Realize you can't avoid the ripple, but you can make it small enough that you can regulate it out. The formula for the capacitance is:
C = I t / tΔV
C - is the capacitance in farads,
I - is the DC load current in amperes,
ΔV - is the allowable ripple across the load, in volts.
In your case, if you're working with 50Hz mains and you can stand, say, 1 volt of ripple, then
C = 100A × 0.01s / 1V = 1F
For a full explanation try this link: