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| Contents | Index |
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Use the Architecture pane for
Click Control Architecture to change the feedback structure and label signals and blocks. The following pane appears:
Select an architecture from the list of block configurations. These include compensator in the forward path, compensator in the feedback path, feedforward controller, and various multi-loop configurations. The window automatically updates to show the selected configuration.
Each configuration has associated Signs and Blocks and Signals panes. This figure shows the Signs pane.
The Blocks and Signals pane displays the generic identifier, for example F for the prefilter block, and a default name.
Click Loop Configuration to configure loops for multi-loop design by opening signals to remove the effects of other feedback loops.
To specify openings for a given open loop, select the loop in the combo box. Click Highlight Feedback Loop to see the effects of the selected openings.
For an example of how to use this window in design, see Multi-Loop Compensator Design.
Click System Data on the Architecture pane to import models into your system. This opens the System Data dialog box, which is shown below.
You can import models for the plant (G), compensator (C), prefilter (F), and/or sensor (H). To import a model:
Select a system in the System column and click Browse. The Model Import dialog box opens, as shown below.
Select a model from the Available Models list. You can import models from:
The MATLAB workspace
A MAT-file
Click Import, then click Close. You can now see the model loaded into the system selected in the System Data dialog.
Click OK. The Graphical Tuning window is updated with the model you loaded.
Alternatively, you can import by entering a valid expression or variable (double or LTI object) in the Data column in the System Data window.
Click Sample Time Conversion to convert the sample time of the system or switch between different sample times to design different compensators.
Choose from Zero-Order Hold, First-Order Hold, Impulse Variant, Tustin, Tustin w/Prewarping, and Matched Pole-Zero.
For a full description, see Continuous/Discrete Conversions Using the Sample Time Conversion Dialog Box.
Use the Compensator Editor for adding or editing gains, poles, and zeros.
Compensator Editor Pane on the SISO Design Task Node
Enter the compensator gain in the text box in the top part of the pane.
Add or remove compensator poles and zeros by right-clicking in the Dynamics table.
Adjust pole and zero settings by entering values directly in the Edit Selected Dynamics group box.
Use the Graphical Tuning pane for
Refocusing on the Graphical Tuning Window
Graphical Tuning Pane on the SISO Design Task Node
Click the Graphical Tuning tab to configure design plots displayed in the Graphical Tuning Window.
In the Graphical Tuning window, use design plots to graphically manipulate system response. These design plots are dynamically linked to the SISO Design Task. When you change the dynamics of your compensator in either the SISO Design Task or the Graphical Tuning window, the design updates in both places.
For open-loop responses, the available plot types are:
Root locus
Nichols
Bode
For closed-loop responses, the available plot type is Bode.
Click New Open/Closed Loops to Tune to open a window for specifying new loops to tune.
Use the pull down menus to select the desired closed loop to tune by specifying the input, output, and blocks for tuning. Using the dialog box, you can select additional closed loops to tune.
Any loop you specify is displayed in the Summary of Available Loops to Tune in the Graphical Tuning pane. The list is also available in the Design plots configuration table of the same pane. You can use the latter for configuring design plots.
Click Show Design Plot to change the focus to the Graphical Tuning window.
Use the Analysis Plots pane for
Opening or Changing the Focus to the LTI Viewer
Analysis Plots Pane on the SISO Design Task Node
The following sections describe the main components of the Analysis Plots pane.
Analysis Plots. You can have up to six plots in one LTI Viewer. To add a plot, start by selecting "Plot 1" from the list of plots. Then select a new plot type from the pull down menu. You can choose any of the plots available in the LTI Viewer. Select "None" to remove a plot.
Contents of plots. Once you have selected a plot type, you can include several open- and closed-loop transfer function responses for display. You can plot open-loop responses for each of the components of your system, including your compensator (C), plant (G), prefilter (F), or sensor (H). In addition, various closed loop and sensitivity response plots are available.
