6 HPWM signal generation with PIC18F4431

[pxidr84]

Hi there,

I'm currently making a 3-phase variable frequency drive.
I'm using the PIC18F4431 (5V - 40 pins - 40MHz), who's perfect for motor control (8 hardware PWM outputs).

Datasheet : http://ww1.microchip.com/downloads/e...Doc/39616d.pdf

I like to generate 3 high-side hardware PWM (HU, HV, HW) and 3 low-side hardware PWM (LU, LV, LW - same as HU, HV, HW but inverted with a low deadtime) for fed my high and low-side IGBTs.
I would like a PWM carrier frequency between 2 and 20kHz (approx.)

Picbasic Pro seems to use CCP1 and CCP2 modules with "HPWM" command, but I get only 2 HPWM outputs.
I have no idea how to use these hardware PWM modules on my PIC.

Thanks for your help.

[HenrikOlsson]

Hi,
PBP (the HPWM command) only suports PWM thru the standard CCP modules, you'll have to set up the PWM registers manually. A quick search for 18F4431 on the forum brings up a couple of threads, this one for example, contains some sample code from Bruce which may serve as a starting point.

[pxidr84]

Hi,
PBP (the HPWM command) only suports PWM thru the standard CCP modules, you'll have to set up the PWM registers manually. A quick search for 18F4431 on the forum brings up a couple of threads, this one for example, contains some sample code from Bruce which may serve as a starting point.

Thanks, I will take a look.

[pxidr84]

Okay, I've a little bit modified the Bruce's program.
It runs well in ISIS Proteus with my defined duty cycles, and all of the 6 PWM outputs works.

But there is a little problem :


As you can see, U and W phases are working properly, but not the V phase (the low-side PWM is not inverted like the others).

Here's my modified code :

DEFINE LOADER_USED 1
DEFINE OSC 20
    
    ' At 20MHz, to figure a PWM frequency of 19.455kHz
    ' TPWM = time period of PWM frequency
    ' PTPER = 12-bit period register PTPERL and PTPERH
    ' PTMRPS = PWM time base prescaler
    ' 
    '        (PTPER+1)*PTMRPS  257
    ' TPWM = ----------------  =  ------------ = 0.0000514 
    '             Fosc/4            5000000
    '
    ' Frequency = 1/TPWM = 1/0.0000514 = 19.455kHz
    '
    ' PWM resolution (bits resolution for duty cycle)
    '
    '              log(20MHz/19.455kHz)    3.01
    ' Resolution = ------------------ = ----------- = 10 bits
    '                    .301              .301
      
    ' so we'll need a word sized var for Duty
uduty VAR WORD
vduty VAR WORD
wduty VAR WORD
   
    PORTB = 0               ' clear port latch
    TRISB = %11000000       ' PWM0,1,2,3,4,5 outputs
    
    TRISC = 2         ' RC1 = FLTA input (ground RC1 to halt PWM)
                            ' RC1 should be pulled high for normal PWM operation
                            ' when fault A is enabled.
    ' PCPWM init
    DTCON = %00000101       ' ~500nS dead-time (for complementary outputs only)
    PTCON0 = %00000100      ' 1:1 postscale, Fosc/4 1:1 prescale, free running mode
                            ' PTCON0 = %00000100 would give 19.45kHz/4
    PTPERL = 0              ' 
    PTPERH = 1              ' PTPER = $0100 or 256d for ~19.45kHz
	
    ' PWM4,5 independent, PWM0,1,2,3 complementary
    PWMCON0 = %01010100     ' PWM[5:0] outputs enabled
    PWMCON1 = 1             ' updates enabled, overrides sync w/timebase
    PTCON1 = %10000000      ' PWM time base is ON, counts up
    FLTCONFIG = %00000011   ' enable fault A, cycle-by-cycle mode


'Phases duty test
uduty = 800              ' ~50%
vduty = 500
wduty = 300
        
pwmlp: ' PWM update loop

'PWM U phase 
PDC0L = uduty.LowByte
PDC0H = uduty.HighByte

'PWM V phase
PDC1L = vduty.LowByte
PDC1H = vduty.HighByte

'PWM W phase  
PDC2L = wduty.LowByte
PDC2H = wduty.HighByte

goto pwmlp

Thanks in advance for any advice.

[HenrikOlsson]

Hi,
Are you sure it's not the W-phase output that isn't complementary?

Look at the PWMCON0 register, you have it set to %01010100 which means that PWM0 and PWM1 is in complentary mode while PWM2 (the W-phase according to your code) is in independant mode.

/Henrik.

[pxidr84]

Hi,
Are you sure it's not the W-phase output that isn't complementary?

Look at the PWMCON0 register, you have it set to %01010100 which means that PWM0 and PWM1 is in complentary mode while PWM2 (the W-phase according to your code) is in independant mode.

/Henrik.

Thanks a lot, you guided me on the right way.
I've read the datasheet, and especially the "PWMCON0" register description. I've modified the value to PWMCON0 = %01000000, and now the 3 phases are working very well (the low-side V phase is now inverted properly).

Now, I've to modify the duty according to a sinus function. I think about it.

[oswalam]

Which Simulator you people are using for viewing waveforms???? Thanks