Description of the interface to control the environment behavior
Layout of the Control System
The AutotunerPID Toolkit simulates a single SISO control loop, which includes a PID with autotuner,
the plant to be controlled, a lowpass filter and some auxiliary blocks to manage the simulation (for
example change the set-point or perform the autotuning or include a measurement noise).
The main component of the Toolkit is the Simulink file autotunerPID.mdl
The following sections describe the role of each blocks in the model. You can view the
general AutotunerPID Function reference in Function Reference.
The regulator is a subsystem composed by two S-functions: pid_isatd.m
which implements a discrete time ISA-PID and pid_autotuner.m which
takes in charge the autotuning process.
The discrete time ISA-PID includes the filter on the derivative action, the set-point weight (but not the weight
of the derivative action which is fixed to c=0). Moreover the PID
implements antiwindup on lower and higher saturation limits of the actuator and bumpless auto-manual switch. The
structure of this "industrial PID" is more complex than the structure of the "scholastic PID" and it closely
resemble the functioning of regulators used in practice.
The autotuner supervisor, instead, rules out the autotuning process mainly
performing the identification of a FOPDT process model (idareas.m)
or a set of characteristics (pid_autotuner.m)
and the synthesis of the new parameters with the methods described (pid_tuning.m).
Moreover it is possible to constrain the structure of the
regulator to be a PI or a PID, or the structure can be automatically selected
by the supervisor (pid_structure.m).
In particular, the identification experiment includes both step response and
relay response with tunable hysteresis and amplitude.
Plant
The plant is a subsystem which model the process that must be controlled
The structure of the plant has been left open by purpose. The user can thus include his own plant in the
simulator since there is no constrain on it: the plant can be linear or nonlinear, continuous or discrete time and so
on. However, the comparative analysis of a step responses and Bode diagrams
is available only for linear plants (for obvious reasons).
Note The comparative analysis is available only when the model is NOT running and
for linear plants. Moreover the name of the blocks inside the Plant subsystem should not be changed since they are used as
references in the functions performing this analysis
PID Control Panel
The PID Control Panel is implemented through a masked S-function
(autogui.m),
which uses the graphical primitives of the MATLAB environment to create a GUI which has a close feeling to that of a real PID.
The aim of this interface is to provide all the inputs and outputs typical of a real industrial PID.
Environment Panel
The Environment Panel is implemented through a masked S-function
(envgui.m).
It controls the parameter of the simulation which are not under direct control of the user, so that they cannot be
included in the PID control panel. For example a measurement noise or a step on the load disturbance can be included.
Moreover, through the environment control panel, a comparative analysis
of all the autotuning methods can be performed, both in time domain and in frequency domain.
Butterworth Analog Filter
The lowpass Butterworth analog filter in the control loop is used as an antialiasing
filter and also to reduce the effects of the measurement noise. The order of the filter and the bandwidth can be set by
the user (butterdesign.m).
Service Blocks
The remaining blocks are inserted just to have a fully functional environment.
set-point: the desired value of the process value;
LoadDisturbance: a value added to the output of the plant;
MeasurementNoise: a white gaussian noise added to the measure of the process value;
SP-PV-CV: a scope block which displays the value of the Set Point SP (yellow),
Process Value PV (magenta) and Control Variable CV (cyan).
Note The GUIs control the value of the set-point, load
disturbance and
measurement noise through a reference to the name of the corresponding blocks. It is suggested
that you DON'T change the name of this block. If you do this, you must also change the references
in the masks of the block "PID Control Panel" and
"Environment Panel"
