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.
文摘通过分析模块化多电平变换器(modular multilevel converter,MMC)各部分之间的功率关系,提出一种MMC综合控制方案,包括直流母线电压控制和桥臂电容电压控制。该方案内环采用桥臂电流直接反馈控制,可实现交流侧电流、直流母线电流和内部环流的三重控制,不需要专门的环流控制器。该方案各桥臂电容电压控制基本相互独立,易于实现分布式控制。提出一种电流前馈控制方案,能有效减小电容电压的动态波动,提高动态响应速度。搭建了10 k VA三相MMC实验样机,实验结果验证了所提控制方案的可行性和有效性,并具有优良的动静态特性。
