Author Topic: Try to make a full Bridge with IGBT and GDT  (Read 2433 times)

Offline JCF

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Try to make a full Bridge with IGBT and GDT
« on: January 14, 2021, 06:11:06 PM »
Hello to all, I am recently on the forum.  I have a small Tesl coil made with 4 IRFP 460. I want make a new one with primaire 18cm (15 turn) et secondaire 55 cm (1000 turns). Driver is a Cloud Leopard Ebay.
For that I have 2 CM200DU1-2F IGBTs that I would like to use to make a full bridge.
see the signal on this 1 picture. I have a lot of parasitic peaks and a false signals on a 200 Ohm resistor which replace the primary to make a test at 50 v max ?
picture 2 signal on Gate IGBT



I do not know what to do now ?, I tested the 2 IGBTs, they are good, Signal of the four GDT secondary outputs on 1 kHoms correct ...




« Last Edit: February 07, 2021, 06:16:09 PM by JCF »

Offline Pete57

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Re: Try to make a full Bridge with IGBT and GDT
« Reply #1 on: January 14, 2021, 08:39:06 PM »
Hi JC78.
I have just joined also, but have been building Tesla Coils for a long time.
Looking at your two waveform samples.
The first screenshot shows excessive low frequency ringing, (Transformer totally un-useable ). The second screenshot is better, but still has ringing and voltage spikes.
I think the best thing you can do is to wind a better Gate Drive Transformer.
I wind my GDTs using cat5 ( outer sheath removed ), cable around an Epcos N30 ferrite core.
I normally wind  11 to 13 turns around the core.  I use the CM200DY-12H IGBT bricks, and find that 11 turns around a 27mm o\d core normally works well.
Make sure you use purpose made snubber caps across C1\E2 of the igbt mods . These will help with the voltage spikes . Also, dont forget to add BI-DIRECTIONAL TVS DIODES across the Gate\Emitter junctions of each igbt. These help protect the gates from voltage spikes.
Hope this helps.

Offline Mads Barnkob

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Re: Try to make a full Bridge with IGBT and GDT
« Reply #2 on: January 15, 2021, 01:36:45 PM »
Hi JC78 and Pete, welcome to HVF!

You can not substitute the primary coil with a 200 Ohm resistor and expect the feedback / gate drive transformers to do their job correct, from a driver that expects a resonant LC feedback current. You need to test with about 100V on the DC bus to avoid excessive IGBT output capacitance ringing and get a proper feedback signal. Instead of a secondary coil that makes sparks, you can place a iron pot/container with water in as a dummy load.

To trouble shoot your GDT waveforms further, this is a great reference: http://www.richieburnett.co.uk/temp/gdt/gdt2.html
https://kaizerpowerelectronics.dk - Tesla coils, high voltage, pulse power, audio and general electronics
https://www.youtube.com/KaizerPowerElectronicsDk60/join - Please consider supporting the forum, websites and youtube channel!

Offline JCF

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Re: Try to make a full Bridge with IGBT and GDT
« Reply #3 on: February 01, 2021, 06:09:03 PM »
Hi, thanks for yours messages.
I remade the GDT with Epcos N30 ferrite core. the test of two GDT give better results.
I also did a GDT output test to check the polarity of the gates commands : good
on the other hand by checking the outputs E1C2 A and B to the primary, without primary, there is zero Ohm ? ? is it normal ? ? ?
maybe it's a stupid question?

« Last Edit: February 07, 2021, 06:29:09 PM by JCF »

Offline davekni

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Re: Try to make a full Bridge with IGBT and GDT
« Reply #4 on: February 01, 2021, 07:17:31 PM »
Are you connecting the driver's feedback input to a signal generator for these tests?

At 0 volts on VCC (H-Bridge supply), there will be a small AC signal on the H-Bridge output due to capacitance from gates to drains.  Not sure how an ohm-meter may react to that signal.  I wouldn't be too concerned.  Just apply a few volts from a current-limited supply to VCC to finish verifying GDT phasing.

BTW, you have the primary resonant capacitor listed as 0.22nF at 1200V.  That is much too low capacitance and voltage for most DRSSTC designs.  Have you tried JaveTC to model your coil?
David Knierim

Offline JCF

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Re: Try to make a full Bridge with IGBT and GDT
« Reply #5 on: February 01, 2021, 08:05:47 PM »
Sorry, a mistake for primary capacitor is 0.22 microF.
When I test the driver for feedback I use a signal generator.
Without power supply for bridge output zéro is curions. If I take a. labo alimentation, with 10v I have a security alert  for the  curent ? Perhaps a fault  with alimentation ?

