High power DC/DC converter 12 V to 360 or 720 V 10kW

Paul E. Schoen · 2006-05-23T08:10:42+00:00

I am planning to make a circuit to convert 12 VDC or 24 VDC (and possibly 48 VDC) battery power to 360 VDC or 720 VDC to drive the DC link of a three phase VF motor controller. I'm sure it could be done with high frequency (20 kHz-200 kHz) magnetics, but I would like to try a somewhat lower frequency. Here is my plan:I will use a nominal 1 kVA (60 Hz) toroid core, and remove the 120/240 VAC windings. I estimate about 0.4 volts per turn. I will drive the transformer with 600 Hz, so that would be about 4 volts per turn. If I use a center tap push pull driver on 24 VDC, I think about 8 turns on each leg would be about right. For 10 kW, I would need close to 400 amps at 24 VDC. I'll use #10 AWG wire with about 8 in parallel for 50 amps each. For the secondary I will try 160 turns of #14 for 20 amps at 480 VAC, into a full wave bridge and capacitors for 720 VDC. If I run it on 12 VDC I should get 360 VDC for the 240 VAC VF controller.Now, for the drive, I will try using a PIC or an SG3526 to generate a simple square wave with some dead time. I may add a capacitor across the primary to reduce high voltage switching spikes. The current sinking components will be power MOSFETs. I may use IRL2203N (30 V, 100 A) for my initial prototype (which will be just 0.75 kW and 12 VDC). For this I figure about 60 amps input, shared by the two MOSFETs. At an ON resistance of 0.007 ohms, the power should be about 25 watts. For my final product, I will use something like STP140NF55, and about four in parallel. They are 55 V, 80 A, and 0.005 ohm. Not bad for $1.56 each. What I will have is a battery powered three phase 15 HP motor controller.What I am unsure about is high voltage spikes and high current surges resulting from using a square wave on the transformer. I tried modeling this using Tina, and it seemed to be OK, but it helped to add a capacitor across the transformer primary and some inductors in series with the legs. I know that uncontrolled transients with this much power can...

May 23, 2006 21 Replies

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Pooh Bear 20 years ago

That took me a second but I got it !

Graham

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Rich Grise 20 years ago

Yep, I've managed to dodge that particular bullet, thank you very much. :-)

Since people always incarnate their own denials, I'd have to be sure that my partner and I have healed all of our own denials first. :-)

(and I am talking about a daemon here, not a human screaming poop machine.)

Cheers! Rich

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