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3-level Inverter with low switching frequency

erka
Prodigy 70 points

Hello 

I am using currently F28335 and also using ti document 3-level SVPWM (SPRABS6). 

Induction Motor(3.3kV) Controlling by Sensorless Vector Control. Our 3-level NPC Inverter's switching frequency (Fsw) is 1.5kHz.

I want decrease the  Fsw about 0.8kHz~1kHz. When using Fsw=1kHz then controlling the motor rated frequency at 50~60Hz, the 3-level SVPWM output reference resolution is decreased.  There is  any method to increase good resolution or high performance 3-level SVPWM output reference? Or how to implement dual interrupt method?

Thanks 

Erka

  • 0
    TI__Mastermind 27240 points

    Hello,

    The only way is to increase Fsw. If Fsw/Fsine is > 21, it should be ok. In your case, it would mean an Fsw of about 1260Hz.

    You can check to see how it behaves if the ratio is 15, or Fsw=900Hz. I would not go below this.

    rgds,

    ramesh

  • 0 in reply to Ramesh Ramamoorthy
    Prodigy 70 points
    Thank you for Ramesh Ramamoor

    1. In Medium Voltage Drive, I was tested until Fsw=1.2Khz with no load condition. Later I will test full load test of Induction Motor (using Vector Control). When I saw some European paper about MV drive, they used Fsw=1050Hz in 50Hz sine of Rated Frequency.
    So Frequency ratio 21 is reasonably value. (Maybe easy to multiply by 3 of 21 value). I do not know exactly.

    2. I want use Dual sampling ADC interrupt method in case of Center aligned 3-level SVPWM. I was tested Dual sampling ADC interrupt method. But my test result was not good.
    Do you have any suggest document about Dual sampling ADC interrupt? Or Center aligned 3-level SVPWM must use single sampling ADC interrupt?
  • 0 in reply to erka
    TI__Mastermind 27240 points

    1. Basically how much coarser should the current waveform be is the designers choice. 21 is my choice, but one could go lower than that.

    2. I don't have direct information, will ask if any of my colleagues can help.

    rgds,

    ramesh