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1kW 200/400V dc/dc converter design tip

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David Hess:
I would not use a switching converter at all unless I had to have a regulated output.  Simpler would be a high frequency inverter to just double the input voltage.

nctnico:

--- Quote from: webgiorgio on January 25, 2019, 12:44:49 pm ---Hello,
I would like to make a DC/DC converter to use it in my Photovoltaic plant, where I need to boost 200 Vdc 5A to 400 Vdc 2.5A, so that I can parallel a string of 6 PV panels with other strings of 12 panels. 1200W.
Vmpp for one panel is 33.3V (200V/6).

--- End quote ---
I don't think this will work. You'll need to mimic the maximum power point tracking (mppt) as well. I'd create 3 strings of 6 panels each. Preferably each on their own inverter DC input channel to maximise mppt effectiveness.

webgiorgio:
A string of 6 panels would not have enough voltage in relation to the input range of the inverter (333V-500V).

I think that the inverter does a good job to make the 12 panels operate at the voltage that corresponds to the maximum power point.
If my DC-DC keeps Vin=Vout/2, this Vin corresponds to the MPP of a series of 6 panels.
I neglected the losses, as I expect about 5W out of 1000W, so 0.5%.

Benta:

--- Quote from: webgiorgio on January 27, 2019, 03:54:31 pm ---I neglected the losses, as I expect about 5W out of 1000W, so 0.5%.

--- End quote ---

Are you talking about the losses in the converter?
If so, that's totally unrealistic, it corresponds to an efficiency of 99.5%.
Expect a power loss of 50...100 W.

webgiorgio:
I meant losses in my dc-dc converter.
Mhh, you are right, 0,5% losses sounds too optimistic.

Using this Sic mosfet C3M0280090D
https://www.wolfspeed.com/media/downloads/825/C3M0280090D.pdf

Rdson=0,28 ohm, switch losses are 50 uJ per period.
At 2.5A average current:
Conduction losses= 0,28*2,5²=1,75W
Switching losses= 50*0.100=5W (from graph 23)

I hanven't look up a transistor, which was suggested as more efficient than a mosfet. Can it be?

This diode STPSC1006D
https://www.mouser.com/datasheet/2/389/stpsc1006-956763.pdf
would have 3,56W losses at 2.5A

If the inductor has 150 mOhm, dissipates 1W.

13,3 W so far. So, 1.33% losses. I still have to quantify the losses in the gate driver and capacitors.
I could also reduce the switching frequency and increase the inductor to reduce the switching losses.

The whole 7 kW PV inverter has 2-3% losses to do MPPT and AC conversion (according to the datasheet, it is a SMA SMC 7000 TL)
I hope that my simple boost converter can have around 2% losses.

Can I reduce the switching frequency at partial load?

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