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| 1kW 200/400V dc/dc converter design tip |
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| jbb:
I'd like to muddy the waters ;D As you're doing this for a PV installation, a fixed gain of 2 is probably sufficient. After all, the PV inverter will have Maximum Power Point Tracking (MPPT), which could interact with the controller for a boost converter in strange ways. So how about a switched capacitor voltage doubler? That offers a fixed voltage ratio and doesn't need fancy control or large inductors. (Texas Instruments has an introductory post...) Switched capacitors are quite efficient when you want an exact voltage ratio and can be made in kW sizes. Note: some small EMI filter inductors are likely required on the input and output to prevent stray radio interference. In terms of magnetic converters: --- Quote from: Benta on January 25, 2019, 04:37:05 pm ---At 1 kW I'd choose a full-bridge converter with transformer coupling. The inductors in boost (this includes flyback) converters of that size tend to be unmanageable large, as they have to store the full energy. A forward converter could also be an option. --- End quote --- I like isolation as much as the next person, but wouldn't designing the transformer (+ filter inductor for forward converter) be more difficult than designing an (admittedly large) boost inductor? Here's what I would consider for a boost converter: * Tight PCB layout is critical. * As Mazo suggested, interleaving is helpful. Currents aren't that high, and duty cycle will be 50% (ish!), so I'm thinking 2 phases. This will help a lot with capacitor selection. * Using a SiC MOSFET (or Gallium Nitride, GaN) + SiC Schottky diode to get high frequency; frequency around 100 kHz * If efficiency is critical, replace SiC Schottky with another SiC MOSFET for improved efficiency (extra for experts) * This yields inductor values in the order of 500 - 800 uH, which you might be able to hit with something from the WE-HCF range (Wuerth Electronics) |
| Benta:
--- Quote from: jbb on January 25, 2019, 09:27:51 pm --- I like isolation as much as the next person, but wouldn't designing the transformer (+ filter inductor for forward converter) be more difficult than designing an (admittedly large) boost inductor? --- End quote --- In my opinion: no. The transformer design for full (and half) bridge circuits is straightforward. The same goes for forward converters. The filter inductor can be bought off-shelf. |
| webgiorgio:
I looked up the voltage doubler, the idea was good at first sight, but then I saw it takes too many switches. To my little knowledge (I am electrical engineer, not electronic) a boost converter is totally fine with a voltage ratio equal 2, which can be done without use of transformers. For this voltage ratio, any topology with a transformer will be less efficient than a single inductor because there is twice the copper and not all the flux is concatenating with the secondary winding. About the inductor for a boost converter, I looked on Mouser and it is possible to buy for about 10-15 €. Ok. Out of curiosity I measured one from a computer power supply. About 500 uH. Wire is 1.32 mm2. So, I would make the prototype with two of those inductors in series. The core is green, with blue side. I am not sure how much flux can take before saturation, but if the wire is fine with the current, I guess that the core is fine with the flux. For higher efficiency, the use of a transistor instead of a mosfet came like a surprise to me. Why is it more efficient? Converters use mosfets most of the time... |
| Amper:
Just for comparison so you see that the problem ist not very difficult here is a picture of a 1975ish laser power supply. Its a Buck converter using only bipolar transistors, two or three OPs and one NE555 for generation of the switching signal. It will generate 200V 30A from 400V three phase. Frequency was around 30khz through an iron core inductor. |
| coppercone2:
what efficiency does it have? The zip-tie density is interesting. I thought that would be too much for terrestrial use. I woulda thought 1/4 of that would be good and 1/3 more then enough. |
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