PID-filter routine (2nd try).

[HenrikOlsson]

Thanks Walter,
That's its biggest drawback I'd say - the information about it being scattered around several threads on the CNCZone, there are some links in that thread you posted that will take you to other threads about it. There's also some info in this Wiki

As you probably figured it's not a comercial drive, it was developed by a CNCZone member called Kreutz in effort to get a DIY drive for high(ish) voltage motors where the original UHU-circuit failed to deliver. Kits were made (and probably IS) available by Paul Harshman (tenmetalman) and Irfan Ulla, also on CNCZone at very reasonable prices.

Being involved since the early stages of the HP-UHU's life I know it pretty well so if you have specific questions regarding it fire away and I'll do my best to answer them. Perhaps it's better to keep it separate from this thread though.

Thanks!
/Henrik.

EDIT: Thank you for embedding the video by the way!

[Ioannis]

Here is my first try on PID control. Obviously failed...

At the attached schematic is the part of the circuit, essentialy a Voltage stabilizer. The PWM from the PIC drives the Power stage while from the output a voltage sample is returned to the ADC.

Unfortunately there is no control at all. When Setpoint is 0 or 1023 the output is always high (pid_out is 511).

Also I noticed that Direction bit is high when Voltage sample is higher than Setpoint. Is this correct?

Test PIC is F887 driving the internal HPWM.

'**************************************************************************
'**************************************************************************
'**		
'**		PWM Controller with voltage level feedback
'**
'**     21.11.2010, v.1.0
'**
'**     PID Control by Henrik Olsson
'**************************************************************************
'**************************************************************************

DEFINE OSC 8

OSCCON = %01110001 'SET SYSTEM CLOCK SWITCH BIT

;----- Configuration bits ------------------------------------------------

@Line1 = _DEBUG_OFF & _LVP_OFF & _FCMEN_OFF & _IESO_OFF & _BOR_ON
@Line2 = _CP_OFF & _MCLRE_OFF & _PWRTE_ON & _WDT_ON & _INTRC_OSC_NOCLKOUT

@ __CONFIG _CONFIG1, Line1 & Line2

@ __CONFIG _CONFIG2, _WRT_HALF & _BOR40V

            	
PORTA=0:PORTB=0:PORTC=0:PORTD=0:PORTE=0

TRISA=%00101101
TRISB=%00000000
TRISC=%10000000
TRISD=%00000011
TRISE=%00000000

OPTION_REG.0=1		'PSA0 PRESCALER SELECT 1:1 TO 1:256
OPTION_REG.1=1		'PSA1
OPTION_REG.2=1		'PSA2
OPTION_REG.3=0		'PRESCALER TO: 1->WDT, 0->TMR0
OPTION_REG.4=0		'T0SE SOURCE EDGE 1->H TO L, 0->L TO H
OPTION_REG.5=0		'T0CS 1->FROM RA4, 0->FROM INT. CLOCK
OPTION_REG.6=0		'INT EDGE SELECT 0->H TO L, 1->L TO H
OPTION_REG.7=0		'PULL UP 1->DISABLE, 0->ENABLE

WPUB = %00111111

'DEFINE HSER_RCSTA 90h
'DEFINE HSER_TXSTA 24h
'DEFINE HSER_BAUD 19200
'DEFINE HSER_CLROERR 1 ' Clear overflow automatically

'************************* Define LCD parameters

ADCON0 = %11000001
ADCON1 = %10000000	'Set PORTA/E analog/digital, right justify result
ANSEL  = %00101101  'lower port A as Analog input
ANSELH = %00000000  'all others Digital inputs

DEFINE ADC_BITS 10  'Number of bits in Adcin result
DEFINE ADC_CLOCK 3  'ADC clock source (rc = 3)
DEFINE ADC_SAMPLEUS 50
                     
but_0           var portd.0
but_1           var portd.1


'**************************************************************************
'****
'****                            Initialization
'****
'**************************************************************************
clear

ADValue VAR WORD                     '<---This is your variable.
Setpoint VAR WORD                    '<---This is your variable.
Direction var PortB.7                '<---Direction bit to motor driver 

p_gain      var word
i_gain      var word
d_gain      var word

Setpoint=200

INCLUDE "incPIDv1.5.pbp"                 'Include the PID routine.

