High power 2kHz DC-DC with iron toroid - success with MOSFET drivers!

I posted awhile back about a DC-DC converter I built which took 12V from = a=20 battery and boosted it to 320VDC for a VFD, and I was able to use it to=20 drive a small tractor, as shown in my YouTube video:=20

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It provided up to about 200-250 watts, = assuming=20

12 volts and 15-20 amps. It's a 2HP motor so this is barely tickling it.

Since then, I made a monitor which reads voltage and current of the = battery=20 and the DC bus, and I wanted to use it for datalogging. But when I = connected=20 the DC-DC converter, it made a rather loud 500 Hz whine even after the=20 capacitors had charged, and I saw it was drawing over 5 amps while it = was=20 previously about 2.5. Then the magic smoke came out of one of the 15 = volt=20 TVS diodes I had from each heat sink to the battery (+).

Using a simulation, there were very high voltage spikes at the 1 uSec=20 deadband between the two push-pull drives. It seemed best to add TVS = diodes=20 from the drains to GND, and also a snubber across the drains. These were =

connected to the two heat sinks, and the primary leads of the = transformer,=20 with common to battery (+).

So, I found that it had shorted, and when I removed the TVS diodes and=20 tested it on a bench supply, I found that it started to become unstable=20 above about 11 VDC, so that the problem was most likely caused by the=20 freshly charged battery. Investigating further, it seemed that the gate=20 drives were very noisy and unstable above a certain voltage. But maybe = this=20 was not too surprising since I was using the output of an LM324 on raw=20 battery voltage. I also found that one of the gate wires was loose, so = one=20 side had only one MOSFET, which explained why the current waveform = showed a=20 difference. But that did not fix the problem.

I added the new TVS diodes (two 15V series, both sides), as well as a =

10V=20 regulator and two gate drivers, TI UCC27321D. I have also upped the=20 frequency from 500 Hz to 2kHz. Now when I power the unit I can go at = least=20 as high as 15V, and the total current draw is much less:

8.5V 0.97A

9.0V 1.02A 10.2V 1.00A 11.5V 1.10A 12.0V 1.28A 13.1V 1.38A 14.2V 1.47A 15.1V 1.55A

Previously, I had this:

12.6V 2.60A 13.1V 3.06A 13.9V 3.82A

There is still a very sharp spike at the transition, but otherwise the=20 voltage waveform looks very clean. I will probably add a snubber, which=20 seemed to help with the simulation. I have attached the ASC file if you = want=20 to see details. I have disabled the overcurrent circuit for now. Next = step=20 is to install this on the tractor again and see how it works. The 2 kHz = is a=20 lot easier on the ears than 500 Hz, and it still seems well within the=20 capability of the iron core (silicon steel) toroid.

If you have any suggestion on "right-sizing" the snubber, or the best=20 placement, please let me know.

