how to calculate dc link capacitor

[hutanga]

Hi,

I'm working on my final year project --> 3-phase power inverter to drive bldc. output current from the inverter is in quasi square wave waveform and i am using 30V dc supply.

i'm having problem in determining dc link capacitor value. frequency of the system is 20 kHz and peak-to-peak input ripple current is 22 A. the equation for calculating capacitance is given by

C = I/Vf

as far as i understood, the voltage in that equation is the ripple voltage. correct me if i'm wrong, but since i'm using dc power supply, the voltage ripple is ideally zero. so how do i calculate capacitance value.

thank you

 

[srizbf]

V - is it not voltage across capacitor ?
the maxm you expect ?

srizbf
17thmay2010

 

[hutanga]

yes. V is the voltage across capacitor. it may sound silly but is that voltage ripple component or DC component (which is 30V)?

thank you

 

[srizbf]

can you give some more information ?
(leave C=.. eqn for sometime).
i would like to understand the situation , if you can give more...

the dc link capacitor is connected from o/p of inverter to bldc motor.
is it correct ?

you want to find the capacitance value for this link.

eqt circuit is voltage source connected to cap and bldc motor .?

with regards
srizbf
18thmay2010