Tune at a Different Operating Point

By default, PID Tuner linearizes your plant and designs a controller at the operating point specified by the initial conditions in your Simulink® model. Sometimes, this operating point differs from the operating point for which you want to design a controller. For example, you want to design a controller for your system at steady-state. However, the Simulink model is not generally at steady-state at the initial condition. In this case, change the operating point that PID Tuner uses for linearizing your plant and designing a controller.

To set a new operating point for PID Tuner, use one of the following methods. The method you choose depends upon the information you have about your desired operating point.

Known State Values Yield the Desired Operating Conditions

In this case, set the state values in the model directly.

  1. Close PID Tuner.

  2. Set the initial conditions of the components of your model to the values that yield the desired operating conditions.

  3. Click Tune in the PID controller dialog box to open PID Tuner. PID Tuner linearizes the plant using the new default operating point and designs a new initial controller for the new linear plant model.

After PID Tuner generates a new initial controller design, continue from Analyze Design in PID Tuner.

Model Reaches Desired Operating Conditions at a Finite Time

In this case, use PID Tuner to relinearize the model at a particular simulation time.

  1. In the PID Tuner tab, in the Plant menu, select Re-linearize Closed Loop.

  2. In the Closed Loop Re-Linearization tab, click Run Simulation to simulate the model for the time specified in the Simulation Time text box.

    PID Tuner plots the error signal as a function of time. You can use this plot to identify a time at which the model is in steady-state. Slide the vertical bar to a snapshot time at which you want to linearize the model.

  3. Click Linearize to linearize the model at the selected snapshot time. PID Tuner computes a new linearized plant and saves it to the PID Tuner workspace. PID Tuner automatically designs a controller for the new plant, and displays a response plot for the new closed-loop system. PID Tuner returns you PID Tuner tab, where the Plant menu reflects that the new plant is selected for the current controller design.

    Note

    For models with Trigger-Based Operating Point Snapshot blocks, the software captures an operating point at events that trigger before the simulation reaches the snapshot time.

After PID Tuner generates a new initial controller design, continue from Analyze Design in PID Tuner.

You Computed an Operating Point in the Linear Analysis Tool

  1. In the Linear Analysis tool, drag the saved operating point object from the Linear Analysis Workspace to the MATLAB Workspace.

  2. In PID Tuner, in the PID Tuner tab, in the Plant menu, select Import.

  3. Select Importing an LTI system or linearizing at an operating point defined in MATLAB workspace. Select your exported operating point in the table.

  4. Click OK. PID Tuner computes a new linearized plant and saves it to the PID Tuner workspace. PID Tuner automatically designs a controller for the new plant, and displays a response plot for the new closed-loop system. PID Tuner returns you PID Tuner tab, where the Plant menu reflects that the new plant is selected for the current controller design.

After PID Tuner generates a new initial controller design, continue from Analyze Design in PID Tuner.

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