modelPIDHysteresis

PID controller with anti-windup, output limiter and output hysteresis

Extends from Modelica.Blocks.Interfaces.SVcontrol (Single-Variable continuous controller).

Information

Block of a controller for set point tracking with a hysteresis element that switches the controller on and off.

If the controller is off, and the control error becomes larger than eOn, then the controller switches to on and remains on until the control error is smaller than eOff. When the controller is on, the set point tracking can be done using a P-, PI-, or PID-controller. In its off-mode, the control output is zero. Thus, the parameters yMin and yMax are used to constrain the output of the controller during its on mode only. This can be used, for example, to modulate a device between 0.3 and 1.0, and switch it to off when the control error is small enough.

Parameters

Type	Name	Default	Description
Hysteresis
Real	eOn	1	if off and control error > eOn, switch to set point tracking
Real	eOff	-eOn	if on and control error < eOff, set y=0
Boolean	pre_y_start	false	Value of hysteresis output at initial time
Set point tracking
Modelica.Blocks.Types.SimpleController	controllerType	Modelica.Blocks.Types.SimpleController.PID	Type of controller
Real	k	1	Gain of controller
Modelica.SIunits.Time	Ti		Time constant of Integrator block
Modelica.SIunits.Time	Td		Time constant of Derivative block
Real	yMax	1	Upper limit of output
Real	yMin	0	Lower limit of output
Real	wp	1	Set-point weight for Proportional block (0..1)
Real	wd	0	Set-point weight for Derivative block (0..1)
Real	Ni	0.9	Ni*Ti is time constant of anti-windup compensation
Real	Nd	10	The higher Nd, the more ideal the derivative block
Boolean	reverseAction	false	Set to true to enable reverse action (such as for a cooling coil controller)
Initialization
Modelica.Blocks.Types.InitPID	initType	Modelica.Blocks.Types.InitPID.DoNotUse_InitialIntegratorState	Type of initialization (1: no init, 2: steady state, 3: initial state, 4: initial output)
Real	xi_start	0	Initial or guess value value for integrator output (= integrator state)
Real	xd_start	0	Initial or guess value for state of derivative block
Real	y_start	0	Initial value of output
Advanced
Boolean	strict	true	= true, if strict limits with noEvent(..)

Connectors

Type	Name	Description
RealInput	u_s (from SVcontrol)	Connector of setpoint input signal
RealInput	u_m (from SVcontrol)	Connector of measurement input signal
RealOutput	y (from SVcontrol)	Connector of actuator output signal

Components

Type	Name	Description
LimPID	PID	Controller for room temperature
Modelica.Blocks.Logical.Hysteresis	hys	Hysteresis element to switch controller on and off
Modelica.Blocks.Math.Feedback	feeBac

Revisions

September 29, 2016, by Michael Wetter:
Removed parameter limitsAtInit because it is no longer used in the PID controller.
April 13, 2016, by Michael Wetter:
Set zer(final k=0) and made swi, zer and zer1 protected which they are also for IBPSA.Controls.Continuous.PIDHysteresis. These changes are not backwards compatible.
March 15, 2016, by Michael Wetter:
Changed the default value to strict=true in order to avoid events when the controller saturates. Also assigned propogated values to be final. This is for issue 433.
February 24, 2010, by Michael Wetter:
Changed PID controller from Modelica Standard Library to PID controller from Buildings library to allow reverse control action.
October 2, 2009, by Michael Wetter:
Fixed error in default parameter eOn. Fixed error by introducing parameter Td, which used to be hard-wired in the PID controller.
February 14, 2009, by Michael Wetter:
First implementation.