Click Add Responses to open a window with three drop-down menus for selecting open and closed loop responses for various input and output nodes in the control architecture block diagram. This allows you to select additional responses for viewing. The Response table updates automatically to include the selected response.
Click Show Analysis Plot to open a new LTI Viewer for SISO Design with the response plots that you selected. All the plots open in one instance of the LTI Viewer.
Use the Automated Tuning pane to select a method for automatic tuning of your compensator design. Automated tuning methods help you design an initial compensator for a SISO loop that satisfies your design specifications.
You can choose among the following algorithms:
Optimization-Based Tuning — Optimizes compensator parameters using design requirements implemented in graphical tuning and analysis plots.
PID Tuning — Searches for initial PID controller parameters using the Robust response time, Parameter search, Ziegler-Nichols, and IMC Based methods.
Internal Model Control (IMC) Tuning — Obtains a full-order stabilizing feedback controller using the IMC design method.
LQG Synthesis — Designs a full-order stabilizing feedback controller as a Linear-Quadratic-Gaussian (LQG) tracker.
Loop Shaping — Finds a full-order stabilizing feedback controller with a desired open loop bandwidth or shape.
After you select a tuning algorithm, the pane updates to display the corresponding options.
Note If the particular automated tuning method you are using does not apply or fails, try selecting different tuning specifications or switch to a different tuning algorithm. |
Knowing the stability of the effective plant in your model may
help you understand which automated tuning methods work for your model.
Some of the automated tuning methods only apply to compensators whose
open loops (
) have stable effective
plants (
).
An effective plant is the system controlled by the compensator you design and contains all elements of the open loop in your model other than this compensator. The following figure shows two examples of effective plants.
For each method, follow these steps to do your design:
Select an automated tuning algorithm from the Design method drop-down menu.
If you select Optimization-Based Tuning, stop here and see Optimization-Based Tuning.
Determine how you want the compensator to perform and set the tuning specifications.
Click Update Compensator and notice the changes in the associated design and analysis plots.
Optimization-based tuning creates a subdesign task to assist in the tuning and optimization of control systems. If you have Simulink Design Optimization software installed, you can use this method to either:
Directly tune response signals within Simulink® models.
Tune responses of LTI systems using a SISO Design Task.
See "Frequency Domain Response Optimization Example" in the Simulink Design Optimization documentation for more details.
PID (proportional-integral-derivative) control is the most popular control technique used in modern industry. Five PID tuning algorithms are provided in the SISO Design Tool, including one that supports most systems (Robust response time). In most cases, the PID controllers resulting from PID tuning provide acceptable performance.
To do a PID design:
Select a controller type from the following options:
P — Proportional-only control (
)
PI — Proportional-integral control (
)
PID — Proportional-integral-derivative control
(
)
PIDF — PID control with a lowpass filter
If you choose this controller type, you may need to specify the N frequency (bandwidth) in rad/s.
Note If you are tuning a PID Controller block and your block is type PI or P, select the same controller type as the block. If your block is type PID, select PID with derivative filter. If your block is type PD or I, you cannot tune the block using the PID tuning algorithms. Instead, tune the block using the Compensator Editor or Graphical Tuning. |
Select an algorithm from the Tuning algorithm list:
Robust response time — This method computes PID parameters to robustly stabilize your system based on the bandwidth and phase margin that you specify.
Parameter search — This method implements robust control design techniques to locate stabilizing PID regions in parameter space.
Ziegler-Nichols open loop — Controller settings are based on a first-order model with a time delay that approximates the plant. This method uses the Chien-Hrones-Resnick (CHR) setting with 20% overshoot.
Ziegler-Nichols closed loop — Controller settings are obtained from a modified Ziegler-Nichols lookup table, based on the ultimate gain and frequency of the system. This method only supports stable plants.
Ziegler-Nichols closed loop does not apply to first-order or second-order systems with time delay. If you select Ziegler-Nichols closed loop for these cases, the tuning algorithm will automatically be switched to Ziegler-Nichols open loop.
