Efficient Powerpath Balancing for Fuel Cell Battery Hybrid Powertrains

For those following my work, thank you and sorry for the long wait for an update!  I am currently writing up my doctorate so as you can imagine I have been a social hermit recently!

Nevertheless, I have now had a journal paper published which may be of interest to those fellow electronics geeks out there and as a bonus it is open access so no charge to view it!

http://www.sciencedirect.com/science/article/pii/S0360319915308065

The paper focuses around balancing a hydrogen fuel cell with a battery with ideal diodes.  These give a tremendous efficiency advantage over traditional diodes.  The powertrain exploits the ability that a fuel cell has to operate at different voltages in order to create a potential long endurance system which still has all the power of a battery at an instant when needed.

Once again, thank you for your interest and I will do my best to answer any questions you have!  The paper is a creative commons license so feel free to use it and build upon it, giving credit for the original work where due!

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Comment by John Rambo on February 10, 2016 at 3:43am

@Simon,

LTC4416/17 Family is an interesting thing indeed. Wonder how did I miss it. I've rejected LTC4370 for the same very reason as you did - it only enables 50/50 load-sharing. Plus, package is to small for diy PCBs.

@Christian,

I've implemented proportional current load-sharing by employing two mirrored (phase-correct) PWM channels on ATTiny85. Was quite a challenge, but Its performing rock-solid. If one FET goes 25% duty, another is going 75% duty inverted. That prevents currents from flowing from source-A to source-B and vice-versa, thus eliminating a need for back-to-back FETs.

LTC1155 is Gate Driver (driving 2x N-FETs on High-side bus thus giving the lowest voltage drop possible - P-FETs can beat this). I've got CSD18536KCS (N-FET) samples from TI - impressive-ones! At 60Amp they're a bit warm even without a heatsink.

ATTiny takes PPM input from receiver. Then you've got an absolute control on behavior of the two power supplies. You can merge both 50/50 or 20/80, you can switch smoothly from one to another based on throttle, you can set a transient window by using trim knobs on receiver, you can use a throttle-cut (or failsafe pin) to i.e. switch to reserve battery.

Comment by Simon Howroyd on February 10, 2016 at 4:29am

Wow, that is awesome.  I need to get back into the fun hobby side rather than the academic work side ;-)

Comment by Martin on February 20, 2016 at 7:33am

This is a very interesting discussion. Some time a go we wanted to add a lipo parallel to li-ion cells to use during the launch phase because the voltage drop was too great and the resulting power output too low. We didn't get quite the result we wanted, also the usable voltage range for a li-ion goes down to 2.5 V vs 3.0 V for a lipo.

@John Rambo, could you share the schematics and source code of your design?

Comment by John Rambo on February 22, 2016 at 2:05am

@Martin - here's the URLto schematics and firmware

I must also apologize Simon for hijacking his original thread.


Your problems seems rather obvious - your battery can't handle high currents or has relatively high internal resistance (likely both).

Have you considered adding a supercapacitor in parralel to the battery? It'll come to you at around 150g (100F, 3 cells voltage, 70 euros). Or, of course, you can do it the same way I did - put 1000mAh 90C battery for takeof/maneuvring and have another-one for idle/hover flight to prolongue flight-time (my board weights ~14g, 1000mAh - high-C - is another 150g).

Comment by Martin on March 7, 2016 at 4:42am

@John, thank you for the schematis and source code.

I think I googled for supercapacitors, but didn't find any suitable. Could you point me in the right direction?

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