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Capacitor for Ripple filter in Shunt Compensators

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sabu31

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Hi,

I would like to know what type of capacitor should be used for ripple filter in case of a shunt connected inverter system like PV inverter or DSTATCOM. Are any ac capacitors suitable. For example (Epcos 10uF ,440Vac, 50/60Hz) or should i use a film capacitor (say Metallized Polypropylene Film Capacitors (MKP)
EPCOS B32774D4106K000 Film Capacitor, B32774 Series, 10 µF, ± 10%, PP (Polypropylene), 450 V ). The ripple filter is used to by pass currents due to switching action of converter system

Thanking you.
 

Your description isn't very clear. Is the ripple filter connected to AC voltage? In this case you probably missed the datasheet specifications about permitted AC voltage.

A capacitor loaded with AC voltage must be rated for AC. Another point is series inductance and resistance (ESL/ESR) and rated ripple current. You should know what the ripple current in your application is.
 

Hi,

For clarity, I am talking about capacitor to be used in ripple filter in the Fig.


I have read the ripple filter removes harmonics generated due to switching action of voltage source converter. I would like to know whether ac power line filters (say schaffner ,FN 3311/FN 3310) does the same functions as a ripple filter or something else. Please refer me some literature regarding . Thanking you.
 

PWM ripple isn't harmonic current. A standard power line filter can absorb pwm ripple to a certain extent, dedicated shunt capacitors might be necessary though to filter the pwm fundamental, depending on its frequency and magnitude. If the ripple current is high, you should also check if the power line filter can handle it.
 

Hi fvm,

I am still not clear. My first question is regarding , the Type of Capacitor to be used in ripple filter mentioned in post 5. The usual values are 5-15uF. Now when i searched for capacitors , I am getting two types




The capacitors are
(EPCOS B32774D8126K000 Film Capacitor, B32774 Series, 12 µF, ± 10%, PP (Polypropylene), 700 V ) and
(DUCATI Film Capacitor, 4.16.10 Series, 15 µF, ± 5%, PP (Polypropylene), 450 VAC, Can ).
Which among the two are suitable for the filtering purpose.
 

Hi,

Just an addendum to previous post, I would like to know if X2 type capacitor can be used as in ripple filter shown in post 4
 

You are looking for an EMI filter; you need to tell us the expected frequency it is going to filter.
 

Which among the two are suitable for the filtering purpose.
Click to expand...
If you manage to read the B32774D8126K000 datasheet, you'll realize that the part is specified as DC link capacitor and explicitly not suited for AC voltage application. X2 capacitors in contrast are well suited for AC, there's also a number of other types specified for AC operation.

You are looking for an EMI filter; you need to tell us the expected frequency it is going to filter.
Click to expand...
As previously mentioned, these filters are possibly not capable of handling high ripple currents, they are usually designed to have maximal attenuation in the standard conducted EMI range above 150 kHz. This way, they are perfectly suited to cut pwm harmonics but fundamental pwm ripple may need dedicated filtering.
 
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