Science and Technology, Beijing Key Subject (No. XK100220555).
文摘The fractal dimensions in different topological spaces of polyferric chloride-humic acid （PFC-HA） flocs, formed in flocculating different kinds of humic acids （HA） water at different initial pH （9.0, 7.0, 5.0） and PFC dosages, were calculated by effective densitymaximum diameter, image analysis, and N2 absorption-desorption methods, respectively. The mass fractal dimensions （De） of PFC-HA floes were calculated by bi-logarithm relation of effective density with maximum diameter and Logan empirical equation. The Df value was more than 2.0 at initial pH of 7,0, which was 11% and 13% higher than those at pH 9.0 and 5.0, respecively, indicating the most compact flocs formed in flocculated HA water at initial pH of 7.0. The image analysis for those flocs indicates that after flocculating the HA water at initial pH greater than 7.0 with PFC flocculant, the fractal dimensions of D2 （logA vs. logdL） and D3 （logVsphere vs. logdL） of PFC-HA floes decreased with the increase of PFC dosages, and PFC-HA floes showed a gradually looser structure. At the optimum dosage of PFC, the D2 （logA vs. logdL） values of the flocs show 14%-43% difference with their corresponding Dr, and they even had different tendency with the change of initial pH values. However, the D2 values of the floes formed at three different initial pH in HA solution had a same tendency with the corresponding Df. Based on fractal Frenkel-Halsey-HiU （FHH） adsorption and desorption equations, the pore surface fractal dimensions （Ds） for dried powders of PFC-HA flocs formed in HA water with initial pH 9.0 and 7.0 were all close to 2.9421, and the Ds values of flocs formed at initial pH 5.0 were less than 2.3746. It indicated that the pore surface fractal dimensions of PFC-HA floes dried powder mainly show the irregularity from the mesopore-size distribution and marcopore-size distribution.
文摘在高电压-大电流的大功率牵引传动系统中,驱动逆变器受到开关损耗和散热条件等的限制,逆变器的最高工作开关频率通常只有几百赫兹。为了提高逆变器的输出性能,通常在中频段采用同步调制策略。针对同步SVPWM,总结了满足半周期奇对称HWS(half-wave odd symmetry)、1/4周期偶对称QWS(quarter-wave even symmetry)和三相对称3PS(quarter-wave even symmetry)的对称性规律,介绍了其中的同步CSVS的脉冲生成规律及发波方式。通过阻感负载下的仿真和实验,对同步CSVS的电流谐波特性进行分析,得到了电流谐波含量随调制比的变化规律以及电流谐波主要集中次数的分布规律,为同步CSVS的应用提供了一定的参考价值。
