In this work, the ratio of rotation rate to advancing speed was fixed to 10 to fabricate friction stir welding (FSW) butt joints of 2195 - T8 plates with 7.5 mm in thickness. The results revealed that the heat input of joints along the vertical direction varied with the welding parameters though these parameters had a same ratio. 500-50 and 600-60 joints failed in the thermal affected zone and thermal mechanical affected zone (TAZ/TMAZ), while other joints all failed in stirred zone (SZ). The hardness profile across the joints showed a similar W shape, while the hardness in bottom area increased with the increasing of parameters. Lazy S and kissing - bond defects appeared in all of these joints, and over - burn defect was also found in 1000-100 joint. It is concluded that the heat input distribution gradient during FSW across the joints becomes non-uniform and a sudden change between upper and lower areas even occurs.
To reduce the power loss in a modular multilevel converter (MMC), hybrid switches with different combinations of Si-IGBT, SiC-MOSFET, Si-FRD and SiC-SBD in parallel or anti-parallel are comparatively investigated. By comparing the power losses in MMC submodule (SM) bridge arm switching devices, one bridge arm of a SM is replaced with a different switch configuration, while the other remains in the conventional Si-IGBT and FRD configuration. Itot
− Esw
and I - V curves are obtained for four switch configurations through SIMETRIX, and brought to SIMULINK simulation over longer time scales to account for the variable switch operating condition. Along with the simulation and experimental results, the loss differences under different switch configurations are verified, obtaining the optimal switch configuration at last, which is instructive for the selection of MMC SM in the future.
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