Plant Cannot Be Linearized or Linearizes to Zero
When you open PID Tuner, it attempts to linearize the model at the operating point specified by the model initial conditions. Sometimes, PID Tuner cannot obtain a nonzero linear system for the plant as seen by the PID controller.
How to Fix It
If the plant model in the PID loop cannot be linearized or linearizes to zero, you have several options for obtaining a linear plant model for PID tuning. The following table summarizes some of the options and when they are useful.
|Approach||Useful When||More Information|
|Linearize at a different operating point||
There is a known operating point suitable for tuning, such as:
|Tune at a Different Operating Point|
|Import a linear model of the plant to PID Tuner||You have an LTI model of the plant at the desired operating condition for tuning in the MATLAB® workspace.||In PID Tuner, in the Plant menu, select Import.|
|Tune the controller using simulated plant frequency-response data||The plant is not linearizable in any operating condition suitable for tuning.||Design PID Controller from Plant Frequency-Response Data|
|Use system identification to estimate a linear plant model from measured or simulated response data||You have System Identification Toolbox™ software. An advantage of this approach is that it yields an analytic plant model that you can use for further analysis.||Interactively Estimate Plant from Measured or Simulated Response Data|