AC-DC and DC-AC converter design

I would like to find out something about the design of AC-DC and DC-AC power convertor (power supply and inverter) designs. What I would like to know is, for a given AC voltage, what would be the optimal DC voltage to make the system most efficient (minimizing heat or other losses)? What about optimal for making it cost the least to build?

What if the input AC voltage is to be different than the output AC voltage? Would the optimal DC voltage have to track more to the input AC or the output AC, or something in between?

I'm curious because I have been looking for, and have not found, a true dual conversion (where it does AC to DC, then back to AC again) UPS that can do 480 VAC input while providing 120 VAC output. I have seen some that offer varying voltages, but when I dig in a little further I find the fine print that says an extra cabinet is required for the mismatched voltage version, which I believe will contain a transformer or three.

What I'd really rather have is a UPS system that does the AC to DC part directly from the 480 VAC input, without a transformer, preferrably with the ability to parallel 2 input units (if one is connected to a generator then it could be effectively the transfer switch as well), parallels the DC with batteries (controller needed here to manage the charge level I presume), and then an inverter to produce AC back out, but at the 120 VAC level. I suspect inputting 3 phase would be better since even a switching type power supply can find effective voltage levels almost all the time on at least one of the phases. Outputting 1 phase would do the job, but if the output is 3 phase WYE with 120 volt hot to neutral, that does the job. 277 VAC would be an alternative where main power is in the WYE configuration, since each leg is 277 volts relative to neutral.

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| Phil Howard KA9WGN       | http://linuxhomepage.com/      http://ham.org/ |
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