Open-Loop Response of Control System for Stability Margin Analysis

This example shows how to use the Linear Analysis Tool to analyze the open-loop response of a control system.

Compute a linear model of the combined controller-plant system without the effects of the feedback signal. Use a Bode plot of the resulting linear model to see the open-loop response.

1. Open Simulink model.

   sys = 'watertank';
   open_system(sys)

   The Water-Tank System block represents the plant in this control system and contains all of the system nonlinearities.

   

2. In the Simulink model window, select Tools > Control Design > Linear Analysis.

   This action opens the Linear Analysis Tool for the model.

   

3. In the Simulink model window, define the portion of the model to linearize:

   • Right-click the PID Controller block input signal (the output of the Sum block). Select Linearization Points > Input Point.

   • Right-click the Water-Tank System output signal, and select Linearization Points > Output Point.

   • Right-click the Water-Tank System output signal and select Linearization Points > Open Loop.

   

   Note   Do not open the loop by manually removing the feedback signal from the model. Removing the signal manually changes the model operating point.

4. In the Plot Result drop-down list of the Linear Analysis Tool, select New Bode.

   

5. Click to linearize the model.

   The Bode plot of the open-loop response appears.

6. Right-click the plot and select Characteristics > Minimum Stability Margins.

   

   The Bode plot displays the phase margin marker. Click the marker to show a data tip that contains the phase margin value.

   

7. Close Simulink model.

   bdclose(sys);

 Related Examples

 More About

Applications of Linearization

Bode Response of Simulink Model

© 1984-2012- The MathWorks, Inc.    -   Site Help   -   Patents   -   Trademarks   -   Privacy Policy   -   Preventing Piracy   -   RSS