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I've been looking at a few MPPT schematics, and I'm confused about the operation. The point of MPPT tracking is to extract the maximum amount of power from the solar panel, which means controlling the amount of current coming from the panel. These circuits are structured as buck converters, which means that at 50% duty cycle, half the time the current coming out of the solar panel is increasing, and half the time its decreasing. Why not have the inductor before the switch, so that the panel current is constant, as shown in the first circuit here?

enter image description here

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  • \$\begingroup\$ Because then it wouldn't work as a buck converter. \$\endgroup\$
    – Finbarr
    Aug 9, 2023 at 10:10

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MPPT controller works when voltage from solar panel is higher than the battery voltage. That means input voltage needs to be reduced. This reduction is done using Buck Converter, which produces lower output voltage but can have higher output current than on the input. The way it operates requires switch before the inductor: when the switch is conducting the current flows through inductor into load and output capacitor. When output voltage reached required level, switch is getting open, but current continues to flow from the energy stored in the inductor (that is why diode is also required as it provides the path for this current). Cycle repeats at high frequency. Duty cycle is controlled depending on output voltage and current required and not fixed at 50%. When input voltage is low duty cycle can potentially go to 100%. Having switch after inductor will prevent normal buck coverter operation

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The following video may be extremely helpful to visually explain the dynamics of buck (and boost) converters, going through different basic (and also incorrect) design ideas and their pros and cons. Voltage is shown as distance (height), and the current magniture by arrow size. The role of inductors and capacitors in a network is especially clarified here.

https://www.youtube.com/watch?v=vwJYIorz_Aw

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  • \$\begingroup\$ Link-only answers are heavily discouraged here. Summarize the important points from the video, instead, then link it in addition to that. \$\endgroup\$
    – Hearth
    Oct 13, 2023 at 17:18
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I will answer by question which points you to core of problem. What happens when your switch connect left 10uF capacitor charged to "high" voltage with right 10uF capacitor discharged to "lower" voltage ? Large current limited by resistance of your switch and capacitors ESR wil flow from left to right and dissipate energy to heat and that is the reason to place inductor between them.

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