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  #51  
Old 06-19-2012, 02:05 PM
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PStechPaul PStechPaul is offline
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Exclamation Re: Open Revolt with IGBT driver blew IGBTs

That helps. But I don't see the freewheeling diode. And a proper snubber is a resistor and capacitor in series, across the motor terminals, or even better might be across the IGBT. Do you have part numbers for the IGBTs? And the specifications for the driver circuit. I'd like to see the gate drive waveform as well. And I think you said the motor was a 12V starter motor, and I think you said you had 30A peak. Is that the peak of the PWM pulses, or the maximum RMS?

Also, your symbol for the battery is reversed. The wide line is positive, at least in my experience. And previously you said the battery pack was 24V, but the schematic shows 12V.

I found another good reference about IGBTs and their characteristics and optimum drive techniques:
http://www.irf.com/technical-info/appnotes/an-990.pdf
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  #52  
Old 06-19-2012, 02:28 PM
swoozle swoozle is offline
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Default Re: Open Revolt with IGBT driver blew IGBTs

Gate is tied to emitter on the other IGBT to keep it off and act as FWD.

Woops on the battery :P

We are performing experiments with both 12V and 24V sources to try to understand this.
The amp numbers are RMS.

The IGBTs are Fuji 2MBI300L-060 (datasheet attached).

The gate waveform has been consistent, looks good as far as we can tell and is pictured in one of the above posts.

Thanks

2MBI300L-060.pdf
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  #53  
Old 06-19-2012, 05:39 PM
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Exclamation Re: Open Revolt with IGBT driver blew IGBTs

I assume this is the gate drive? It looks like the peak gate voltage is almost 25 volts, while the absolute maximum is 20, so you should be around 15V. And this waveform looks like about 120 uSec out of 160 for a duty cycle of 75% and a frquency of 6.25 kHz.



But your more recent screen shots of the C-E voltage look more like about 20% duty cycle at 8 kHz, and the saturation voltage looks way to high, especially if you are running only 30 amps RMS. But at 20% duty cycle that's 150 amps peak.

You really should not be seeing such high spikes if the FWD of the upper IGBT is working properly. And the other transition about 30 uSec after turn-off may be some additional inductive ringing or noise that is getting to the gate and causing the IGBT to turn on again.

If you can measure the actual current through the IGBT then it might be more clear as to what is going on. And it may help to put about a 1k resistor and a 15V zener from the base to emitter. If you want to keep the -5V turn off drive then you will also need a 5V zener in series.

Have you tried again with a resistive load? IIRC even that was not quite right. You should get a very clean waveform and very low VceSat. Until you do, and until you provide the correct base drive, you should not attempt an inductive load.
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  #54  
Old 06-19-2012, 09:31 PM
swoozle swoozle is offline
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Default Re: Open Revolt with IGBT driver blew IGBTs

Ya, simple little scope that's hard to decipher: the 0V on that trace is the small purple triangle to the right. The turn on is ~ +15V and the turn off is ~ -8V.

The duty cycle is unfortunately all over the place with our pics. Apologies.

We did do the resistive load and thought it looked pretty good.

Here's a better view of the recent progression: 12V, resistive load (low current level), 30R gate resistor, old 3uF snubbers
IMG_7348 resistive 12V old snub white cap 30R.jpg

Same 12V and old snubbers but with starter motor in place of resistive load. The screwy double-turn-offs (or is it ons?) kick in. The voltage spikes are understated in this trace capture. They were worse.
IMG_7353 12V white cap 30R old snub.jpg

Same 12V and starter motor but with new 5uF snubbers. Lower spikes on turn-off, flatter off-voltage but still the screwy double-kick. And upping to 24V seriously messed it up as in the set of pics posted a couple of days ago.
IMG_7356 12V white cap 30R new snub.JPG
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  #55  
Old 06-19-2012, 10:01 PM
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Default Re: Open Revolt with IGBT driver blew IGBTs

Leads me to think either the frequency is too high for the diode, it can't recover in time, or something is just wrong with the diode regardless. Those IGBTs are supposed to work at 300 amps 600 volts, no way they'd work like this at that power level, something is wrong

Could you try 1 ot 2 kHz or is that not adjustable with the PWM controller that you're using?
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  #56  
Old 06-19-2012, 10:40 PM
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Wink Re: Open Revolt with IGBT driver blew IGBTs

Is the first picture with the 15V signal the gate drive or the C-E waveform? The gate drive should be rock solid and should not spike or sag as it appears to. Are you sure it is DC coupled, and the probe is properly compensated?