Thanks,

Paul

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D

Version 4 SHEET 1 880 680 WIRE 256 96 224 96 WIRE -208 112 -272 112 WIRE 176 112 -208 112 WIRE -272 128 -272 112 WIRE -208 128 -208 112 WIRE 256 128 256 96 WIRE 320 128 256 128 WIRE 432 128 384 128 WIRE 496 128 432 128 WIRE 560 128 496 128 WIRE 592 128 560 128 WIRE -48 144 -160 144 WIRE 0 144 -48 144 WIRE 64 144 0 144 WIRE 96 144 64 144 WIRE 496 144 496 128 WIRE -48 160 -48 144 WIRE -272 192 -432 192 WIRE 224 192 224 96 WIRE 320 208 288 208 WIRE 432 208 432 128 WIRE 432 208 384 208 WIRE 592 208 592 128 WIRE -640 240 -704 240 WIRE -576 240 -640 240 WIRE -496 240 -576 240 WIRE -448 240 -496 240 WIRE -208 240 -208 208 WIRE -208 240 -448 240 WIRE 96 240 96 224 WIRE 96 240 -208 240 WIRE 288 240 288 208 WIRE 496 240 496 208 WIRE 496 240 288 240 WIRE -432 256 -432 192 WIRE -48 256 -48 224 WIRE -48 256 -432 256 WIRE 0 256 0 208 WIRE 96 256 96 240 WIRE 288 272 288 240 WIRE 288 272 224 272 WIRE 320 272 288 272 WIRE 416 272 384 272 WIRE -320 288 -384 288 WIRE -80 288 -256 288 WIRE 496 288 496 240 WIRE -384 304 -384 288 WIRE -640 320 -640 240 WIRE -704 336 -704 240 WIRE -256 336 -256 288 WIRE 80 336 0 336 WIRE 96 336 80 336 WIRE -48 352 -48 320 WIRE 0 352 0 336 WIRE 0 352 -48 352 WIRE -496 368 -496 240 WIRE -80 368 -80 288 WIRE 96 368 -80 368 WIRE 192 368 160 368 WIRE 256 368 256 128 WIRE 320 368 256 368 WIRE 416 368 416 272 WIRE 416 368 384 368 WIRE 496 368 496 352 WIRE 496 368 416 368 WIRE 592 368 592 288 WIRE 592 368 496 368 WIRE -160 384 -160 144 WIRE 0 384 0 352 WIRE 592 384 592 368 WIRE -576 416 -576 240 WIRE 96 416 48 416 WIRE 192 416 192 368 WIRE 192 416 160 416 WIRE 736 416 192 416 WIRE 176 432 176 112 WIRE 384 432 176 432 WIRE 336 448 112 448 WIRE 416 448 336 448 WIRE 528 448 496 448 WIRE 736 448 736 416 WIRE -320 464 -320 288 WIRE -208 464 -320 464 WIRE -80 464 -80 368 WIRE -48 464 -80 464 WIRE 384 464 384 432 WIRE -80 480 -160 480 WIRE 176 480 176 432 WIRE 272 480 256 480 WIRE 320 480 272 480 WIRE 352 480 320 480 WIRE -320 496 -320 464 WIRE 48 496 48 416 WIRE 48 496 -320 496 WIRE 272 496 272 480 WIRE 528 496 528 448 WIRE 528 496 416 496 WIRE 576 496 528 496 WIRE 672 496 656 496 WIRE 336 512 336 448 WIRE 352 512 336 512 WIRE -704 528 -704 400 WIRE -640 528 -640 384 WIRE -640 528 -704 528 WIRE -576 528 -576 480 WIRE -576 528 -640 528 WIRE -544 528 -576 528 WIRE -496 528 -496 448 WIRE -496 528 -544 528 WIRE -432 528 -432 256 WIRE -432 528 -496 528 WIRE -384 528 -384 384 WIRE -384 528 -432 528 WIRE -304 528 -384 528 WIRE -256 528 -256 416 WIRE -256 528 -304 528 WIRE -208 528 -256 528 WIRE -80 528 -80 480 WIRE -80 528 -128 528 WIRE 0 528 0 480 WIRE 0 528 -80 528 WIRE 32 528 0 528 WIRE 112 528 112 448 WIRE 320 528 320 480 WIRE -304 592 -304 528 WIRE 272 592 272 576 WIRE 272 592 -304 592 WIRE 320 592 272 592 WIRE 384 592 384 528 WIRE 384 592 320 592 WIRE 736 592 736 544 WIRE 736 592 384 592 WIRE -544 608 -544 528 FLAG -544 608 0 FLAG 592 384 0 FLAG 560 128 Vout FLAG -448 240 in FLAG 64 144 m1 FLAG 80 336 m2 SYMBOL ind2 80 128 R0 SYMATTR InstName L1 SYMATTR Value 180=B5 SYMATTR Type ind SYMATTR SpiceLine Rser=3D100u SYMBOL ind2 80 240 R0 WINDOW 0 45 35 Left 2 WINDOW 3 41 61 Left 2 SYMATTR InstName L2 SYMATTR Value 180=B5 SYMATTR Type ind SYMATTR SpiceLine Rser=3D100u SYMBOL ind2 240 176 M0 SYMATTR InstName L3 SYMATTR Value 32m SYMATTR Type ind SYMATTR SpiceLine Rser=3D10m SYMBOL nmos -208 384 R0 SYMATTR InstName M1 SYMATTR Value IRFZ44N SYMBOL nmos -48 384 R0 SYMATTR InstName M2 SYMATTR Value IRFZ44N SYMBOL voltage -496 352 R0 WINDOW 123 0 0 Left 2 WINDOW 39 24 132 Left 2 SYMATTR SpiceLine Rser=3D8m