mppt flowchart-need help

System
System Posts: 2,511 admin
in Solar Skeptics, Hype, & Scams Corner #1
hi currenty studying about solar..
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  • lorelec
    lorelec Solar Expert Posts: 200 ✭✭
    #2
    Re: mppt flowchart-need help

    OK, I’ll take a stab at it. The text says that we’re talking about a boost controller. I’m assuming when they say “overvoltage” they mean the output of the controller, which can get dangerously high if not monitored/regulated. So comparator 2 is probably monitoring a fraction of the output voltage and comparing it with a reference. An output voltage that is too high triggers the comparator, which calls the interrupt service routine and checks for the comparator 2 interrupt flag. Assuming the flag is set, the duty cycle of the controller is decreased, lowering the voltage. If the resultant duty cycle is below some minimum value, then the duty cycle is made equal to that minimum value (at zero percent duty cycle, the PV would be connected directly to the output, so from zero on up to some small value is probably too low to be useful). It’s also worth noting that as the duty cycle of a boost controller gets around 90% and beyond, the efficiency really suffers. They don’t explain the function of comparator 1, but it looks to have to do with the MPPT dither.

    Hope that helps?

    Marc
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,485 ✭✭✭✭
    #3
    Re: mppt flowchart-need help

    Looks like algorythm for an intermediate micro inverter that has MPPT boost inverter on each panel. They boost each panel to several hundred volts D.C. to feed a secondary central GT inverter.

    Likely produces 350vdc to 450 vdc that can directly be converted to 240 vac with a simple H-bridge at central unit.

    It performed the MPPT function at each panel's micro boost inverter. The micro boost inverter has to have a safegard if all the cumulative contribution from all the panels lets the single high voltage bus come close to exceeding what the central inverter can tolerate based on its max power capability or when grid goes down. The central inverter lightens its GT push if high voltage D.C. get close to the low end voltage requirement of about 350 vdc when the panel inverters are not generating a lot of output.
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  • Robin Gudgel
    Robin Gudgel Registered Users, Solar Expert Posts: 58 ✭✭
    #4
    Re: mppt flowchart-need help

    This appears to be an over simplified chart. I don't think any commercial products work this way.
    "The load dictates how much current will be taken out of the solar panels"
    If the load is a battery and it is not at bulk voltage, then the load will accept everything the MPPT can give it. If the load is the grid, then it will always accept the maximum. There are a ton of other things going on at the same time that also affect PWM settings. The voltage that the solar panels are running at is controlled by the electronics and it is constantly changing due to numerous factors. Some of these factors are closely guarded secrets of the design engineers.
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