Sine wave power inverter

[sougata]

Hi there,

What I have planned is having a sinelook up table calling periodically through timer overflow interrupt and a closed loop voltage monitoring to adjust the value of the lookup table on the fly to minimize voltage drifts and sinewave distortion. Now the problem is that the PIC takes altleast 21us for the ad conversion then comes the calculation part. Also I am unsure which PWM freq. to use (over audible range) and how to design the parallel mosfet power output stage. For overload protection I am going to use a different comparator and do a pulse by pulse limitimg through high priority interrupts. What is the best way to protect the mosfets. I don't know how to design a RCD snubber but my scope shows ringing and peaks during switch off in a normal square wave design. I beleive they are the reason for MOSFET heat up. I have searched and read quite a lot appnotes from SOA limiting to optimizing gate drive but still experience counts. So if anybody out there please help. By the way mat I don' t want a word from your source can you at least guide on the flow.

Regards

Sougata

[mat janssen]

I will draw a block diagram and I will post it here.

[sougata]

Hi mat,

That would be of great help to all the pic-ers here.

Regards

Sougata

[mat janssen]

Here is the block diagram for the output stage.
When you use the SG3524 at the inputstage to make the 320V dc out of the 24Volts.
I will also make a block diagram for the sw but that will take a while.

[mat janssen]

It is very hard for me to make a flowchart of the program without telling how the programm works. So here is a small tekst.
There is a table of 200 numbers what is the pulse width of the pwm.
Timer 1 is loaded with a 16 bit number eg $FE5F.
every interrupt the PWM gets int new number out of the table.
The table number is set to the new number (old number + 1)
if number => 200 then number = 0..

I will look if it is a problem to post the table. If not then I will post the data of the table.

[sougata]

Hi Matt,

I will work the other way round. Rather I would try to post a flow chart (I am not so good at it) so that you and other members can go through it to detect any possible flaws or betterment suggestions. BTW thanks for the block. I was out-of town hence the delay in reply

Regards

Sougata

[mat janssen]

Normaly I also make the flowdiagram first and then write the program and when it is a simple aplication i don't make a flowdiagram.This program was made a few years ago so I have to look to the comment and in that time I did not make a flowchart.
Here is the data of the pwm of a sine wave in 200 steps.

128,132,136,139,143,147,150,154,158,161,165,169,17 2,176,179,182,186,189,192,195,
199,202,204,207,210,213,215,218,220,223,225,227,22 9,231,233,235,237,238,240,241,
242,243,244,245,246,247,247,247,248,248,248,248,24 8,247,247,247,246,245,244,243,
242,241,240,238,237,235,233,231,229,227,225,223,22 0,218,215,213,210,207,204,202,
199,195,192,189,186,182,179,176,172,169,165,161,15 8,154,150,147,143,139,136,132,
128,124,120,117,113,109,106,102, 98, 95, 91, 87, 84, 80, 77, 74, 70, 67, 64, 61,
57, 54, 52, 49, 46, 43, 41, 38, 36, 33, 31, 29, 27, 25, 23, 21, 19, 18, 16, 15,
14, 13, 12, 11, 10, 9, 9, 9, 8, 8, 8, 8, 8, 9, 9, 9, 10, 11, 12, 13,
14, 15, 16, 18, 19, 21, 23, 25, 27, 29, 31, 33, 36, 38, 41, 43, 46, 49, 52, 54,
57, 61, 64, 67, 70, 74, 77, 80, 84, 87, 91, 95, 98,102,106,109,113,117,120,124

The data is the on period of the pwm.