SYMATTR InstName V1 SYMATTR Value 12 SYMBOL diode 384 288 M270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D2 SYMATTR Value MUR460 SYMBOL diode 320 224 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D3 SYMATTR Value MUR460 SYMBOL polcap 480 288 R0 WINDOW 3 24 64 Left 2 SYMATTR Value 1000=B5 SYMATTR InstName C1 SYMATTR Description Capacitor SYMATTR Type cap SYMATTR SpiceLine V=3D400 Irms=3D30 Rser=3D0.2 Lser=3D0 SYMBOL res 576 192 R0 SYMATTR InstName R1 SYMATTR Value 300 SYMBOL voltage -384 288 R0 WINDOW 123 0 0 Left 2 WINDOW 39 -43 57 Left 2 WINDOW 3 148 308 Left 2 SYMATTR SpiceLine Rser=3D47 SYMATTR Value PULSE(0 10 0.5u 10n 10n 499u 1000u 100) SYMATTR InstName V2 SYMBOL voltage -256 320 R0 WINDOW 123 0 0 Left 2 WINDOW 39 -43 57 Left 2 WINDOW 3 21 307 Left 2 SYMATTR SpiceLine Rser=3D47 SYMATTR Value PULSE(0 10 500.5u 10n 10n 499u 1000u 100) SYMATTR InstName V3 SYMBOL diode 320 144 R270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D1 SYMATTR Value MUR460 SYMBOL diode 384 384 M270 WINDOW 0 32 32 VTop 2 WINDOW 3 0 32 VBottom 2 SYMATTR InstName D4 SYMATTR Value MUR460 SYMBOL polcap -592 416 R0 WINDOW 3 24 64 Left 2 SYMATTR Value 2200=B5 SYMATTR InstName C2 SYMATTR Description Capacitor SYMATTR Type cap SYMATTR SpiceLine V=3D25 Irms=3D20 Rser=3D100m Lser=3D0 SYMBOL polcap 480 144 R0 WINDOW 3 24 64 Left 2 SYMATTR Value 1000=B5 SYMATTR InstName C3 SYMATTR Description Capacitor SYMATTR Type cap SYMATTR SpiceLine V=3D400 Irms=3D30 Rser=3D0.2 Lser=3D0 SYMBOL cap -656 320 R0 SYMATTR InstName C5 SYMATTR Value .47=B5 SYMATTR SpiceLine V=3D250 Rser=3D100u SYMBOL schottky -688 400 R180 WINDOW 0 24 64 Left 2 WINDOW 3 24 0 Left 2 SYMATTR InstName D5 SYMATTR Value MBRB2545CT SYMATTR Description Diode SYMATTR Type diode SYMBOL res -112 512 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R3 SYMATTR Value .001 SYMBOL res 128 512 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R4 SYMATTR Value 1k SYMBOL schottky 96 352 M90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D6 SYMATTR Value 1N5818 SYMATTR Description Diode SYMATTR Type diode SYMBOL schottky 96 400 M90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D7 SYMATTR Value 1N5818 SYMATTR Description Diode SYMATTR Type diode SYMBOL Opamps\\LT1013 384 432 R0 SYMATTR InstName U1 SYMBOL res 288 592 R180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R5 SYMATTR Value 1k SYMBOL res 160 496 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName R6 SYMATTR Value 100k SYMBOL res 400 464 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName R7 SYMATTR Value 100k SYMBOL res -224 112 R0 SYMATTR InstName R8 SYMATTR Value 10 SYMBOL cap -288 128 R0 SYMATTR InstName C6 SYMATTR Value .47=B5 SYMATTR SpiceLine V=3D250 Rser=3D100u SYMBOL npn 672 448 R0 SYMATTR InstName Q1 SYMATTR Value 2N3904 SYMBOL res 672 480 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R9 SYMATTR Value 1k SYMBOL cap 304 528 R0 SYMATTR InstName C7 SYMATTR Value .47=B5 SYMATTR SpiceLine V=3D250 Rser=3D100u SYMBOL zener -64 256 R0 WINDOW 3 -132 12 Left 2 SYMATTR InstName D8 SYMATTR Value DFLZ33 SYMATTR Description Diode SYMATTR Type diode SYMBOL zener -32 224 R180 WINDOW 0 24 64 Left 2 WINDOW 3 24 0 Left 2 SYMATTR InstName D9 SYMATTR Value DFLZ33 SYMATTR Description Diode SYMATTR Type diode SYMBOL cap -16 144 R0 SYMATTR InstName C4 SYMATTR Value .47=B5 SYMATTR SpiceLine V=3D250 Rser=3D100u SYMBOL res -16 352 M180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R2 SYMATTR Value 10 TEXT 32 88 Left 2 !K1 L1 L2 L3 0.995 TEXT -528 632 Left 2 !.tran 0 200m 0 1u startup TEXT -352 88 Left 2 ;Primary 2x8 turns 2V/turn at 600 Hz=20

