Plasma behaviour and the scaling relations in a coaxial plasma opening switch （POS） using hydrogen plasma are studied self-consistently based on the two-dimensional magnetohydrodynamic （MHD） equations in conjuncti...Plasma behaviour and the scaling relations in a coaxial plasma opening switch （POS） using hydrogen plasma are studied self-consistently based on the two-dimensional magnetohydrodynamic （MHD） equations in conjunction with the generalized Ohm＇s law. The vacuum region on the right of POS is included in the model and the influence of downstream flow on the conduction characteristics is discussed. It is found that with the penetration of magnetic field, the pure hydrogen plasma is pushed downstream significantly; and POS still conducts current after the magnetic field arrives at the load edge of POS, which is different from the previous experimental results in a multispecies POS. It is because that the noticeable downstream plasma in the pure hydrogen POS may continue to conduct the current, while in the multispecies POS, the downstream plasma is unimportant so that the conduction phase ends soon after the magnetic field reaches the load edge. The scaling relation obtained from the simulations including the downstream region is consistent with the experimental results.展开更多
The two-dimensional energy balance in a coaxial plasma opening switch （POS） is studied based on the single-fluid magnetohydrodynarnic （MHD） equations coupled with the generalized Ohm＇s law. The energy transfers b...The two-dimensional energy balance in a coaxial plasma opening switch （POS） is studied based on the single-fluid magnetohydrodynarnic （MHD） equations coupled with the generalized Ohm＇s law. The energy transfers between the plasma and the magnetic field are considered during the penetration of the magnetic field as the Ohmic heating is included in the energy-balance equation. The focus is on the energy partition between the magnetic-field energy and the dissipated magnetic-field energy in a high-density POS with different rise-in-time electric currents at the generator boundary. The simulation code is tested in two cases： the constant-in-time current case and the linear rise-in-time current case. For the sinusoidally rise-in-time current similar to that of the experiments, it is shown that at the end of the conduction phase the dissipated magnetic-field energy is 36.5% of the input electromagnetic energy, which is consistent with the experimental results.展开更多
Experiments have been conducted on a plasma opening switch (POS) test-bed to investigate the influence of cathode materials made of aluminum, stainless steel, molybdenum and tungsten on opening performance for conduct...Experiments have been conducted on a plasma opening switch (POS) test-bed to investigate the influence of cathode materials made of aluminum, stainless steel, molybdenum and tungsten on opening performance for conduction time up to 3 microseconds, conduction current up to 100 kA. Remarkaly different opening characteristics have been shown for these materials,with tungsten being of the best opening performance.展开更多
在传统云平台网络带宽分配机制中,网络带宽仅在虚拟机创建时分配.虚拟机创建后已分配的带宽难以更改甚至无法更改,这在一定程度上造成了资源的浪费.因此,在不影响网络服务质量下,虚拟机需要一种有效的带宽分配机制来提高带宽的利用率....在传统云平台网络带宽分配机制中,网络带宽仅在虚拟机创建时分配.虚拟机创建后已分配的带宽难以更改甚至无法更改,这在一定程度上造成了资源的浪费.因此,在不影响网络服务质量下,虚拟机需要一种有效的带宽分配机制来提高带宽的利用率.本文以开源云平台Open Stack为实验环境,以虚拟交换软件Open v Switch和监控软件Ceilometer为工具,提出并实现了基于云平台的动态带宽分配策略.测试结果表明,本策略有效的提高了带宽的使用率.展开更多
