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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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