Input current filter
Consider the output capacitor (say 100 uF for convenience) that feeds the converter. Assume it is charged to some typical voltage level (maybe 10 volts again for convenience). If the converter input current (I) is 10 amps (during a peak) then, the change in voltage on that capacitor is: -

\$\dfrac{dv}{dt}\$ = I/C = 100 kV per second or 0.1 volts per micro second.

If the duty cycle of the converter is (say) 50% and the average capacitor voltage remains at 10 volts then, the current from the solar cell must be 5 A. A higher duty cycle means the panel supplies a higher average current.

So, the real dv/dt reduces to 0.05 volts per micro second.

Next, consider that the converter switches "on" for 10 us and "off" for 10 us (as per the previously mentioned duty cycle of 50%). During the "on" period, the capacitor voltage will reduce by 0.5 volts and, for the "off" period, it will rise back by 0.5 volts hence capacitor ripple is 0.5 volts p-p.

If the input voltage to the inductor (from the panel) is constant and the inductor is (say) 100 uH, it will see a change in voltage of 0.5 volts over a 10 us period.

Now here's a little cheat - assume that that voltage change is instantaneous (it's a triangle in reality) and, using V = L di/dt you can "estimate" what di/dt will be into the inductor.

I "calculate" di to be 0.5V x 10 us / 100 uH = 0.05 amps.

Like I say, this is just an estimation based on me cheating by saying the change in voltage across the inductor is instantaneous (rather than triangular shaped). So, I would expect to see the panel feed an average current of 5 A with a superimposed ripple of no more than 50 mA p-p. Might be worth simulating......



Hmmm, not far off - output ripple voltage is spot on and input ripple current (barely visible) is one-quarter of my somewhat exaggerated calculation.

That's the power of simulation.

The simulation also tells you that there might be a significant transient on power up that might exceed the input supply limit on the converter - watch out for this.