6 HPWM signal generation with PIC18F4431

[pxidr84]

Hi,
How about:

'PWM U phase calculation
uduty=((sin(t)+128)*4)  
      
'PWM V phase calculation
vduty=((sin(t+85)+128)*4)
    
 'PWM W phase calculation
wduty=((sin(t+170)+128)*4

Attachment 5180

It's true that you can't mutliply by 0.5 but you can divide by 2. You can also use the ** operator to multiply by units of 1/65536 so instead of doing x=y*0.72 you do x=y**47186 (where 47186 comes from 65536*0.72)

/Henrik.

Thanks a lot for your tips
Just a question : what simulator are you using ? (because my ISIS Proteus gives me very weird results):



It's your code with angle phase offsets...

[HenrikOlsson]

Hi,
I'm not using a simulator, I just sent the values to the PC and plotted them with EXCEL. Here's the exact code I used to test with:

DEFINE LOADER_USED 1
DEFINE OSC 20
DEFINE HSER_BAUD 19200
 
i VAR BYTE
T VAR BYTE
uDuty VAR WORD
vDuty VAR WORD
wDuty VAR WORD
 
Main:
For i = 0 to 2   'Make three periods
  T=0
    
   for T=0 to 255
   ' PWM U phase calculation
   uduty=((sin(t)+128)*4)  
      
   ' PWM V phase calculation
   vduty=((sin(t+85)+128)*4)
    
   ' PWM W phase calculation
   wduty=((sin(t+170)+128)*4)
   
   HSEROUT [DEC uDUTY, ",", dec vDUTY, ",", dec wDUTY, 13]
  next
NEXT
WereDone:
Goto WereDone

Try removing C3, C6 and C8 to start with.

[pxidr84]

Hi,
I'm not using a simulator, I just sent the values to the PC and plotted them with EXCEL. Here's the exact code I used to test with:

DEFINE LOADER_USED 1
DEFINE OSC 20
DEFINE HSER_BAUD 19200
 
i VAR BYTE
T VAR BYTE
uDuty VAR WORD
vDuty VAR WORD
wDuty VAR WORD
 
Main:
For i = 0 to 2   'Make three periods
  T=0
    
   for T=0 to 255
   ' PWM U phase calculation
   uduty=((sin(t)+128)*4)  
      
   ' PWM V phase calculation
   vduty=((sin(t+85)+128)*4)
    
   ' PWM W phase calculation
   wduty=((sin(t+170)+128)*4)
   
   HSEROUT [DEC uDUTY, ",", dec vDUTY, ",", dec wDUTY, 13]
  next
NEXT
WereDone:
Goto WereDone

Try removing C3, C6 and C8 to start with.

In reality, I think that my RC filter in Proteus is bad.

If I watch the raw PWM outputs, it seems perfectly good (with correct phase angles and duty cycles). However, in extreme duty (like 0 or 1023), the PWM "jumps" (like before, I think it's a sim issue, I will try the PIC in the real life with an oscilloscope).

In other words, my code is working quite well now, thanks for the "**", I didn't know this operator before, until now.

[HenrikOlsson]

Hi,
Like I said in an earlier post, I think it is the dead-time insertion that makes the waveform "jump" at the extreme ends. Do try it with real hardware and let us know how it goes. Just remember that if you low-pass filter the PWM to watch it on a scope might not see any artifacts introduced by the deadtime insertion - if indeed that is what's causing it. So make sure you watch the "raw" PWM signals as well in order to see if it behaves as in the simulator.

As a simple test, try removing the deadtime insertion from the code and see if it still looks strange in the simulator.

/Henrik.

[pxidr84]

Hi,
Like I said in an earlier post, I think it is the dead-time insertion that makes the waveform "jump" at the extreme ends. Do try it with real hardware and let us know how it goes. Just remember that if you low-pass filter the PWM to watch it on a scope might not see any artifacts introduced by the deadtime insertion - if indeed that is what's causing it. So make sure you watch the "raw" PWM signals as well in order to see if it behaves as in the simulator.

As a simple test, try removing the deadtime insertion from the code and see if it still looks strange in the simulator.

/Henrik.

Yes, of course I've readed your post above. I've modified the code (add +3 to the end of each line), now the PWM signal doesn't "jump" anymore.
However, if I remove the deadtime or even modify it, the jumpy PWM remains.

Now signals are better, but sine are not perfect for the highest frequencies, I think that my low-pass filter hasn't good R and C values (1k and 1000nF).

[senertek]

hi ,
I have already developped many ac inverters range 0.75 kw to 915 kw..with . I seen this thread ..it s very good..to see picbasic projects in this field....
Designing one 3 phase ac inverter is not easy project...you must know many kind of points about high voltage igbt , drivers , dcbus topologys ,emc ,emi , multi tasking etc...(it take many years)
If you want , I can help for your project..
I can try your codes with my high voltage kits , igbt driver modules ...and inform you ..codes works or not...

savas

[pxidr84]

hi ,
I have already developped many ac inverters range 0.75 kw to 915 kw..with . I seen this thread ..it s very good..to see picbasic projects in this field....
Designing one 3 phase ac inverter is not easy project...you must know many kind of points about high voltage igbt , drivers , dcbus topologys ,emc ,emi , multi tasking etc...(it take many years)
If you want , I can help for your project..
I can try your codes with my high voltage kits , igbt driver modules ...and inform you ..codes works or not...

savas

Thanks.

Well, I'm doing studies in electrical engineering, so I've a litte knowledge about this.
I'm using an intelligent IGBT module from STMicroelectronics, the STGIPS20K60 (datasheet : http://www.st.com/internet/com/TECHN...CD00244265.pdf).

No drivers needed (they're integrated), just optocouplers.