Offline davekni

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Re: Try to make a full Bridge with IGBT and GDT
« Reply #6 on: February 01, 2021, 08:55:19 PM »
At 10V VCC across the H-Bridge and no primary coil connected, current should be quite low.  What current was being drawn?  It sounds like there is either a wiring error or a GDT phasing error.  (Or a fried IGBT or TVS diode.  That seems less likely if you haven't run at full power yet.)
David Knierim

Offline JCF

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Re: Try to make a full Bridge with IGBT and GDT
« Reply #7 on: February 02, 2021, 08:23:02 AM »
Stupid boy....This night I found the mistake : bad soldering with 2 short circuit. I must do the correction and after I think all is ok for the bridge output. The two GDT get  the same soldering error !
« Last Edit: February 02, 2021, 08:29:43 AM by JCF »

Offline JCF

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Re: Try to make a full Bridge with IGBT and GDT
« Reply #8 on: February 02, 2021, 05:10:21 PM »
Now tests with 50V DC and frequency feedback 90khz et 300KHz.
the signal in yellow is an additional winding to make measurements with the scope, on IGBT gates the signal is identical and not very good ?

the signal in red is taken on the output of the hybrid bridge towards the primary with a 0.22uF capacitor provided for a resonant frequency of approximately 350KHz.
By increasing the frequency of the signal FeedBack the form  of the primary signal looks better on the other hand yellow the primary is not beautiful ?

I do not understand the strange look on the signals, especially at 300KHz on the gate signal

2 HT 50V DC F90KHz FB 3V SDS00007 nb sonde scope x10 yellow signal = 20V

3 HT 50V DC F300KHz FB 3V SDS00008

is somebody can redirect me for an help in "insertion picture" ?





 [ Invalid Attachment ]
« Last Edit: February 07, 2021, 06:29:42 PM by JCF »

Offline davekni

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Re: Try to make a full Bridge with IGBT and GDT
« Reply #9 on: February 02, 2021, 11:17:35 PM »
Are you using a differential probe to measure the H-Bridge output?  (BTW, to my understanding, the "H" in H-Bridge is because the topology looks like the letter "H".  It has nothing to do with "hybrid".)  Even with the scope and/or power supply isolated from line ground, connecting a scope "ground" lead to an active signal can cause problems.  There is usually significant capacitance on the "ground" lead.  Unless using a differential probe, I suggest connecting the scope ground to the H-bridge ground and scoping one output at a time.

Is the gate waveform you are showing of the GDT output (or of your added winding for scoping)?  The gate waveform will be different due to the 5-ohm series resistors.  (BTW, most IGBT drive circuits include diodes across the gate series resistors to speed up turn-off.  Your IGBTs may be fast enough to get away without those diodes.)

Your GDT output waveform shows about 0.7 to 0.8us time to charge/discharge the gates.  If operating below 100kHz, that is probably fast enough.
David Knierim

Offline JCF

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Re: Try to make a full Bridge with IGBT and GDT
« Reply #10 on: February 03, 2021, 06:05:55 PM »
Thank you for help. the gate signal in CH1 is taken from a specific secondary winding. on the IGBT gate the signal is the same (?... )

To day, I made measurements with 75 V DC and on CH2 I have the current waveform with a triad current sensor (1: 300 on 100 ohms.)

At 110KHz the current is very low



At 210KHz the resonance is close and the current is maximum (the secondary is in place but not connected to earth). see picture

https://highvoltageforum.net/index.php?action=dlattach;topic=1386.0;attach=9968

VNA measurement primary resonance frequency with 0.22µF


tomorrow I take measurements with a differential probe of the output of the bridge.




https://highvoltageforum.net/index.php?action=dlattach;topic=1386.0;attach=9968;image


« Last Edit: February 04, 2021, 03:47:45 PM by JCF »

Offline davekni

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Re: Try to make a full Bridge with IGBT and GDT
« Reply #11 on: February 03, 2021, 09:03:52 PM »
The current waveform is starting to clip at ~-30V (90A).  There may be a TVS diode inside the CT to prevent excess voltage.  I suggest reducing the CT burden resistor from 100ohms to 10ohms.

