# Open source isolated 12kW charger



## PStechPaul (May 1, 2012)

I'm willing to help, at least to second guess design decisions and possibly do some of the PCB design.

My suggestion would be to use a transformer design rather than a buck converter. It requires a different sort of ferrite from what is used for inductors. So it basically converts one voltage to another based on the turns ratio and then current regulation can be done with PWM and a relatively small inductor/capacitor output filter.

I think it may be good to use 2kW or so modules in parallel so that various power levels may be obtained in 2 kW sections that might be made for about $100 each (ballpark). This would provide some redundancy and also make it practical to have SMT boards machine assembled in quantity to bring cost down.

The same basic design would also function as a DC-DC converter. I would be very interested in proceeding with my own design of a 2 kW bidirectional DC-DC for 24 or 48 VDC to 240 or 480 VDC for small EVs as I am currently working on, so I might be able to have a proof-of-concept prototype shortly. 

Good luck!


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## valerun (Nov 12, 2010)

PStechPaul said:


> I'm willing to help, at least to second guess design decisions and possibly do some of the PCB design.
> 
> My suggestion would be to use a transformer design rather than a buck converter. It requires a different sort of ferrite from what is used for inductors. So it basically converts one voltage to another based on the turns ratio and then current regulation can be done with PWM and a relatively small inductor/capacitor output filter.
> 
> ...


Thanks Paul!

Yes, we would use a transformer-based design. Otherwise we can't get isolation. We will use a buck-derived topology for that stage but it will be transformer-based, yes.

Some tech details: 

1. We have settled on an Asymmetric Half-Bridge architecture for our first prototype. Benefits are: low device count, simplicity of control, zero-voltage switching on both switches to eliminate primary switching losses. It is a fairly well-tested architecture and has routinely been reported to get 95% efficiency for higher voltage outputs. For some good intro info, see http://www.fairchildsemi.com/Assets...ymmetric-Half-Bridge-(AHB)-Converters-PPT.pdf. There are 3-4 other good papers you can find - PM me if you want PDFs. 

2. We will use the same 200A 600V IGBT half-bridge switches as used in our chargers today. This way we can offer lower end-user pricing and more reliable design (as we know those switches VERY well by now). 

3. ZVS will allow us to run these IGBTs at up to 40kHz which makes high-power magnetics design easier. We may need to beef up our driver circuits a bit to run at this frequency but that's a minor effort. 

4. I like the idea of modularity but we want to get the base cell to operate at at least 7kW. This way we will have a viable single-stage product for Level 2 charging power level available everywhere. The final target power for some of the use cases we are targeting is over 25kW so having 10+ 2kW stages becomes an assembly chore in itself.

5. Similar to our current design, we will have Arduino directly control the PWM on the isolation stage (i.e. no separate hardware controller). This allows maximum flexibility in control and is a pre-requisite for some of the use cases.

6. We will likely be using our new Due-based control board - see http://www.diyelectriccar.com/forums/showpost.php?p=364445&postcount=1410 and posts around it for more info. We will use the additional speed to try things like real-time current monitoring to ensure optimal deadtime for ZVS on the switches, etc.

7. We will use toroid Ferrite cores (such as Ferroxcube T140/106/25) for the transformer. Toroids are much easier to cool than any other core topology and have the lowest flux loss and leakage inductance. The current prototype transformer is in the photos below and has 2 stacked cores. The shown version was wound for 16kHz operation and turned out to have too much leakage inductance so will be rewound in the next day or so for 30-40kHz and better winding technique.

We will be testing our initial simplistic prototype in the next 3 days. It will be a fixed duty cycle 1:1 isolation stage operating at 20kHz, loaded with the resistive 5kW load.

We need people who are proficient in magnetics design to validate / help with the transformer design. We feel that we have a good start but we do not have true magnetics gurus on the team [yet]

Thanks,
Valery.


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## palmer_md (Jul 22, 2011)

would our old units be capable of upgrading, or would we have to scrap them to gain isolation?


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## valerun (Nov 12, 2010)

palmer_md said:


> would our old units be capable of upgrading, or would we have to scrap them to gain isolation?


upgradeable but likely with an addition of a separate box. front-end rectifier and PFC stage / voltage doublers will be reusable


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## Old.DSMer (May 18, 2012)

Can I pre-order a kit?

I've been trying to figure out how do achieve isolated charging. My discussions with electricians have all led to off-the-shelf industrial isolation transformers between the charger and mains.

So I'm in when this is ready!


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## brainzel (Jun 15, 2009)

What voltage ranges do you plan in- and output side?

wishlist:
My dream charger could charge at 230V and 400V (germany ; 110V for US).

An easy way to limit input current (values adjustable) would be great, depending on charge port at your destination.
230V (1phase) 10A
400V (3phase) 16A/32A/63A
Perhaps including the european charge station protocol to detect automatically.

Output: 162V to 288V cut off charge voltage would be fine for me 
Adjustable charge current and cut off current, of course.

< $3000 dollars? Would be great ;-)


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## valerun (Nov 12, 2010)

Old.DSMer said:


> Can I pre-order a kit?
> 
> I've been trying to figure out how do achieve isolated charging. My discussions with electricians have all led to off-the-shelf industrial isolation transformers between the charger and mains.
> 
> So I'm in when this is ready!


we will open ordering when we will have a working prototype at 12kW. We don't yet know how successfull we will be and on what timeframe so I don't want to take money from people just yet ;-)

BTW here's some pics of what we have done so far - built the test rig that should be capable of getting to 20kW at 450V output. 

We have achieved 92% efficiency in regular (symmetric) half-bridge at ~2kW power level. Next is to upgrade the rectifier diodes to faster recovery and move to asymmetric half-bridge to take advantage of ZVS. 

Stay tuned

V


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## valerun (Nov 12, 2010)

valerun said:


> We have achieved 92% efficiency in regular (symmetric) half-bridge at ~2kW power level. Next is to upgrade the rectifier diodes to faster recovery and move to asymmetric half-bridge to take advantage of ZVS.


decided to try SiC zero-recovery diodes to limit secondary side losses - en route from DigiKey now. 

Will also be rewinding the transformer for lower leakage inductance. Should have some updates in a couple of days.

Valery.


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## valerun (Nov 12, 2010)

cross-posted from http://www.mynissanleaf.com/viewtopic.php?f=44&t=13349&start=340:

------------
quick update - with SiC diodes on the secondary (zero recovery charge so no switching losses), we just recorded 94% efficiency at 4.2kW output power. 260V in, 130V out. getting more interesting now. will try to rewind the transformer in the next 2 days (EV Rally tomorrow so no time) which should help further (maybe 0.2-0.4%). Also, as we raise the output voltage to 450V, the current ~1.5V diode drop will become 0.35% of that instead of 1.2% it is now - hence some additional gains. 

OTOH, the above is recorded at 6khz so going to 12kHz (our initial target for more or less release-able design) will likely compensate for those gains. 

stay tuned.


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## hbthink (Dec 21, 2010)

Is this charger intended for DIY'rs or existing OEM systems like Chademo and SAE DC ? If so there are very specific requirements for the OEM DC systems. In addition to isolation the engine must be capable of both voltage and current control modes in quick succession. The voltage hold mode is used for isolation testing so the system must also contain some type of isolation monitoring device or circuit (ie Bender or custom). 

Additionally the UL listing process is time consuming and expensive for such chargers. 

None of this is insurmountable but adds to cost and needs to be considered up front. Chademo specification shows a design that is typically deployed (8kHz or so). An alternate approach is digital (20khz+) switched systems built to smaller scale 5/10kW and stacked. Eaton, Tepco and Tesla use this approach in their DC quick chargers. Its better from a maintenance and reliability, since they can operate in degraded mode and the smaller chargers are typically used also onboard and tend to be quite robust. Stacking Brusas is an example of this type of approach, but the internals must be capable of syncing across independent units.

