Controller Performance Deteriorates When Switching
Time Domains
After you obtain a well-tuned, continuous-time controller using PID Tuner, you can
discretize the controller using the Time Domain selector button in the PID Controller
block dialog box. Sometimes, the resulting discrete-time controller performs poorly or
even becomes unstable.How to Fix It
In some cases, you can improve performance by adjusting the sample time by trial and
error. However, this procedure can yield a poorly tuned controller, especially where your
application imposes a limit on the sample time. Instead, if you change time domains and
the response deteriorates, click Tune in the PID Controller block dialog box to design a
new controller.NoteIf the plant and controller time domains differ, PID Tuner discretizes the plant (or
converts the plant to continuous time) to match the controller time domain. If the plant
and controller both use discrete time, but have different sample times, PID Tuner
resamples the plant to match the controller. All conversions use the tustin method (see
“Continuous-Discrete Conversion Methods” (Control System Toolbox).See Also
Discrete PID Controller | Discrete PID Controller (2DOF) | PID Controller | PID Controller
(2DOF)More About
- “When Tuning the PID Controller, the D Gain Has a Different Sign from the I Gain”
on page 7-216 - “Introduction to Model-Based PID Tuning in Simulink” on page 7-3
Controller Performance Deteriorates When Switching Time Domains