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IGBT Sine Wave Dimmer

Discussion in 'General Electronics Discussion' started by Divedeep, Feb 6, 2015.

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  1. Divedeep

    Divedeep

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    0
    Feb 2, 2014
    Hi,
    I am quite interested in sine wave dimming of AC voltages.
    I understand the concept on which it works but there doesnt seem to be much in the way of schematics for reference.
    I have however stumbled upon this link

    http://gaoweiming.blogspot.co.uk/2012/12/smart-sinewave-dimmer.html

    I am a little bit stuck with whats going on with the overall scematic in Figure13.
    I have marked in bold the parts i am struggling with, maybe someone can help.

    This is Figure 11,
    [​IMG]

    My understanding is that we have a bridge rectifier with an IGBT inside. Switching the IGBT (VF1) will give voltage at uo.
    L1 and C1 is an input filter L2 and C2 are an output filter. VD1 and VC1 are for protection of the IGBT.

    How does VD1 and VC1 protect the IGBT?
    At a mains frequency of 50Hz - 60Hz what would be the ideal values for L1 and C1?
    At a output frequency of 50Khz what would be the ideal values of L2 and C2 in order to filter everything except for the 50Hz to 60Hz line frequency?


    The document says that to allow for resistive, capacitive and inductive loads. they introduce a converter.

    Figure12.

    [​IMG]

    VF2 and VF3 have been introduced here but i have no idea what they would be for to allow for resistive, capacitive and inductive loads. How would they be controlled? are they switched at the same frequency as VF1??
    The device i would like to build will need to control both resistive and inductive loads at various wattages.

    The last figure, Figure 13 is the complete schematic.

    [​IMG]

    Introduced here is RC1 and C3 this creates an RC output filter that is supposed to prevent LC harmonic oscillation problems. I assume this problem would come from L2 and C2?? Can anyone elaborate as to what will be goin on here??

    Sorry for the long post but there isnt much about this around so need a little help from someone :)
    Thanks
    Also what would ideal values be for R1 and C1?
     
  2. Bluejets

    Bluejets

    4,094
    859
    Oct 5, 2014
    Do you have a problem with using triacs as they are designed for this type of work, simpler to use and less components.
     
  3. Divedeep

    Divedeep

    57
    0
    Feb 2, 2014
    I dont have a problem. In fact i use triacs in a design already. The problem with using a triac for dimming is there is a lot of EMF and you can also get a slight flicker using incandescant bulbs.
    Using sine wave dimming there is no EMF caused from harmonics so its better for the grid. Also dimming is smoother with no flicker at all.

    Although triacs are designed for ac switching its very old technology. I am developing a high end device that would benefit from sinewave dimming.
     
  4. Bluejets

    Bluejets

    4,094
    859
    Oct 5, 2014
    I thought triac phase control was sine wave control.
    There are many high tech dimmers out there already which use both leading and trailing edge dimming to overcome the problems you encounter with incandescents and with LED dimming.
    These days, incandescent are on the way out and they themselves are considered "old technology".
     
  5. Divedeep

    Divedeep

    57
    0
    Feb 2, 2014
    Triacs utilise zero crossing and chop up the sinewave, commonly known as phase angle control. The main problem is that when you fire the triac at 50% the voltage goes from 0v to 240v instantly causing lots of emf. The way to combat this is to use a massive inductor to filter the emf.

    Using an igbt you can pulse the mains at about 50khz and then filter it. The result is a sine wave with a reduced amplitude rather than a chopped up ugly looking sinewave.
     
  6. Bluejets

    Bluejets

    4,094
    859
    Oct 5, 2014
    No "massive" inductors in the ones we use here and all comply with relevant worldwide authorities, come on a case no more than 20*20*30mm.
    Many different types for just as many applications.
     
  7. hevans1944

    hevans1944 Hop - AC8NS

    4,495
    2,092
    Jun 21, 2012
    It's too bad the Chinese to English translation is as poor as it is. Clearly the first circuit is a high-frequency (50 kHz) chopper that is pulse-width modulated. This will provide, after filtering out the harmonics of the 50 kHz switching frequency, a reduced amplitude sinusoidal waveform whose amplitude is proportional to the duty cycle of the chopper.

    The second circuit consisting of two IGBTs in series opposition with steering diodes across the IGBTs, all connected across the output of the chopper circuit, is probably used (somehow) for power factor compensation in conjunction with the output LC network. It provides an alternative path for circulating energy stored in the output LC network, but I don't know how it is switched to perform power factor correction allowing resistive, capacitive, or inductive loads.

    The series RC circuit across the output appears to be for the suppression of "spikes" that are generated as a consequence of the power factor correction circuit, but this is just an educated guess on my part. If I were you I would concentrate on research that explains how the power factor correction circuit would work.

    Clever, those Chinese engineers are. But I would almost be willing to bet the "technology" involved is described somewhere in the open literature. You just need to select the proper search string. You might want to start here. Or maybe here...
     
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