As for protocols the Chademo is well documented and now available but the Tesla is proprietary as is SAE, although they use known EV2Grid open standard across Homeplug.

Steve


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## valerun (Nov 12, 2010)

hbthink said:


> Is this charger intended for DIY'rs or existing OEM systems like Chademo and SAE DC ? If so there are very specific requirements for the OEM DC systems. In addition to isolation the engine must be capable of both voltage and current control modes in quick succession. The voltage hold mode is used for isolation testing so the system must also contain some type of isolation monitoring device or circuit (ie Bender or custom).
> 
> Additionally the UL listing process is time consuming and expensive for such chargers.
> 
> ...


Thanks Steve. This will work with OEM systems. We know the requirements for control & voltage swing tests. Our non-isolated system has been successfully demonstrated to charge through OEM DC port on a Nissan Leaf already. The only thing we are missing is galvanic isolation.

Smaller 10kW modules is a viable approach, of course. In the end, we might take that approach instead of a larger 20kW module.


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## hbthink (Dec 21, 2010)

OK, isolation comes with the transformer. Typically the topology requires a full bridge on primary and secondary. Can I see your design? (tried in eagle gave warning, mostly I use Altium) pdf would be fine. If you provide me with specifications I can design a transformer quickly and verify it in Matlab(or geckoMagnetics). Probably want to use something like one of the Aros Nuclei or similar for core material? How'd you get past the Nissan leakage tests w/o isolation? Did it set any error codes?

At these power levels even well designed transformers and inductors get real hot!!

Steve


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## valerun (Nov 12, 2010)

hbthink said:


> OK, isolation comes with the transformer. Typically the topology requires a full bridge on primary and secondary. Can I see your design? (tried in eagle gave warning, mostly I use Altium) pdf would be fine. If you provide me with specifications I can design a transformer quickly and verify it in Matlab(or geckoMagnetics). Probably want to use something like one of the Aros Nuclei or similar for core material? How'd you get past the Nissan leakage tests w/o isolation? Did it set any error codes?
> 
> At these power levels even well designed transformers and inductors get real hot!!
> 
> Steve



Thanks - this is exactly what we need.

As you have probably seen in the previous posts, we have picked the following design parameters for the first prototype:

1. IGBT-based design switching at 16-30kHz. Reason: lower conduction losses at high power levels, extensible into high-voltage application (e.g., 600V 3-phase supply), relatively low frequency makes layout etc easier. The switches' datasheet is attached. output capacitance of ~800pF (for the purposes of deadtime calculations).

2. An asymmetric half-bridge on the primary. Reason: simple control, ZVS switching, only one half-bridge module required and can use our favorite IGBT 600V 195A modules up to ~25kW (based on just IGBT losses), transformer utilization is the same as in full bridge.

3. Full-wave secondary rectifier running off the center-tap secondary winding. Reason: limit the conduction loss in the diodes (avoid 2 diode drops we'd have in a full-bridge rectifier. The core size at this power level and frequency tends to not be limited by winding window size so extra wire is not a big problem). We are using SiC 1200V diodes to minimize the switching losses - datasheet attached. 

So the resulting specs of the transformer are:
1. Primary voltage: 200V (half of the PFC stage output voltage)
2. Primary current: up to 120A (ok to design for 60A for the initial prototypes) 
3. Secondary voltage: variable 350-450V (standard range of battery voltage in production cars)
4. Magnetizing inductance: 1-2 milli-H
5. Leakage inductance: 10 micro-H to keep the duty loss below 15-17% at full power
6. Max duty cycle: 40% (to allow for up to 20% duty cycle loss - deadtime + loss due to leakage inductance discharge)
7. The transformer will be actively cooled - either by forced air or liquid via potting into a shaped aluminum block. We expect to be able to remove ~150W of continuous heat from a transformer with this kind of physical size. We also are designing a transformer with 2:1 to 3:1 copper:core loss ratio to account for the heat transfer resistance from within the core relative to the copper wire on the outer surface.

We have built a fully operational test rig using an interim lower-voltage transformer. We have taken it to 6kW so far at 91% efficiency at 60A / 100V output. 4kW at 30A/130V output is 94% efficient. We attribute this difference almost entirely to the increased loss in the output shottky diodes (which is almost quadratic to the output current).

Our current design of the transformer (interim lower-voltage, lower-frequency):
1. Core: 2x T140/106/25-3C90 Ferroxcube toroids (expensive at $125 apiece!). This was the largest core from Ferroxcube and rated (according to their core selection software) at up to ~8kW at 20kHz. Datasheet attached.
2. Primary turns: 35 (to get 1700 gauss AC flux swing at 10kHz and 200V). 6 strands of AWG 16
3. Secondary turns: 90, 3 strands of AWG 16

Unfortunately, the winding techniques we used were not quite world class (non-uniform wire distrubution, mostly), which has contributed to the leakage inductance of 25uH - too high for running more than 10kW at more than 10kHz due to excessive duty cycle loss.

We are now planning to rewind the transformer for higher voltage / lower leakage inductance. This is where your help would be awesome.

Our next iteration design of the transformer was going to be the following:
1. same core
2. Primary turns: 20 (to get 1500 gauss AC flux swing at 20kHz and 200V). 8 strands of AWG 16. 
3. Secondary turns: 110, 4 strands of AWG 16
This would get us ~15W total core loss, 30W copper loss at 12kW, ~80W at 20kW.

I don't yet have a clean schematics - will try to put this together if really needed but I think the above should have enough info to start?

PS. On your question re Leaf isolation tests with our non-isolated design - we just don't ground the vehicle... Not the best practice but works for testing.

Thanks,
V.


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## hbthink (Dec 21, 2010)

The efficiency of a half rectifier at these power levels is 1/2 that of a full rectifier. The losses with two additional diodes is a fraction of this, I'd recommend full rectifiers on both ends. Toroid magnet is probably not going to cut it way too much air gap, which will lead to additional losses would have to be a rectangle, suggest using fine Litz wire, the windings are critical they need to be machine wound tight Higher frequency will reduce dimensions but your battling switching losses beyond 16kHz, soft switching is mandatory here to reduce these dynamic losses, fast switching IGBTs help here too. I'll compare those you have to Semikrons which I've used.

Steve


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## valerun (Nov 12, 2010)

hbthink said:


> The efficiency of a half rectifier at these power levels is 1/2 that of a full rectifier. The losses with two additional diodes is a fraction of this, I'd recommend full rectifiers on both ends. Toroid magnet is probably not going to cut it way too much air gap, which will lead to additional losses would have to be a rectangle, suggest using fine Litz wire, the windings are critical they need to be machine wound tight Higher frequency will reduce dimensions but your battling switching losses beyond 16kHz, soft switching is mandatory here to reduce these dynamic losses, fast switching IGBTs help here too. I'll compare those you have to Semikrons which I've used.
> 
> Steve


Thanks Steve - this is awesome!

Not sure I understand the rectifier point though. The 2-diodes+center-tap is a full wave rectifier. I thought that the only downside of center-tap is that the winding window is not used as effectively as in the full-bridge rectified secondary. This design is unlikely to be limited by the winding area so we thought that center-tap is best. The only other consideration I see is that the voltage stress on secondary diodes in a full bridge is ~1/2 of that for half-bridge full-wave we are using. Hence one can use 600V devices and not 1200V that we had to use. The forward voltage drop IS a bit lower on 600V devices but not by 2x - more like 20% I think.

