Induction heating. Low tq thyristors 2

[Skogsgurra]

Self-commutated H bridge. Running at 400-600 Hz with DC up to 2 kV and output current up to 1 kA.

The original design uses three thyristors in each "leg" of the H. The reason is that fast thyristors were not available at 2 kV at the time of its conception and birth.

It seems to be time to refresh this granddad and give it better legs where a single thyristor handles each leg. That would make things a lot simpler (four thyristors instead of twelve) and make it less sensitive to snubber and voltage divider problems.

The I[sub]gate[/sub] is standard, couple of volts and 1-2 A. Nothing special there. The t[sub]q[/sub] is where the problem is. Tests have been made with long t[sub]q[/sub] (like 200 us)and with no luck.

Been searching the Net for some time but don't find anything suitable. Any tips from EngTips?

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[LionelHutz]

What's the voltage rating of the 3 devices in series? You probably should be above 90% of 3X that rating with the new single SCR to match the original design. Typical low-voltage puck devices are 1200-1800V each which would put you around a 4kV device.

You have the same issue with the 2 legs of the bridge as you do with the series devices. The devices won't share the voltage if they don't turn off at the exact same time.

There are technical reasons that lower voltage rated series devices are still a good choice. Lower Tq, lower gate drive requirements, devices switch faster, lower clamping force, distributing the heatsinking across multiple devices.

When you want big, then look at Dynex Power or CRRC Times Electric. Both specialize in big devices.

ABB does sell useful semiconductors. But I would agree that the HVDC center likely doesn't want to do walk-in sales.

 

[electricuwe]

Hi Gunnar,

during my time in induction heating business 20 years ago we did similar inverters with approx. 1000 V DC-link voltage using thyristors rated 2200 V with a tq of 100 us.

One of our classic competitors in this business used the series connection as you describe it here and this design has been copied by one supplier from India at least.

The market for fast thyristors is very small today, as the high power induction heating is the only relevant application today, and hence nearly all major suppliers have discontinued these parts. Westcode was aquired by IXYS as already mentioned. Recently IXYS became part of Littlefuse, this is the only company keeping still some focus on these devices.

Due to this I think that it is unlikely that you will find a device suitable to replace the series connection of three devices by a single one as there was no much further development, but you might be able to reduce the number of series devices to only two. But would this be worth the effort ?

My recommendation is to keep the series connection as it is. Major concern in replacement parts is that you most probably need parts with matched Qrr values.

 

[Skogsgurra]

Thanks, Uwe.

It so happens that there's a workshop/conference on "Wide Bandgap" (SiC etcetera) power semiconductors in Stockholm this week-end and a couple of days after that.

https://www.ri.se/en/scape-2019

I participated in last year's conference, but don't have the possibility this year. Anyhow, IXYS had a few guys there and I think they will be there this year as well. I talked to a friend that goes there and I hope that he can discuss the matter with the IXYS people. They seem to be the right guys. If they don't have it, or can't give any directions, I think that we can skip the plans on reducing the number of thyristors.

Hutzy told me. And you strengthened that.

My thinking was "sure, there must have been some development" but I think I was wrong.


Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.