Internal Model Control (IMC) based tuning — Controller settings are derived from a full-order IMC controller with model reduction techniques (note that this is different from selecting Internal Model Control (IMC) Tuning as the full-order compensator tuning method). This method only supports stable plants.
Set the tuning options available for your selected tuning algorithm type.
If you choose Robust response time, adjust the following performance metrics:
Bandwidth
Phase margin
You can adjust these metrics using the slider bar. You can also adjust the metrics by entering a known value in the text field or incrementally adjusting the value in the text field using the up and down arrows.
To increase or decrease the Bandwidth by 10x, click the right or left double arrows, respectively.
If you chose Parameter search, select one of these options from the Performance metric list:
Integral Absolute Error (IAE)
Integral Square Error (ISE)
Integral Time Absolute Error (ITAE)
Integral Time Square Error (ITSE)
These are typical controller performance criteria based on time response.
If you chose Ziegler-Nichols open loop, select a tuning preference by clicking one of these option buttons:
Setpoint tracking
Load disturbance rejection
If you chose Ziegler-Nichols closed loop, select a tuning formula by clicking one of these option buttons:
Ziegler-Nichols
Tyreus-Luyben
Astrom-Hagglund
If you chose Internal Model Control (IMC) based tuning, use the slider bar to set the Dominant closed-loop time constant.
IMC design generates a full-order feedback controller that guarantees closed-loop stability when there is no model error. It also contains an integrator, which guarantees zero steady-state offset for plants without a free differentiator. You can use this tuning method for both stable and unstable plants.
To design an IMC controller:
Specify a value in the Dominant closed-loop time constant field. The initial value is set as 5% of the open-loop settling time. In general, increasing this value slows down the closed system and makes it more robust.
Specify a value in the Desired controller order field using the slider. After you obtain a full-order feedback controller, you can try to reduce its order. You may lose performance and closed-loop stability if you reduce the order.
LQG tracker design generates a full-order feedback controller that guarantees closed-loop stability. It also contains an integrator, which guarantees zero steady-state error for plants without a free differentiator.
To design an LQG controller:
Specify your preference for controller response using the Controller response slider.
Move the slider to the left for aggressive control response.
This means that large overshoot is more heavily penalized so that the controller acts more aggressively. If you believe your model is accurate and that the manipulated variable has a large enough range, an aggressive controller is more desirable.
Move the slider to the right for robust control response.
Specify your estimation of the level of measurement noise using the Measurement noise slider.
Move the slider to the left for small measurement noise.
This means that you expect low noise from the process output measurement. Because this measurement is used by the Kalman estimator, process disturbances are picked up more accurately by the estimated states. In this case, the controller is freer from robustness considerations.
Move the slider to the right for large measurement noise. This results in a controller that is more robust to measurement noise.
Specify your preference for controller order using the Desired controller order slider.
Loop shaping generates a stabilizing feedback controller to match as closely as possible to a desired loop shape. You can specify this loop shape as a bandwidth or an open loop frequency response. If you have Robust Control Toolbox™ software installed, you can use loop shaping for SISO systems. For more information see the section on H-Infinity Loop Shaping in the Robust Control Toolbox User's Guide.
To design a controller using loop shaping:
Select a tuning preference by clicking one of these option buttons:
Target bandwidth — Allows
you to specify a target loop shape bandwidth (
). This results
in a loop shape of your specified bandwidth over an integrator (
).
Target loop shape — Allows you to specify the target open loop shape in one of the following representations: state-space, zero-pole-gain, or transfer functions.
Set the tuning options available for your selected tuning preference as follows:
If you chose Target bandwidth, specify the desired Target open-loop bandwidth in the editable box.
If you chose Target loop shape, do the following:
Enter the desired Target open-loop shape (LTI).
This can be a state-space representation, a zero-pole-gain representation, or a transfer function.
Enter the desired Frequency range for loop shaping [wmin,wmax].
Specify your preference for controller order using the Desired controller order slider.
Click Update Compensator.
 | Using the SISO Design Task Node | SISO Design Task Graphical Tuning Window |  |
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