Which power IGBTs for 100 kvar compensator

[al3ko]

Hi there,
I am writing on a report (university) and I am stuck with the selection of IGBTs and snubber diodes. First of all some information about the compensator (two level topology):

It is a 3 phase compensator for the low voltage grid (line voltage is 400 V). The fundamental of the converter current is around 144 A (rms). The DC voltage is around 562 V and the fundamental of the converter voltage is 203 V (rms).

The next step is to find suitable IGBTs and (snubber) diodes. My teacher wrote that the IGBTs should withstand 1200 V. My question is: Why 1200 V? I know that the voltage increase at some time but that much? Furthermore I am a bit confused about the current. I looked at Farnell for IGBTs. Why is there always given a "DC collector current"? I guess that the DC stands for direct current. Am I then right when I say that I take the 144 A (rms) for my maximum? I mean the rms is defined as if a DC current would flow. Do you agree with it?

Long story short:
I am supposed to find IGBTs and Diodes for at least 1200 V and 144 A?

If any information are missing, please let me know.

Thank you very much

Kindly,
al3ko

 

[mtwieg]

1200V devices are overkill, but generally the next step down will be 600V devices, which aren't enough. Not much is available in between.

For switching converters, the rated DC current is pretty much meaningless because most of your losses will come from switching losses. So the actual current the device can handle will depend greatly on switching frequency and operating voltage.

 

[al3ko]

Hi mtwieg,
first of all: thanks for your reply.

1200V devices are overkill, but generally the next step down will be 600V devices, which aren't enough. Not much is available in between.

okay, that makes sense.

For switching converters, the rated DC current is pretty much meaningless because most of your losses will come from switching losses. So the actual current the device can handle will depend greatly on switching frequency and operating voltage.

Okay, I guess I have some questions here. It is clear that the IGBTs are used as a switch. But still, there will be a current through the IGBT. The switching frequency is 50 Hz. Am I missing anything? :/

Thank you very much.

 

[Orson Cart]

You will need 250 amp IGBT's to be on the safe side, to allow for start up transients (if any) and when large devices are switched onto the mains in parallel with your device that may cause brief control disruption or higher than usual currents in your IGBT's. Regards, Orson Cart.

 

[al3ko]

Hey Guys,
sorry for bothering you again. It is still a bit unclear. Orson Cart, you said:

You will need 250 amp IGBT's to be on the safe side,

How do you know to choose 250 A IGBTs? I mean, the fundamental of the current is calculated to be 144 A. And then to get a margin, you choose 250 A IGBTs, is that correct? It was my intention as well, to choose higher current IGBTs. On the other hand, the price goes up very fast.

Another question: Where can I look for IGBTs and Diodes? I only know Farnell. Are there any other websites or manufacturers to look for suitable IGBTs?

Thank you very much, again.

Kindly,
al3ko

 

[mtwieg]

Okay, I guess I have some questions here. It is clear that the IGBTs are used as a switch. But still, there will be a current through the IGBT. The switching frequency is 50 Hz. Am I missing anything? :/

Thank you very much.

Okay maybe I'm getting phase compensator confused with another circuit... could you show what the circuit is and what it does?

 

[al3ko]

Hi mtwieg,
I agree. Showing a schematic might be better

The fundamental of the current [latex]I_C[/latex] is calculated to be 144 A (Q is 100 kvar and the line voltage [latex]U_{ab}[/latex] is 400 V. The phase displacement between current and line voltage is 90° so only reactive power is exchanged. I chose the reactance to be 2 mH and the DC voltage is then 582 V.

Do you need anything else?

Kindly,
al3ko

 

[Orson Cart]

You have, as you say 144 amps rms in the igbt's, this is 203 amps peak, + a bit of ripple, so 250 amp IGBTs is a good safe figure to settle on. In a 6 switch (3 phase) bridge the average current per device will be less, which allows for better thermal performance of each device.
There are many makers of IGBT's, powerex, semikron, IXYS, being three reputable brands, no doubt a thorough web search will find a maker or distributor near you.
Regards, Orson Cart.

 

[al3ko]

Hi Orson,
thank you very much. I'll build up on that information.

Kindly,
al3ko