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Design Two-Degree-of-Freedom PID Controllers

Use the PID Tuner to tune two-degree-of-freedom PID Controller (2DOF) blocks to achieve both good setpoint tracking and good disturbance rejection.

About Two-Degree-of-Freedom PID Controllers

A two-degree-of-freedom PID compensator, commonly known as an ISA-PID compensator, is equivalent to a feedforward compensator and a feedback compensator, as shown in the following figure.

The feedforward compensator is PD and the feedback compensator is PID. In the PID Controller (2DOF) block, the setpoint weights b and c determine the strength of the proportional and derivative action in the feedforward compensator. See the PID Controller (2DOF) block reference page for more information.

Tuning Two-Degree-of-Freedom PID Controllers

PID Tuner tunes the PID gains P, I, D, and N. For the PID Controller (2DOF) block, the tuner also automatically tunes the setpoint weights b and c. You can use the same techniques to refine and analyze the design that you use for tuning one-degree-of-freedom PID controllers.

To tune a PID Controller (2DOF) block in a Simulink® model:

  1. Double-click the block. In the block parameters dialog box, click Tune.

    PID Tuner opens, linearizes the model at the model initial conditions, and automatically computes an initial controller design that balances performance and robustness. In this design, PID Tuner adjusts the setpoint weights b and c if necessary, as well as the PID gains. To see the tuned values of all coefficients, click Show Parameters.

  2. Analyze and refine the initial design, described in Analyze Design in PID Tuner. All the same response plots, design adjustments, and options are available for tuning 2DOF PID controllers as in the single-degree-of-freedom case.

  3. Verify the controller design, as described in Verify the PID Design in Your Simulink Model.

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