6 HPWM signal generation with PIC18F4431

[pxidr84]

Okay, the code is now capable to calculate 3 sine waves (one for each phase).

I can modify the frequency (by increasing or decreasing freqdiv), but I've difficulties to set a phase angle (0-120-240° for U, V and W respectively) and I've difficulties to set a sinus amplitude (for exemple, if I want a 0-50% dutycycle, I will write uduty=uduty*0.5, but PBP does not support float maths).

Thanks for your help. I use Darrel Taylor's interrupt system for sine-wave generation loop.

'PIC initialization
DEFINE LOADER_USED 1
DEFINE OSC 40      


'DT interrupt system include
INCLUDE "DT_INTS-18.bas"     ' Base Interrupt System
INCLUDE "ReEnterPBP-18.bas"  ' Include if using PBP interrupts


'PWM calculation variables
uduty VAR WORD     'U phase duty
vduty VAR WORD     'V phase duty
wduty VAR WORD     'W phase duty
t VAR byte         'Incremental value


'Inverter U/F variables
freqdiv var WORD   'Frequency diviser
FREQdiv=0          'Range : 0-65535


'Port registers configuration
PORTB=%0          ' Clear ports
TRISB=%11000000   ' PWM 0,1,2,3,4,5 outputs

                            
'PCPWM registers configuration
DTCON=%110        ' Deadtime (600ns)
PTCON0=%100       ' 1:1 postscale, Fosc/4 1:1 prescale, free running mode
PTCON1=%10000000  ' PWM time base is ON, counts up, 19.45kHz/4
PTPERL=%0         ' PWM low-side
PTPERH=%1         ' PWM high-side

	
'PWM registers configuration
PWMCON0=%1000000  'PWM 0,1,2,3,4,5 set in pair mode
PWMCON1=%1        'PWM timer sync configuration


'Interrupt processor
ASM
INT_LIST  macro    ; IntSource, Label, Type, ResetFlag
        INT_Handler   TMR1_INT,  _pwmint,   PBP,  yes
    endm
    INT_CREATE     ; Creates the interrupt processor
ENDASM


'Timer configuration
T1CON=%10000001            ; Prescaler = 1:1, TMR1ON, 16-bit counter
@ INT_ENABLE  TMR1_INT     ; Enable Timer 1 interrupts


'Main loop
mainlp:

    pause 1000

goto mainlp

'PWM calculation and update interrupt
pwmint:
t=0
    
    for T=0 to 255 step 1

    'Frequency diviser
    pauseus freqdiv

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

    'PWM U phase update
    PDC0L=uduty.LOWbyte
    PDC0H=Uduty.HIGHByte

    'PWM V phase update
    PDC1L=vduty.LOWbyte
    PDC1H=vduty.HIGHByte

    'PWM W phase update
    PDC2L=wduty.LOWbyte
    PDC2H=wduty.HIGHByte

    next t

@ INT_RETURN

[HenrikOlsson]

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

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.

[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).