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Registered Member #1960
Joined: Thu Feb 05 2009, 11:57PM
Location:
Posts: 48
Steve Conner wrote ...
Sorry to hear it :( In future you might like to try an optoisolated gate driver like the TLP250 series, so a failure in the converter won't take the Arduino with it.
Another thing to ponder: You said that the control loop can be slow because you're charging a battery. This is true, but a good worst-case design should address the possibility of the battery accidentally being disconnected while charging. This implies a means of shutting the gate drive off quickly on overvoltage, and an output filter capacitor big enough to soak up all the energy in the inductor, with a voltage rise less than the difference between the overvoltage trip point and the MOSFET's voltage rating.
Yeah, that is sound advice. Higher switch frequency and foolproofing is definitely projects for the future. Extra samples from TI proved useful, found a replacement gate driver. Found a new AVR IC for the Uno, the rest of the board works. Up and running again :D
Thanks for the suggestion Sulaiman :) I'm not going for the off shelf solution as I'm looking for experience with these converters. Certainly have soaked in a lot of literature by now. This is a fast project, using the parts I can get my hands on within a week - one could say.
The converter runs nicely in DCM now. Current feedback is weak, and I think I better have this in place before I run CCM - so working on this now. Added is screenshots and pictures of the setup. The first scope plot show Vds (red) vs Pwm in (blue). The second scope plot show Vds (red) vs Current feedback (blue).
With the arduinos 10bit ADC, if I'm lucky, I'll have 0,5A current resolution (with heavy filtering, surely). This is next.
Registered Member #1960
Joined: Thu Feb 05 2009, 11:57PM
Location:
Posts: 48
Turns out the arduino and the allegro hall IC is simply too low range (Edit: was high range) for proper feedback. Will devise a new way to do this, maybe a sense resistor or a different Hall IC.
The MOSFET remains cool in DCM, but produces significant amounts of heat in CCM - I added a bit of airflow over the whole converter. Running at 150W ('Lab' PC PSU goes into cutoff higher than this) produces this waveform over the MOSFET. I'll maybe look into a suitable snubber for turn off, or slowing down switching - or bringing the gate to 10V (-25% RDSon).
I have a suitable 51V server psu, so I know I could run the MOSFET up to around 600W - and that is my final goal. My battery pack was 900Wh, its certainly less now - so a bit over an hour to charge. That suits me.
As for LabVIEW for Arduino; not impressed. Could have made the same progress with a AVR and a development board, and at this point it would be easier for me to change things up. I love LabVIEW, but not LIFA.
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Boost converter topology for battery charging
