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Design Options in the SISO Tool Using the SISO Design Task Node on the Control and Estimation Tools Manager |
The SISO Design Tool is made up of the following:
The SISO Design Task in the Control and Estimation Tools Manager, a user interface (UI) that facilitates the design of compensators for single-input, single-output feedback loops through a series of interactive pages (referred to in this document as the SISO Design Task node).
The Graphical Tuning window, a graphical user interface (GUI) for displaying and manipulating the Bode, root locus, and Nichols plots for the controller currently being designed. This window is titled SISO Design for Design Name.
The LTI Viewer associated with the SISO Design Task. For instructions on how to operate the LTI Viewer, see LTI Viewer.
The SISO Design Tool facilitates the design of compensators for single-input, single-output feedback loops, and lets you iterate rapidly on your designs and perform the following tasks:
Manipulate closed-loop dynamics using root locus techniques.
Shape open-loop Bode responses.
Add compensator poles and zeros.
Add and tune lead/lag networks and notch filters.
Inspect closed-loop responses (using the LTI Viewer).
Adjust phase and gain margins.
Convert models between discrete and continuous time.
Automate compensator design.
This section shows how to open the SISO Design Tool with the DC motor example developed in Building Models
If you have not built the DC motor model, type
load ltiexamples
at the MATLAB prompt. This loads a collection of linear models, including the DC motor. To open the SISO Design Tool and import the DC motor, type
sisotool(sys_dc)
at the MATLAB prompt.
This command opens both the SISO Design Task node on the Control and Estimation Tools Manager and the Graphical Tuning window with the root locus and open-loop Bode diagrams for the DC motor plotted by default.
SISO Design Task Node (Architecture Page View)
Graphical Tuning Window with the DC Motor Example
The SISO Design Task node in the Control and Estimation Tools Manager contains the following pages for specifying controller design and behavior:
Architecture:
Change the feedback structure and label signals and blocks.
Configure loops for multi-loop design by opening signals to remove the effects of other feedback loops.
Import models into your system.
Convert the sample time of the system or switch between different sample times to design different compensators.
Compensator Editor:
Directly edit compensator poles, zeros, and gains.
Add or remove compensator poles and zeros.
Graphical Tuning:
Configure design plots in the Graphical Tuning window.
Use design plots to graphically manipulate system response.
Analysis Plots:
Configure analysis plots in the LTI Viewer.
Use analysis plots to view the response of open- or closed-loop systems.
Automated Tuning:
Automatically generate compensators using optimization-based, PID, internal model control (IMC), linear-quadratic-Gaussian (LQG), or loop shaping methods.
Use optimization-based methods that automatically tune the system to satisfy design requirements (available when you have the Simulink Design Optimization product).
If you type
sisotool
at the MATLAB prompt, the Control and Estimation Tools Manager opens with the SISO Design Task node and an empty Graphical Tuning window. You can import the DC motor model by clicking System Data on the Architecture page, shown in the following figure.
This opens the System Data dialog box, which is shown in the following figure.
To import the DC motor model:
Select G and click Browse. The Model Import dialog box opens, as shown in the following figure.
Select sys_dc from the Available Models list. Click Import, and then click Close. You can now see sys_dc loaded into G in the System Data dialog box.
Click OK. The Graphical Tuning window is updated with the DC motor model, as shown in the following figure.
The SISO Design Tool by default assumes that the compensator is in the forward path, i.e., that the feedback structure looks like this figure.
Default Feedback Structure — Compensator in the Forward Path
In this figure, the lettered boxes represent the following:
G — plant
H — sensor dynamics
F — prefilter
C — compensator
The default values for F, H, and C are all 1 (you can see this in the System Data dialog box). Note that this means that by default, the compensator has unity gain. G contains the DC motor model, sys_dc.
While in the Architecture page, click Control Architecture to open the Control Architecture dialog box.
You can use the Signs and Blocks and Signals panes to change the sign of the feedback signal into a summing junction and rename blocks and signals in the diagram respectively. See "Modifying Block Diagram Structure" for more details.
On any page in the SISO Design Task node on the Control and Estimation Tools Manager, click Show Architecture to see the current architecture and a list of the identifiers and names associated with the components.
As you select different compensator designs, you may find it convenient to be able to examine the various loop responses (for example, step or impulse responses) for a particular design. To view, for example, the closed-loop step response, click the Analysis Plots tab. This opens the Analysis Plots page containing the list of available responses, with none initially selected, as shown in the following figure.
Select the plot types for each plot in the Analysis Plots group box, and then select the plots to appear in the Plots list in the Contents of Plots table, as shown in the following figure.
Analysis Plots Loop Response Selection
After you have selected a plot, the LTI Viewer with the appropriate response(s) opens. You can also click Show Analysis Plot to open the LTI Viewer.
The following figure shows the resulting plot for the closed-loop step response of the DC motor.
LTI Viewer Showing the Step Response for the DC Motor
As this plot shows, the step response of the DC motor is about 1.5 seconds, which is too slow for many applications. Also, there is a large steady-state error. The following sections show how to use Bode diagram techniques for improving the response time and steady-state error of the DC motor step response.
As you select different compensator designs, the LTI Viewer associated with your SISO Design Task will automatically update the response plots you have chosen for a particular design.
The Graphical Tuning window is a graphical user interface (GUI) for displaying and manipulating the Bode, root locus, and Nichols plots for the controller currently being designed. Most tasks can be accomplished using the pages in the SISO Design Task node on the Control and Estimation Tools Manager. Many of these tasks can also be done in the Graphical Tuning window, though you will find it easier to use the pages in the SISO Design Task node on the Control and Estimation Tools Manager. However, there are a few tasks, such as adjusting the bandwidth, that can only be done using the Graphical Tuning window.
This section describes some of the methods for navigating in and manipulating the appearance of the Graphical Tuning window.
The Graphical Tuning window shows
Poles as x's
Zeros as o's
Gain and phase margins (by default) in the lower-left corners of the Bode magnitude and phase plots
The SISO Design Tool provides editors for setting plot options in the Graphical Tuning window. If you want, for example, to change the frequency units on all the Bode plots created in the SISO Design Tool from rad/s to Hertz, select SISO Tool Preferences from the Edit menu in the SISO Design Task node on the Control and Estimation Tools Manager, as shown next.
This opens the SISO Tool Preferences dialog box.
Use the options on the Units page to make the change. This unit change persists for the entire session.
For more information about property and preference settings, see Customization.
The SISO Design Tool has right-click menus available in any of the plot regions. Open the Bode magnitude menu by right-clicking your mouse in the white space of the Bode magnitude plot. The following menu appears.
Right-Click Menu for the Bode Magnitude Plot
Although the menus for each plot generally contain the same options, there are some options specific to each plot type; for example, where the Closed-Loop Bode Editor right-click menu has a Select Compensator option, the Open-Loop Bode Editor right-click menu has a Gain Target option instead.
The right-click menus contain numerous features. The DC motor example uses many of the available features; for a complete discussion of the right-click menus, see the help for the SISO Design Tool in "Using the SISO Design Tool and the LTI Viewer."
 | Quick Start for Tuning Compensator Parameters Using the SISO Design Tool | Bode Diagram Design |  |
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