Am I off here?

Thanks again for your help!


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## PStechPaul (May 1, 2012)

I just tried a simulation of a FWCT and a FWB circuit to see if there is any difference in efficiency or other parameter:










As you can see, the output voltages are essentially identical (the FWCT is about 600 mV higher), and there is some difference in the input power (the FWCT has 611 mW more, probably because of the higher output voltage), but out of 232 watts it is inconsequential. D1 and D3 dissipate 791 mW, while the diodes in the FWB dissipate about 850 mW each. So the FWCT seems to be more efficient.

However, for the same output voltage, the two diodes of the FWCT see about twice the voltage that those in the FWB see. So one must weigh the cost of two diodes in the FWCT of twice the voltage rating of four in the FWB. Also the transformer will need the center tap connection for the FWCT, but as I have shown it, both secondaries are present and they can be connected in series with CT or parallel.


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## valerun (Nov 12, 2010)

PStechPaul said:


> I just tried a simulation of a FWCT and a FWB circuit to see if there is any difference in efficiency or other parameter:
> 
> 
> 
> ...


Thanks Paul. That's what I thought. 

For me, the lower the component count, the better it is. There is no way we would be able to have success with our kits if they had the typical component load found in commercial supplies... Sometimes that does mean some compromises.

Steve - any thoughts on that transformer. We are going to be rewinding our prototype unit tomorrow / Fri. I want to make sure that we take your input into it.

Thanks,
V


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## PStechPaul (May 1, 2012)

I had forgotten that this design is an asymmetric half-bridge converter, with zero voltage switching. I took another look at the application note and now I understand a bit more what is proposed. The blocking capacitor makes this possible. The example is for a 192 watt converter running at 100 kHz, so for your 12 kW converter running at 20 kHz it will need to be roughly 300 times larger than the 220nF, or 69 uF. and it would need to carry continuous current approximately 12000/400 = 30A. Looking for a stock capacitor that would be suitable, I found:
http://www.mouser.com/ProductDetail/Kemet/C4DEHPQ6100A8TK/?qs=sGAEpiMZZMv1cc3ydrPrF6J%2fmgefPq%252bt78QdTHewScs%3d

It is about $60 and, here is the data sheet:
http://www.mouser.com/ds/2/212/F3303_C4DE-123885.pdf

It is rated for 100 amps and an ESR of 800uOhm so its resistive losses would be about 0.72W at 30 amps. This seems like a good idea and would work well even if ZVS were not used. If I understand the concept, the capacitors shown from drain to source of the MOSFETs represent their intrinsic capacitance, and the idea of ZVS is to allow the voltage to discharge as the body diode begins conducting so that the charge will not be dissipated by the forward conduction of the MOSFET.

Another advantage to this design is tolerance for imbalance of the driving waveform. With direct coupling of a full bridge, there could be a net DC voltage and saturation of the transformer. If one of the switching elements opens or shorts, it may result in the destruction of the transformer, whereas for the capacitively coupled design only the MOSFETs or IGBTs might be damaged or destroyed.

A less expensive alternative would be two of these 50 uF 500V capacitors at about $12 each, which are rated 16A and ESR of 4.4 mOhm, which would have losses of about 1 watt each:
http://www.mouser.com/ProductDetail...GAEpiMZZMv1cc3ydrPrF7yRxWMKYHonRMG0LdR%2bEXg=
http://www.mouser.com/catalog/specsheets/EZP-E.pdf

The compromise of FWCT vs FWB is not as significant since it only involves rectifiers and not IGBTs, so their cost should be fairly low.


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## valerun (Nov 12, 2010)

Yes we are using a large film cap in series with transformer. I think we are going to just build this as a 1:1.2 isolation module that can be inserted between our pfc stage and the buck stage. We will have it run at a fixed 45% duty with a few microsecond deadtime. 1.2 to give us max efficiency on the pfc side. I feel like we can get 93% isolation stage efficiency at 12kw. Combined with 97% on the pfc stage and 98% efficiency on the buck stage at 400v output, we would get a combined efficiency of 88% for the whole thing.


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## valerun (Nov 12, 2010)

ok it's being rewound tomorrow. If you have any input, please let us know now. Toroid core 2x T140/106/25-3C90. See above for our current parameters for the transformer & let us know if you have any input


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## valerun (Nov 12, 2010)

valerun said:


> ok it's being rewound tomorrow. If you have any input, please let us know now. Toroid core 2x T140/106/25-3C90. See above for our current parameters for the transformer & let us know if you have any input


done. 

Primary: 20 turns of 12x AWG 16
Secondary: 120 turns of 4x AWG 16 with center tap

Primary magnetizing inductance (measured): 4.4 milli-H
Leakage inductance (from primary side): <4 micro-H

Turned out to be really good. Maybe too good for ZVS... ;-/

Will see tomorrow.

V


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## valerun (Nov 12, 2010)

309V, 20.8A in
344V, 18.1A out (6.2kW)

efficiency: 96.9%

at least according to the instruments we have available. 

this is with new transformer and a system running at fixed 50% duty cycle (symmetric) with ~2uS deadtime, 14kHz switching.

With fans and regular charger heatsink, semiconductor temp rise is <5C. Transformer temp at 10 minutes: 55C. Ambient: 25C

Something tells me that beyond 12kW we will need better cooling for the transformer...

V


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## Cor (Sep 17, 2013)

Valery,
Is it the wire that heats up or the core?
In case of the wire, you could use more/finer strands.
In case it is the core, there is little to improve but
airflow or using more cores.


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## Siwastaja (Aug 1, 2012)

Dividing the current to a larger number of cores makes sense because the core price (and total power) is approx ~ to the weight, but you increase the cooling surface area and decrease the thickness of the material (for the heat coming inside of the core to get out) by using more cores.


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## valerun (Nov 12, 2010)

Cor said:


> Valery,
> Is it the wire that heats up or the core?
> In case of the wire, you could use more/finer strands.
> In case it is the core, there is little to improve but
> airflow or using more cores.


according to our calculations, at this power level (6.2kW), it's 50:50 and total transformer loss should be at ~30W

at 12kW, it will be 1:4 loss (wire loss is 4x the core). This is by design - as the wire is much easier to cool in forced air.

We use 12 strands of AWG 16 on the primary. AWG 16 is optimal gauge for 20-25khz as it provides good balance between DC and AC resistance from skin effect. 4 strands of same on the secondary. Again, the wire loss is concentrated on the outside of the transformer (in the secondary) by design.

At 12kW, we calculate Core loss at ~15W, Primary copper loss at ~15W, Secondary copper loss at ~35W - for the total of 65W. In still / slow-moving air, that would result in ~70C temp rise on the transformer. About half that with some aggressive forced air cooling. 

Based on the loss limits alone, we expect to be able to use this transformer up to 20kW. Our output diodes will have to be upgraded before we can do that. We plan to use 2x of Cree's SiC 1200V 30A diodes in each leg. Hence $120 in just secondary diodes - but their switching is so beautiful ;-)

Wish we could use SiC MOSFETS, too - but a 165A half-bridge from Cree is over $400 on DigiKey so maybe next time ;-)


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## valerun (Nov 12, 2010)

Siwastaja said:


> Dividing the current to a larger number of cores makes sense because the core price (and total power) is approx ~ to the weight, but you increase the cooling surface area and decrease the thickness of the material (for the heat coming inside of the core to get out) by using more cores.


you are right, of course. But the pain to wind these things is doubled 

Also, total space taken is likely to be higher.

Once we have this unit working at satisfactory power level, I want to try integrated magnetics setup, when output inductor is integrated onto the same core as the main transformer. That's still in the advanced domain for me but just a month ago, the whole isolation stage was there, too....