    'These variables are declared by the incPID routine but
    'the user needs to assign values to them.
'    pid_Kp = $0700                     'Set Kp to 7.0
'    pid_Ki = $0080                     'Set Ki to 0.5
'    pid_Kd = $0225                     'Set Kd to 2.14
    pid_Ti = 8                         'Update I-term every 8th call to PID
    pid_I_Clamp = 100                  'Clamp I-term to max ±100
    pid_Out_Clamp = 511                'Clamp the final output to ±511
     
  Start:
    Gosub analog                        'Get speed from tacho and setpoint pot - NOT SHOWN HERE.
    
    pid_Kp=p_gain:pid_Ki=i_gain:pid_Kd=d_gain
                                     
    pid_Error = Setpoint - value     'Calculate the error

    Gosub PID                          'Result returned in pid_Drive

    Direction = pid_Out.15             'Set direction pin accordning to sign
    pid_Out = ABS pid_Out              'Convert from two's comp. to absolute
    HPWM 1, pid_Out, 500             'Set PWM output
    
    'Just for monitoring
    serout2 portc.6,16468, [27,"[10;0H","P:",dec5 p_gain,"  I:",dec5 i_gain,"  D:",dec5 d_gain,"  PID out:",#pid_out,"    ",27,"[12;0H","Vout:",dec5 value,"  SP:",dec5 setPoint,"  pid_err:",dec5 pid_error, 27,"[14;0H","Direction: ",#direction]

Goto Start                           '...and do it again.

analog:
    adcin 0,value
    gosub average
    adcin 2,p_gain
    p_gain=p_gain<<2
    adcin 3,i_gain
    i_gain=i_gain>>2
    adcin 4,d_gain
    d_gain=d_gain<<2
    
    'Two digital inputs for setting Setpoint level
    if !but_0 then
        if Setpoint>0 then
            setpoint=setpoint-2
        endif
    endif
    if !but_1 then
        if Setpoint<1021 then
            setpoint=setpoint+2
        endif
    endif 
return

END

I am using 3 Analog inputs to set the P,I,D values as it is clear from the analog subroutine.

Whatever the values the pid_out stays at 511 and plays a litle at the point where Setpoint is almost equal to the Vout level.
Any inputs welcome.

Ioannis

[Darrel Taylor]

Ioannis,

I think you need to limit the pid_Out values to only positive numbers, and discard the negative values instead of converting them to positive ones.

The way you have it ... the more it tries to reduce the voltage, the higher the output goes.

After it gosubs to the PID routine ... Try this ...

    IF pid_Out.15 THEN pid_Out = 0   ' limit to positive values
    HPWM 1, pid_Out, 500             'Set PWM output

[HenrikOlsson]

Hi Ioannis,
I'll just second what Darrel said. For unidirectional control, ie when you can only apply more or less power, not remove power from your "plant" you can't have the output swing negative (which the ABS convert to positive again).

The example was for controlling a motor where the direction signal basically controls the polarity and the applied torque is controlled by a PWM signal corresponding to the absolute value of the PID signal. That way torque can be applied in both directions.

In your case you can only apply more or less power, you can't 'reverse' or remove 'power'. Because of that you can't allow negative 'drive'.

As fir the polarity of the direction bit, that's just a matter of matching it to the hardware I used at the time. If I reversed the polarity of the motor I'd have to reverse the "polarity" of the direction signal. Again, you don't need it in this application.

/Henrik.

[Ioannis]

Ok, thanks both. I was stupid.

Now, I 've got a wonderful oscillator!

No matter the level of P,I,D (except for 0) it does oscillate.

I suppose it is a matter of tuning, but even with the trimmer as analog inputs to the P,I,D variables, it seems hard to fine tune it.

When I think I done it, after a power cycle it start again at a rate of 2-5Hz.

Ioannis

[Darrel Taylor]

Whatever the values the pid_out stays at 511

Oh, and clamp the output to 255 for the HPWM command.

You may want to use 10-bit PWM for finer control.

[Ioannis]

Hi Darrel.
Yes I did clamp the output to 255 although it was not mentioned in my previous post.

You may want to use 10-bit PWM for finer control.

Is this possible with PBP or do I have to mess directly with the PIC registers?

My next step will be to use MiBAM, as I do not have hardware PWM on the final PIC.

Ioannis