Unstable sine PWM output

[pxidr84]

Sometimes it's just there, staring you in the face all along and you still don't see it.... I guess this is one of those of times. It's pretty obvious now that you found it, which I'm glad you did!

Now that it works properly with DIV32 I see no reason to change to N-Bit math.

Maybe your new routine with n-bit maths is more accurate?

Anyway, I think that I will open an another thread soon for this 3-phase VFD, with a YouTube video, the source code, schematics, etc. Because it works fine on my 250W 3-phase motor (in theory my IGBT module is capable of 2,2kW of output power). It will be cool.

[HenrikOlsson]

Hi,
I tried both methods for both accuarcy and speed, here are the results:

N-BIT:  Frequency: 1.8Hz   Reload: 3808    Cycles: 4497
DIV32:  Frequency: 1.8Hz   Reload: 3809    Cycles: 333
N-BIT:  Frequency: 2.0Hz   Reload: 9981    Cycles: 4593
DIV32:  Frequency: 2.0Hz   Reload: 9981    Cycles: 345
N-BIT:  Frequency: 2.2Hz   Reload: 15031    Cycles: 4579
DIV32:  Frequency: 2.2Hz   Reload: 15032    Cycles: 349
N-BIT:  Frequency: 2.5Hz   Reload: 21092    Cycles: 4743
DIV32:  Frequency: 2.5Hz   Reload: 21092    Cycles: 337
N-BIT:  Frequency: 3.0Hz   Reload: 28499    Cycles: 4583
DIV32:  Frequency: 3.0Hz   Reload: 28500    Cycles: 349
N-BIT:  Frequency: 4.0Hz   Reload: 37759    Cycles: 4282
DIV32:  Frequency: 4.0Hz   Reload: 37759    Cycles: 349
N-BIT:  Frequency: 5.0Hz   Reload: 43314    Cycles: 4528
DIV32:  Frequency: 5.0Hz   Reload: 43314    Cycles: 337
N-BIT:  Frequency: 6.0Hz   Reload: 47018    Cycles: 4272
DIV32:  Frequency: 6.0Hz   Reload: 47018    Cycles: 349
N-BIT:  Frequency: 8.0Hz   Reload: 51648    Cycles: 3971
DIV32:  Frequency: 8.0Hz   Reload: 51648    Cycles: 353
N-BIT:  Frequency: 10.0Hz   Reload: 54425    Cycles: 4313
DIV32:  Frequency: 10.0Hz   Reload: 54425    Cycles: 337
N-BIT:  Frequency: 15.0Hz   Reload: 58129    Cycles: 4270
DIV32:  Frequency: 15.0Hz   Reload: 58129    Cycles: 333
N-BIT:  Frequency: 20.0Hz   Reload: 59981    Cycles: 4002
DIV32:  Frequency: 20.0Hz   Reload: 59981    Cycles: 341
N-BIT:  Frequency: 30.0Hz   Reload: 61833    Cycles: 3959
DIV32:  Frequency: 30.0Hz   Reload: 61833    Cycles: 337
N-BIT:  Frequency: 40.0Hz   Reload: 62759    Cycles: 3705
DIV32:  Frequency: 40.0Hz   Reload: 62759    Cycles: 345
N-BIT:  Frequency: 50.0Hz   Reload: 63314    Cycles: 3617
DIV32:  Frequency: 50.0Hz   Reload: 63314    Cycles: 349
N-BIT:  Frequency: 70.0Hz   Reload: 63949    Cycles: 3420
DIV32:  Frequency: 70.0Hz   Reload: 63949    Cycles: 349
N-BIT:  Frequency: 80.0Hz   Reload: 64148    Cycles: 3412
DIV32:  Frequency: 80.0Hz   Reload: 64148    Cycles: 349
N-BIT:  Frequency: 90.0Hz   Reload: 64302    Cycles: 3298
DIV32:  Frequency: 90.0Hz   Reload: 64302    Cycles: 353
N-BIT:  Frequency: 100.0Hz   Reload: 64425    Cycles: 3420
DIV32:  Frequency: 100.0Hz   Reload: 64425    Cycles: 349
N-BIT:  Frequency: 110.0Hz   Reload: 64526    Cycles: 3333
DIV32:  Frequency: 110.0Hz   Reload: 64526    Cycles: 345
N-BIT:  Frequency: 120.0Hz   Reload: 64611    Cycles: 3351
DIV32:  Frequency: 120.0Hz   Reload: 64611    Cycles: 345

For N-Bit I used 1111111/frequency and for DIV32 I used 11111*100 DIV32 Frequency. As you can see the results are pretty much spot on, the small difference there is likely due to 11111*100=1111100. What is surprising is that DIV32 is about 10 times faster than N-Bit in this particular case so I wouldn't change if I were you - it's just way more power than you need for this, and it comes a cost.

Yes, please do post the project.

/Henrik.