LC Filter for a Full Wave Bridge Rectifier?

According to what I've read on a few websites and PDFs (http://www.irjes.com/Papers/vol2-issue6/Version-1/E02064249.pdf is an example) using an inductor-capacitor filter to assist AC to DC rectification in ripple management is much better than using either component by themselves. (In the example PDF capacitor was sized down by 75% & inductor was sized down by 94%)

How can I size the inductor and capacitor such that I can get a certain voltage ripple after being rectified by a full wave bridge rectifier? (Even in the paper they recommended a trial and error method, essentially guessing 25% for the capacitor and manually finding the inductance for the inductor)

I haven't taken differential equations yet, but I'm past Calculus III if you prefer to answer in a non algebraic way. (Although algebra is preferred)

I'm running 1kW (split phase, plans on moving to 3-phase) through this bridge (full wave) for high power electrochemistry: $$972W = 18V * 54A$$

• so, you want a formula that will emit capacitor and inductor sizes for a given ripple level? where are you planning to buy custom sized capacitors from? Jun 3, 2016 at 4:30
• When you get into the tens of amps, direct (mains frequency) rectification stops being a good idea, unless you really have to do things that way, I'd recommend an off-the-shelf smps, it'll have a much higher efficiency and will already have all the filtering builtin (the conduction losses in the rectifer alone will be 50+ watts, maybe even 100W, most diodes have between 0.5 - 1V drop and two are on at any one time in a full bridge rectifier)
– Sam
Jun 3, 2016 at 4:48
• @Jasen What are you talking about? You could just round the capacitance to the next highest number that people sell.... Jun 3, 2016 at 5:04
• @Tom So either switch the frequency, or go with SMPS? As far as I can tell, SMPS still use bridge rectifiers though. Jun 3, 2016 at 5:12
• I should also mention that most kW+ smps units have some kind of Power Factor Correction (PFC) so that the current pulled from the mains is sinusoidal, if you wanted to use a big ol' mains transformer, there's no reason why you couldn't use pfc on the low voltage side to keep the transformer currents and voltages sinusoidal while providing a stable dc output after the pfc stage.
– Sam
Jun 4, 2016 at 21:30

did you read the last sentence of the paper? "Since there is no mathematical formula available for designing a combined capacitor - inductor filter, the verified ATP model will help seniors, graduate students, and design engineers to design a filter to limit the ripple to a specified value in an AC to DC converter."

If there is no mathematical solution available, you can only use try and error using a computer model or a real rectifier circuit.

• I was uncertain if there actually was a mathematical formula and they didn't know about it/couldn't derive it/was found after publishing. Jun 4, 2016 at 4:07

Have a look at:

http://www.circuitstoday.com/filter-circuits

Ripple Factor = Vac rms/Vdc = (√2/3)(Xc/XL) = (√2/3)(1/[2wc])(1/[2wL]) = 1/(6√2w2LC)