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According to this project I saw many design use same principle by using MPPT to adjust PWM of buck converter.

I totally get MPPT algorithms except the DC to DC converter part.

Let's call solar panel the source.

From this link, this picture shows current at the source (input side):

current waveform of buck converter

As you see, input current is not continuous. From IV characteristic of solar panel, I think current should be constant to obtain correct data. So I think it shouldn’t work this way.

Questions:

  1. Did I get something wrong?
  2. Are there any theories to explain how this works?
  3. If I was right, how to correct this design?
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  • \$\begingroup\$ Sure it can work that way - why would you think it wouldn't? What does correct data mean in this context - is there some data communications going on that you haven't mentioned? Buck converter picture that might help: researchgate.net/publication/319597764/figure/fig1/… \$\endgroup\$
    – Andy aka
    May 17 '20 at 15:07
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    \$\begingroup\$ Hint : Input reservoir capacitor. \$\endgroup\$ May 17 '20 at 15:11
  • \$\begingroup\$ Andy - when measure VI characteristic, I should be constant for precise measurement. but input current of buck seem discrete. \$\endgroup\$
    – M lab
    May 17 '20 at 15:58
  • \$\begingroup\$ Brian - I think. I assume my assumption is correct there for input capacitor should be large. if we need smooth current. why we not apply LC filter or LC pi network for more smooth current? \$\endgroup\$
    – M lab
    May 17 '20 at 16:00
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For long time of searching I found my answer in research paper DC-to-DC Converter With Low Input Current Ripple for Maximum Photovoltaic Power Extraction From this paper

the dc-to-dc converters must assure continuous input and output current to provide maximum energy flow from the source to the load.

The current ripple creates problem in power electronic systems, which affects the voltage and, thus, the power. The extent of the loss problem due to PV current ripple is a feature realized for the first time in this paper. The exponential curve of the PV cells causes nonlinear mapping in the current axis which in turns leads to high loss of output power due to the input current ripple.

This paper also suggest efficient DC converter which have continuous input and output power. Foranswer

Did I get something wrong?

No, this paper support my idea.

Are there any theories to explain how this works?

It's use LC component to filter input current but still high ripple.

If I was right, how to correct this design?

We can us other type of DC converter such as SEPIC, Cuk or D type converter

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