The PI controller has initial gains of P = 0.01 and I = 0.01, provided externally to the PID
block via "P" and "I" inports. Having external P and I gains allows you to change them
after new gains are computed by the Open-Loop PID Autotuner block later.The Open-Loop PID Autotuner block is inserted between the PID block and the engine
model. The start/stop signal is used to start and stop an open-loop experiment. When no
experiment is running, Open-Loop PID Autotuner block behaves like a unity gain block,
where the "u" signal directly passes to "u+Δu". When the experiment ends, the block
tunes PID gains and outputs them at the "pid gains" port.There are a few things you need to be aware of when using the Open-Loop PID Autotuner
block against a physical plant in real time:- The plant must be asymptotically stable because an open-loop experiment is
conducted during the tuning process. If your plant has a single integrator, you can still
use the block by choosing not to estimate plant dc gain. In both cases, however, you
must closely monitor the plant behavior during the tuning process and intervene
promptly if the plant gets too close to an undesirable operating condition. - To help estimate plant frequency responses more accurately in real time, there should
be minimum load disturbance occurring during the tuning process. The block expects
the plant output to be the response to the injected perturbation signals only, and load
disturbance distorts this output. - The "tracking mode" (the TR inport) in the PID block is turned on, which enables the
PID block to track the real plant input "u+Δu" during the tuning process. This feature
should be used all the time to provide a bumpless transfer when the loop is closed and
PID block resumes control after the tuning process is completed.
8 PID Autotuning