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## valerun (Nov 12, 2010)

[EDITED to provide corrections for transformer losses]

------------------------------
In: 300V, 52.3A
Out: 308V, 48.0A

Power out: 14.8kW
Eff: 94.2%

Exec Summary: I think we can take this design up to 20kW with some relatively well understood adjustments and some additional thinking on the transformer design per below.


Details:

Transformer temp rise too high to run for more than a few minutes. Need more cooling and reduce losses. Right now the transformer is ~10" away from a small 70CFM fan, with the semi heatsink between the two. Clearly not enough. Also we need to optimize transformer design further (see below). 

Overall losses (calculated, ZVS scenario):
1. Transformer: ~300W (80%+ of which are wire losses). Clearly too much. 
2. Secondary diodes: ~135W (2.2V drop at 20A * 2 in parallel*0.9 duty)
3. Conduction losses on IGBTs: 190W (1.5V drop at 115A primary current)
4. Switching losses: if no ZVS, would have been 640W. 
5. Output inductor: ~40W
6. Input Capacitors: ~160W (0.08R ESR at 14kHz, 8 in parallel, 125A ripple current)
7. Wiring, output capacitors, etc: 20W (? - judging by no perceptible temp rise on any)

TOTAL calculated (if zero switching loss): ~840W 
TOTAL measured: ~900W (from 94.2% efficiency)
Close enough.

Analysis:
1. Input elcaps are driven outside of their ripple current rating and dissipate too much. 2 solutions: (a) film caps on input or (b) moving to full-bridge that does not stress input caps. (a) may be expensive as we need ~250uF of film caps at 20kW 20kHz. (b) is expensive and a bit unknown... Film caps solution is 2 legs of 5x 60uF 250VDC caps like http://www.digikey.com/product-detai...223-ND/2783185 - total of ~$100 so not too bad.
2. Transformer would need to be rethought again. EDIT: in previous version of this post we have not accounted for losses due to flux swing from magnetizing current. We got a hint that it might be significant from looking at the scope and seeing a very small curved section on the primary current towards the end of the ON time on one of the IGBT legs when pushed to 16kW. Accounting for flux swing from mag current increases calculated core loss by 10x - from 8W to 75W(!). Needless to say, this is problematic as we can't cool the core very effectively. I think we might have to think about this one a bit more. Parallel transformers might not work as it would be hard to make them absolutely identical for perfect load sharing. Otherwise we could use some standard transformers like http://www.wcmagnetics.com/images/pdf/wcm409.pdf - 2-3 of the larger ones. Perhaps we should try to wind the transformer on a large HighFlux core... Will do some calculations...
3. 50A output current is too much for 32A rated SiC diodes. In production, we would use 2x 43A rated packages per leg. At the above power level, the diode loss would go from 135W to ~80W, or ~50W savings

If these three sources of losses are further optimized (film caps would eliminate input caps loss altogether, optimized transformer would save ~100W, parallel diodes would save 50W), we should be able to get ~250W back, which is ~1.6% of efficiency. That would bring us back to 95-96% territory - which is pretty good for a few weeks of design & testing work.


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## PStechPaul (May 1, 2012)

I have always thought it might be better to use multiple sections of maybe 1-2 kW each. With higher volume of individual components, the cost should come down, and may be better suited to machine assembly of the PCB and the transformers. The surface area of the magnetic components as well as the semiconductors would also increase for better cooling. And there would be redundancy in case of failure, and a means for tailoring the assemblies for various power requirements.

What about using synchronous active rectification? You can get 600V MOSFETs with about 200 mOhms resistance for about $2 each, so a FWCT circuit at 10A each for two devices in series at 50% duty cycle would be about 40 watts for each bridge, and 80 watts for two in parallel at 40 amps. By adding more devices in parallel you might get to 40 watts total with 16 devices or $32. Just a rough estimate, but may have some promise. Some devices that might work:

http://www.mouser.com/ProductDetail...=sGAEpiMZZMshyDBzk1/WixSubO1eivmDRr0KpbEi6Wc=
http://www.mouser.com/ProductDetail...=sGAEpiMZZMshyDBzk1/WixSubO1eivmDtyMd4nZTSw4= ($4, but 125 mOhms and 30A)
http://www.mouser.com/ProductDetail...=sGAEpiMZZMshyDBzk1/WiwDTgRIUBA/0tDhwcyURfPg= ($5, but 67 mOhms and 47A)

I have not really worked with synchronous rectifiers, but it seems that you could make a single bridge from four of the last one that would be able to provide 40 amps with about 54 watts dissipation. Perhaps I should run a simulation to see if this is about right.

Also, I found Cree 1200V 2x20A rectifiers for about $40 each:
http://www.mouser.com/ProductDetail...=sGAEpiMZZMtQ8nqTKtFS/Cwtife2N73I17Hl6A1UGQ4=

And there are 1000V 30A ultrafast diodes with about 1.3V at 30A for about $2 each:
http://www.mouser.com/ProductDetail...=sGAEpiMZZMtbRapU8LlZDyPeqYFMplPFuJTEk8CxmYM=
http://www.st.com/st-web-ui/static/active/en/resource/technical/document/datasheet/CD00096486.pdf

and 1200V 40A fast diodes with 1.4V at 40A for $4 each:
http://www.mouser.com/ProductDetail...GAEpiMZZMtbRapU8LlZDwjeQ4GsRwB75LLLqJytF%2bQ=
http://www.mouser.com/ds/2/427/94103-87610.pdf


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## valerun (Nov 12, 2010)

thanks Paul. You may be right, yes. The assembly work does double and cost of components does not scale linearly. 

The sync FETs would need to be rated at 1200V for this application which makes regular FETs not applicable and SiC FETs are super-expensive. 

The diodes like you mentioned do exist but again, we would need 1200V for secondary tap config. Also, the regular silicon diodes have large reverse recovery charges which results in switching losses and voltage overshoots. 

Perhaps if we limit this beast to our standard power rating (12kW), we could take these less ideal avenues. We will try a couple more times with various core materials to see if we can push this to 20kW without undue losses.


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## PStechPaul (May 1, 2012)

I liked the wcmagnetics transformers. I sent an inquiry about pricing for a small 5W transformer and also a 2-5 kW model. I like toroids but they do tend to be more expensive, harder to wind, and harder to mount. As a rough estimate of what may be possible in terms of price and performance, I use the 1000 or 1500 watt automotive inverters which are about $50, but of course those are made in ridiculous quantities in China and they are likely to be actually about 500-800W. Still, even $0.10/watt would make a 20 kW switching device about $2000, so it's a reasonable ballpark estimate.

I did a simulation of a synchronous rectifier circuit with FWCT transformer and four MOSFETs on the output. I understand what you are saying about needing better than 600V MOSFETs for a 300-400V output, but perhaps a design with multiple modules in series could produce higher voltages with lower rated devices.

Here's the simulation, FWIW:










I'm not sure how much better the SiC diodes are compared to the ultrafast diodes I found. The SiC Schottky diodes have zero recovery current, but it does have 65-400 uA reverse current which at 600V is as much as 240 mW. Not very significant, but the 2.2-3 volt forward drop at 20A is 44-60W. The Fast 1200V device has just 1.4V at 40A and about 1V at 20A, or 20W, for comparison. The recovery characteristic is 6A for 450 nSec. I'm not sure how to figure the power loss, but if it is 6A at 600V that is 3600W for a duty cycle of about 400 nSec/40 uSec at 25 kHz which is 36W. But that is probably a very high estimate. The ultrafast device has a recovery current of 24A and 50 nSec, so by the same figuring it would be 18W. But the ultrafast versions in the 1200V rating have much higher forward voltage (2V to 4V).

