PD Control Algorithm

[StudentSA]

Hi,

Im having trouble designing a control algorithm for a temperature controller.

My uC (PIC16F690) has functionality to allow the user to set a "setpoint" and it is integrated with a LM35 Temp Sensor. I read the 10bit A2D channel to get the temperature into a variable TEMP and TEMP+1. The user selected setpoint is stored in variable SETPOINT and SETPOINT+1. The control method works by driving the PWM pin to control the brightness of a globe. This is my control algorithm extract:

CALC_CORR_ACT:								; Determine the required corrective action
											; Subtract Setpoint from TEMP
											; Check if positive
											; If positive Globe on
											; If negative globe brightness down
											; a TEMP b Setpoint
Calculate_Diffrence		
		MOVF	TEMP,W
		SUBWF	SETPOINT,	W
		MOVWF	ERRER
		MOVF	TEMP+1, 	W
		BTFSS	STATUS,		C
		INCFSZ	TEMP+1,		W				; Result was neg
		SUBWF	SETPOINT+1, W
		MOVWF	ERRER+1
		BTFSS	STATUS, 	C
		GOTO	NegativeResult
		BCF		FLAGS,		5
		GOTO	Determine_Error_Range
NegativeResult
		COMF	ERRER+1,F
		BSF		FLAGS,		5				; Indicates a negative result
Determine_Error_Range
		MOVF	ERRER+1, F
		BTFSS	STATUS, Z
		GOTO	ErrorOutOfRange
		BTFSS	FLAGS,5
		GOTO	ErrerIsPos
ErrerIsNeg
		COMF	ERRER,F
		INCF	ERRER,F						; Make Errer Positive
ErrerIsPos
		MOVF	LEVEL4CORR, W
		SUBWF	ERRER,		W
		BTFSC	STATUS,		C
		GOTO	ErrorOutOfRange				; Result Pos so ERRER > 80 ( Level4 ) 
		MOVF 	LEVEL4CORRVALUE,W			; Result Neg so ERRER LESS THAN 80	
		MOVWF	DELTAPWM
		
		MOVF	LEVEL3CORR, W
		SUBWF	ERRER,		W
		BTFSC	STATUS,		C
		GOTO	ErrorInRange				; Result Pos so 80 > ERRER > 40 ( Level4 ) 
		MOVF 	LEVEL3CORRVALUE,W			; Result Neg so ERRER LESS THAN 40
		MOVWF	DELTAPWM		
		
		MOVF	LEVEL2CORR, W
		SUBWF	ERRER,		W
		BTFSC	STATUS,		C
		GOTO	ErrorInRange				; Result Pos so 40 > ERRER > 20 ( Level4 ) 
		MOVF 	LEVEL2CORRVALUE,W			; Result Neg so ERRER LESS THAN 20
		MOVWF	DELTAPWM	
		
		MOVF	LEVEL1CORR, W
		SUBWF	ERRER,		W
		BTFSC	STATUS,		C
		GOTO	ErrorInRange				; Result Pos so 20 > ERRER > 10 ( Level4 ) 
		MOVF 	LEVEL1CORRVALUE,W			; Result Neg so ERRER LESS THAN 10
		MOVWF	DELTAPWM			

		MOVF	ERRER,F
		BTFSC	STATUS, Z
		CLRF	DELTAPWM
		GOTO	ErrorInRange
ErrorInRange
		BTFSC	FLAGS,5
		GOTO  	Errorwasneg					; NEG Error
		MOVF	DELTAPWM,W				
		SUBWF	PWM,F
		BTFSC	STATUS, C
		RETLW	PWM	
		CLRF	PWM
		RETLW	PWM
Errorwasneg	
		MOVF	DELTAPWM,W
		ADDWF	PWM,F
		BTFSS	STATUS,C
		RETLW	PWM
		MOVLW	B'11111111'
		MOVWF	PWM
		RETLW	PWM
ErrorOutOfRange
		BTFSS	FLAGS,5
		GOTO	SetPWMOffAndExit		; Large Positive Error
SetPWMFullAndExit
		MOVLW	B'11111111'
		MOVWF	PWM
		RETLW	PWM
SetPWMOffAndExit
		MOVLW	B'00000000'
		MOVWF	PWM
		RETLW	PWM


SETUP_PWM_DUTY_CYCLE:
		MOVF	PWM,F
		BTFSS	STATUS,Z
		GOTO	PWMNotZero
		BSF		STATUS,RP0				; Bank 1
		BTFSS	TRISC, 5
		BSF   	TRISC, 5
		BCF		STATUS, RP0				; Bank 0
		RETLW	0
PWMNotZero
		MOVF	PWM,W
		MOVWF	CCPR1L                	; 8 MSB of PWM
		BSF		STATUS,RP0				; Bank 1
		BTFSC	TRISC, 5
		BCF   	TRISC, 5
		BCF		STATUS, RP0				; Bank 0
		RETLW	0

Currently my code really does not work "well" .

The functions CALC_CORR_ACT and SETUP_PWM_DUTY_CYCLE are called every two seconds using a timer interrupt.

Basically i am not sure what is the correct way to go about implementing this... I think I need to include a Derivative term to the control.

Any advice is appreciated.

Regards,
StudentSA

 

[be80be]

Check this out it's in basic but he gos in to all the details **broken link removed**

 

[Mosaic]

This worked for me in asm.
**broken link removed**

Edit: Figure 6 flowchart is the key.