How to calculate the DC Bus voltage of the UPS in Datacenter application?

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ramyadevi89

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Hi,

I am currently working on a specification of UPS in datacenter. How to calculate the DC bus voltage for 480V ac input/ 480v ac output UPS? And what are the important specifications i need to focus on when reviewing the UPS submittals. Can anyone please share any good literature on UPS system operating modes for Tier-4 datacenter?
Thanks :)
 
ramyadevi89 said:
Hi,

I am currently working on a specification of UPS in datacenter. How to calculate the DC bus voltage for 480V ac input/ 480v ac output UPS? And what are the important specifications i need to focus on when reviewing the UPS submittals. Can anyone please share any good literature on UPS system operating modes for Tier-4 datacenter?
Thanks :)
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I think the starting point is the UPS voltage.
 
I wouldn't be much concerned by the DC bus voltage, it's whatever the manufacturer uses.

How big a UPS? 20 KVA, 200KVA, 2000KVA? There will be a huge difference in specs and designs, and when you get to the larger ones, there are only a few companies making them and they'll have a lot of engineering material.
 
Not to be unkind, but it sounds like you're a bit over your head on this. For that total load, I'd expect multiple 400-600KVA systems into parallel/redundant distribution systems so there's no single point of failure.

That said, aside from the expected capacity, there's--
expected run time at various loads
single or multiple independent inputs or outputs?
what sort of maintenance bypass arrangements are needed?
power factor and harmonics on both input and output
what/how much redundancy do you want or need?
how much space do you have to put it?

You might start, actually, by contacting some of the manufacturers for engineering support; ABB, Vertiv/Leibert, Schneider, etc.

(Does the IEEE have anything relevant?)
 
United you are from Redmond, home of Microsoft. There should be numerous UPS vendors in Redmond to assist you.
And I agree use multiple smaller UPSs
 
I don't think it makes a whole lot of difference what the DC bus voltage is. It will be whatever the manufacturer uses for the size of UPS you need.
 
A UPS, or anything that rectifies AC to DC, will have an average DC bus voltage of the input line voltage x the sq. rt. of 2 (1.41), so roughly 679VDC in the case of a 480V input. But it’s not something you specify, it just is what it is.
 
Please verify my math:
V(line-to-line, peak)= 480 x 1.414 = 678.82 V

The supply voltage to neutral = 678.82/ 1.732 = 391.92 V (call this as VS)

Then, the average DC output voltage from the 3-phase full-wave rectifier is:

VDC = (3 x 1.732)/(3.1416) x VS =1.654 x VS = 1,654 x 391.92 = 648.23 VDC
 
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