Simulink Control Design™ - MathWorks

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:

• A simulation snapshot
  time at which the plant is
  in a linearizable steady
  state.


• Known state values or a
  previously trimmed
  operating point at which
  the plant is linearizable.

“Tune at a Different

Operating Point” on page 7-

19

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” on page 7-49

7 PID Controller Tuning