I Want to know how to convert AC to pure DC & from DC to pure AC using filters? I want to design a filter for any given application. Any links or references or Text Books are greatly appreciated.

I Need this to work on my project "Flexible Power Electronic Transformer" where i require atleast two filters one to convert ac to pure dc & the other to convert dc to pure ac.

If you don't use the DC, why invest in filter(s) there? Put your money where it counts: on the AC side.
Also there is no such thing as "pure" AC. You should define which standards you want to meet (IEC likely). This will drive your filter design and you will also need converters. Filters don't do AC/DC conversion while your converter design will influence your filter design. Are you going for a 6-12-24 pulse?

I am asking for the filter design to improve my voltage waveform after it has been converted or inverted, i might use a 6 pulse converter

There are a number of IEC standards that will apply. What is the size of your transformer? There is a classification based on how much current your transformer will draw. Is-it <15 A?

Using the right standard, you will be able to figure out how much harmonic emissions is allowed. Depending on your design, you will be able to assess how much you are sending into the network and how much filtering is required. You will then design your filters and test for compliance. This could be done by simulation...and its a lot of fun.

The Transformer is Single phase 50Hz 230V/250V current rating is around 10amps and KVA rating is around 4-5 KVA, i mainly want to eliminate the 3rd and 5th harmonics and if possible the minor harmonics too

Devan,

You are designing a solid state transformer with your project (fllexible electronic transformer) using AC/DC conversion, DC/DC up/down conversion, and DC/AC inversion, is that right?

You did not mention what maximal % of output ripples are permissible.

There's a general tradeoff between the quality of the output signal (voltage/current) and quantity, size of the switching and storage elements (costly).
Smoothness of the output signal, to say minimum voltage or current ripples, depends a lot on your specific design. As mentioned above, a 12 or 24 pulse for the inverter provides you much smoother output ripples, 6 pulse is rougher ripples and needs further filtering if so required.

You can design in a very large expensive cap to even out your DC voltage after conversion, makes the DC voltage rocksolid - but is it even needed? The following
DC/DC converter will chop this DC power into smaller quantities to store in the LC elements. What signal quality do you need at this point? The DC/AC inverter chops the output signal again. Then, you can use an extra filter stage or two, three or more filters. The lattter is too costly while you only want to achieve accetaple output quality. Many filtering questions can already be accommodated through a clever design of the inverter/converters.

One book I recommend is (not sure whether available outside of NA):
Mohan, Undeland and Robbins, Power Electronics: Converters, Applications, and Design, 3rd Edition, John Wiley & Sons.
Though, there are many other alternative textbooks to give a good understanding of the basic principles of switched mode power electronics.