# DC bus capacitor for 1.1kw motor

3 replies to this topic

### #1 Carl

Carl

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Posted 01 October 2005 - 06:56 AM

Hello forum
Does anybody know the value for the dc bus capacitor, for a 1.1kw single phase input three phase output; for an induction motor.
The switching is normal sinosoidal PWM. It would be interesting to know how this cap is selected.

Thanks
Carl

### #2 marke

marke

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Posted 01 October 2005 - 08:24 AM

Hello Carl

The DC bus capacitor must be selected to be able to hadle the ripple current and to minimise the ripple voltage.

Determine the acceptable ripple voltage and size the minimum capacitance accordingly.
Determine the ripple current and ensure that the capacitor can carry that ripple current continuously.

Best regards,

### #3 BigMax

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Posted 03 October 2005 - 02:42 AM

Carl,

I agree with Marke's comments for how the capacitor value is selected in general.

In addition, as a practical example, I have in front of me some service info for some VSDs (brand intentionally not mentioned). For a 1.5kW 240VAC single phase input VSD, the DC buss capacitance total is 1320uF, made up of 4 x 330uF 400VDC capacitors.

Note the use of multiple parallel connected capacitors. This provides the best temperature versus ripple performance, over a single capacitor.

Hope this helps.

Cheers!

BigMax

### #4 Carl

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Posted 07 October 2005 - 05:59 PM

Thanks Mark and BigMax
That’s a big help I was going to ask what is the considered to be an acceptable ripple on the cap…but I can now work that out from the data supplied from BigMax from the formulae.

CMIN= (2Pin)/[ (V^2max - V^2min) * Frect ]

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