Setting Parameters
01/02 AWB8230-1413GB
118
Setting the PID parameters
Values for the PID parameters must be chosen depending on the
application and the system’s control characteristics. The following
points are important to achieve effective PID control:
• A stable steady-state behaviour
• A fast response
• A small system deviation in the steady state
Parameters K
p
, T
i
and K
d
must be set within the stable operating
range. As a general rule, increasing one of the parameters K
p
, K
i
(= reduction of T
i
) and K
d
results in a faster system response. A
very large increase however, causes system instability, as the
returned actual value will begin to oscillate, in the worst case,
resulting in divergent behaviour (
a
fig. 118 to fig. 121):
The following table provides guidelines for setting each
parameter.
Table 22:
Setting the control times
Figure 118: Divergent behaviour
w: Setpoint
a
Output signal
Figure 119: Oscillation, dampened
w: Setpoint
a
Output signal
w
t
a
w
t
a
Figure 120: Good control characteristics
w: Setpoint
a
Output signal
Figure 121: Slow control, large static system deviation
w: Setpoint
a
Output signal
A setpoint
change
causes a slow response:
Increase proportional
component (K
p
)
causes a fast but unstable
reaction
Set a lower P
component
Setpoint and
actual value
differ greatly
Reduce integral
component (T
i
)
approach each other after
oscillation:
Set a higher I
component
After
increasing K
p
the response is still slow
Increase D component
(K
d
)
the response is still
unstable
Set a lower D
component
w
t
a
w
t
a
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