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I know that thyristors are used for rectification, that results in choppy DC. But what about other side of line? How do they convert such high voltage back to AC? Highest voltage IGBT I found is 6.5kV.

Do they connect them in series to achieve higher voltage for inverters (is it even possible)?

Would inductive loads cause harmonics, like in automotive 12VDC/230VAC inverters connected to motors (blender, power drill)?

Ri Di
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Many years ago, straight series connection of IGBTs to form a two or three level inverter.

These days, it's all MMC (modular multilevel converter), still using IGBTs. Schematic borrowed from https://www.plexim.com/support/application-examples/938

enter image description here

Inductive loads functions pretty much as in your AC grid overwise, they rob VA rating without active power. HVDC stations tend to have a round P-Q-graph so to support inductive or capacitive current, available peak active power will drop. Image borrowed from https://www.researchgate.net/publication/329473821_Exponential_Phase-Locked_Loop_Photovoltaic_Model_for_PHIL_Applications enter image description here

winny
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  • (What's DER? Distributed Energy Resources? (Like windmills? what use would over- or under-excitation be unless advantageous for the grid?)) – greybeard Jan 12 '23 at 07:48
  • @greybeard Seems so yes. I haven't seen the term used in this regard before, but the graph was what I was after. – winny Jan 12 '23 at 07:56
  • You can increasingly get modules for MMCs that use SiC MOSFETs, too. As I understand it, they're not quite common in power transmission systems yet, but they probably will be in the near future. – Hearth Jan 12 '23 at 15:45