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Old 11-24-2015, 02:42 AM   #2365 (permalink)
e*clipse
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Quote:
Originally Posted by MPaulHolmes View Post
That looks like a good way to split it up. I'll do that. I was thinking more about the boosting. Here's my attempt to figure out the boost current requirement without simulation, just so I can get my head wrapped around it. Let's say we are doubling the DC voltage:

DC Power from batteries = Vbatt * Ibatt
DC Power from the capacitor bank to the 3 phase inverter = Vcaps * Icaps =
2*Vbatt * 0.5*Ibatt

Now, the power to the 3 phase inverter is
PowerInverter = 1.5 * Vcaps * IphasePeak (I always use this one. it's my favorite format)

So, 1.5 * Vcaps * IphasePeak = Vcaps * Icaps. So,
1.5*IphasePeak = Icaps.
So, 1.5*IphasePeak = 0.5*Ibatt
So, 3*IphasePeak = Ibatt.
Ok, so let's say we have a 75kW inverter and Vcaps = 650V
75kW = 1.5 * 650V * IphasePeak
IphasePeak = 76.9A Great! NBD for 3 TO-247 switches.

So what I was advocating was to run the battery voltage closer to the bus voltage. In the example I worked out, Vbatmin = 144 cells * 3.25V (below that, there's not much power available anyway)
Vbatmin = 468V or 468V/650V = 0.72
Using your last equation:
1.5*IphasePeak = 0.5*Ibatt >>>changes slightly >>> 1.5*IphasePeak = 0.72*Ibatt
so,
2.08*IphasePeak = Ibatt

Given IphasePeak = 76.9A for a 75kW inverter,
2.08*76.9A = 160A

The number is a bit lower than the TI app note's maximum switch current of 202A, but two completely different methods produced close results.

- E*clipse
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