You really should have a dual trace scope for this. And I don't understand why the PWM duty cycle (and frequency) are not constant. It's important to know if the IGBT stays fully ON during the high gate drive. And when it is off, the voltage should quickly reach the battery voltage and stay there. Is the battery voltage solid? Also if there is a large inertial load on the starter, it may act as a generator, but only if it is a PM motor and not series wound. However I have no experience with these motors and controllers so I'm just tossing ideas into the mix.

Also, do you have the other components for the VLA500 IGBT driver, as shown in the following?:
http://www.pwrx.com/pwrx/docs/bg2a_application_note.pdf

I see that you are using the P&S controller, which IIRC has been modified for IGBTs. I found a schematic on their website:
http://ecomodder.com/wiki/index.php/...er_.28Rev2A.29

It would be helpful to see a modified schematic showing the changes that were made for the IGBTs.

Last edited by PStechPaul; 06-19-2012 at 11:08 PM.
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  #57  
Old 06-19-2012, 11:12 PM
cpate cpate is offline
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Default Re: Open Revolt with IGBT driver blew IGBTs

The PWM duty cycle is not constant because it is a constant-current controller, so it is adjusting the PWM to get the motor current to match the throttle input. The first picture with the 15v signal is the C-E waveform in swoozle's latest post.

Unfortunately I don't have the programming know-how to change the firmware to a 2khz drive signal. I agree there is something about the diode. I don't think we are out of the safe operating area, because we are measuring the current and voltage across the IGBT and neither are near the maximum rated. The saturation voltage is definitely something to look into, as a symptom that will tell us more about our problem. Our gate drive is very slow right now because of the 30 ohm resistor. However, with the 5.6 ohm resistor, we seemed to be having the same double-switching issues.

I think the gate drive is fine but I will check again. You are right about the resistive load though, the voltage graph was surprisingly spiky for very small current and voltage.

Looking at the diode reverse recovery time, it says 300ns for 900a/us di/dt and -10v Vge. So this should switch more than fast enough for our uses. Unless it's not switching fast enough because Vge is 0v for the side of the IGBT that we're using as the diode, because G and E are directly connected?
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  #58  
Old 06-19-2012, 11:27 PM
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PStechPaul PStechPaul is offline
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Question Re: Open Revolt with IGBT driver blew IGBTs

Maybe the problem is with the current/torque mode control. An unloaded series wound motor is very difficult to control, because there will be very little current to work with. Can you put some sort of load on the motor shaft, like a fan? Can you take a scope reading on the output of the LEM current sensor? Are you monitoring the speed of the motor? And how are you setting the throttle?
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  #59  
Old 06-20-2012, 04:37 AM
z_power z_power is offline
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Default Re: Open Revolt with IGBT driver blew IGBTs

For low current testing of P&S controller i took LEM off the busbar and routed a few turns of cable trough it - it reads actual current multiplied trough loops number, it makes PID more stable with low power levels; I used 12V 50W lightbulb, then 80W wiper motor and 160W radiator fan, the last one was quite easy to control trough ~3/4 of throttle range.
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  #60  
Old 06-23-2012, 12:03 PM
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Default Re: Open Revolt with IGBT driver blew IGBTs

We have tested the output signal of the controller and of the IGBT driver and determined that the strange double-turn off is not coming from the controller! It is coming from the IGBT driver. We are not sure why the IGBT driver is doing this though. I have placed the oscilloscope on the 15v supply and it is as solid as a rock. I am thinking it my be because I disabled the short-circuit protection so I will re-enable it and see if that gets us anywhere. This is very strange behavior from the VLA500. The presence of the motor doesn't matter, it just always does this at low duty cycles, when you first twist the throttle. It even does the double-turn off with no load.
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