DC bus capacitor for DC-DC converter

[zuq]

Hi Guys

I am trying to make a motor drive (Half bridge) for permanent magnet DC motor,
What do I need to consider to choose the size of DC bus capacitor,
Power source is a 24V battery.

Thanks

 

[atripathi]

I think you need a capacitor which can carry the AC current, so regular electrolytic type C filter capacitor may not work.

 

[vimalkhanna]

What you need is a 40VDC tank capacitor which carries high ripple currents and exhibits LOW ESR .
These are used in SMPS designs for high wattage converters .
The available versions are 200VDC or higher .from Nichicon ,Nippon Chemicon.and boast upto 22000ufd .
However , kindly indicate power levels of the motor so that commutation currents can be calculated .

 

[zuq]

]Thanks vimalkhanna
I am designing for a 3kw motor,
Where does this ripple come from?? Is it due to switching??
And why must you have Dc bus caps???my guess is " because battery leads and internal inductance wont allow current to flow very rapidly so we use caps with low ESR for lower voltage drops and heating??"" correct???
Also how did you come up with 40vdc for rating??

Thanks again