high power ac/dc converter.

I am working with an ac/dc converter giving a 28V output @70 A max. it's intended to be used as a battery charger. the input to the ac/dc is single phase, but i want to run it from a three phase supply. the dc voltage at the output terminals of the existing single ph br is 330 v.i have tested a three phase bridge rectifier and have got the output voltage set to 340 volts. i want to dissconnect the existing br and replace it with the 3 ph br. my question is this. on the ac line input to the existing br there are three inductors. why is this inductance there? will i need to provide inductance on the input to the 3 ph br before connection to the rest of the circuitry? any ideas or sugestions would be greatly appreciated. thanks.

 

[jbartos]

Suggestion: The input inductances are reducing input harmonics and the upstream power supply harmonic contamination due to this nonlinear load.

 

[Lewish]

What is the input single phase voltage?
Are there more than 4 leads coming out of the bridge?
Does this unit possibly have PFC?

 

thanks to all for the responses. the single phase input voltage is 230V @50 Hz. there is no powerfactor correction and the device shows as a capacitive load to the supply. the bridge used on the unit at present has two inputs (~ ~) and two outputs (+ -). the bridge i am planning on using has three inputs (~ ~ ~) and two outputs (+ -).
the ac supply line (L) passes through a fuse then a toroidal inductor and a cap before terminating at the bridge. the ac supply line (N) passes through a toroidal inductor and a cap array (two in series with the center tap poind tied to gnd and one in mesh) then another cap before terminating at the bridge.
i think this is a means of filtering rf from travelling back onto the supply but i am not sure! the final system is to run from the output of a generator set so this filtration may not be needed. any help or ideas would be great. thanks.

 

[electricuwe]

Seems to be an rf-filter. If you do not add a suitable three-phase rf-filter you may broadcast some rf disturbances (rf is not harmful to the generator , but may be harmful to other equipment even if is not directly connected to the same circuit).

 

the final aplication of this system may mean other electrical/electronic systems in the vacinity such as other generators, tx/rx equipment, computers, gps. etc. if the ac/dc converter is likely to interfere with such systems this poses a problem !
does anyone agree that a good remedy would be to make two duplicates of the filter curcuit on the unit at the moment, and use the coppied curcuits on each of the other two phases? or ..... is there a way of intergrating sellected components in order to reduce the final part count?

 

[jbartos]

Suggestion: The EMI filters are usually considered and applied differently from harmonic filters/reactors.

 

[electricuwe]

You can buy rf-filters for three phase applications from a lot of suppliers e.g. EPCOS. The problem with this topic ist that not the filter is the expensive part but the selection of an approbiate filter is quite expensive (may be 10 to 1000 times the cost of the component).

Usually an EMC-laboratory is asked to choose a filter which is necessary to fulfil the applicable standards (which have to be specified by you).

Try to find a power supply for you application already having three phase input and an approbiate filter or ask the supplier of your supply to modify the supply.