This paper proposes a novel clamping device for leveling equipment mounted on offshore oil platform jacket,which solves the problem of leveling equipment clamping lifting force of more than 2000 tons.The main features...This paper proposes a novel clamping device for leveling equipment mounted on offshore oil platform jacket,which solves the problem of leveling equipment clamping lifting force of more than 2000 tons.The main features are that lifting force transmits to clamp claw through wedge force amplifier,embed the teeth of claw into the pile,and the embedded depth increases with the lifting force,resulting in a gravitational self-locking function.This theoretical model of clamping device was established,and the force and material characteristic were analyzed,and the feasibility of the theoretical model was verified by thin shell elastic-plastic stability theory and thin-walled structures theory.An experimental prototype of clamping device was produced to test gravity self-locking function and bearable leveling force.Compared with the theoretical model and the experimental results,it proved that the embedded clamping devices have gravitational self-locking function and can meet the need of actual leveling equipment.展开更多
高速磁浮交通牵引变流器采用24 MVA背靠背三电平有源中点钳位拓扑,其中两台整流器和两台逆变器共用直流母线。该文分析整流侧和逆变侧在不同功率因数下中点电压(neutral point voltage,NPV)偏移机理及不同电压矢量对NPV的具体影响。据此...高速磁浮交通牵引变流器采用24 MVA背靠背三电平有源中点钳位拓扑,其中两台整流器和两台逆变器共用直流母线。该文分析整流侧和逆变侧在不同功率因数下中点电压(neutral point voltage,NPV)偏移机理及不同电压矢量对NPV的具体影响。据此,针对高速磁浮逆变器并联和串联两种模式,建立NPV偏移模型,得到在调制比和功率因数同时变化时NPV的可控区域。为在全速范围保证NPV平衡,提出一种基于平移调制波的协同控制策略。为减轻整流器功率因数和调制比对NPV的影响,采用一种具有相电压半波对称性的载波脉宽调制,并证明其具备NPV自平衡能力。仿真和硬件在环实验表明,所提策略具有NPV恢复到平衡状态所需时间短、可控范围大等优点,可在高速磁浮全速工况下保证NPV平衡。展开更多
为降低中点箝位型(neutral point clamped,NPC)三电平整流器的电流谐波,在dq同步旋转坐标系下推导出带中点电压耦合项的NPC三电平整流器数学模型,并分析中点电压对电流控制的影响。对模型中的中点电压耦合项和交流侧等效电阻会增大电流...为降低中点箝位型(neutral point clamped,NPC)三电平整流器的电流谐波,在dq同步旋转坐标系下推导出带中点电压耦合项的NPC三电平整流器数学模型,并分析中点电压对电流控制的影响。对模型中的中点电压耦合项和交流侧等效电阻会增大电流谐波及无法通过常规方法进行准确估计的问题,设计一种混合参数自适应的迭代学习控制方法,以进行解耦控制并消除不确定参数的影响。通过构造Lyapunov函数和理论推导验证控制方法的稳定性。在整流器硬件平台上进行试验验证,结果表明,所设计的控制方法可有效降低电流谐波。展开更多
<strong>OBJECTIVE</strong><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-...<strong>OBJECTIVE</strong><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><strong>:</strong></span></span></span></span><span><span><span><b><span style="font-family:""> </span></b></span></span></span><span><span><span><span style="font-family:""><span style="font-family:Verdana;">To compare maternal preoperative and postoperative hemoglobin variation after cord clamping. </span><b><span style="font-family:Verdana;">METHODS: </span></b><span style="font-family:Verdana;">Randomized clinical trial performed in Porto Alegre, RS from January to December 2012. It was included 356 women with habitual risk gestations. In the immediate cord clamping group</span></span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">,</span></span></span></span><span><span><span><span style="font-family:""><span style="font-family:Verdana;"> the umbilical cord section was realized between 0 and 60 s (group 1) while in the delayed cord clamping group it was realized >60 s (group 2). </span><b><span style="font-family:Verdana;">RESULTS:</span></b><span style="font-family:Verdana;"> The mean (±standard deviation [SD]) preoperative hemoglobin was 12.13 ± 1.06 in the group 1 and 12.13 ± 1.11 in the group 2. The mean (±SD) postoperative day 2 hemoglobin level was 10.19 ± 1.46 in the group 1 and 10.24 ± 1.42 in the group 2. </span><b><span style="font-family:Verdana;">CONCLUSIONS: </span></b><span style="font-family:Verdana;">Delayed umbilical cord clamping resulted in a similar maternal hemoglobin level reduction at postoperative day 2.</span></span></span></span></span>展开更多
文章针对中点钳位(neutral point clamped inverter,NPC)类逆变电路存在的直流电容短路风险提出一种高可靠三电平逆变电路构造方法。首先,详细分析NPC逆变电路存在的2类电容直通风险以及当前高可靠三电平逆变电路存在的不足,总结出构造...文章针对中点钳位(neutral point clamped inverter,NPC)类逆变电路存在的直流电容短路风险提出一种高可靠三电平逆变电路构造方法。首先,详细分析NPC逆变电路存在的2类电容直通风险以及当前高可靠三电平逆变电路存在的不足,总结出构造高可靠NPC逆变器的2条原则。并基于此原则介绍新型高可靠NPC逆变电路的构造过程,发明一种分裂电感型复合中点钳位逆变器(split inductor hybrid neutral point clamped inverter,SI-HNPC)。所得电路的所有输出桥臂均由二极管与开关管串联构成,而与电容串联的开关管回路中含有分裂电感,有效地避免直流电容直通短路问题。此外,电路采用开关管和二极管的混合钳位结构,保持电压应力减半的基础上也保持零电平续流模态多样性。详细分析所提SI-HNPC运行特性与防直通能力,并搭建仿真模型和试验样机验证新型电路工作原理的正确性和短路抑制能力的有效性。展开更多
文摘This paper proposes a novel clamping device for leveling equipment mounted on offshore oil platform jacket,which solves the problem of leveling equipment clamping lifting force of more than 2000 tons.The main features are that lifting force transmits to clamp claw through wedge force amplifier,embed the teeth of claw into the pile,and the embedded depth increases with the lifting force,resulting in a gravitational self-locking function.This theoretical model of clamping device was established,and the force and material characteristic were analyzed,and the feasibility of the theoretical model was verified by thin shell elastic-plastic stability theory and thin-walled structures theory.An experimental prototype of clamping device was produced to test gravity self-locking function and bearable leveling force.Compared with the theoretical model and the experimental results,it proved that the embedded clamping devices have gravitational self-locking function and can meet the need of actual leveling equipment.
