Sine wave power inverter

[mincing]

Hi sougata,

Hope everything is fine !

I have difficulty in reading the feed back and adjusting the PWM.
Presently I am reading a DC proportional to the output voltage.PWM is continuously adjusted and checked with the feed back.
However the moment ckt enter the closed loop out put becomes unstable.It keeps changing continuously.

Could you please throw some light on this./

Thanks,

[sougata]

Hi,

I think I have not come across any schematics, code snippets. I don't even know which PIC at what Fosc you are using. May be I missed something as I am not regularly visiting this forum. Details...Please.

[mincing]

Dera Sougata,

I have attached a simple block diagram of Inverter I am working on.

Hope this would give an Idea of my circuit.

Kindly suggest what should be feed back routine.
We are using C with MPLab.

Thanks and waiting for your reply

[sougata]

Hi,

I am not an expert on C (uNsUrE of my expertise of PBP aswell ) so may be cannot help much with the code (which has not been posted ) but here are some tips.

According to your schematic:

1. Feedback is from one cycle only (not recommended)
2. Driving through inverters means both MOSFETs doing PWM (wasting energy)
3. Use Flux reset when changing phase
4. Be sure that the computed PWM is not eating up cycles and resulting in uneven spread of the modulating PWM

Please report what happens when no feedback is used. Use a lower duty cycle lookup table to ensure that your MOSFETs are not fried due to full drive. Or use a lower input supply to the Bridge.

[Navneet Vinaik]

Hi,

I am not an expert on C (uNsUrE of my expertise of PBP aswell ) so may be cannot help much with the code (which has not been posted ) but here are some tips.

According to your schematic:

3. Use Flux reset when changing phase
.

Dear Sougata,

What is flux reset when changing phase, can you please give me some more information about it.

Regards,

Navneet

[mincing]

I was just trying to understand this concept of flux imbalance control.

However I could not make out how we do it practically.Do we have to implement it in software or hardware.

I observed lot of noise while the current wave drops tozero and below.NO load voltage waveform is a correct sinewave.

Kindly tell me how to implement the flux balance control.

regards,

Hi,

I am not an expert on C (uNsUrE of my expertise of PBP aswell ) so may be cannot help much with the code (which has not been posted ) but here are some tips.

According to your schematic:

1. Feedback is from one cycle only (not recommended)
2. Driving through inverters means both MOSFETs doing PWM (wasting energy)
3. Use Flux reset when changing phase
4. Be sure that the computed PWM is not eating up cycles and resulting in uneven spread of the modulating PWM

Please report what happens when no feedback is used. Use a lower duty cycle lookup table to ensure that your MOSFETs are not fried due to full drive. Or use a lower input supply to the Bridge.

[mincing]

When feed back is not used the out put is pure sinewave.
."

However I could not make out how we do it practically.Do we have to implement it in software or hardware.

I observed lot of noise while the current wave drops tozero and below.NO load voltage waveform is a correct sinewave.

I would also like to understand " I was just trying to understand this concept of flux imbalance control

Kindly tell me how to implement the flux balance control.

regards,

Hi,

I am not an expert on C (uNsUrE of my expertise of PBP aswell ) so may be cannot help much with the code (which has not been posted ) but here are some tips.

According to your schematic:

1. Feedback is from one cycle only (not recommended)
2. Driving through inverters means both MOSFETs doing PWM (wasting energy)
3. Use Flux reset when changing phase
4. Be sure that the computed PWM is not eating up cycles and resulting in uneven spread of the modulating PWM

Please report what happens when no feedback is used. Use a lower duty cycle lookup table to ensure that your MOSFETs are not fried due to full drive. Or use a lower input supply to the Bridge.

[sougata]

Hi,

I am not qualified enough to explain. So I would suggest you to go through these links.

http://techtrain.microchip.com/webse...MPS_090106.pdf

http://www.intersil.com/data/an/AN1246.pdf

In my software I do this while changing phase.

1. Switch off the High Side MOSFET
2. Wait for the dead time.
3. Switch on both low side (flux reset)
4. Switch off both low side
5. Switch on the other High Side
6. Start PWM on the corresponding low side.

If you are not getting sinewave in your output while you apply feedback then its your correction algo that is not working. I cannot release our code here without permission from pramod but there is certainly an example of a Sinewave Inverter using C which uses a delta lookup scheme to make computations easier. Here is the link

http://rapidshare.com/files/43362188/C_Sinewave.rar

Hope this helps.

[mincing]

Dear Sougata,

It was a great help indeed.


C-sinewave has lots of info.

However I would like to know little back ground.Thewre are three tables used ,one for sine wave,one reference sine wave and one error/delta correction.I was not able to understand how he arrive at those tables and the values in the tables.Little more deep in to back ground would probably a great help.

thanks very much,

[mincing]

Also I would like to know what is the nominal DC volatge used.in that scheme.