# Dc to AC inverter inductor calculation

1. Apr 26, 2010

### dincer78

Hi all,
i am working on an 110W inverter (Dc to AC) project that the input voltages varies from 700Vdc-1000Vdc and the output voltage is 220Vac.
The system operates, however i have problem with output choke. The output choke temperature increases instantly even in no load operation. My operation freq is: 12,5kHz
output C=3uF
I think the inductor value that i put in system is not correct. So if you know any calculation method or you have any suggestion according to this issue Please help me to solve out this problem.
regards

2. Apr 26, 2010

### Staff: Mentor

Welcome to the PF. Please check out the Related Threads listed at the bottom of the page. You may find what you are looking for in those similar threads.

3. May 7, 2010

whats your structruer of the inverter? full bridge?

Last edited by a moderator: May 7, 2010
4. May 7, 2010

### dincer78

I am using two IGBT's one for neutral and one for phase.
Also i found the right choke for the system. 12mH E type choke with 3uF capacitor i get clean sinus waveform. And the temp. of the choke does not rise.

5. May 7, 2010

You mean you are succesfull, congratulations!
how much is the the inverter power?

Last edited by a moderator: May 8, 2010
6. May 8, 2010

### dincer78

thanks, actually studied on 110w inverter but the power components we used is for 1kva so you can load it to 1kVA. This inverter is DSPic controlled so just need to change its controlling parameters. Next stage of this product will be 12-24-48 or 110VDC input and 220Vac output.

7. May 8, 2010

### Phrak

I read your posts. I think your success was a result of finding a choke capable of handling the 700 milliamp peak DC current (current levels at 60Hz are essentially DC at 12KHz operation) without saturation.

8. May 10, 2010

### dincer78

Hi Phrak,
thank you for your interest. Could you please give more detailed info about your calculation. Because i found the correct inductor value just by playing with the values of it and checking the sinus waveform and measuring the temp. Actually our output is 220Vac-50Hz but i think the frequency 50 or 60Hz will not effect your calculation.

9. May 14, 2010

### Phrak

Sorry. Somehow this thread got away from me. In case you're still there:-

What you have is a low pass filter. It passes 50 Hz and blocks the 12.5 KHz. You have 220 VAC output and 110W. Both are AC so the RMS current is 500mA and 1.414*500mA = 707mA peak current. (Hmm. Sorry if this appears to be talking down to you. It's difficult to tell the level of expertise of someone within a few posts. So consider it background noise otherwise.)

At the peak there is a 707mA current in the inductor plus the ripple current from the 12.5 KHz driving the input side. Optimally the ripple is very small in comparison.

Typically you want to pick an inductor to lose about half it's inductance due to the 707 mA bias. So you initially pick an induction value that is twice as large without the 707 mA. Obtaining the optimum core and winding count is half random chance and half art.

In case you are using a toroidal core and winding your own, try this manufacturer. They are the only manufacture I've found that will actually enable you to make an intelligent design choice:

http://www.mag-inc.com/products/powder-cores" [Broken]

They have all the parametric curvers you need to play against each other, but I don't know if you can get anywhere without some background in magnetics.

Last edited by a moderator: May 4, 2017