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Does MPPT convert to ac first rectified to dc?

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  • Does MPPT convert to ac first rectified to dc?

    Can anyone explain me the working of dc-dc (buck)converters circuits in relation to ac vs dc.
    Oscilators converts dc to ac or pulsed dc ?

    When can say it is AC?




  • #2
    Can't say specifically how any one mppt converter is done, but DC-DC converters can generally be thought of as charge pumps. A packet of energy is charged at the input voltage, then cut loose and connected to the output circuit at a lower voltage but higher current which is then smoothed back to DC. This is done at a relatively high frequency of maybe 20 to 50kHz as the components involved get smaller and less $$ as the frequency increases. You really can't call these pulses AC as the current direction never changes and it is definitely not sinusoidal.
    BSEE, R11, NABCEP, >1700kW installed

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    • #3
      This article talks about pwm as ac (square) wave. Thats why im confused
      Attached Files

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      • #4
        PWM is not always a square wave, and it is different than MPPT. PWM is simply a fast switch turning the PV panels on and off from the batteries, with more OFF time as the batteries approach Full.
        Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
        || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
        || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

        solar: http://tinyurl.com/LMR-Solar
        gen: http://tinyurl.com/LMR-Lister

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        • #5
          Ok Mike. The module (s) of MPPT do convert to ac first and then rectified to dc or not?

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          • #6
            Originally posted by GeorgeF View Post
            Ok Mike. The module (s) of MPPT do convert to ac first and then rectified to dc or not?
            The module has to convert power from one combination of DC voltage and current to another combination of DC voltage and current.
            The conversion happens by converting the input DC to pulsed DC or AC which is then converted back to DC to the output side.
            What makes MPPT different from PWM is that PWM cannot increase the output current above the input current available from the panel string(s) while MPPT can. It is the DC to DC conversion that allows this to be accomplished.
            As long as you do not make the distinction between pulsed DC and AC, your statement is correct. But the conversion is NOT as simple as converting DC to AC and running it through a transformer to get a new voltage and then rectifying that to DC. That would not allow a variable conversion between the input and output voltages. Hard as it may be to understand without diagrams and associated hand waving, the reference by Solarix to putting energy into a packet (which is stored temporarily in the form of the magnetic field in an inductor) at one voltage and pulling the energy out at another voltage is fundamentally correct.
            SunnyBoy 3000 US, 18 BP Solar 175B panels.

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            • #7
              Thanks for above replies.
              Here someone talks about "small AC variations" when he explains some types of dc-dc converters
              Attached Files

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              • #8
                MPPT converters take DC at one voltage, calculate how heavy to load the PV array (to find the max power point) and then uses either a capacitor or inductor in the circuit to pulse the power to a different voltage (battery charge voltage). Generally inductors accomplish this storage/conversion more economically than caps.
                Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
                || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
                || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

                solar: http://tinyurl.com/LMR-Solar
                gen: http://tinyurl.com/LMR-Lister

                Comment

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