GENERAL SIMULINK TIPS



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GENERAL SIMULINK TIPS

The following are general tips and should be used often.

  1. In order to save your work, select Save from the file menu and give the file that you want to save a name (or choose an old name if you are ``writing over'' an old version), and click the ok button (using the left-most mouse button). Realize that you have a choice of the ``folder'' that the file is saved in.

  2. The PID Controller block parameters are entered in as: , , .

  3. The following transfer function (in the Laplace domain)

    is entered into the transfer function icon by double clicking on the transfer function icon and entering the numerator and denominator polynomial coefficients. The numerator coefficients would be entered as [2 1] and the denominator coefficients are entered as [10 5 1].

  4. The following state-space A matrix

    is entered into the state space icon as [1.0 -2.8;-3.1 0.2].

  5. The results of a simulation can be sent to the MATLAB window by the use of the to workspace icon from the Sinks window. Open the to workspace icon and select the variable name that you want the results stored in the MATLAB workspace.

  6. If your simulation has n state (or output) variables and you want to save them as different names, then you have to use a special connection called a Demux (as in demultiplexer) icon which is found in the Connections window. Basically, it takes a vector input and converts it into several scalar lines. You can set the number of outputs (scalar lines) by double clicking on the icon and changing the number of outputs. A Mux icon takes several scalar inputs and multiplexes those in a vector (useful sometimes in transferring the results of a simulation to the MATLAB workspace, for example).

  7. You can generate white (random) noise by selecting the white noise icon from the Source window.

  8. You can use a Gain icon from the Linear window if you need to multiple a signal by a constant number.

  9. You can convert back to physical variables after a state-space or transfer function simulation by using the Constant icon from the Sources window and a Sum icon from the Sources window. To do this for a scalar output signal, just enter the value of the steady-state into the Constant icon and add this to the scalar output using the Sum icon. For a vector output, you must first "break-up" the vector into scalar outputs using the Demux icon and then add the steady-state value to each scalar output.

  10. The signs of the Sum icon may be changed to negative (in order to subtract) by double clicking on the Sum icon and changing the sign from a positive to a negative sign. The number of inputs to the Sum icon may be changed by double clicking on the Sum icon and setting the number of inputs in the window.

  11. Make sure to set the integration parameters in the simulation menu. In particular, the default minimum and maximum step sizes must be changed (they should be around 1/100 to 1/10 of the dominant (slowest) time constant of your system).

  12. Parameters can be "passed" to SIMULINK from the MATLAB window by using the parameter in a SIMULINK block or parameter box and defining the parameter in the MATLAB window. For example, say that one wants to run the simulation with many different process gains, then in the transfer function icon the gain (in the numerator) can be given the symbol k (or any symbol) and then at the MATLAB prompt define k = 1.0. Run the simulation, then at the MATLAB prompt redefine k = 1.5, etc. This is very useful if the student wants to study the influence of a parameter on the dynamic behavior of a process (important in determining stability).

  13. In order to print the block diagram, first save the block diagram. Then, at the MATLAB prompt, type:

    print -sname-of-simulink-block

    where name-of-simulink-block is the name that you saved the block diagram under. For example, if you saved the block diagram as homework1.m, then you would type:

    print -shomework1

  14. Time delays (deadtimes) can be simulated in SIMULINK easily by using a transport delay icon from the Nonlinear window. Double click on the transport delay icon to set the value of the deadtime.

  15. Nonlinear systems can be simulated in SIMULINK using an s-function icon from the Extras window. The nonlinear ordinary differential equations must be specified in an m-file, and the name of this m-file is specified in the s-function by the user. We will generally supply the student with the m-file containing the nonlinear ordinary differential equations.



next up previous
Next: TABLE OF SIMULINK Up: No Title Previous: BLOCK DIAGRAM CONSTRUCTION



Lou Russo, Howard P. Isermann Dept. of Chemical Engineering