由于开关器件故障是有源中性点箝位(active neutral point clamped,ANPC)三电平逆变器故障的主要类型,快速定位故障器件对提升ANPC三电平逆变器的可靠性具有重要意义。针对ANPC三电平逆变器开关器件开路故障,从传播路径的角度分析了不...由于开关器件故障是有源中性点箝位(active neutral point clamped,ANPC)三电平逆变器故障的主要类型,快速定位故障器件对提升ANPC三电平逆变器的可靠性具有重要意义。针对ANPC三电平逆变器开关器件开路故障,从传播路径的角度分析了不同调制算法下开关器件故障对输出电流的影响以及输出电流与负载侧电压的相位差对故障电流波形的影响。以三相输出电流作为故障特征量,提出一种基于切换调制策略的ANPC三电平逆变器开路故障诊断方法。首先采用电流平均值法先对故障开关器件的大致范围进行判定,然后切换调制策略以实现故障器件的精确定位。最后,通过仿真与实验验证了该方法可以在1个基波周期内实现故障定位,具有检测速度快、抗干扰能力强的优点,且无需额外增加用于故障检测的传感器。展开更多
基金National Natural Science Foundation of China(No.10376003)
文摘Plasma behaviour and the scaling relations in a coaxial plasma opening switch （POS） using hydrogen plasma are studied self-consistently based on the two-dimensional magnetohydrodynamic （MHD） equations in conjunction with the generalized Ohm＇s law. The vacuum region on the right of POS is included in the model and the influence of downstream flow on the conduction characteristics is discussed. It is found that with the penetration of magnetic field, the pure hydrogen plasma is pushed downstream significantly; and POS still conducts current after the magnetic field arrives at the load edge of POS, which is different from the previous experimental results in a multispecies POS. It is because that the noticeable downstream plasma in the pure hydrogen POS may continue to conduct the current, while in the multispecies POS, the downstream plasma is unimportant so that the conduction phase ends soon after the magnetic field reaches the load edge. The scaling relation obtained from the simulations including the downstream region is consistent with the experimental results.
基金supported by the National Science Foundation of China(No.10376003)
文摘The two-dimensional energy balance in a coaxial plasma opening switch （POS） is studied based on the single-fluid magnetohydrodynarnic （MHD） equations coupled with the generalized Ohm＇s law. The energy transfers between the plasma and the magnetic field are considered during the penetration of the magnetic field as the Ohmic heating is included in the energy-balance equation. The focus is on the energy partition between the magnetic-field energy and the dissipated magnetic-field energy in a high-density POS with different rise-in-time electric currents at the generator boundary. The simulation code is tested in two cases： the constant-in-time current case and the linear rise-in-time current case. For the sinusoidally rise-in-time current similar to that of the experiments, it is shown that at the end of the conduction phase the dissipated magnetic-field energy is 36.5% of the input electromagnetic energy, which is consistent with the experimental results.
文摘Experiments have been conducted on a plasma opening switch (POS) test-bed to investigate the influence of cathode materials made of aluminum, stainless steel, molybdenum and tungsten on opening performance for conduction time up to 3 microseconds, conduction current up to 100 kA. Remarkaly different opening characteristics have been shown for these materials,with tungsten being of the best opening performance.
文摘在传统云平台网络带宽分配机制中,网络带宽仅在虚拟机创建时分配.虚拟机创建后已分配的带宽难以更改甚至无法更改,这在一定程度上造成了资源的浪费.因此,在不影响网络服务质量下,虚拟机需要一种有效的带宽分配机制来提高带宽的利用率.本文以开源云平台Open Stack为实验环境,以虚拟交换软件Open v Switch和监控软件Ceilometer为工具,提出并实现了基于云平台的动态带宽分配策略.测试结果表明,本策略有效的提高了带宽的使用率.
文摘由于开关器件故障是有源中性点箝位(active neutral point clamped,ANPC)三电平逆变器故障的主要类型,快速定位故障器件对提升ANPC三电平逆变器的可靠性具有重要意义。针对ANPC三电平逆变器开关器件开路故障,从传播路径的角度分析了不同调制算法下开关器件故障对输出电流的影响以及输出电流与负载侧电压的相位差对故障电流波形的影响。以三相输出电流作为故障特征量,提出一种基于切换调制策略的ANPC三电平逆变器开路故障诊断方法。首先采用电流平均值法先对故障开关器件的大致范围进行判定,然后切换调制策略以实现故障器件的精确定位。最后,通过仿真与实验验证了该方法可以在1个基波周期内实现故障定位,具有检测速度快、抗干扰能力强的优点,且无需额外增加用于故障检测的传感器。
