Frequency converter problem

[Zedman]

Hi all,

I found this freq converter: **broken link removed**

I built it, but since the firmware is not free, I decided to make my own.
The site says PWM frequency is 4,88 kHz and it's resolution is 128.
Freq. for the motor can be set from 1-75 Hz. It does not change the amplitude, just the frequency.
The resolution of PWM values / sine wave is not known. I set it to 64.

So I had to make a base square signal for the PWM with 75*64*128 -> 307200 Hz
and play this 3 times, modulated with a sinus table and phase shifted with 120 degree each.

It can be observed well on a scope at PICs outputs and also on the MOSFETs' gates.

But I put on a 120W motor it doesn't run, I can just hear the PWM's sound, and
if I put on a transformator between 2 of any of the three outputs I can see the attached signal on the scope, which is not really like a sinus wave...

any ideas, suggestions?

thanks,
Zedman

 

[Zedman]

I figured out why this wave looks like this, because transformator rips off the DC part of the high part.

And if I look closer, then I can see the sinus modulation in it.

 

[Zedman]

But the motor still doesn't run.