- Preview plant response and adjust the settings for PID autotuning before tuning the
controller in real time. Doing so helps ensure that real-time tuning does not drive your
system out of the desirable operating range.
For more information, see “PID Autotuning for a Plant Modeled in Simulink” on page 8-
9.
Closed-Loop vs. Open-Loop PID Autotuning
The PID autotuning tools let you tune:
- In a closed-loop configuration, with your plant under control of an existing PID
controller (Closed-Loop PID Autotuner block). - In an open-loop configuration (Open-Loop PID Autotuner block). With open-loop
autotuning, if the plant is in a feedback loop, the autotuner opens the loop for the
duration of the tuning process.
In general, if you do not have an initial PID design, start with open-loop autotuning, and
switch to closed-loop autotuning for retuning or refinement. If you have an initial PID
design for your plant, use closed-loop tuning, which is safer for your plant. With closed-
loop autotuning, the controller remains in the loop to:
- Reject unexpected plant disturbances to maintain safe operation of the plant during
the estimation experiment. - Reduce the risk that the perturbations used for the experiment drive the plant away
from the desired operating point.
Additional advantages of the closed-loop autotuning approach include:
- Closed-loop tuning works with multiple-integrator plants. In contrast, you cannot use
open-loop autotuning for multiple-integrator plants. Even single-integrator plants risk
drifting away from the desired operating point during open-loop tuning. - Because the feedback loop remains closed, there is no concern about controller
saturation during the tuning process. In contrast, with open-loop autotuning, a
controller with integral action can saturate while the loop is open. Such saturation can
create a jump at the plant input when the tuning process ends. With open-loop tuning,
you must take additional steps to ensure that the controller continues to track
autotuner block output during tuning. (See, for instance, “PID Autotuning for a Plant
Modeled in Simulink” on page 8-9.)
When to Use PID Autotuning