Woodward easYgen-2000 Series User Manual page 270

Configuration
Configure Application > Configure Controller
Fig. 96: Behavior of the derivative
PID tuning example
270
Derivative, sometimes called "preact" of "rate", is very difficult to
draw an accurate analogy to, because the action takes place only
when the process changes and is directly related to the speed at
which the process changes.
Merging into high speed traffic of a freeway from an "on" ramp is
no easy task and requires accelerated correction (temporary over‐
correction) in both increasing and decreasing directions. The appli‐
cation of brakes to fall behind the car in the first continuous lane or
passing gear to get ahead of the car in the first continuous lane is a
derivative action.
parameter
If the system is unstable, make sure the governor is the cause.
This can be checked by closing the valve limiter until it has control
of the actuator output. If the governor is causing the oscillation,
time the oscillation cycle time. A rule-of- thumb is, if the system's
oscillation cycle time is less than 1 second, reduce the Proportional
gain term. A rule-of-thumb is, if the system's oscillation cycle time
is greater than 1 second, reduce the Integral gain term (propor‐
tional gain may need to be increased also).
On an initial startup with the easYgen, all PID dynamic gain terms
will require adjustment to match the respective PID's response to
that of its control loop. There are multiple dynamic tuning methods
available that can be used with the easYgen's PIDs to assist in
determining the gain terms that provide optimum control loop
response times.
The following method can be used to achieve PID gain values that
are close to optimum:
1. Increase Derivative Ratio (DR) to 100.
2. Reduce integral gain to 0.01.
3. Increase proportional gain until system just starts to oscillate.
4. Record the control gain (Kc) and oscillation period (T) in sec‐
onds.
5. Set the dynamics as follows:
For PI control G=P(I/s + 1) set:
n
–
–
–
For PID control G=P(I/s + 1 + Ds) set:
n
–
–
–
–
ð This method of tuning will get the gain settings close,
they can be fine-tuned from this point.
easYgen-2200/2500 | Genset Control
The optimum gain for this step is when the
system just starts to oscillate and maintains a
self-sustaining oscillation that does not increase
or decrease in magnitude.
Proportional gain = 0.45*Kc
Integral gain = 1.2/T
Derivative ratio = 100
Proportional gain = 0.60*Kc
Integral gain = 2/T
Deriv ratio = 8/(T*Integral Gain) for feedback domi‐
nant
Deriv ratio = (T*Integral Gain)/8 for input dominant
37535B