Looks like your primary resonance is 210kHz.  Do you know your secondary resonant frequency with top-load in place?  You will want the primary frequency slightly below secondary.
David Knierim

Offline JCF

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Re: Try to make a full Bridge with IGBT and GDT
« Reply #12 on: February 04, 2021, 03:21:20 PM »
to day :
the resonant frequency of the secondary mesured with the top load is about 300KHz (too hight ?)

below is the output signal of the bridge connected to the primary (75V DC) measured with the differential probe. the signal connected to the feedback input is 220KHz.
is it good ? for the primary signal that it is the interpretation, I do not understand?

I must change the primary capacitor from 0.22 to 0.12µF to raise the resonance frequency of the primary. (see calcul)






« Last Edit: February 04, 2021, 03:58:24 PM by JCF »

Offline davekni

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Re: Try to make a full Bridge with IGBT and GDT
« Reply #13 on: February 04, 2021, 07:16:22 PM »
It looks like one of the IGBTs isn't conducting - open connection on one of its terminals.  That is my guess.  Clearly there is something wrong with the positive half-cycle.  H-Bridge output should look like a square wave.

Yes, 300kHz is on the high side for DRSSTCs, but is possible.  Will likely require a lot of phase-lead compensation given the slow gate transitions.  Are you using a driver capable of phase-lead?

BTW, most DRSSTC designs drive gates with higher voltage, +-18V to +-24V.  That allows pushing IGBTs to higher current and makes gate waveform imperfections less critical.
David Knierim

Offline JCF

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Re: Try to make a full Bridge with IGBT and GDT
« Reply #14 on: February 06, 2021, 09:47:53 AM »
Hi David, thank you for the precious help.
yes, there was no signal on the G2 gate of module A: welding under defective sheath.
here are the measurements after the repair.
There is phase shift and the driver I use has no self adjustable.
if there is dephasage, there is less energy in secondary school?
maybe I can add a small CI with the components? but I don't have a self adjustable.




Offline davekni

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Re: Try to make a full Bridge with IGBT and GDT
« Reply #15 on: February 06, 2021, 07:18:52 PM »
I suggest you get another driver, preferably UD2.7 or similar one that has phase lead and is well documented.  Your existing driver is on the weak side for driving IGBT bricks.  Looks like it was intended for smaller TO247 IGBTs.  (This is based on your GDT waveforms indicating driver output impedance is around 1-ohm or a bit more and only 15V.)  The GDT waveforms you have now could work for a low-frequency coil.  At 300kHz you need faster gate drive and phase lead compensation.  (With stronger GDT drive, you will also need to add diodes across the gate series resistors to maintain dead-time.  Most H-Bridge gate circuitry includes diodes across gate resistors.)

If your H-Bridge interconnect has very low parasitic inductance, there is a chance you could run at 300kHz and your existing driver at conservative power levels.  Without images of your build and scope traces at operating currents, I can't tell how good your H-Bridge interconnect is.  The key is low inductance on the bus supplies from IGBTs to the bypass capacitors, especially to the 5uF film capacitor.  Low inductance is best achieved with parallel copper planes for bus supplies (VCC and Gnd in your schematic).  Multiple capacitors helps reduce inductance further.
David Knierim

Offline JCF

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Re: Try to make a full Bridge with IGBT and GDT
« Reply #16 on: February 07, 2021, 05:37:11 PM »
About the UD 2.7 driver, I can't solder the CMS, I asked loneoceans (reply: For the UD2.7C driver boards, I am currently unable to sell populated boards).
For today's measurements:
I mounted the DRV power supply to 20V to improve the signal on the gates (CI 4x FDD8424H drivers as for UD 2.7).
I added and connected the topload plus a copper wire 15CM to the toroid, and the secondary coil end to earth. the sine wave generator still on the FB input (3Vmax), I looked for the maximum current at the primary and at 75V DC, I found a maximum current for 210 kHz primary 12 turns and 20nF. Current sense 1:300 10 Ohms



After I passed the primary capacitor to 10nF, search for maximum current the resonance frequency goes to 322Khz, 75V DC and still noisy sparks.
The red signal is shape of GDT signal gate : the bridge switches but the signal gate is no longer square.



red signal below :  output GDT secondary for test



Questions :
1 is this the true resonance signal of the secondary (at 20nF and 10nF)?

2 seek to lower the resonance frequency of the primary by adding a flat aluminum plate to close the torus (f measured theoretical secondary frequency  280KHz, primary 210Khz with 0.22nf)

3 what can happen by increasing the HT to 300V (lack of saturation of the IGBT, and overheating)

4 what will the phase shift compensation bring to the FB input (more energy to secondary)

thank's for your reading
« Last Edit: May 08, 2021, 05:54:13 PM by JCF »

Offline davekni

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Re: Try to make a full Bridge with IGBT and GDT
« Reply #17 on: February 07, 2021, 07:34:55 PM »
Did you add diodes across the 5-ohm gate resistors?  Knowing that will help me interpret your waveforms.

