In the U.S., AC power is NOT converted from AC to DC and then back to AC at any point on the power grid from the time it’s generated and the time it exits your wall sockets, excepting apparently a very small number of HVDC interconnects. It’s AC all the way for the U.S. baby!
Only solar goes from DC to AC, and only some wind generators make the AC-DC-AC conversion. IS that inefficient and expensive, with additional complexity and additional points of failure? yes. very.
All other AC to DC conversion is done by rectifiers in various parts of end-use electronic equipment in the home and industry ...
Is the HVDC you’re talking about the Pacific DC Intertie? Learned about this DC transmission system in the 80’s.