Regen braking bridge rectifiers

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bga
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Regen braking bridge rectifiers

Post by bga » Mon, 09 Nov 2009, 16:20

Ding! - out of the corner again Image

TJ - 120 Amps RMS - that is exotic.

I have ordered some film caps from china (mentioned in other threads) for Richo and myself.

I was sizing them conservatively, based on the maximum average IGBT current in the controller (300Amps)

The caps are coming from (EACO capacitor through Yesiya in Shenzhen - SHD caps) 390uF at 900 Volts ans 51 Amps RMS. These have really low ESR at 3mR and tremendous pulse capabilility -- shoud be able to take the corner off a screwdriver! Image
I am intending using 6 for a total of 2340uF and ~300 Amps RMS. The ESR should be in the 500 (micro) R territory, giving an ESR-induced ripple of about 0 Volts. The ripple will be almost entirely derived from the capacitance, estimated at about 20 Volts, worst case.

I would expect that because the ESR is in the order of 10% of an equivalent electrolytic capacitor network, the heating should be corrrespondingly much lower.

Some other advantages are:
The overall capacitance is low so that not so much energy is needed to pre-charge the caps at startup.
Dry film capacitors don't have electrolyte problems and are rated for times like 100,000 hours at 70 deg.C
The caps are rated for 900V, so no series-parallel network needed.
EACO is reasonably priced at about $50 each for the above type.
Epcos caps are blue because that's the colour you become when the supplier tells you the price Image

The capacitors buffer the motor current each time the power transistors switch. This varies with the motor torque primarily.
At low speed and high acceleration this will be very high, but reduce greatly at cruise.

[edit: Add]
At low speed (high motor current and low battery current) the diodes conduct most of the time.
Last edited by bga on Mon, 09 Nov 2009, 05:22, edited 1 time in total.

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Johny
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Regen braking bridge rectifiers

Post by Johny » Mon, 09 Nov 2009, 16:51

acmotor wrote: Would you stop pulling that VFD apart and put it in an EV !! Image
I finally got those 200 Amp 1200V IGBTs from Germany. They took 10 weeks!
My pull-apart now gets really interesting (16/22kW -> 50/75kW) or BLAM!

The restoration part is taking all the time and effort but I have done so much work on the house that my brownie points are through the roof. As soon as the school year settles down (wife is Math coordinator and VCE marker) then I have her blessing to "go for it" big time. She will be doing the interior alongside me doing the EV stuff.

Meantime, I have to get my fix somehow. Image

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Regen braking bridge rectifiers

Post by HeadsUp » Mon, 09 Nov 2009, 19:29

Johny wrote:
acmotor wrote: Would you stop pulling that VFD apart and put it in an EV !! Image
I finally got those 200 Amp 1200V IGBTs from Germany. They took 10 weeks!
My pull-apart now gets really interesting (16/22kW -> 50/75kW) or BLAM!

The restoration part is taking all the time and effort but ........ I have her blessing to "go for it" big time. She will be doing the interior alongside me doing the EV stuff.. Image


i had a feeling they would turn up... i once had a mystery ebay time-warp delay from the USA , my box arrived _3 months_ after ordering.

did you measure the gate and emitter voltages on the 22 kW unit or get them from the spec sheets ?

is there any discernable difference from the 200 ampers ?

very interested to see how it works


Image

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Regen braking bridge rectifiers

Post by Johny » Mon, 09 Nov 2009, 19:47

HeadsUp wrote: did you measure the gate and emitter voltages on the 22 kW unit or get them from the spec sheets ?
Ummm. I actually haven't sighted the IGBTs in the VFD-to-be-upgraded yet....
Sort of relying on faith, and good common practise.

Faith #1. The driver boards on my 33/45Kw and 16/22Kw appear to be identical. Hoping they used Gate drives that could do either sized VFD.

Faith #2. Industrial VFDs appear to use IGBTs rated at twice the current that they expect to use continuously.

This tends to indicate that the IGBTs on the smaller VFD will be 75Amps devices and the IGBTs on the larger VFD will be 100 Amp devices.

Other than reasonable switching speeds, VCE saturation etc. The thing that changes most as you size IGBTs up (besides physical size) is Gate capacitance/charge.
100 Amp (non-trench) Mitsubishu IGBTs are about 23nF. The Dynex ones I bought are 25nF - very close (that's why I wanted these ones - it might make it easier). The IGBTs terminal spacing should be OK (note the elongated holes in the Lenze photos a few posts back).
The heatsink mounting may require a little drilling.

After that - assuming it still works - I have to fugure how to "lie" to the current sensing system. I'll know more after the disassembly...

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Regen braking bridge rectifiers

Post by HeadsUp » Mon, 09 Nov 2009, 19:52

yes

and maybe compare the heatsinks ability to dissipate the extra heat or upgrade heatsink maybe ?
Image

keen-as here
.

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Regen braking bridge rectifiers

Post by Johny » Mon, 09 Nov 2009, 20:22

The heatsinks are identical on the two models. Considering the continuous power requirements of an EV (not racing), the 30kW continuous rated VFD should handle it with ease - except maybe on 46 degree days in which case the VFD will warn me and back off anyway.

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Regen braking bridge rectifiers

Post by HeadsUp » Wed, 18 Nov 2009, 05:06

HeadsUp wrote:
No idea what these price at , but they bolt direct to the IGBT's

and will align in the same plane as the heatsink , so allowing the same heatsink to cool both the IGBT's and capacitors


Image

.



got a price reply for those big phat EPCOS capacitors

$ 800 each minimum order x 4

rated a bit big for my needs , so looking for something a bit smaller.
.

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Regen braking bridge rectifiers

Post by bga » Thu, 19 Nov 2009, 01:55

Just as I suspected: all was going well until the price got mentioned.

The EACO soup cans are looking attractive.
(See previous for url)

Still waiting for them to ship and then arrive. Eventually, I'll be able to comment more authoritatively on them as a supplier.

[edit : less is more]
Last edited by bga on Wed, 18 Nov 2009, 14:58, edited 1 time in total.

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Regen braking bridge rectifiers

Post by brandon_costa » Sat, 22 Jan 2011, 15:10

acmotor wrote: Well here are the exact Fuji's used in the Danfoss VLT5042 !!

Image
Image

These are used to 97.5A total motor current for 60 seconds.


Does FUJI still manufacture GE VFDs? I'm having a hard time finding data on an older GE VFD made by FUJI. The closest that I could find was their new 5000G11.

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Regen braking bridge rectifiers

Post by unheardofinstruments » Sat, 01 Dec 2012, 19:19

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