ControlPI (FB)¶

FUNCTION_BLOCK ControlPI

Functional Description¶

Proportional integral acting controller (PI controller)

The direction of the action (inverted / direct) is also adjustable.

Typical application: Controlled systems with actuators that do not have a storage character.

Portrayal¶

Interfaces¶

Inputs¶

Name
Datatype

Range

Init-Value

Function

rX REAL
Analog actual value

rW REAL
Analog setpoint

xEn BOOL
Enable the controller

Outputs¶

Name
Datatype

Range

Init-Value

Function

rY REAL 0.0
Output signal of the controller

rDiff REAL
Control deviation

rPartP REAL
proportional component at output signal

rPartI REAL
Integral term at output signal

xLimitActive BOOL
Status - Exceeding the limit value

Setpoints / Parameters¶

Name
Datatype

Range

Init-Value

Function

rMax REAL 100.0
Upper absolute limit value of the output signal

rMin REAL 0.0
Lower absolute limit value of the output signal

rTn REAL 0.0 ... 200.0
Reset time 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
Switch-off 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

Functional Description¶

General¶

This function block contains a proportional-integral acting level (PI controller).
The output signal of the controller rY is calculated as follows when the controller is enabled (xEn = TRUE) and in the controller automatic mode (eManModeN = eManNum.Auto):

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 before the current time t by the sampling time
sampling time ... Time duration between two calls of the function block
t ... current time point

Controlling / Properties - reset time rTn

This may only accept values > 0.
rTn >>> sampling time: The integral part remains constant
Control deviation = 0: The integral part remains constant

Depending on the direction of action of the eAction controller, the actual and setpoint 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 limit values:
Upper limit = rMax - proportional part
Lower limit = rMax - proportional part

Enabling input xEN¶

If the enabling input is not active (xEn = FALSE), the switch-off value rYDisabled is transferred to the output rY
(Requirement: eManModeN = eManNum.Auto) and limited by the absolute limits. The integral part is set to 0.0.

When the enable input is active (xEn = TRUE), the output signal is calculated according to the formula above and transmitted to the output rY
(Requirement: eManModeN = eManNum.Auto) and limited by the absolute limits.

At each rising edge at the enable input xEn the controlling process is restartet.

Restart of the controller¶

At each rising edge at the enable input xEn the controlling process is restartet. (Requirement: 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 formula above.

Proportional part at the signal output rPartP¶

The proportional part of the output signal is always available at this output, see description above.

Integral part at the signal output rPartl¶

The integral part of the output signal is always available at this output, see description above.

Absolute rMin and rMax limits¶

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

Status - limit exceeded xLimitActive¶

The status of the limit value overstepping is activated (xLimitActive = TRUE) if the limit value is exceeded up or down (xEn = TRUE).
The status of the limit value exceedance is not activated (xLimitActive = FALSE) if there is no limit value exceedance or the enable signal is deactivated (xEn = FALSE).

A limit value violation occurs if the output signal of the controller rY reaches/exceeds the upper limit value rMax or
reaches/falls below the lower limit rMin.

Operating mode for the output signal of the eManModeN controller¶

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

eManModeN rY
Function

eManNum.Auto
Signal according to the formula / switch-off value

Automatic operation - Output signal

eManNum.Man rManValue
Manual operation - Output signal

Visualization¶

Information¶

Element
Authors

Date
Version
Notes

Function
Adam Bartod 03.2017 1.0
Initial version

Programming
Adam Bartod 03.2017 1.0
Initial version

Test Jochen Reu 11.2017 1.0
Initial version

Documentation
Jochen Reu 11.2017 1.0
Initial version

Codesys¶

InOut:

Scope	Name	Type	Initial	Comment
Input	rX	REAL		Analog actual value
	rW	REAL		Analog setpoint
	xEn	BOOL		Enable the controller
	rYMax	REAL	100	Upper absolute limit value of the output signal
	rYMin	REAL	0	Lower absolute limit value of the output signal
	rTn	REAL	200	Reset time time in seconds
	rKp	REAL	2	Gain factor
	rOffset	REAL	0	Offset
	rInitValue	REAL	0	initialization value for the output signal
	rYDisabled	REAL	0	Switch-off 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
Output	rY	REAL	0	Output signal of the controller
	rDiff	REAL		Control deviation
	rPartP	REAL		proportional component at output signal
	rPartI	REAL		Integral term at output signal
	xLimitAktiv	BOOL		Status - Exceeding the limit value