Quite a few trade-offs.


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## valerun (Nov 12, 2010)

Paul, you seem to be very good at building these simulations pretty quickly. Can you simulate a full circuit - with transformers, parasitics, etc? May be worth a go.

Yes, your losses calculation is about right. In a tapped secondary, voltage stress on diodes is at least 2x the output voltage. Hence 900V in this design. In http://www.st.com/st-web-ui/static/active/en/resource/technical/document/datasheet/CD00096486.pdf you mentioned, reverse recovery charge is ~4 micro-C at 30A output current. Times 900V, that means ~3.6 milli-Joules of loss every time it switches. There are 2 diodes switching every cycle, so call it 7 milli-Joules. 20kHz * 7 mJ = 140W total loss. This is at 450V output, this is ~1% of efficiency. 

Note that this is not counting any losses from the snubber circuits that you will most likely have to put in to avoid ringing and voltage overshoots from fast reverse recovery.

These things do add up. So generally speaking, SiC devices are much better at these voltage levels. They are expensive, yes, but at least for diodes, once you consider all the adjacencies, using them is actually less expensive (smaller / less complex heatsinks, lower volume, fewer auxiliary parts, etc).

I would say that we got the design into a fairly good place, with the only non-trivial outstanding issue being scaling the transformer beyond ~12kW. After that power level, the losses are just too high.

There are two options I see for solving this:

1. Change core material. I have just done some calculations using datasheets from Magnetics-Inc on their MPP cores. Looks like 2x 133mm OD MPP 125 core may be much better than 2x Ferroxcube 140mm OD we are using. The core loss would be about the same BUT MPP material is spec'ed to 200C, as is the wire insulation. The higher the temp we can run this transformer at, the easier it is to remove the heat. We would also increase the # of strands of wire & make it AWG 20 (instead of 16) to allow us to go to 20kHz without worrying about skin effect.

2. Split the transformer into 2. This is less understood. Anybody has experience at this? Can it be done reliably?

V


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## PStechPaul (May 1, 2012)

I received a quote from West Coast Magnetics for some transformers I may need. 

2-5 watt $79.50 each (1-9) + $495 NRE engineering

1000 watt $195.50 each (1-9) + $195 NRE engineering (if second item)

5000 watt $429.50 each (1-9) + $125 NRE engineering (if third item)

+ $5 shipping for each order.

I had thought these units were stock or semi-stock which should be cheaper, but there are so many combinations of input and output voltages and power levels that I can understand them being custom. A bit rich for my blood, but perhaps in true production quantities price would drop substantially.

As for simulating the entire circuit with all parameters, that can be difficult, but I can try if you provide the schematic and parts data. I use LTSpice which has models for most of their ICs, and many other parts such as MOSFETs and IGBTs have models available. I had some problems with even this simple circuit because of the high frequency oscillations, but probably some well-placed snubbers and better parameters would eliminate that and allow faster processing. But I can't really simulate a microcontroller.


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## valerun (Nov 12, 2010)

PStechPaul said:


> I received a quote from West Coast Magnetics for some transformers I may need.
> 
> 2-5 watt $79.50 each (1-9) + $495 NRE engineering
> 
> ...


I haven't received mine yet but if your quote is any indication, we won't be interested for sure. It's way cheaper for me to buy cores in volume and have my techs to wind them by hand  I am afraid to even think how much they would charge for a toroid transformer ;-0

Re simulation - will do. We would want to simulate only the power circuit but with all parasitics. So ~40-50 components total, with simple square wave input to gates. Will get you the schematics soon.

BTW we have traced our core saturation issue to heating. As ferrite heats up, its ability to hold flux drops. At some point, it resulted in slight saturation that we saw on the scope. So the transformer is fine at 16kW but only until the core heats up to 60-70C. Only if we had a way to cool the core directly... Imagine a liquid cooling loop under the windings, for example. I wonder if anyone seen this done...

Thanks!
V


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## valerun (Nov 12, 2010)

major update on the isolation stage. 

With some improved cooling of the transformer from the last pictures posted, we had our first continuous run at 12kW charging one of our converted BMWs (340V CV point, LiFePo4 pack)! 

Some stats (steady state):
* Switching at 14kHz
* Efficiency: 94% (isolation stage only)
* Ambient: 22C
* IGBT: <40C 
* Secondary rectifier diodes: <40C (note how tiny their common heatsink is! those SiC diodes are amazing!)
* Transformer (outer windings): <60C
* Input caps (elcaps): ~30C
* Blocking cap (large film): ~40C
* Output inductor: <30C

No signs of core saturation. Which proves our hypothesis that previous slight signs of core saturation were caused by the core heatup given inadequate cooling. This time we had a large 40W AC fan blowing directly into the transformer and then into the heatsinks. As you can see, helped quite a bit. After shutting down, temp of transformer surface never exceeded 75C, which probably means that the core did not go above 80-90C.

What does this all mean? It means that our core selection and sizing was not that bad after all. Running a few more strands of somewhat finer wire for the primary and secondary should get us to higher power (as I mentioned before, I think we can get to 20kW with this setup largely unchanged now that we get the transformer run cooler). 

This also means that we now have an alternative to $750/kW BRUSA chargers. 

This will be released as open source for non-commercial use - same as our non-isolated charger products (http://emotorwerks.com/VMcharger_V12P/ for an idea). 

As with our other kits, we will be pricing this around the total cost you would have to pay to procure all the components (including shipping etc). We think it's a pretty good deal. For reference, our 12kW PFC charger kits are ~$1,300 (non-isolated). This is pretty close to the total parts cost + shipping you'd have to pay to 20+ different suppliers ordering in single volume (and some suppliers won't even talk to you for that quantity). That's ~$110/kW. The isolation stage kit, based on our current BOM, would run at less than that. So the complete 12kW isolated charger kit would likely be around $2,500, which is ~$200/kW. Maybe less...

Of course, once we get this stage up to 20kW and connect it to our 25kW controlled PFC stage, economics become even better. 

I am pretty excited about this. Are you? ;-)

V

PS. Some quick snaps below. 1) our 12kW PFC charger pumping out ~12kW into the isolation stage. 2) messy prototype of the isolation stage (final production design would be ~ half the size). 3) scope capture - TOP: transformer primary current (100A per major division) showing +/-100A swings at 14kHz. smooth transition between positive and negative is indicative of zero-voltage-switching that saves us ~3% of efficiency (!). also, no signs of core saturation. BOTTOM: gate drive signal for the bottom IGBT.


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## valerun (Nov 12, 2010)

a good update on this at http://www.mynissanleaf.com/viewtopic.php?f=44&t=13349&start=400


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## valerun (Nov 12, 2010)

another set of great updates at http://www.mynissanleaf.com/viewtopic.php?f=44&t=13349&p=339816#p339816 (also read a couple of preceding pages)

Summary:
1. rewound the transformer a few times on a few different cores
2. got to 20kW peak into a 330V battery (18kW continuous) without any overheating of the transformer
3. expect to get to 25kW at Leaf battery voltage of ~400V
4. still 94% efficiency
5. ready to package up into a standard 10x10x8 box (isolation stage only, full charger requires a regulated PFC stage to feed the isolation stage and control the output - that PFC stage is the same device as our 25kW PFCdirect charger mentioned in http://www.diyelectriccar.com/forums/showthread.php/25-40kw-pfc-charger-high-voltage-82629p5.html
6. getting close to testing full quick-charge protocol on this hardware. Hoping to get to a real demo on a real Nissan Leaf in the next ~4 weeks.

power electronics is fun!

