The new three-phase 5-level current-source inverter (CSI) proposed in this paper was developed by connecting three separate single-phase 5-level CSIs in series, and its operational principle was analyzed. There are tw...The new three-phase 5-level current-source inverter (CSI) proposed in this paper was developed by connecting three separate single-phase 5-level CSIs in series, and its operational principle was analyzed. There are two major problems existing in current-source multilevel inverters, one is the complex PWM control method (2-logic to 3-logic conversion), and the other is the problem of current-unbalance between different levels. A simple current-balance control method via DC current feedback is applied in each single-phase 5-level CSI cell to implement the current-balance control between different levels. And to reduce the output current harmonics, POD PWM control technique was used. Simulation and experimental results showed that this new three-phase 5-level CSI topology operates correctly.展开更多
目的了解西安市3~18儿童维生素D[25(OH)VitD,简称VitD]的营养状况及影响因素。方法选择2015年7月到2017年2月期间的寒、暑假在西安交通大学第一附属医院儿保科做健康体检的533例3~18岁西安市儿童为研究对象,采用酶联免疫吸附法(ELISA)...目的了解西安市3~18儿童维生素D[25(OH)VitD,简称VitD]的营养状况及影响因素。方法选择2015年7月到2017年2月期间的寒、暑假在西安交通大学第一附属医院儿保科做健康体检的533例3~18岁西安市儿童为研究对象,采用酶联免疫吸附法(ELISA)检测其血清VitD水平,并分析季节和性别的影响;进一步按照被研究儿童所处学校的性质,将其分为幼儿园组,小学组和中学组,比较三组儿童VitD的营养状况。结果儿童血清VitD水平为24.94±1.03ng/mL,VitD缺乏和不足的检出率分别为34.71%(185/533)和34.15%(182/533)。寒假与暑假儿童VitD水平(21.20±11.01ng/mL vs 27.71±8.68ng/mL,t=7.62,P<0.001)及不同VitD水平的检出率差异均有统计学意义(57.71%vs 17.64%,χ~2=93.13,P<0.001)。男童与女童VitD水平(25.06±10.67ng/mL vs 24.72±9.52ng/mL,t=0.38,P>0.05)及VitD缺乏检出率(35.03%vs 34.17%,χ~2=0.04,P>0.05)差异均无统计学意义。幼儿园组、小学组和中学组VitD水平分别为31.93±10.02ng/mL、22.33±8.34ng/mL和19.45±7.27ng/mL(各组间比较t值分别为10.56、10.49和2.19,均P<0.05),且三组儿童不同水平VitD的检出率差异存在统计学意义(χ~2=125.82,P<0.05)。结论西安市3~18岁儿童VitD缺乏率较高,尤其是中、小学阶段的儿童更为突出,医务人员应重视对该部分儿童VitD营养的保健指导。展开更多
基金Project (No. 50477033) supported by the National Natural Science Foundation of China
文摘The new three-phase 5-level current-source inverter (CSI) proposed in this paper was developed by connecting three separate single-phase 5-level CSIs in series, and its operational principle was analyzed. There are two major problems existing in current-source multilevel inverters, one is the complex PWM control method (2-logic to 3-logic conversion), and the other is the problem of current-unbalance between different levels. A simple current-balance control method via DC current feedback is applied in each single-phase 5-level CSI cell to implement the current-balance control between different levels. And to reduce the output current harmonics, POD PWM control technique was used. Simulation and experimental results showed that this new three-phase 5-level CSI topology operates correctly.
文摘目的了解西安市3~18儿童维生素D[25(OH)VitD,简称VitD]的营养状况及影响因素。方法选择2015年7月到2017年2月期间的寒、暑假在西安交通大学第一附属医院儿保科做健康体检的533例3~18岁西安市儿童为研究对象,采用酶联免疫吸附法(ELISA)检测其血清VitD水平,并分析季节和性别的影响;进一步按照被研究儿童所处学校的性质,将其分为幼儿园组,小学组和中学组,比较三组儿童VitD的营养状况。结果儿童血清VitD水平为24.94±1.03ng/mL,VitD缺乏和不足的检出率分别为34.71%(185/533)和34.15%(182/533)。寒假与暑假儿童VitD水平(21.20±11.01ng/mL vs 27.71±8.68ng/mL,t=7.62,P<0.001)及不同VitD水平的检出率差异均有统计学意义(57.71%vs 17.64%,χ~2=93.13,P<0.001)。男童与女童VitD水平(25.06±10.67ng/mL vs 24.72±9.52ng/mL,t=0.38,P>0.05)及VitD缺乏检出率(35.03%vs 34.17%,χ~2=0.04,P>0.05)差异均无统计学意义。幼儿园组、小学组和中学组VitD水平分别为31.93±10.02ng/mL、22.33±8.34ng/mL和19.45±7.27ng/mL(各组间比较t值分别为10.56、10.49和2.19,均P<0.05),且三组儿童不同水平VitD的检出率差异存在统计学意义(χ~2=125.82,P<0.05)。结论西安市3~18岁儿童VitD缺乏率较高,尤其是中、小学阶段的儿童更为突出,医务人员应重视对该部分儿童VitD营养的保健指导。
