ControlPI

ControlPI (FB)

FUNCTION_BLOCK ControlPI

Short description

Proportional-integral acting controller (PI controller) The direction of action (inverted / direct) is also adjustable. Typical application: control loops with actuators that have no storing character.

Representation

Interfaces

Inputs

Name	Data type	Value range	Initial value	Function
rX	REAL			Analog measured value
rW	REAL			Analog setpoint
xEn	BOOL			Enable of the controller

Outputs

Name	Data type	Value range	Initial value	Function
rY	REAL		0.0	Controller output signal
rDiff	REAL			Control deviation
rPartP	REAL			Proportional part of the output signal
rPartI	REAL			Integral part of the output signal
xLimitActive	BOOL			Status - limit exceeded

Setpoints / parameters

Name	Data type	Value range	Initial value	Function
rMax	REAL		100.0	Upper absolute limit of the output signal
rMin	REAL		0.0	Lower absolute limit of the output signal
rTn	REAL	0.0 …	200.0	Reset time in seconds
rKp	REAL	0.0 …	2.0	Gain factor
rOffset	REAL		0.0	Offset
rInitValue	REAL		0.0	Initialization value for the output signal
rYDisabled	REAL		0.0	Disabled value
eAction	eControlMode		eControlMode.Inverted	Direction of action of the controller (Inverted, Direct)
eManModeN	eManNum		eManNum.Auto	Operating mode for the controller output signal
rManValue	REAL			Output signal in manual mode

Function description

General

This function block contains a proportional-integral acting controller (PI controller). The controller's output signal rY is calculated when the controller is enabled (xEn = TRUE) and in the controller's automatic operating mode (eManModeN = eManNum.Auto) as follows: Output signal: rY = Proportional part + Integral part Proportional part: Proportional part = rKp * control deviation Control deviation: Control deviation = rW - (rx + rOffset) [Direction of action - Inverted: eAction = eControlMode.Inverted] Control deviation = rX - ( rW + rOffset ) [Direction of action - Direct: eAction = eControlMode.Direct] Integral part: Integral part = (Proportional part * (sampling time / reset time)) + Integral part (t-sampling time) Legend: t-sampling time … time point that was one sampling time before the current time t Sampling time … time interval between two calls of the function block t … current time

Control / Properties - reset time rTn

It may only take values > 0. rTn >>> Sampling time: The integral part remains constant Control deviation = 0: The integral part remains constant Depending on the controller's direction of action eAction the measured and set values are determined as follows:

| **eAction** | Control deviation | Function | |-------------------------|-------------------------------|-----------------------| | eControlMode.Inverted | *rW* - ( *rx* + **rOffset** ) | Direction of action - Inverted | | eControlMode.Direct | *rX* - ( *rW* + **rOffset** ) | Direction of action - Direct |

Integral part

The integral part is limited both upwards and downwards by the following absolute limits: Upper limit = rMax - Proportional part Lower limit = rMin - Proportional part

Enable input xEn

If the enable input is not active (xEn = FALSE) the disabled value rYDisabled is transferred to the output rY (precondition: eManModeN = eManNum.Auto) and limited by the absolute limits. The integral part is set to 0.0. If the enable input is active (xEn = TRUE) the output signal is calculated according to the above formula and transferred to the output rY (precondition: eManModeN = eManNum.Auto) and limited by the absolute limits. On each rising edge of the enable input xEn the control process is restarted.

Restart of the controller

On each rising edge of the enable input xEn the control process is restarted. (Preconditions: eManModeN = eManNum.Auto and xEn = TRUE) The integral part is set to the difference between rInitValue and the proportional part.

Control deviation rDiff

The control deviation corresponds to the value of the control deviation according to the above formula.

Proportional part of the output signal rPartP

This output always provides the proportional part of the output signal, see description above.

Integral part of the output signal rPartI

This output always provides the integral part of the output signal, see description above.

Absolute limits rMin and rMax

The controller's output signal rY is limited downwards by the absolute limit rMin and upwards by rMax . The absolute limit rMin is set to the current value of rMax - 0.1 if it is >= the current value of rMax . The only exception is manual operation for the controller output signal (eManModeN = eManNum.Man).

Status - limit exceeded xLimitActive

The limit-exceeded status is activated (xLimitActive = TRUE) if a limit is exceeded upwards or downwards (xEn = TRUE). The limit-exceeded status is not activated (xLimitActive = FALSE) if no limit is exceeded or the enable signal is deactivated (xEn = FALSE). A limit is considered exceeded if the controller's output signal rY reaches / exceeds the upper limit rMax or reaches / falls below the lower limit rMin .

Operating mode for the controller output signal eManModeN

The parameter eManModeN allows switching the output signal rY from automatic to manual mode and vice versa. In manual mode the output signal rY takes over the output signal in manual mode rManValue. The integral part is set to the difference between rInitValue and the proportional part.

eManModeN	rY	Function
eManNum.Auto	signal according to formula / disabled value	Automatic mode - output signal
eManNum.Man	rManValue	Manual mode - output signal

Codesys

InOut:

Scope	Name	Type	Initial
Input	rX	REAL
Input	rW	REAL
Input	xEn	BOOL
Input Const	rYMax	REAL	100
Input Const	rYMin	REAL	0
Input Const	rTn	REAL	200
Input Const	rKp	REAL	2
Input Const	rOffset	REAL	0
Input Const	rInitValue	REAL	0
Input Const	rYDisabled	REAL	0
Input Const	eAction	eControlMode	eControlMode.Inverted
Input Const	eManModeN	eManNum	eManNum.Auto
Input Const	rManValue	REAL
Output	rY	REAL	0
Output	rDiff	REAL
Output	rPartP	REAL
Output	rPartI	REAL
Output	xLimitAktiv	BOOL