Let me elaborate more on this very point. Each of your HS drivers need a bootstrap circuit. Look at your schematic again. You need to rearrange the whole schematic....
=You haven't mentioned what the gate driver supply voltage is. Look at that again.
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There's no DC bus in a "direct converter", which constitutes already some of the circuit problems.you appear to have no caps across the DC bus ...
It is not an DC-AC inverter, it is an AC-AC converter. IGBT's connected the way how a bidirectional switch operates. The PCB is (3Pin 1Pout) only 1 phase power module of a 3Pin3Pout system.=Your IGBTs are not properly connected.
According to datasheet and my need (peak Ig current 0.6A) Rg > (15-5)/0.6 = 16,67, so Rg choosen as 22ohm to reduce a bit emi.=See the "Applications Information" section of the driver datasheet and follow the recommendations there. Your PCB layout is poor. Also take note of Figure 19.
It's 15V, since I'm using low power IGBT I don't need negative voltage to turn-off. And yes, my isolated 15V sources schematic is below. There is bulk and hf cap at Vout, ready for PWM (I think).=You haven't mentioned what the gate driver supply voltage is. Look at that again.
=Your test points and signal supply points: The wires that you are connecting your signal generator and oscilloscope probes to are way too long. Are they even soldered? Pogo pins are preferrable.
That GW INSTEK power supply is a switched-mode type power supply (do not doubt this, I have it) with a lot of ripples. You need to properly decouple them.
I do not understand why the triangular waveform of your signal generator is active instead of the square wave. That does not correlate with the near square wave that is being displayed on the scope though but you may need to consider checking that out. I also see a type of output labelled "GATE", maybe you should check what that is. Have you properly tuned you oscilloscope and other BNC probes that you are using?
It is rheostat. Yes it's a good source of EMI. Also it screams with high frequencies (seriously). It's surface is earthed. I can try moving it further.The peforated metallic stuff lying on the bench to the left of your setup, what's that? Hope it's not a source of EMI.
Let me elaborate more on this very point. Each of your HS drivers need a bootstrap circuit. Look at your schematic again. You need to rearrange the whole schematic.
Measurement taken at the SAAR collector and Neutral (Vout point in schematics)It's not clear where you measure the "IGBT output".
n channel igbt and common emitter causes 180degree phase shift.Why we see a negative pulse although the positive switch SAAF is operated?
I was planning to build clamp circuit later but as you point out the bleeding wound I guess I need it quicker. Thank you. I'll be on this neAccording to oscilloscope waveform, overshoot occurs on turn off. Overshoot can be expected with unclamped switching of the inductive rheostat load. Don't know what's the intended final converter application. Some means to clamp inductive overvoltage may be required to protect the IGBTs, e.g. active clamping.
This is the gate driver supply schematic. Do you advice me to lower the capacitor values ?You seem to supply the gate drivers by an external power supply, may be even a lab supply. Did you realize that the gate driver supply must have low output capacitance and sufficient isolation for mains voltage? A dedicated gate driver DC/DC converter should be used.
No. I referred to the isolation capacitance, e.g. the transformer interwinding capacitance. The linear voltage regulator circuit is O.K. But it's not so good to have the power supply and transformer 1 m apart from the gate driver circuit. You create large antennas radiating switching noise.This is the gate driver supply schematic. Do you advice me to lower the capacitor values ?
Do you mind to mark the connection of both probes in your circuit? I still can't relate your description to the shown waveforms.Measurement taken at the SAAR collector and Neutral (Vout point in schematics)
15V supply enclosures are metal and well earthed. I have to use long cables for first prototype. Do you advice me to use twisted pair cables ? Shielded cables ? Ferrite Choker ?No. I referred to the isolation capacitance, e.g. the transformer interwinding capacitance. The linear voltage regulator circuit is O.K. But it's not so good to have the power supply and transformer 1 m apart from the gate driver circuit. You create large antennas radiating switching noise.
Do you mind to mark the connection of both probes in your circuit? I still can't relate your description to the shown waveforms.
Disconnecting the oscilloscope's protective earth wire in mains connection doesn't provide good isolation. Besides safety issues, there's still a considerable capacitive load between probe ground and earth affecting the measurement signals.Oscilloscope earthing is isolated. Another terms, oscilloscope has no earthing for some reasons.
How can you measure with different ground connection for blue and yellow trace simultaneously? The real circuit must be somehow different.
Disconnecting the oscilloscope's protective earth wire in mains connection doesn't provide good isolation. Besides safety issues, there's still a considerable capacitive load between probe ground and earth affecting the measurement signals.
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It's 15V, since I'm using low power IGBT I don't need negative voltage to turn-off. And yes, my isolated 15V sources schematic is below. There is bulk and hf cap at Vout, ready for PWM (I think).
View attachment 155525
The wire I'm using for signals are shielded cables (6x0.22). Circuit and cables are earthed. Earth cable yes, it's long and consist of few bad condition cables.
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Rheostat is a simple one, 100ohm total, 250Watt. Snubber is not an option at this point. If those overshoots are not a measurement error, I'll try varistor to oppress/suppress (I couldn't decide which one is suitable) or try a clamp like below.That rheostat must be a very large one. It must be having significant inductance and switching its current abruptly like that might be causing the spike across the SAAF IGBT. Do you mind comnecting a snubber across it?
How probes can be tuned?
You just connect the oscilloscope probe BNC end to a channel on your scope and then connect clip end to the trigger output (two metal connection points) of your scope as if to measure the trigger signal. When you are done with the connection, you adjust the pot on the scope probe until you get a nice square waveform on the scope display.
Schematics doesn't show but it's isolated with a transformer. AC IN 151 means terminals of seconder coil 1 (independent from other 2.3...).Why powering the driver with a supply not isolated from the mains?
If you are telling me to use gw instek power supply unit, I don't believe in that power supply channel's are totally isolated. (Channels are in independent mode - series or parallel modes inactive).You should consider using channel 4 of your bench power supply to power it. That way you would be free from mains supply and multiple earthing connections and possible ground loop.
Earthing cable, it's not a good cable but It does the job. It consist of multiple cables added to each other. That's what I ment with bad condition.By bad condition cables, what do you mean?
When inputs are AC 3Phase, GNDGRID means grid neutral. For testing it's DC supply 0/neutral.What is GNDGRID referring to in your schematic of Post #1?
I'll consider this advice and use a variac/autotransformer and test AC with 1/4 of grid voltage.All the things I have suggested are for the DC testing only. You would have to analyze the risks before you carry out the AC testing.
I'm behind a few fuses, circuit breakers and leakage current protection relays (I'm not sure if the last one is translated correctly). Also I'm keeping a 1kg small fire extinguisher.Do not attempt these measurements if you are not sure what you are doing. Oscilloscope measurements on mains powered circuits are a major safety concern.
The earthing cable should be a solid copper conductor of a certain cross-sectional area. You know it already. You're just ignoring it.
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View attachment 155539
Even when you have a differential probe, you still have be able to tune your conventional oscilloscope probes to display correct waveforms when you are using them. You see that round stainless steel on the scope probe that looks like the head of a screw, that's where you adjust for the nice square wave I talked about earlier on.
Adjustment is either at the probe or the probe connector. Why don't you read the manual?
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