Simulation Scenario View :: Reference for the Design Tool GUI (Model Predictive Control Toolbox™)

Simulation Scenario View

This view appears whenever you select one of your scenario specification nodes (see Tree View). It allows you to specify simulation settings and independent variables. All have default values, but you will want to change at least some of them (otherwise all independent variables will be constant). Defaults for a plant with three inputs and two outputs appears below.

The middle table won't appear unless you have designated at least one input signal to be a measured disturbance.

The following sections describe the view's main features:

Simulation Settings

Use this section to set the following:

Controller - Select one of your controllers,
Plant - Select the plant model that will act as the "real" plant in the simulation, i.e., it need not be the same as that used for controller predictions.
Duration - The simulation duration in time units.
Close loops - If cleared, the simulation will be open-loop.
Enforce Constraints - If cleared, all controller constraints will be ignored.

The Control interval field is display-only, and reflects the setting in your Controller selection. You can change it there if necessary (see Model and Horizons Tab).

Setpoints

Note Setpoint specifications affect closed-loop simulations only.

Use this table to specify the setpoint for each output. In the example below, which is for an application having two plant outputs, the first would be constant at 0.0, and the second would change step-wise.

The Name and Units columns are display-only. To change them, use the signal definition view. (See Signal Definition View. Any changes apply to the entire design.)

The Type column specifies the setpoint variation. To change this, click the cell and select a choice from the resulting menu.

The significance of the Initial Value, Size, Time, and Period columns depends on the Type. If a cell is gray (noneditable), it doesn't apply to the Type you've chosen.

For details on the signal types, see Signal Type Settings.

If the Look Ahead option is selected (i.e., on), the controller will use future values of the setpoints in its calculations. This improves setpoint tracking, but knowledge of future setpoint changes is unusual in practice.

Note In the current implementation, selecting or clearing the Look ahead option for one output will set the others to the same state. Model Predictive Control Toolbox™ code does not allow you to Look ahead for some outputs but not for others.

Measured Disturbances

Use this table to specify the variation of each measured disturbance. In the example below, which is for an application having a single measured disturbance, the "Steam Rate" input would be constant at 0.0.

The Name and Units columns are display-only. To change them, use the signal definition view. (See Signal Definition View. Any changes apply to the entire design.)

The Type column specifies the disturbance variation. To change this, click the cell and select a choice from the resulting menu.

The significance of the Initial Value, Size, Time, and Period columns depends on the Type. If a cell is gray (noneditable), it doesn't apply to the Type you've chosen.

For details on the signal types, see Signal Type Settings.

If the Look Ahead option is selected (i.e., on), the controller will use future values of the measured disturbance(s) in its calculations. This improves disturbance rejection, but knowledge of future disturbances is unusual in practice. It has no effect in an open-loop simulation.

Note In the current implementation, selecting or clearing the Look ahead option for one input will set the others to the same state. Model Predictive Control Toolbox™ code does not allow you to Look ahead for some inputs but not for others.

Unmeasured Disturbances

Use this table to specify the variation of each measured unmeasured disturbance. In the example below, all would be constant at 0.0.

Unmeasured Disturbance Locations

You can simulate an unmeasured disturbance in any of the following locations:

The plant's unmeasured disturbance (UD) inputs (if any)
The plant's measured outputs (MO)
The plant's manipulated variable (MV) inputs

All of the above will appear as rows in the table. In the case of a measured output or manipulated variable, the disturbance is an additive bias.

The Name and Units columns are display-only. To change them, use the signal definition view. (See Signal Definition View. Any changes apply to the entire design.)

The Type column specifies the disturbance variation. To change this, click the cell and select a choice from the resulting menu.

The significance of the Initial Value, Size, Time, and Period columns depends on the Type. If a cell is gray (noneditable), it doesn't apply to the Type you've chosen.

For details on the signal types, see Signal Type Settings.

Open-Loop Simulations

For open-loop simulations, you can vary the MV unmeasured disturbance to simulate the plant's response to a particular MV. The MV signal coming from the controller stays at its nominal value, and the MV unmeasured disturbance adds to it.

For example, suppose Reflux Rate is an MV, and the corresponding row in the table below represents an unmeasured disturbance in this MV.

You could set it to a constant value of 1 to simulate the plant's open-loop unit-step response to the Reflux Rate input. (In a closed-loop simulation, controller adjustments would also contribute, changing the response.)

Similarly, an unmeasured disturbance in an MO adds to the output signal coming from the plant. If there are no changes at the plant input, the plant outputs are constant, and you see only the change due to the disturbance. This allows you to check the disturbance character before running a closed-loop simulation.

Signal Type Settings

The table below is an example that uses five of the six available signal types (the Constant option has been illustrated above). The cells with white backgrounds are the entries you must supply. All have defaults.

Constant

The signal will be held at the specified Initial Value for the entire simulation.

Step

Prior to Time, the signal = Initial Value. At Time, the signal changes step-wise by Size units. Its value thereafter = Initial Value + Size.

for where y₀ = Initial Value, t₀ = Time

for where M = Size

Ramp

Prior to Time, the signal = Initial Value. At Time, the signal begins to vary linearly with slope Size.

for where y₀ = Initial Value, t₀ = Time

for where M = Size

Sine

Prior to Time, the signal = Initial Value. At Time, the signal begins to vary sinusoidally with amplitude Size and period Period.

for where y₀ = Initial Value, t₀ = Time

for where M = Size, /Period

Pulse

Prior to Time, the signal = Initial Value. At Time, a square pulse of duration Period and magnitude Size occurs.

for where y₀ = Initial Value, t₀ = Time

for where M = Size, T = Period

Gaussian

Prior to Time, the signal = Initial Value. At Time, the signal begins to vary randomly about Initial Value with standard deviation Size.

for where y₀ = Initial Value, t₀ = Time

for where M = Size

randn is the MATLAB® random-normal function, which generates random numbers having zero mean and unit variance.

Simulation Button

Click the Simulate button to simulate the scenario. You can also press Ctrl+R, use the toolbar icon (see Toolbar), or use the MPC/Simulate menu option (see Menu Bar).

Tuning Advisor Button

Click Tuning Advisor to open a window that helps you improve your controller's performance. See Tuning Advisor.

Right-Click Menus

Copy Scenario

Creates a new simulation scenario having the same settings and a default name.

Delete Scenario

Deletes the scenario.

Rename Scenario

Opens a dialog box allowing you to rename the scenario.

Note Each scenario in a design project/task must have a unique name.

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