V


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## brainzel (Jun 15, 2009)

Perhaps my question disturbs, but what about three phase AC input?
Would it be possible to design such a charger with perhaps another input transformer to satisfy european needs?
Michael


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## ishiwgao (May 5, 2011)

great news. looking forward to see the charger with the nissan leaf!


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## valerun (Nov 12, 2010)

ishiwgao said:


> great news. looking forward to see the charger with the nissan leaf!


awesome news, guys - we have just announced limited general availability of our 20kW ISOLATED EV charger in EAA National Magazine. Copy is on our product page for this charger at
http://www.emotorwerks.com/products...erks-isocharge-20000-20kw-isolated-ev-charger

tell us what you think.


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## valerun (Nov 12, 2010)

some related news: http://www.mynissanleaf.com/viewtopic.php?f=44&t=13349&p=347456#p347456


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## arber333 (Dec 13, 2010)

I have more food for the brain.
I am converting 12kW NonPFC charger to full 3phase. It worked for 6months now at 3phase halfbridge with common N connected to battery negative. Although it worked with 6kW i was not satisfied since it stressed my fuses up to 16A per phase, even though it gave only 42A at 150V at output.

I think i have trouble with 600VDC input because buck charger is asymetrical load by design. So my 3phase is making all kinds of strange things to my IGBT. Lately i burned one 300A 1200V.

Also since it is not isolated, it could be interference from battery/BMS/even static from me!
I was thinking of doing a simple forward converter using three planar transformers each cca 2kW like Paul suggested. I would use single igbt with fixed duty at 16kHz to 20kHz. Actual buck stage would remain the same with your inductor and arduino control. 

Like here:
http://www.electronicproducts.com/images2/F127ONSE0507a.gif

What do you think? By your experience would this simple isolated converter work? It would benefit me by being isolated to use at EU stations. 
Do you have some documents how to calculate transformers for cca 20kHz, 2kW for 600VDC. Specialy planar transformers. It would also work at 320V but at half power!


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## arber333 (Dec 13, 2010)

Previous post was couple days old. I am educating myself on simple power supplies....
In the course i found just right topology for my use. It is dual switch forward converter. 

As i gather using two IGBTs opening simultaneously would only load IGBTs with input voltage and releive transformer reverse reaction. That way i would only need single primary winding.

They mention that upper IGBT has to use high side driver. Can anyone explain to me what is the difference aplication-wise?

Here is topology:
http://www.eetimes.com/document.asp?doc_id=1273232

It would work at 16kHz - 20kHz - like... Input would be 3phase full bridge rectified for 600VDC input. Transformer would lower voltage with 1:2 (maybe 1.8) ratio. So i could use standard buck at 300VDC. My output would be at 150VDC. 
On the secondary i would simply connect my existant buck converter. The primary side i would have to add anew. 

I am also thinking, if i connected single phase i would get 320VDC on primary and 160VDC out of secondary yes?  That way i could use both connections if i wanted.


tnx

A


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## PStechPaul (May 1, 2012)

I like the two-switch converter circuit. My idea used two MOSFETs in a half-bridge configuration and must use dead-time control to avoid simultaneous conduction and subsequent destruction of the bridge components. The only advantage to the half-bridge (or full bridge) topologies is that the output is a square wave and does not need the output inductor for energy storage. I am not trying to regulate or adjust the output, and with a square wave there will always be a fixed ratio of output to input, which is OK for my purposes.

I'll have to do a simulation of this and compare to what I found for my circuit. Maybe I will also build a prototype and try it. I now have a 0-60V 5A lab supply to see how my other circuit works at its intended design voltage of 48 VDC.

Here is the simulation. The diodes in the input need to be fast (Schottky) and able to handle high current (50 amps). As shown, it produces about 789 watts with 280V into 100 ohms, with 860 watts input (92% efficiency).










That is at 25 kHz. The same circuit at 12.5 kHz drops to 82% efficiency, while at 50 kHz it goes up to 94.5%. I figured it was because of the magnetizing current of the transformer, so I doubled the inductance (which is adding 40% more windings). With that, I was able to get 786 watts out and 869 watts in, or 90.4% efficiency. Here is another image showing the start-up over the first 20 mSec:










One more thing. I changed the duty cycle to 25% and I got 144V out, 219W in and 208W out, for 94.9% efficiency.

However, when I tried 75% duty cycle, the input power shot up to 6.7 kW, with just 198V out. So, that's not good! 

With 52.5% duty cycle, I got 292V as opposed to 280, and efficiency is 90.8%. There must be some critical point where the energy stored during the ON cycle is not fully transferred during the OFF cycle, and the current just builds up. 

With a 1000 ohm load, and 52.5% duty cycle, the output rises to 362V and 131W, with 322W input. Not good - but I'm not sure where the power is lost. The primary diodes dissipate about 15 watts each and the MOSFETs about 6 watts each. That's 42 watts, but where is the 230 watts? It might be that the output has not yet stabilized, so what appears to be power loss is actually just energy being stored in the output capacitor. 

So, now with 10 uF it should stabilize much more quickly. There is a 492V peak at about 800 uSec, and then by 20 mSec it stabilizes at 362 volts. This shows 326W input and 131W output. Still not good. 50% duty cycle gives 374V with 269W input and 139W output. Better, but not good. I'll try 25%, where it stabilizes at 295V with no overshoot, input 95.6W, output 87.4W, efficiency 91.4%.

Bottom line, although this appears to be a very good and simple topology, there are some "gotchas" as demanded by Murphy's Law, and the PWM duty cycle must be adjusted to produce the desired output. It appears that this would work well for a regulated supply, as long as the feedback loop maintains good control and does not enter the "danger zone". Further analysis may be necessary. Each simulation takes several minutes, but at least they have shown some pitfalls with this circuit, and no components were harmed, although quite a few electrons were terribly inconvenienced in my 'puter.


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## arber333 (Dec 13, 2010)

PStechPaul said:


> I like the two-switch converter circuit. My idea used two MOSFETs in a half-bridge configuration and must use dead-time control to avoid simultaneous conduction and subsequent destruction of the bridge components. The only advantage to the half-bridge (or full bridge) topologies is that the output is a square wave and does not need the output inductor for energy storage. I am not trying to regulate or adjust the output, and with a square wave there will always be a fixed ratio of output to input, which is OK for my purposes.
> 
> I'll have to do a simulation of this and compare to what I found for my circuit. Maybe I will also build a prototype and try it. I now have a 0-60V 5A lab supply to see how my other circuit works at its intended design voltage of 48 VDC.
> 
> ...


Excellent!!!

I never imagined to be able to control secondary voltage with primary transistors . I considered to use existent buck stage for control.
My ratio N1/N2 will be 1,6 to be able to use 600V 3phase. I intend to use it without PFC stage since i dont have the space in my car. Anyway i think 3phase will level ripple substantialy...

Can you tell me something? Can i use the double IGBT transistor as two transistors in schematic? 
One would be driven by A3210 high side driver (i already have it) and the other by some low side driver. Diodes i will add later. 
Are the two transistors firing at the same time or do they have some delay? 

Those are two questions .

EDIT: I also found why you got Vout error in your simulation. I guess for two switch forward goes when you have transistor on time, the off time has to be at least equal to the on time for primary flux to reach zero. Otherwise it will build-up and.... I got this and some equasions here: http://schmidt-walter.eit.h-da.de/smps_e/hdw_hilfe_e.html

tnx

A


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## PStechPaul (May 1, 2012)

Very good information.  Yes, both transistors switch on and off at the same time, and if there is any delay it will not be a problem. It should be possible to drive the bottom switch directly, and the top with the isolated driver.

