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    Inductor core selection filtering AC (Final year project)

    Hello everyone.
    I am designing an H-Bridge based SPWM inverter converting 330VDC(48V converted to 330VDC by Full Bridge converter) to 220VAC. The problem has come down to the filtering issues. When I used only 48VDC to convert it into an AC, I achieved a pure sinewave with ta toroidal core(dont know the material). But when I perform the same testing with the 330VDC, I am not getting the sinewave. I think the core is saturating because I connected a resistor in series with the inductor(a second order LC filter), and I was achieving a pure sinewave but with a lot of power being dissipated across the resistor.
    Please give any suggestions related to this problem. Also, if the core IS saturating, kindly tell me which core should I use for filtering?
    Thankyou a lot. (This is my Final Year Project and is in the last stages. So, kindly help asap)

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    Re: Inductor core selection filtering AC (Final year project)

    details of your output choke? which you assume is saturating? if you put an RC filter on the o/p of your H bridge, you can look at this on a scope and you should see a sine wave, if you operate your inverter with no load, unless the filter is properly damped (and not resonant at Fsw or Fo/p) you may well see some interesting things on the o/p esp if your deadtime is large, so add some load to your inverter and look again and post observations...



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  3. #3
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    Re: Inductor core selection filtering AC (Final year project)

    Quote Originally Posted by Easy peasy View Post
    details of your output choke? which you assume is saturating? if you put an RC filter on the o/p of your H bridge, you can look at this on a scope and you should see a sine wave, if you operate your inverter with no load, unless the filter is properly damped (and not resonant at Fsw or Fo/p) you may well see some interesting things on the o/p esp if your deadtime is large, so add some load to your inverter and look again and post observations...
    I am using a toroidal core and yes, I have tried and used multiple load resistors of 2k, 1.5k, 330 ohms etc. Also, by using the RC filter only, I get a square wave, not a sinewave.
    This is the sinewave for 48Vdc.Click image for larger version. 

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    But for 330VDC, and with the same filter specs, I am getting a very distorted shaped waveform(dont have the picture for that right now). And also, there is some loading effect on the previous dcto dc converter stage too.
    Last edited by usama14; 11th June 2016 at 09:54.



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    Re: Inductor core selection filtering AC (Final year project)

    for the higher voltage out of the H bridge you will need higher L and lower C, else you will overload the circuit with excessive filter currents (reactive)

    - - - Updated - - -

    a toroidal core that is not iron powder (i.e. ferrite, high mu) will saturate at very low currents...



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    Re: Inductor core selection filtering AC (Final year project)

    Quote Originally Posted by Easy peasy View Post
    for the higher voltage out of the H bridge you will need higher L and lower C, else you will overload the circuit with excessive filter currents (reactive)

    - - - Updated - - -

    a toroidal core that is not iron powder (i.e. ferrite, high mu) will saturate at very low currents...
    So what should I do now?
    1) You think using an ETD34(3C90) core will help?
    2) Also, do you mean that I should increase the switching frequency?



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  6. #6
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    Re: Inductor core selection filtering AC (Final year project)

    you need to choose the L/C ratio carefully depending on power level and freq, ferrite needs to be gapped to make an effective inductor, ETD34 may be too small depending on power level...



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    Re: Inductor core selection filtering AC (Final year project)

    Quote Originally Posted by Easy peasy View Post
    you need to choose the L/C ratio carefully depending on power level and freq, ferrite needs to be gapped to make an effective inductor, ETD34 may be too small depending on power level...
    Here are my specs:
    Power=600W
    Switching SPWM frquency=2 KHz
    Current(max)= 5A to be drawn
    Voltage= 220VAC
    Now, kindly any idea about the L/C ratio Sir?
    Also, ETD59 will be good?



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