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P E Schoen
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from a=20

to=20

[snip]

New data, 2 kHz, FWB, with output capacitors in parallel, non-doubling

10.0V 1.10A 117.8V 11.1Win 12.0V 1.27A 140.3V 15.2Win 15.0V 1.52A 176.3V 22.8Win 16.5V 1.63A 194.8V 26.9Win 20.0V 1.90A 235.0V 38.0Win 25.0V 2.32A 310.0V 58.0Win

With a 925 ohm load:

10.0V 2.35A 116.6V 27.5Win 14.7Wout 12.0V 3.26A 139.0V 39.1Win 20.9Wout 15.0V 4.00A 173.7V 60.0Win 32.6Wout 16.5V 4.36A 191.7V 71.9Win 39.7Wout 20.0V 5.20A 231.0V 104Win 57.7Wout

The efficiency is only about 55% at this power level. But if you = subtract=20 the core losses of the unloaded operation, it's about 88%. I need a = higher=20 power load and a higher capacity power supply than my HY3006. It's about =

ready to connect to two batteries in series and have the output drive my = VFD=20 and the utility vehicle.

I am assuming that the core loss will stay about the same and be = dependent=20 on the applied voltage, while any additional losses will be due to = resistive=20 losses in the MOSFETs, transformer windings, and the rectifier. I also = ran=20 it without the output capacitors, except for a 0.01 uF metal film, and = the=20 DC was perfectly solid. The core loss values were as follows, so the=20 capacitors add to the losses somewhat:

10.0V 0.99A 117.8V 9.90Win 12.0V 1.20A 140.3V 14.4Win 15.0V 1.35A 176.3V 20.3Win 16.5V n/a 20.0V 1.69A 235.0V 33.8Win 25.0V 2.00A 310.0V 53.3Win

I should probably try it also at 1kHz and 4kHz to see how much = difference it=20 makes for core losses. I don't expect to see saturation at 1kHz 24V, = since I=20 ran it at 500Hz 12V with no problems. My design goal is 1.5kVA or 2HP. = I'm=20 hoping for at least 90% efficiency but I'll be happy with 85%. I also = should=20 add two more MOSFETs in each leg which will reduce conduction losses=20 somewhat. And I also have a shunt of about 100A and 100mV on the common, = so=20 that adds to the losses. But at 5 amps it's only 25mW, and at full = output=20 with about 60 amps it's just about 4 watts, and really insignificant.

Paul=20

Reply to
P E Schoen

I realized that I had forgotten to add the additional load of 25k = bleeder=20 resistors across the capacitors, so here are corrected values:

2 kHz, FWB, with output capacitors in parallel, non-doubling 10.0V 1.10A 117.8V 11.1Win 1.11Wout 12.0V 1.27A 140.3V 15.2Win 1.57Wout 15.0V 1.52A 176.3V 22.8Win 2.49Wout 16.5V 1.63A 194.8V 26.9Win 3.04Wout 20.0V 1.90A 235.0V 38.0Win 4.42Wout 25.0V 2.32A 310.0V 58.0Win 7.20Wout

With an 861 ohm load (including bleeders):

10.0V 2.35A 116.6V 27.5Win 15.8Wout 57.4% 96.2% 12.0V 3.26A 139.0V 39.1Win 22.4Wout 57.3% 93.9% 15.0V 4.00A 173.7V 60.0Win 35.0Wout 58.4% 94.2% 16.5V 4.36A 191.7V 71.9Win 42.7Wout 59.3% 94.7% 20.0V 5.20A 231.0V 104Win 62.0Wout 59.6% 93.9%

The higher efficiencies were adjusted by removing the core loss = determined=20 by the first test. This is just to give a prediction of what it might be =

under higher loads, where core loss is less significant. But conduction=20 losses will obviously lower that value

I also performed similar tests at 4kHz:

10.0V 1.00A 117.8V 10.0Win 1.11Wout 12.0V 1.13A 140.0V 13.6Win 1.57Wout 15.0V 1.36A 176.5V 20.4Win 2.49Wout 16.5V 1.45A 194.2V 23.9Win 3.02Wout 20.0V 1.68A 234.0V 33.6Win 4.38Wout 25.0V 1.98A 294.0V 49.5Win 6.91Wout

With an 861 ohm load (including bleeders):

10.0V 2.85A 117.6V 28.5Win 16.1Wout 56.3% 86.8% 12.0V 3.35A 138.9V 40.2Win 22.4Wout 55.7% 84.1% 15.0V 4.10A 174.1V 61.5Win 35.2Wout 57.2% 85.6% 16.5V 4.50A 191.7V 74.3Win 42.7Wout 57.5% 84.8% 19.3V 5.20A 223.0V 100Win 57.7Wout 57.5% 86.5%

and 1kHz with an 861 ohm load (including bleeders):

10.0V 2.85A 115.2V 28.5Win 15.4Wout 54.1% 83.3% 12.0V 3.35A 137.3V 40.2Win 21.9Wout 54.5% 82.2% 15.0V 4.11A 172.2V 61.6Win 34.4Wout 55.8% 83.5% 16.5V 4.47A 188.7V 73.8Win 41.3Wout 56.1% 83.0% 19.1V 5.14A 221.0V 98.2Win 56.7Wout 57.8% 87.8%

I need to restore the overcurrent PWM disable system before connecting = this=20 to batteries and the VFD and motor. The results are interesting. The = core=20 losses seem better at 4kHz than at 2kHz, but efficiency under load seems =

better at 2kHz, especially when core losses are taken out. Of course, = the=20 core losses at 2kHz are higher, so this is not surprising, and the only = real=20 test will be at higher power levels.

Paul=20

Reply to
P E Schoen

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