I posted the LTSpice file if you want to play with it:
http://enginuitysystems.com/files/48V-320V_DCDC_Two_Switch_12kHz.asc


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## arber333 (Dec 13, 2010)

PStechPaul said:


> Very good information.  Yes, both transistors switch on and off at the same time, and if there is any delay it will not be a problem. It should be possible to drive the bottom switch directly, and the top with the isolated driver.
> 
> I posted the LTSpice file if you want to play with it:
> http://enginuitysystems.com/files/48V-320V_DCDC_Two_Switch_12kHz.asc


Very good thank you.
Huh i tought i had to use isolated drivers in any case. I will probably supply it from transformer because i beleive DCDC to be too flimsy.
Would it be ok if i used one dual IGBT(halfbridge) and drive it with single dual driver. How would i connect snubber diodes?

Edit: I guess that wouldnt be good.... I will have to use two transistors. But i could use two half bridge modules and use the other half of the module as diode yes?


tnx

A


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## PStechPaul (May 1, 2012)

I think you can use the body diode of the other device, but check the specs to see if it switches quickly. I might be able to use Schottkys for my 48V design, but for higher voltage input you may need SiC-Schottky diodes which are rather expensive.

With two half-bridge devices you could use a full-bridge driver and possibly get more power.


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## arber333 (Dec 13, 2010)

PStechPaul said:


> I think you can use the body diode of the other device, but check the specs to see if it switches quickly. I might be able to use Schottkys for my 48V design, but for higher voltage input you may need SiC-Schottky diodes which are rather expensive.
> 
> With two half-bridge devices you could use a full-bridge driver and possibly get more power.


Paul you know what you are doing, so can you check me?
I would use two IGBT transistors at 20khz for two switch forward converter: http://si.farnell.com/stmicroelectronics/stgw40n120kd/igbt-1200v-80a-240w-to247/dp/2344080
Would they be up to the task, since Vin would be 580VDC rectified from 3phase? Load on the other side would be cca 6kW. That would be cca 10A in but 40A out. I can see now that with current cooling i cant reach more continuously. 

I would drive them with the same driver A3210 so i would have isolation and simplicity. Can i do that?

Also i would use output voltage loop for duty control so i could have small Vout span, say from 120V to 180VDC output. But if i wanted more i would have to retain buck stage after secondary, hm?

tnx

A


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## PStechPaul (May 1, 2012)

It looks like these would be able to handle it. I was surprised that Newark does not list them, but Farnell does, and they are also available from Mouser in the US for about $4 each. Here is the spec sheet:
http://www.farnell.com/datasheets/1722907.pdf

Note that the forward saturation voltage as well as the reverse diode drop are both about 2 volts at 10 amps, or 20 watts. But there may be much higher power from switching losses. At 20 kHz with a switching time of about 100 nSec, there could be as much as 300V * 5A = 1500W in the linear region, with a duty cycle of 0.100 / 25 = 0.4% or 6 watts. So that seems to be OK as well. The worst case thermal is less than 2C / watt so at 25 watts that would be 50C, but you also need to consider the heat sink. 

I have not actually built anything at this power level so my estimates may be off for real-world results. And my simulation seemed to show about 90% efficiency even at less than 1kW power levels (although with MOSFETs and not these IGBTs). Realistically, I would expect such a converter to run 90-95%, which means as much as 600 watts of heat for 6000 watts output. I think it would be better to make multiple units of 1000-1500 watts each and run the outputs in parallel. You might want to make a prototype at this level and see what efficiency you can get, and extrapolate from there to see if a single circuit can do the job. It may also be difficult to obtain magnetic components at the 6kW level, whereas 1-2kW are fairly common.

It would be good if someone else, with more experience with high power switching circuits, would participate in this thread.


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## valerun (Nov 12, 2010)

you guys rock. 

I would use (as we actually are in our isolated designs) an asymmetric half-bridge topology. Also 2 switches but arranged differently. Works very well and is tested up to 23kW so far. 

The transformer design is going to be your main issue. You need just the right leakage inductance to get full benefits of this topology. Once you do that, you can expect efficiency of up to 96% on the isolation stage - which is very very good.

Use SiC diodes on a secondary to reduce ringing and again increase the efficiency.

Valery.


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## arber333 (Dec 13, 2010)

valerun said:


> you guys rock.
> 
> I would use (as we actually are in our isolated designs) an asymmetric half-bridge topology. Also 2 switches but arranged differently. Works very well and is tested up to 23kW so far.
> 
> ...


Valery

Would it be ok to get a glimpse into your power schematic, to see the topology AND the secondary wiring.

Do not forget i will be using nonpfc power source for simplicity. Also i wouldnt need more than 10kW. I think if i used smaller IGBTs (less current) i could switch them faster. So at 35kHz my transformer would be wery much smaller... Also for 3phase 600VDC i could use IGBTs with less current rating. They would be smaller and thus easier to place. 

In this case is better for me to use halfbridge so i can get more output. But i guess control is more difficult.

tnx

A


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## valerun (Nov 12, 2010)

arber333 said:


> Valery
> 
> Would it be ok to get a glimpse into your power schematic, to see the topology AND the secondary wiring.
> 
> ...


I don't really have the latest schematics - we have done 3 versions of prototypes but a lot of that was tweaking PCBs. I can send you PCB files if you like


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## MAGNOEDU (Oct 30, 2011)

will you share with us schematic and drawings already and that open source.
I read about your charger isolated, was wondering if you could share your drawings, because I want to build a system of this. 
we are starting to crawl on that subject, I set up a bank of batteries 30 x 200Ah batteries 450v I am trying to power a truck s10'll assemble everything on the bench then I will install in the vehicle. 
can you help me


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## valerun (Nov 12, 2010)

MAGNOEDU said:


> will you share with us schematic and drawings already and that open source.
> I read about your charger isolated, was wondering if you could share your drawings, because I want to build a system of this.
> we are starting to crawl on that subject, I set up a bank of batteries 30 x 200Ah batteries 450v I am trying to power a truck s10'll assemble everything on the bench then I will install in the vehicle.
> can you help me


Hi MAGNOEDU - 

We don't yet have those ready. This product is not yet suitable for kit construction. 

We are hoping to have the kit version done in the next couple of months. 

Our non-isolated products are available as kits now.

Valery


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## MAGNOEDU (Oct 30, 2011)

I'll wait out your kit, I have a buck, not isolated from Semikron, but I do not think it's safe, I want to have an isolated system in feeding three-phase 380vca it's 530vdc ,is not safe.


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## Merzie (Jan 24, 2011)

valery,

I've been in contact with Sergei about juicebox distribution in Nashville, but I've also expressed interest in Leaf charger upgrades and installation. Nashville is where Leafs are made, and all the dealers have quite substantial inventory.

-What is the status of this isolated version of the 12kW charger? 

-How would it be installed (under the hood, in the trunk, or solely external through Chademo?)?

-What is the estimated cost?

-Do you need any assistance with packaging, enclosure sourcing, or machining?

-What is the primary concern using the non-isolated charger as an external box? 

-Is there an easy method of tapping the pack without using chademo? Does that rule out using the bms for emergency cut off?

Lots of questions, but I do not know where to look to have some of these answered. I'd love to get a bigger charger for my 2012 SL, otherwise I'm going to try to upgrade to a 2013 as a bare minimum (I drive 200 miles a day). If I could get rolling with one your open source designs in the next few months, it'd be ideal. I meet a lot of leaf owners and know of at least one person who may be interested as well.

