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sine wave inverter

Discussion in 'High Voltage' started by aamir shabbir, Jan 8, 2014.

  1. aamir shabbir

    aamir shabbir Member

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    hi friends i want to make a pure sinewave inverter using pwm techinique i have done a part of it i ve made out the reference sine wave from controller and passing it through LC filter i get a pure sine wave i want to use those pulses and increase the output to 220V and about 5A output current means 1KW inverter what should be the next step after making the reference sine wave
     

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  2. Misterbenn

    Misterbenn Active Member

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    You mentioned a 12V battery, that must be one big battery for a 1kW inverter...

    Once you have your sine wave, put it into a transformer to step up the voltage. you'll need a ~1:10 turns ratio to get your output voltage, at 5A output that would mean a 50A input current. Make sure your H-bridge can handle that, look at your conduction & switching losses!

    You'll also need a largish transformer to make sure it doesn't saturate.
     
  3. aamir shabbir

    aamir shabbir Member

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    is there any circuit or any other idea to do so ?
     
  4. dave

    Dave New Member

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  5. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Your yellow 'scope trace is not PWM. It looks like a high frequency mixed with a low frequency.

    Mr Benn's idea does not use PWM. He is simply using a huge hot linear amplifier to drive a huge transformer and wasting nearly half of the battery power making heat.

    Do it like this:
    Make a low frequency low voltage sinewave. Make a high frequency low voltage triangle-wave.
    Feed both to a comparator that will have PWM at its output.
    Then:
    1) Use the low voltage PWM to drive high voltage Mosfets and filter their output.
    OR
    2) Use the low voltage PWM to drive high current, low voltage Mosfets that drive a high frequency power transformer then filter its output.

    You will also need voltage regulation of the filtered output sinewave, Low battery shutdown and overload shutdown.
     
  6. aamir shabbir

    aamir shabbir Member

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    audio guru thanx a lot but on what u see on the scope is actually a PWM but its not clear ive made the reference signal that u r talking about the low voltage triangular wave and all that thing ive done with controller see the image and guide what should i do next plz
     

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  7. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Now you showed 4 'scope photos with no titles:
    The 1st yellow trace is a low frequency and a high frequency mixed together, not PWM. The blue trace is the low frequency.
    The 2nd is a square-wave.
    The 3rd is positive wide pulses that might be created with PWM.
    The 4th is positive narrow pulses that might be created with PWM.

    In my post #4 I told you what to do next.
     
  8. tomizett

    tomizett Active Member

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    As audioguru said, you need to decide where you want to do the step-up to 220v:

    Either use a high-frequency transformer to generate a high-voltage (350v ish) DC, and then use a PWM amplifier to generate a 220v AC from that,
    OR
    Use a low voltage PWM amplifier to generate a line-frequency (50Hz or whatever) sine wave at your battery voltage, and then step this up using a line frequency transformer.

    Of these two, I'd go with the second unless you have good reason to do otherwise. It should be safer, if nothing else.
    Ignore the power transformer for a start, and begin by building a high-current PWM amplifier. You could control it directly from the microcontroller since you have one available. A driver IC like the IRF2011 would be a good place to start.
     

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