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Entry type: Application example Entry ID: 44364150, Entry date: 08/11/2010
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Configurating of Continuous Control with Pulse Width Modulation

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The project example on hand shows the application of a continuous controller with pulse width modulation to a simulated plant. The target of the application is showing the aspects of engineering and commissioning of controllers with pulse width modulation.

Objective of the Application
A continuous control loop with pulse width modulation consists of a conventional PID controller and a pulse modulation function. The pulse generator block modifies the analogous manipulated variable signal of the controller into a sequence of digital pulses with pulse length (or pulse/break ratio) equivalent to the analogous manipulated variable. This configuration is applied for switching actuators (e.g. heating on/off or valve open/close).
This use case has to be distinguished from step controllers. A step controller is applied for integrating actuators (e.g. motor driven valves) commanded by binary output signals open/stop/close. The function blocks PIDStepL or CTRL_S for step controllers are available in the Advanced Process Library or in the PCS 7 Standard Library, whereas a pulse generator function block does not exist in the PCS libraries. The function block PULSEGEN is provided only in the CFC-Library ELEM_400.

Main contents
The following issues are discussed in this application note:

  • Interaction of a continuous controller and pulse width modulation with regard to controller tuning, parameter specification and choice of the sampling time.
  • Interaction of a continuous controller and pulse width modulation with respect to mode switch over.
  • Simulation example.

Validity
This entry was created with SIMATIC PCS 7 V7.1, the procedure is transferable to PCS 7 V7.0 SP1 and higher versions.

Downloads
  Documentation - Configurating of Continuous Control with Pulse Width Modulation (511,7 KB) 

History
08/2010 First release


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