Ideal for Automatic Control classes, students and designers.

ControlTeacher is a simulation program developed by Raczynski Consulting, Mexico City, 2005. It was created using the PASION Simulation Software. See the bottom of this page for the PASION demo.  ControlTeacher program simulates a closed loop control system with a P, PID or switching controller. The PID may have the anti-windup mechanism, and the switching controller can be 2- or 3-point with histeresis. Also the sampled data digital controller can be simulated.

The structure of the simulated system is shown in the following figure.

The program is designed for teachers and students of the elementary automatic control course, so the user is supposed to be familiar with all concepts and simulated control elements.

Controller can be one of the following:

   Proportional controller

   Conventional PID controller

   Anti-windup PID controller

   Switching 2-point

   Switching 2-point

   General 3-point with histeresis

Actuator saturation is a saturation function with the slope of the proportional part equal to one and with given saturation level.

Delay represents a pure delay element on the process input.

The process can be a first-, second- or third-order linear dynamic process, with the following transfer function

Measurement. It is supposed that the measurement only introduces a first order inertia, and that the measurement error in the steady state is equal to zero. If you permit the inertia, you must define the corresponding time-constant.

Sample-and-hold.  This element can be activated when the measurement includes sampling. The last sampled value is being hold during the sampling period. You must give the value of the sampling period.

SIMULATION

 ControlTeacher simulates your model and displays the system time-response, as well as the response of the controlled process in open loop. The simulation program was created as a modified version of the code generated by the Signal Flow Module of the PSM++ Simulation System. The integration of the model equations is done in 10,000 time-steps, using the Runge-Kutta Fehlberg method.

Process response. After defining the model, you may see the time-response of the controlled process, including delay element and the measurement element. This can be useful while checking the model and assessing the possible final simulation time for the closed loop. Anyway, if your system is stable and the controller settings are appropriate, the closed-loop response should be faster than the open loop one. To compare the results, you should define the same final time for the open and closed loop case. In this, as well as in the closed loop simulation the set point is constant, equal to 50.

Closed loop simulation. This is the main simulation run of ControlTeacher. Note that not all system blocks (except the controller and the process) must be active. On the system block diagram the active blocks are shown in white, and the disabled ones in blue. While running the simulation you are asked to give the final simulation time. You may also declare the "varying parameter"  simulation mode, described below.

As the result of the simulation you will be able to select the signals to be plotted. First, the signals are shown in a multiple plot with a common scale. Then, the curves appear one-by-one, automatically normalized. Finally, you can see the phase-plane plot for the controlled variable. This plot shows the system trajectory on the plane with coordinates X and dX/dt, X being the process output. This plot is particularly useful while simulating systems with switching controllers.

The following figure shows an example of the results screen. This is a set of curves which describe the response of a system with a PID anti-windup controller, actuator saturation, third order controlled process and measurement inertia (sample-and-hold disabled).

Varying parameter mode. To design the system you need to compare its behavior for various combinations of controller settings and other parameters. The varying parameter mode facilitates this task. The following parameters can be selected to carry out the experiment, one parameter per simulation run. 

Controller gain
Integration time Ti
Differentiation time Td
PID windup saturation level
Switching controller amplitude
Switching controller histeresis
Actuator saturation level
Process delay time
Measurement time-constant
Sample-and-hold interval   

 Of course, the corresponding block must be active. After selecting the parameter, you will define the initial and final value, and the number of steps (should not be greater than 30 steps, otherwise the plot will not be very clear. The curves appear on one plot, starting with the initial parameter value. On the following figure you can see the result of a varying parameter experiment. The controller is a conventional PID and the process is of the second order with delay and measurement inertia. The varying parameter is the controler gain. The growing oscillations in the response is caused by growing controller gain.

Other useful plot is the phase plane. Below you can see the phase-plane image for a switching 3-point controller with histeresis. The plot shows the value and the velocity for the process output.

Sampled-data digital controller can also be simulated. The following figue shows the controller and the process outputs. The controller is a digital PID, and the controlled process is described by a transfer function of the second order. This option is very illustrative while changing yhe sampling period and observing the system response.

Platform: PC, Windows 98 or later, NT or XP, recommended 1024x768 resolution.

Copyright Stanislaw Raczynski © 2005.

PSM++  DEMO: Click here    to download the PSM++ demo. Unzip and save it in a new directory on your hard disk. Then execute DEMO32.EXE. NOTE that PSM++ (new version of PASION)  was used to create ControTeacher, but it is not required to run it. ControlTeacher is a stand-alone application that only needs Windows98 or later, XP or NT.

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