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TMS320F280049: Digital harmonic filter

Part Number: TMS320F280049

Dear C2000 expert,

Currently one of my power requires to filter out the harmonics from the AC input voltage. For example, the ac input voltage contains 3rd, 5th, 7th, 9th harmonics, then I'd like to filter out them all harmonics to get pure sine signal. Can you please share some suggestions?

The ac voltage input frequrency is 45HZ - 200HZ. Thanks...

  • If you are trying to design an AC power source from the one that has harmonics (as you indicated) then you will need an active power filter (APF). Attached is a reference paper on that. We dont have any reference design available on this. There are many other papers available on this that uses C2000 MCU.

    If your application requires just a filtered AC signal from the one that has harmonics (as you indicated) then you will need a digital low pass filter. You sense the input voltage with harmonics and then implement the low pass FIR filter to attenuate the harmonics. Attached is another reference paper on this.

    Shamim

    APF_paper1.pdfLab6.pdf

  • Hi Shamim,

    Thanks for this info. My application is in the second situation which requires to filter AC signal from one that has harmonics.

    If I want to get the 1st base frequency sine signal, and suppose to use digital low pass filter. And further suppose the 1st frequency, 3rd frequency,...other hormonics show as below:

    - 1st sine frequency: 50Hz                Amplitude: 1 

    - 3rd sine harmonic freq: 150Hz       Amplitude: 1/3

    - 5rd sine harmonic freq: 250Hz       Amplitude: 1/5

    - 7rd sine harmonic freq: 350Hz       Amplitude: 1/7

    - 9rd sine harmonic freq: 450Hz       Amplitude: 1/9

    ...

    If I'd like to filter out all those harmonics, then I have to set a cut off frequency less than 150HZ at least. The result shows to me that there is a big phase delay between low pass filter output and 1st base frequency sine signal. And the harmonics can't be filtered out completely. It seems it's not meet what I want. 

    Here I list what I have do a simulation in matlab with using 1st order,  2nd order, 3rd order low pass filter, and set the cut off frequency to 100Hz.

  • Hi Shamin,

    Actually I'm designing a 3 phase pfc, and my purpose is to filter out the current harmonics, do you have some suggestions? Thanks.

  • Instead of low pass filter use notch filter for each harmonics 3rd, 5th, 7th, 9th.

    Shamim

  • Hi Shamim,

    Thanks for your suggestion here.

    In matlab simulation, I have used the standard notch filter to filter out the harmonics. The results shows to me that this filter works well if the sine frequency is fixed.

    But my application requires the allow sine frequecy change from 45HZ to 200HZ. When the sine frequency was increased or decreased, the ouput from notch filter is not good during the frequency transition. The parameter w0 and sine wave frequency update simultanousely in my simulation model.

    Please see the bottom waveform I have got from matlab, the filter output signal seems get distorted while sine frequency changes. Can you share some suggestion during the frequency transition? 

  • Why cant you change the notch filter frequency when your application frequency  changes from 45HZ to 200HZ.?