How to generate a Modified sin wave...?

Discussion in 'The Projects Forum' started by RRITESH KAKKAR, Dec 17, 2012.

  1. RRITESH KAKKAR

    Thread Starter Senior Member

    Jun 29, 2010
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    Hi,

    Recently I am working on Inverter. After using a SG3524 PWM chip for square wave with output 220V regulation on load.
    now i want to go for modified sin wave as the current drawn on square wave is also high than modified sin wave and some appliance does not work well.

    Audio guru has posted a M. sin wave ckt in my previous thread using 4047 and 4001 which is working but there is no feed back option in it...
    so, kindly help me if u have any idea related

    sorry i can't upload image don't know why??
    i have seen this but how to generate it!!
    http://upload.wikimedia.org/wikipedi...2C_3_level.PNG
     
  2. Dodgydave

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  3. RRITESH KAKKAR

    Thread Starter Senior Member

    Jun 29, 2010
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    Hi
    I have used sg3524, now i want to go with any other chip to have modified sine wave..
     
  4. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Start studying "class D" amplifiers, as they put out a modified sine wave. The higher the carrier frequency the closer to a sine wave the output gets.

    Here is a link to a pure sine wave inverter - http://www.wpi.edu/Pubs/E-project/Available/E-project-042507-092653/unrestricted/MQP_D_1_2.pdf

    This is not going to be a single chip solution, or a simple solution. If it was, you could not build one yourself for the price of a store bought one.

    The voltage regulation would come from the output being rectified and then fed back to the SG3525.
     
  5. RRITESH KAKKAR

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    can't we use pic micro controller ??
     
  6. Dodgydave

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    a pic will only give a square wave
     
  7. RRITESH KAKKAR

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    Why??
    If we make a use of timer and interrupt for few msec as per freq then there
     
  8. bertus

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  9. RRITESH KAKKAR

    Thread Starter Senior Member

    Jun 29, 2010
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    Hi,

    audio guru can u help me??
     
  10. Brownout

    Well-Known Member

    Jan 10, 2012
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    You can use a PIC to generate a modified sine wave. Keep in mind, however, that a modified sine wave isn't anywhere close to a real sine wave, and cannot be used wiht every appliance that a sine wave can be used with.
     
  11. MrChips

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    Oct 2, 2009
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    What is a modified sine wave?
     
  12. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    Where?

    If you don't want to use a uC you could use the following:
    - fixed frequency oscillator for the PWM switching frequency
    - transform this into a triangle wave
    - generate a reference sinewave of your mains frequency (see this post)
    - compare triangle with sine wave, the output will be PWM
    - feed this to an H-bridge with a 60Hz transformer or a LC filter , depends on if you want it isolated or not

    You now have an inverter.

    You now decide if you want a simple rectifier-battery-inverter configuration or rectifier-battery and static switch/bypass/inverter.
     
  13. wayneh

    Expert

    Sep 9, 2010
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    Depends what you mean by "close". I think that's a key point often missed. English words like "modified" are not adequate - you need to specify just how close to a real sine wave you need. Square not close enough? How about a triangle? How about stair-stepped square wave with n steps. How big does "n" need to be? How about RC simulation of sine?

    Somebody must have developed a suitable terminology for this, that captures notions of maximum error, maximum time-averaged error and such.
     
  14. praondevou

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    Not a real sinewave, but something step-like, horrible THD.
     
  15. Brownout

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    Jan 10, 2012
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    "Modified" sine wave is more of a marketing gimmik than a tecnical description. It's important to understand the difference. As I said, it's not even close to a real sine wave, either in shape or what it's capable of driving. For example, I can use a Modified Sine Wave to drive a resistive heater, but not for many electric motor applications.

    I once plugged my little compressor into a Mod SW invertor. It just grunted and blew the circuit breaker.
     
  16. Audioguru

    Expert

    Dec 20, 2007
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    I don'think anybody makes an extremely simple square-wave inverter anymore because many electronic products and motor speed controls rely on the much higher peak voltage of a sine-wave from the mains.

    But a modified sine-wave is used today for most cheap inverters. It is really a modified square-wave with peak voltages almost the same as a sine-wave from the mains and "off-times" so that the average voltage is almost the same as the RMS voltage from the sine-wave from the mains.
     
  17. shortbus

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    The higher the frequency of the triangle wave the closer the out put will look like a sine wave. But the OP doesn't want to learn how to do it, he wants a working circuit given to him. :(
     
  18. RRITESH KAKKAR

    Thread Starter Senior Member

    Jun 29, 2010
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    I want to go with uC b'coz it is latest and stable...
     
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  19. MrChips

    Moderator

    Oct 2, 2009
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    What's wrong with using a look-up table feeding a DAC to produce a decent sine wave?
     
  20. RRITESH KAKKAR

    Thread Starter Senior Member

    Jun 29, 2010
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    OK, if we will have sin wave then how will we switch mosfet in linear region??
     
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