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Solar System ( Panels + Buck ) doubts

BDrt

Jun 20, 2016
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Jun 20, 2016
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Hello,

I'm studing a System for an array of solar panels (240W each, 16 in series).
I'm considering using a buck converter to charge a high voltage battery pack (from 300V to 380V when full) from the pannels.

the circuit i'm considering is attached.

During the simulation of the circuit, when i use an ideal voltage source as Vi for the buck converter, I obtained a pulsed current (as the attached image )
When i placed a solar panel as Power source for the buck converter, the Input current was completly diferent. It was constant ( attached the image ).

Can anyone help me understand the wave forms and which one corresponds to the correct wave forms in a system like this ?

Thank you.
 

Attachments

  • Simulation with ideal DC source.PNG
    Simulation with ideal DC source.PNG
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  • Simulation with pannel.jpg
    Simulation with pannel.jpg
    178.9 KB · Views: 101
  • Capturar.PNG
    Capturar.PNG
    12.9 KB · Views: 69

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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A buck converter will not work (properly) with solar panels. You need something which does MPPT or even a linear regulator.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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oh, and i would say that neither is correct.
 

BDrt

Jun 20, 2016
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Hi Steve,

Can you explain me, please, why wont that work ?
The ideia is to use the buck to charge the battery pack, with the maximum power available on the panels.

Why is neither correct ? how will the panel behave when conected to a buck?

Thank you.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
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A buck regulator draws whatever current it needs to in order to supply the power demanded by the load. If the input voltage falls, the demanded input current rises.

An MPPT regulator determines the maximum power it can draw from the source and dumps it into the load.

The practical upshot is that a buck regulator will not transfer maximum power from the panels to the load. On the positive side, its way better than a boost regulator.
 

BDrt

Jun 20, 2016
3
Joined
Jun 20, 2016
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Exactly.
But since the idea is to charge the batteries at the maximum power available, the controler must perform the mppt to know the max. power available and then, considering the output voltage and available power, calculate the maximum current.

My problem is to understand how will the wave forms in the panel be, with this converter, based on the simulation i've made.
I've seen that the buck converter is sometimes used as mppt and the results are similar to those i obtained with the panel model, but i want to be sure and understand what will have using that converter.

Thank you.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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Jan 21, 2010
25,510
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in an MPPT controller the buck regulator is controlled so as to achieve maximum power to the load.

A simple way is to maximize the output current. This works when charging batteries because the output voltage can be considered as fixed. Note that this CANNOT be done with simple feedback as at any point either an increase or a decrease in duty cycle may be required to move toward the max power point
 
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