Ringing in MOSFET H bridge when connected load through LC filter

Discussion in 'Power Electronics' started by cjaya09, Jan 9, 2018.

  1. cjaya09

    Thread Starter New Member

    May 1, 2017
    1
    0
    I'm currently making a pure sine inverter using a MOSFET H bridge with following specs.

    Vin=360VDC
    Vout=230VAC at 50Hz
    Output Power=750W
    Switching frequency=16kHz

    [​IMG]

    I use Sine modulated PWM(SPWM) as shown below.

    [​IMG]

    At this stage I'm still operating in 100VDC.Earlier I had problems with voltage spikes appearing in the DC bus line which was solved by moving C11 & C12 closer to the H bridge in the PCB layout.when i connect a resistive load directly to the bridge, the waveform of Q2 are almost perfect as shown below with no spikes when Q2 is off and Q4 is switching as in the previous question.

    Vgs:cyan Vds:purple Id:Green

    [​IMG]

    However when I connect the LC filter, a ringing appear in Vds.

    [​IMG]

    What is the reason for this?
    How can i minimized or avoid this ringing?
    How this affects the MOSFETS?
    Thanks in advance...
     
  2. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    This isn't your real schematic is it? How far are the driver chips from the actual mosfets? How are you expecting 50Hz output when switching at 16kHz? Without a transformer how will you get 230VAC output from 360VDC input? Many unanswered questions in this.
     
  3. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
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    TS is running a PWM, with the duty cycle modulated with a 50Hz sine wave, so the output when averaged will be a 50Hz sine wave. The peak of 230VAC is about 330V so there is no difficulty getting that from a 360VDC supply with the h-bridge doing the polarity reversal.
     
  4. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    That's why I asked him about the real schematic. Since it can't be done with what he showed.
     
  5. tsan

    Member

    Sep 6, 2014
    85
    14
    It could be that there is no freewheeling current path for inductive current. Have you checked that all four mosfets are correctly wired?
     
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