Growth and passivation of tunnels within Al foil by on-off controlling DC etching in 6 wt.% HCI solution has been investigated. It was found that, in a given etchant solution at a special temperature, the longest tunn...Growth and passivation of tunnels within Al foil by on-off controlling DC etching in 6 wt.% HCI solution has been investigated. It was found that, in a given etchant solution at a special temperature, the longest tunnel length was only a function of the turn-on interval of DC. The potential of Al foil broke at on-off controlling DC by the result from anode polarization curves and potential-time （E-t） responding curves. When DC was switched on, the potential increased abruptly over pitting potential, leading to nucleation of pits at the surface and the growth of tunnels at special length. When DC was switched off, the potential decreased rapidly to a passive value, leading to stoppage of nucleation and death of tunnels. By this way, the longest tunnel length can be controlled and a non-piercing layer can be obtained. Hence, etching of Al foil at this current is beneficial for maintaining a good mechanical strength.展开更多
基于模块化多电平变换器的固态变压器(modular multilevel converter based solid state transformer,MMC-SST)是实现交直流混合配电网柔性互联及能量多向流动的关键装备。针对固态变压器输入级MMC子模块电容纹波电压过大,导致装置的体...基于模块化多电平变换器的固态变压器(modular multilevel converter based solid state transformer,MMC-SST)是实现交直流混合配电网柔性互联及能量多向流动的关键装备。针对固态变压器输入级MMC子模块电容纹波电压过大,导致装置的体积和成本增加的问题,提出一种基于比例重复控制的MMC-SST改进纹波电压抑制策略。首先利用基于比例重复控制的电容电压闭环得到调整后的功率移相角。然后,通过双有源桥变换器将子模块电容纹波功率传递到低压直流母线,从而有效抑制MMC子模块的各频次纹波电压,达到减小电容值的目的。最后,仿真结果表明在网侧电压对称或不对称工况下,基于比例重复控制的MMC-SST子模块电容纹波电压抑制策略均具有良好的纹波电压抑制能力。展开更多
基金This study was financially supported by Beijing Education Commission,China.
文摘Growth and passivation of tunnels within Al foil by on-off controlling DC etching in 6 wt.% HCI solution has been investigated. It was found that, in a given etchant solution at a special temperature, the longest tunnel length was only a function of the turn-on interval of DC. The potential of Al foil broke at on-off controlling DC by the result from anode polarization curves and potential-time （E-t） responding curves. When DC was switched on, the potential increased abruptly over pitting potential, leading to nucleation of pits at the surface and the growth of tunnels at special length. When DC was switched off, the potential decreased rapidly to a passive value, leading to stoppage of nucleation and death of tunnels. By this way, the longest tunnel length can be controlled and a non-piercing layer can be obtained. Hence, etching of Al foil at this current is beneficial for maintaining a good mechanical strength.
文摘基于模块化多电平变换器的固态变压器(modular multilevel converter based solid state transformer,MMC-SST)是实现交直流混合配电网柔性互联及能量多向流动的关键装备。针对固态变压器输入级MMC子模块电容纹波电压过大,导致装置的体积和成本增加的问题,提出一种基于比例重复控制的MMC-SST改进纹波电压抑制策略。首先利用基于比例重复控制的电容电压闭环得到调整后的功率移相角。然后,通过双有源桥变换器将子模块电容纹波功率传递到低压直流母线,从而有效抑制MMC子模块的各频次纹波电压,达到减小电容值的目的。最后,仿真结果表明在网侧电压对称或不对称工况下,基于比例重复控制的MMC-SST子模块电容纹波电压抑制策略均具有良好的纹波电压抑制能力。