FDD8424H FETs are capable of high drive current.  The driver board may not be sending enough gate voltage to the FDD8424H FETs.  Or, there may be resistors on the driver board between FDD8424H drains and the GDT primary terminals.  Those are the only two reasons that come to mind to explain your GDT test winding waveform shape.

20V is better even though it didn't change the waveform shape.

Can you scope the H-Bridge outputs?  (The C2E1 terminals)  The key reason for phase lead is to minimize switching spikes.  Switching slightly before current reaches zero is much better than switching after current crosses zero.  Switching after current crosses zero causes the internal IGBT diodes to stop conducting rapidly.  The diode's reverse-recovery charge makes large switching current and voltage spikes.  If your H-Bridge power connections are low inductance (overlapping parallel planes for VCC and Gnd), then it may handle this hard switching.

BTW, some people have made through-hole versions of UD2.7.  Search this forum for such if you are interested.  I don't have any references off-hand.
David Knierim

Offline JCF

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Re: Try to make a full Bridge with IGBT and GDT
« Reply #18 on: February 08, 2021, 12:16:51 PM »
yes :  there are diodes across the 5-ohm gate resistors

The resistor on output of FDD8424H is 15 ohms, as on the UD 2.7 driver. SPEC of my  driver is 20a GDT output.

here under is the bridge with copper bus. It is not very compact !





Output H Bridge E1C2 - HT 50 V DC (noise and spike...)



 [ Invalid Attachment ]


« Last Edit: February 08, 2021, 04:32:15 PM by JCF »

Offline davekni

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Re: Try to make a full Bridge with IGBT and GDT
« Reply #19 on: February 08, 2021, 09:03:47 PM »
The 15-ohm resistor is for damping.  There is a capacitor from FDD8424H to driver output (to GDT input), C30 in the typical UD2.7 schematic.  This capacitor conducts most of the gate current.  The resistor (sometimes with a separate capacitor in series) is across C30 to damp oscillations between C30 and GDT inductance.  Is this driver using an electrolytic capacitor from FDD8424H to output?  Whatever cap the driver is using may have high internal resistance (ESR) causing the ramped GDT waveform.

With open-loop operation (signal generator to driver feedback input), phase will depend on drive frequency.  It appears here that you are slightly above resonant frequency.  This causes phase-lead, so voltage switching is quite a ways before zero-current.  It would be interesting to see the same E1C2 measurement slightly below resonant frequency where phase will lag.  That will be a better indication of where your coil will run without phase-lead compensation.  There will be voltage spikes either way, but will likely look different.

What bus voltage do you plan to run eventually?  The biggest issue with spikes is when they exceed the 600V rating of the IGBTs.  The ~90V spikes in this scope capture will not grow linearly with voltage, but will grow.  They tend to be more proportional to current at the time of voltage switching.  Monitor the spike voltage as you increase bus voltage to make sure peak voltage stays below 600V.  To be clear, peak voltage is operating bus voltage added to the spike voltage.  It is the peak across any IGBT that needs to stay below 600V.

Your layout is plenty compact.  I see other designs that look similar.  When running 1200V IGBTs on 565Vbus, or 600V IGBTs on 300Vbus, the spikes may be within IGBT limits.  To reduce spikes, Vbus (VCC and Gnd in your schematic) interconnect needs to be implemented with overlapping parallel planes.  (Bends are fine as long as VCC and Gnd remain overlapping and closely-spaced.)  I posted an example using TO247 IGBTs:
https://highvoltageforum.net/index.php?topic=1324.msg9795#msg9795
I don't have any examples using bricks so far.  There are some good builds posted here, but I don't recall specific links.  I'm working on a brick H-Bridge for my QCW coil.  Plan to publish that here eventually.  It is a flat layout, however, so couldn't be used exactly as is for your design.

The VBus copper does not need to be thick.  0.1mm or more is fine.  Of course, there is some advantage to mechanical rigidity that thick copper provides.  The key is wide planes that overlap and are closely spaced (overlap with thin insulation between the two overlapped planes).
David Knierim

High Voltage Forum

Re: Try to make a full Bridge with IGBT and GDT
« Reply #19 on: February 08, 2021, 09:03:47 PM »

 


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