文摘高速磁浮交通牵引变流器采用24 MVA背靠背三电平有源中点钳位拓扑,其中两台整流器和两台逆变器共用直流母线。该文分析整流侧和逆变侧在不同功率因数下中点电压(neutral point voltage,NPV)偏移机理及不同电压矢量对NPV的具体影响。据此,针对高速磁浮逆变器并联和串联两种模式,建立NPV偏移模型,得到在调制比和功率因数同时变化时NPV的可控区域。为在全速范围保证NPV平衡,提出一种基于平移调制波的协同控制策略。为减轻整流器功率因数和调制比对NPV的影响,采用一种具有相电压半波对称性的载波脉宽调制,并证明其具备NPV自平衡能力。仿真和硬件在环实验表明,所提策略具有NPV恢复到平衡状态所需时间短、可控范围大等优点,可在高速磁浮全速工况下保证NPV平衡。
文摘为降低中点箝位型(neutral point clamped,NPC)三电平整流器的电流谐波,在dq同步旋转坐标系下推导出带中点电压耦合项的NPC三电平整流器数学模型,并分析中点电压对电流控制的影响。对模型中的中点电压耦合项和交流侧等效电阻会增大电流谐波及无法通过常规方法进行准确估计的问题,设计一种混合参数自适应的迭代学习控制方法,以进行解耦控制并消除不确定参数的影响。通过构造Lyapunov函数和理论推导验证控制方法的稳定性。在整流器硬件平台上进行试验验证,结果表明,所设计的控制方法可有效降低电流谐波。
文摘<strong>OBJECTIVE</strong><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><strong>:</strong></span></span></span></span><span><span><span><b><span style="font-family:""> </span></b></span></span></span><span><span><span><span style="font-family:""><span style="font-family:Verdana;">To compare maternal preoperative and postoperative hemoglobin variation after cord clamping. </span><b><span style="font-family:Verdana;">METHODS: </span></b><span style="font-family:Verdana;">Randomized clinical trial performed in Porto Alegre, RS from January to December 2012. It was included 356 women with habitual risk gestations. In the immediate cord clamping group</span></span></span></span></span><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;"><span style="font-family:Verdana;">,</span></span></span></span><span><span><span><span style="font-family:""><span style="font-family:Verdana;"> the umbilical cord section was realized between 0 and 60 s (group 1) while in the delayed cord clamping group it was realized >60 s (group 2). </span><b><span style="font-family:Verdana;">RESULTS:</span></b><span style="font-family:Verdana;"> The mean (±standard deviation [SD]) preoperative hemoglobin was 12.13 ± 1.06 in the group 1 and 12.13 ± 1.11 in the group 2. The mean (±SD) postoperative day 2 hemoglobin level was 10.19 ± 1.46 in the group 1 and 10.24 ± 1.42 in the group 2. </span><b><span style="font-family:Verdana;">CONCLUSIONS: </span></b><span style="font-family:Verdana;">Delayed umbilical cord clamping resulted in a similar maternal hemoglobin level reduction at postoperative day 2.</span></span></span></span></span>
文摘文章针对中点钳位(neutral point clamped inverter,NPC)类逆变电路存在的直流电容短路风险提出一种高可靠三电平逆变电路构造方法。首先,详细分析NPC逆变电路存在的2类电容直通风险以及当前高可靠三电平逆变电路存在的不足,总结出构造高可靠NPC逆变器的2条原则。并基于此原则介绍新型高可靠NPC逆变电路的构造过程,发明一种分裂电感型复合中点钳位逆变器(split inductor hybrid neutral point clamped inverter,SI-HNPC)。所得电路的所有输出桥臂均由二极管与开关管串联构成,而与电容串联的开关管回路中含有分裂电感,有效地避免直流电容直通短路问题。此外,电路采用开关管和二极管的混合钳位结构,保持电压应力减半的基础上也保持零电平续流模态多样性。详细分析所提SI-HNPC运行特性与防直通能力,并搭建仿真模型和试验样机验证新型电路工作原理的正确性和短路抑制能力的有效性。