Input filter for solar charger

Hi!
Is an input LC filter required in a buck topology solar MPPT?
Without an input filter, the very nature of a buck converter would result in discontinuous current being drawn form the solar panels. How can one expect high efficiency if the panel current is discontinuous?
Surprisingly, if we just google search for "MPPT circuit" and see the images, they all lack an LC input filter.
Another person just designed a buck based MPPT and without an input filter and was managing an efficiency of 70% power from the panel. I wonder how it even reached 70%. If it is a buck based converter with 50% duty cycle, the panel efficiency should not be more than 50%, since half the duty cycle it would simply be OFF. (Probably the self inductance of the cable connecting MPPT to the panels did some good work)

My question is:
Is an input LC filter required for a buck based MPPT?

Thanks

If you are drawing zero current from your solar cells, then you've got zero percent efficiency? Or is it infinite efficiency? Your basic premise wrong. What you want is a battery, or a large capacitor, between your cells and your convertor so that you can store unused energy.

To get efficient use from a PV panel, draw current continuously, at the maximum power it can provide. An LC input filter is a simple method to do this. It feeds the buck converter with a current waveform which alternately goes higher and lower than PV panel output.

The LC action is not readily obvious by simply looking at a schematic. However its benefit is quickly seen by comparing runs on a simulator.

I would have thought just a capacitor at the output of the panel was necessary.
There is middlebrooks theorem about input impedance of an smps and stability....so i woudl think you need cap there.....but then again, some of these panels have
microcontroller based control loops where its kind of a "mamaged open loop" situation, so maybe some get away without needing an input cap......but surely in the interest of small current loops, you really woudl be better with a cap there.
I dont think you need an L at input..the impednace of the panel gives you enough series impedance.
Just Cap needed at input

Many MPPT charger designs are having a very lower low capacitance only at the buck I/P but practically all are working efficiently.

Although the input capacitor alone gives some benefit by smoothing the supply current waveform, the effect is maximized when the inductor is added.



My simulation is based on MPPT 12V at 1.18A. Notice smooth current draw from the supply (constant 1.18 A). However the buck converter itself processes Ampere levels which peak over twice that amount. The load receives 2A at half the voltage.

Using a large electro on the input - it is possible to calc the ripple voltage on the Vin bus from the worst case Iripple drawn by the buck converter - as long as the Vripple seen by the panel is less than ~ 100mV ( 12V panel) then the panels will still supply DC to the circuit. Obviously an LC filter will be better, but not essential...