I also want to go for flip flop for proper and complete shutdown. But which one. RS I presume. Thinking on it. The fact that the output is indeterminate in some cases is scaring me. .
555 timer that closes the relay 0.5 - 1.0 sec after power up to the timer Vcc
So if an IGBT module is rated at say 10-20A, what rating inverter can it be used for?
Hi,
Some words, hopefully of wisdom.
* Layout is everything. You need as little inductance between your DC link and DC snubber caps across the DC terminals of the module. This minimizes overshoot across the devices when they interrupting a large fault current.
* Proper IGBT gate drive is also very important.
* When I design an inverter, I go through a set of tests that I call pulse testing. This ranges from using an inductor to take the DC link volts, normally 600 in my cases. This should then take about 100us to hit headline rating of the device. The inductor goes across one device and you switch the other device into it. You then let the current decay a bit, then switch on for a short period extra. You can then watch the commutation of the opposite diode and hopefully pick something up from this. Repeat test the other way round with upper and lower device transposed.
* The later test is to purposely cause a shoot through, such that the protection works, and your gate drive solution remains stable. The shoot through scenario is your worst case event. Most IGBT's have a 10us short circuit rating. Personally I test this at room temperature, and at the device externally heated to the devices headline rating, 150°C for instance. IGBT's tend to work quicker when they are cold. The faster the device switching, the higher the voltage spike when interrupting a large shoot through current. If your gate drives goes unstable during a shoot through, then clearly all bets are off.
* Use a gate drive circuit that has internal soft turn off so that the device Vge is reduced and then turned off. I am using an ACPL-302J in my latest design. This vastly reduces the voltage overshoot at turn off at shoot through.
When you have done your pulse testing then you will have confidence that the inverter will stand up to most things. I have used this method upto 300kW and produced a very robust and reliable inverter. Until you have done all these tests then you don't *really* know.
Test gear required: Isolated DSO eg Tektronix , pulse generator, high voltage bench supply. Good to have if the test gear can be remotely triggered/driven over LAN, particularly for bigger inverters. Don't fancy being anywhere near it if it lets go. My last job at 20mF of caps at 700V on the DC link so do the sums.
Hope that helps.
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