Simulink Control Design™ - MathWorks

The control signal u from the PID controller feeds into the u port of the autotuner block.

The u+Δu port feeds into the plant input. Before you begin the autotuning process, the

autotuner block feeds the PID control signal directly from u to u+Δu and the plant input.

In that state, the autotuner block has no effect on plant or controller behavior. During the

autotuning process, the block injects test signals at the plant input and measures the

response at y.

The start/stop signal controls when the autotuning process begins and ends (see “Step

2. Configure Start/Stop Signal” on page 8-11). When the experiment ends, the block
   calculates PID gains and returns them at the pid gains port.

For a more detailed example of a Simulink model configured for closed-loop PID

autotuning, see “Tune PID Controller in Real Time Using Closed-Loop PID Autotuner

Block” on page 8-39.

Bumpless Transfer for Open-Loop Tuning

The Open-Loop PID Autotuner block opens the loop between u and u+Δu during the

estimation experiment. If your controller includes integral action, you can use signal

tracking to avoid integrator windup while the loop is open. Signal tracking enables the

PID controller to continue to track the real plant input while it is out of the loop. Without

it, your system can experience a bump when the control loop is closed at the end of the

tuning process. In system of the following illustration, the PID controller is a Simulink PID

Controller block with the Enable tracking mode parameter on. The plant input feeds

into the tracking input of the controller block.

8 PID Autotuning