Thanks for your assistance,
Evan


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## PStechPaul (May 1, 2012)

Perhaps there needs to be a bit more discussion on the relative merits and concerns with isolation, grounding, and GFCI protection. The AC power source may or may not have a neutral, and if it does, it may have considerable voltage on it, so it cannot be used for a connection to the enclosure or other exposed parts of the charger. A separate safety ground must be used, or the enclosure can be made from non-conductive material.

The concern with non-isolated circuits is that one or both of the output connections may have a dangerous voltage and a conductive path to earth ground, so that if someone is touching something that is grounded, or has a low impedance path to ground (resistive and/or capacitive), and also touches either of the output connections, a dangerous and possibly lethal current can flow. If this is 50/60 Hz AC, it can cause VFIB which renders the heart incapable of pumping blood, and death soon occurs, even if the person is no longer connected to the source. The DC output of battery charges, and the batteries themselves, does not cause fibrillation, but can stop the heart as well as cause muscular contraction that can cause a person to grab tightly and hold on to an energized conductor.

A GFCI detects a difference in current between the conductors supplying the power, and will disconnect the source if this exceeds a safe threshold, typically 5 to 20 mA. This difference becomes harder to detect at higher current levels, so a 12kW system might not be capable of effective protection. There is also the issue of normal leakage of insulation into the protective ground, versus detecting current through a person.

There is no way to protect against electric shock caused by someone touching both energized output conductors, as this will be seen as "normal mode" current flow, rather than "common mode" or "differential" current. 

The point I am trying to make is that direct-connected chargers and converters may not be as dangerous as some may think, and isolated designs are not totally safe. With either design, the output connections must be handled with equal caution, and it may be that a good GFCI system may be safer than an isolated unit, and probably cheaper.

As to the design details of a non-isolated switching buck converter versus an isolated type using a high frequency transformer, there may be some important differences. A PWM buck converter uses energy stored and then released from an inductor, and it can have issues with saturation, especially in continuous mode. A transformer type converter does not have a net DC component in the inductor, so saturation is not as much of an issue, but the size of the magnetic components may be twice as large. A transformer type circuit is especially good for boost converters with a large step-up ratio, and they can be constructed as autotransformers which lose isolation but can reduce size and power losses by 50%.

*Disclaimer:* What I have written above represents my own understanding and opinion, and may not be 100% correct. This is intended as a benefit for future discussion.


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## valerun (Nov 12, 2010)

PStechPaul said:


> Perhaps there needs to be a bit more discussion on the relative merits and concerns with isolation, grounding, and GFCI protection. The AC power source may or may not have a neutral, and if it does, it may have considerable voltage on it, so it cannot be used for a connection to the enclosure or other exposed parts of the charger. A separate safety ground must be used, or the enclosure can be made from non-conductive material.
> 
> The concern with non-isolated circuits is that one or both of the output connections may have a dangerous voltage and a conductive path to earth ground, so that if someone is touching something that is grounded, or has a low impedance path to ground (resistive and/or capacitive), and also touches either of the output connections, a dangerous and possibly lethal current can flow. If this is 50/60 Hz AC, it can cause VFIB which renders the heart incapable of pumping blood, and death soon occurs, even if the person is no longer connected to the source. The DC output of battery charges, and the batteries themselves, does not cause fibrillation, but can stop the heart as well as cause muscular contraction that can cause a person to grab tightly and hold on to an energized conductor.
> 
> ...


this is pretty accurate, Paul. The only correction is that even in isolated designs there are inductors with DC bias that do saturate just as a non-isolated buck would.


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## PStechPaul (May 1, 2012)

Yes, I was thinking more of a voltage converter where the transformer would not see any net DC component. But when you want to filter the output or make the voltage adjustable, or generate a current, then inductors with DC component and possible saturation would be required. But I think they could be made much smaller.

One technique for a high power converter is to use essentially a multi-phase converter so that the raw regulated output would have only a few percent ripple, and for a charger, it may not require much filtering.

http://www.google.com/patents/US5278489

http://ww1.microchip.com/downloads/en/AppNotes/01114A.pdf

http://electronicdesign.com/power/power-supply-ics-go-multiphase-take-100-loads


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## valerun (Nov 12, 2010)

PStechPaul said:


> Yes, I was thinking more of a voltage converter where the transformer would not see any net DC component. But when you want to filter the output or make the voltage adjustable, or generate a current, then inductors with DC component and possible saturation would be required. But I think they could be made much smaller.
> 
> One technique for a high power converter is to use essentially a multi-phase converter so that the raw regulated output would have only a few percent ripple, and for a charger, it may not require much filtering.
> 
> ...


Multi-phase will result in smaller individual inductors but the total size and weight will still be the same. 

I think more promising approach is a topology with coupled inductors - Cuk converter or a coupled inductor add-on like this: http://www.audiodesignguide.com/ClassD/azrtatad.pdf

V


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## PStechPaul (May 1, 2012)

Thanks for the link. That may reduce the size of the smoothing capacitors. But I think a multi-phase topology would virtually eliminate them, at least on the output. Energy storage will still be needed for single phase power input, of course, but once you get enough capacitance or inductance to hold a workable voltage during AC line zero crossing, high frequency power conversion can be used.

And I still think it may be advantageous to use transformers with bipolar energy transfer into secondary storage elements, rather than a unipolar design such as flyback or Cuk which relies on the magnetics to store and release the energy. If you just transfer it, it might be possible to use a less expensive ferrite core without the air gap for a transformer.

Something else to look into is zero-voltage-switching and resonant converters. I haven't actually built one but some of the principles seem quite promising. 

http://scholar.lib.vt.edu/theses/available/etd-09152003-180228/unrestricted/Ch4.pdf

http://ecee.colorado.edu/copec/book/slides/Ch19slide.pdf

http://schmidt-walter.eit.h-da.de/snt/snt_eng/snteng4b.pdf

http://www.resonant-converters.eu/fairchild-llc.pdf

http://www.infineon.com/dgdl/Applic...e6cb4&fileId=db3a30433a047ba0013a4a60e3be64a1


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## valerun (Nov 12, 2010)

PStechPaul said:


> Something else to look into is zero-voltage-switching and resonant converters. I haven't actually built one but some of the principles seem quite promising.


yes, those are nice. Our isolation stage runs in ZVS mode with SiC diodes on the output so no switching losses at all.


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## tuca (Jun 23, 2016)

this project is dead?or live? i trying at this time to make one ,y have problems with control y trying to IR2153 and the hcpl2130 and skm200 ,but y no have control at out please help-me ,how you make the control circuit ,how integrated circuit you used to control


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## PStechPaul (May 1, 2012)

I think Valery has either abandoned this project or at least no longer offers kits or full documentation. I might do something with it at some point, but right now I am working on the non-isolated EMW charger with a retrofit circuit.

What exactly have you tried? Please post a schematic of what you have.

You might do better by looking through the following thread:

http://www.diyelectriccar.com/forums/showthread.php/sic-llc-modular-charger-design-162082.html


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## MAGNOEDU (Oct 30, 2011)

hello friend thanks for indication, and well what I'm trying, you could please share your drawings, I wanted to build one to study and learn the operation.
my drawings is not finished and not work .


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## PStechPaul (May 1, 2012)

Please post whatever drawings you have and any information about what you have tried, and just what you mean by "not working". If you already have a non-isolated buck charger that works, you can add an isolation stage for the input. Here is a simulation of a DC-DC converter designed for 48 VDC input and nominal 320 VDC output. You would just need to change the components of the primary side for 160 to 350 VDC depending on your source of power. It would be best to add a PFC stage to get the DC from a single phase AC line.










It may be better to use Tony Boggs's design, but I don't think he has posted complete schematics yet. You may also look at my threads on a modular isolated charger, and the one for analyzing and fixing the EMW DIY charger.


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