# Filter for rectifier

#### erle4581

Joined May 12, 2006
5
Hi

I need help with filter design, I have a circuit that contains a three phase rectifier now I want to filter the output DC from the rectifier. The incoming three phase AC to the rectifier has varing amplitude and frequency see figure 1. Now the filter is going to need a big capacitor to filter the output from the rectifier. After the rectifier and the filter a three phase DC to AC inverter is attached to to invert the DC to AC and after the inverter a transformer is put to transform the AC from the inverter to a AC that can be connected to the grid. Now to the filter I need the big capacitor for the big rippels but after the big capacitor a LC pui-filter is connected to reduce the ripples further. but the filter have other functions like reducing harmonics and so on, figure 2 shows the circuit.

Now to the question I need help with the values on the capacitors and inductors is there any easy way to calculate these values and is there more things to think about. I have heard that different types of capacitor takes care of different frequencys like ceramic capacitors and electolytic capacitor. The big capacitor is there to work as a battery to deliver current to the inverter at all time, the pi filter is there to take care of ripples and harmonics and so on.

#### kubeek

Joined Sep 20, 2005
5,791
tell us the amplitude and current draw from the source, then it is possible to tell you some values.

#### erle4581

Joined May 12, 2006
5
Originally posted by kubeek@May 16 2006, 11:33 AM
tell us the amplitude and current draw from the source, then it is possible to tell you some values.
[post=17153]Quoted post[/post]​
Hi

Here are the values but these values are going to change over time, so would rather see some equations so I can use diffrent input values. and maybe some help with choice of capacitor ceramic, electrolytic... and what I need to think of when connecting to a inverter should the circuit be inductive or capacitive....
V(line to neutrual max)=60V
I(max) = 18A

hope you can help me

thanks