Electric load controller high voltage capacitor

[Jeroen Humasol]

Hi guys,

We're going to install an electric load controller (ELC) for a turbine in a small village in Peru. The goal of this ELC is to balance the power consumption in an isolated grid powered by the turbine. The ELC should be able to dissipate 5kW maximum. We would use an IGBT for pulse width modulation steering of our dumpload (R4). This ELC has of course a high power circuit (5kW). You can see it below.

C7 needs to be a capacitor with a voltage rating of 400V and 10µF capacity. The IGBT will switch on and off at a max frequency of 10kHZ. The problem is that i can't find immediatly a good capacitor for this job.

Does anyone have ideas?

I was thinking about this one: https://www.electronicspoint.com/threads/electric-load-controller-high-voltage-capacitor.277964/ but i'm not sure that he will survive the high frequencies

 

[Harald Kapp]

Your link points to this same thread.
You cannot use an electrolytic capacitor as it is in the AC part of the circuit. A foil capacitor is required, such as this one, for example.

 

[Jeroen Humasol]

I'm sorry wrong link it should be this one: http://be.farnell.com/kemet/r75ir51004040j/cap-film-pp-10uf-250v-rad/dp/2456380

At the moment we're also having struggles because there are currents of 16A going through it in our simulations :/

 

[Harald Kapp]

This capacitor looks o.k., although I recommend using a 400V type.
The impedance of 10µF at 50Hz is ~320Ω. At 220V (RMS) I'd expect a current of ~1A peak, unless you have a resonance with inductor L3.

 

[Jeroen Humasol]

Sorry i somehow succeeded to post once again the wrong link.. You're correct it should be a 400V type because 220V*sqrt(2)>250V

Here is finally the correct link: http://be.farnell.com/kemet/r60mr51005040k/cap-film-pet-10uf-400v-rad/dp/2446302

I'm going to discuss our simulations again because, my team and i calculated way higher currents then 1A

 

[Harald Kapp]

When do you see this high current? When the IGBT turns on? When it is off?

 

[Ajay Shukla]

A minor fluctuation in voltage can cause an electronic equipment to malfunction or break down. To avoid this, servo voltage stabilizer have been invented which maintain accurate output and save expensive electrical appliances from damage caused by power alterations at homes, offices, cement plants, flour mills, engineering units, and various other places.

 

[CDRIVE]

It would seem logical that high current would occur when the IGBT turns on. This is going to require an extremely low ESR cap. The problem here is most AC caps designed for AC motor application are actually 2 electrolytic caps wired in series +[ ]- -[ ]+ or -[ ]++[ ]- . As far as I know they're not particularly low ESR.

Chris

 

[CDRIVE]

Question: Why do you need such a relatively large cap across the AC Mains?

Chris

 

[Harald Kapp]

A kind of PFC / low pass filter so the harmonics from the PWM modulated load are not visisble on the mains?

 

[Alec_t]

Here's my sim for the cap current when the IGBT (I cheated with a FET) is switched at 10kHz 5% duty cycle. RMS current is nearly 6A, with >30A peaks.

 

[CDRIVE]

Harald, thanks for the explanation.
Alec, thanks for the sim but I'm not surprised at the results. That 10uF cap is going to be working its ba!!s off!

Chris