Sine wave power inverter

[Navneet Vinaik]

Thanks Psdayama, Mat and Sayzer.

I have downloaded the code and paper.
Can anyone guide me hw to calculate the pulse width's effectively?

[pramodsinha]

hi, everybody!
In the market lots of sine wave inverter available in pic 16f72 they are using software pwm not hardware pwm in the entire forum no body has discuss about software pwm , as 16f72 is very cheap and easily available.
I think we should explore about generating software pwm to create sine wave in a bridge configuration, I am trying to develope it and hope it will be successful in this month after finishing i will be able to put some light on it.
thanks

[sougata]

Hi,

My original design was based on a 18F452. Using both of the hardware PWMs and a sine weighted lookup table to modulate the PWMs at regular intervals. The interrupt routine also triggers an ADC to correct distortion on the output. So the ADC was sampled after every PWM steps. I found that the internal ADC was not giving me good results so used an external one. Now I realize that I actually complicated my design.



After the Master's Conference in Gurgaon India me and Pramod would be jointly working on a software based PWM sine wave UPS/Inverter this month. It is again a commercial project but we can sure shed some light and guide people by at least suggesting a way. A normal home UPS/Inverter does not need (at least here) a distortion free clean Sinewave. So we are restricting ourselves to the following criteria.

1. Low Cost
2. Low component count
3. Decent sinewave generation with only average variation for voltage regulation and no THD management.

Hope we successfully complete the same. We will get back here, since this is the place where we met.

[psdayama]

Dear Sougata,
Im very glad to see Ur post after long time. I wish U all the best for
seminar and subsequent planned development.
I too agree with Ur aims on this project. Please add few more:
a. The THD required is just around 10% and not 2-3% as claimed by
commercial units.
b. Voltage regulation of +/- 10% is also good which is same better than
what we get from regular utility cos.
c. It will be useless to get separate 2 HWPWM outputs as only one required.
All U have to do is get 4 steering outputs. 2 are used for alternate pulses
for PWM and 2 for half-cycles. If U use little hardware then (U have to use
it for deadtime) then 2pins can be freed and U need only 2 pins for halfcycles.
This way lot of real time saved and U can have more processing time for
interrupts.

Few posts ago somebody has posted the table for sinewave. I am surprised
that most people make table for 200 steps. I think that table should be of
1024 steps.One only has to generate 256 values for 0 to 90 degrees and mirror them for 90 to 180 degrees
to complete first half cycle and mirror entire thing for other half cycle.
This will give freq of 50*1024= 51200 Hz and carrier freq. half of that is
near to 25Khz for optimum use of Ferrite Txr instead of metal txr.
If internal ADC of 16f72 cant handle this then external one should be used
which can be as fast as 200Ksamples MCP3202 but this may increase cost by abt Rs.100/-
Dear PRAMOD, very glad to hear from U after long time.
I am still trying to find out if Hardware type card can be made within Rs.500/-
and hope to post same if successful.
regards,
psdayama