Buck Converter MPPT

Discussion in 'The Projects Forum' started by jayzac, Apr 25, 2011.

  1. jayzac

    jayzac Thread Starter New Member

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    Below attached my design for buck MPPT
    All of the port will connect to pin header and to the microcontroller board. I wish to test this buck converter board individually without connecting to the MCU board. So, the buck is supplied with 18V from DC power supply in order to step down to 12V battery charging voltage. I am giving PWM signal to IR2104 driver at pin 2 using signal generator. However I fail to turn on my NMOS because there is no output at IR2104. After sometime the R7 of 100 Ohm resistor at current sense burned. Is there any problem with the current sense circuit ?

    1. Is my way of testing correct?
    2. Is my design for buck converter works for MPPT application ?

    Thank you

    Attached Files:

    • buck.pdf
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  2. russpatterson

    russpatterson Member

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    I would isolate just the driver section and see if you can get your MOSFET's to swtich the way you expect. I'm working on a similar circuit for MPPT for solar. I gave up on the high-side NMOS for the time being and went with a P-Channel FET. The problem I ran into was generating the voltage higher than my panel voltage necessary for turning on the NMOS. I've got mine working now, (still has some issues but basically it functions). Let me know if you want that schematic.
  3. jayzac

    jayzac Thread Starter New Member

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    Can i have a look at your design ? Thank you
  4. russpatterson

    russpatterson Member

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    Sure thing. Here's the schematic. I've built this on the bench but am expecting a PCB of this design later this week. [​IMG] You can get the PCB here if you want but it's yet untested. http://www.batchpcb.com/product_info.php?products_id=58595&check=8570465f4e3d4f44206c587865acb773

    Ignore the second MOSFET on there. That's for experimenting with eliminating the diode, D3, for improved efficiency.

    So on the tests on the bench I was able to put out 30V on my bench supply and buck it down to 12V (or whatever target voltage I set in the firmware). I've been running it at 5Khz but plan to speed that up.

    I've been having a lot of issues due to the sudden current change when I switch off the supply voltage. It causes voltage drops/spikes that my 7805 voltage regulator is not handling well and sometimes resetting the MCU.

    Attached Files:

  5. jayzac

    jayzac Thread Starter New Member

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    I wonder if this design is able to run at 50khz ? Because my inductor of 220uH limit my frequency.
  6. russpatterson

    russpatterson Member

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    Good question. I would say, in a simulator, yes. Maybe you might want to eliminate R4, I added that to slow switching as I was getting a large voltage spike on the gate when that switched on. However going with a PMOS with lower gate charge helped that quite a bit.

    Things are different on the bench than they are in the simulator, that's for sure. I also have a PCB with just the high side driver circuit (w/out the caps) that can be available on BatchPCB if you're interested. You can build up your circuit and test it.

    I'll give it a try at 50Khz but it may be a couple of weeks before I get to that.
  7. jayzac

    jayzac Thread Starter New Member

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    I am interested with the other approach that you mention about the high side driver. Can i have a look for it please ? Thank you .
  8. russpatterson

    russpatterson Member

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    jayzac likes this.
  9. s.chandrashekar020

    s.chandrashekar020 New Member

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    Hi all, Am writing C code for MPPT algorithm and got struck in between, please help me to sort the issue. My query is
    "For every environmental condition there is a voltage-current array, from which we choose the pair that gives maximum power, I generated this array by varying the duty cycle of the DC-DC buck converter, by assuming its input is not changing while varying and then choose the pair for which am getting maximum power and then giving this voltage-current pair to the battery". But am not sure this is the right way or not, please help me. Thanks in advance.
  10. russpatterson

    russpatterson Member

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    Have you seen this app note from Microchip? http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1824&appnote=en536175

    I think the idea is that you alter the duty cycle and then calculate the power coming out of your circuit and into the battery or load (watts = current * voltage). You then look for the highest power output. Change the duty cycle every 5 seconds or so and if power goes up, good, if it goes down then go the other direction. You should probably start a new thread though.
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