Dc to AC inverter inductor calculation

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Discussion Overview

The discussion revolves around the design and calculation of an output choke for a DC to AC inverter project. Participants explore issues related to inductor values, temperature management, and waveform quality in the context of an inverter operating at 12.5 kHz with input voltages between 700Vdc and 1000Vdc, and an output of 220Vac.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant reports issues with the output choke temperature rising even under no load conditions, suggesting that the inductor value may be incorrect.
  • Another participant describes their successful implementation of a 12mH E type choke, which resolved the temperature issue and produced a clean sinusoidal waveform.
  • A participant mentions using two IGBTs for the inverter's operation and indicates that the system can handle loads up to 1kVA despite being designed for 110W.
  • Concerns are raised about the inductor's ability to handle peak DC current without saturation, particularly at the operational frequency of 12.5 kHz.
  • One participant discusses the characteristics of the low pass filter formed by the choke and capacitor, noting the importance of selecting an inductor that can accommodate both the peak current and ripple current.
  • Another participant expresses a need for more detailed calculations regarding inductor values, indicating that their previous adjustments were based on empirical testing rather than theoretical calculations.

Areas of Agreement / Disagreement

Participants express differing views on the appropriate inductor value and the methods for determining it. While some have found solutions that work for their systems, there is no consensus on a single correct approach or calculation method.

Contextual Notes

Participants reference varying design parameters and operational conditions, which may affect the calculations and choices made regarding inductor selection. There is also mention of the complexity involved in selecting the right core and winding for inductors, indicating a reliance on both empirical and theoretical knowledge.

Who May Find This Useful

This discussion may be useful for engineers and hobbyists working on inverter design, particularly those interested in the selection and calculation of inductors in power electronics applications.

dincer78
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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
 
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dincer78 said:
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

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.
 
whats your structruer of the inverter? full bridge?
 
Last edited by a moderator:
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.
 
You mean you are succesfull, congratulations!
how much is the the inverter power?
 
Last edited by a moderator:
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.
 
dincer78 said:
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

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.
 
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.
 
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"

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:

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