slow changes and an appropriate frequency contribu-
tion for quick changes can be preset. This is done
using the speed regulation in parameter 420
Speed
PID Differentiator gain limit
and Process regulation in
parameter 443
Process PID Differentiator gain limit
.
Lowpass filter
If there is a lot of noise in the feedback signal, these
can be dampened using an integrated lowpass filter.
A suitable lowpass filter time constant is preset.
If the lowpass filter is preset to 0.1 s, the cut-off fre-
quency will be 10 RAD/sec, corresponding to (10 / 2
x ) = 1.6 Hz. This will mean that all currents/voltages
that vary by more than 1.6 oscillations per second will
be dampened. In other words, there will only be regu-
lation on the basis of a feedback signal that varies by
a frequency of less than 1.6 Hz. The appropriate time
constant is selected in Speed Regulation in parameter
421
Speed PID lowpass filter time
and in Process Reg-
ulation in parameter 444
Process PID lowpass filter
time
.
Inverse regulation
Normal regulation means that the motor speed is in-
creased when the reference/setpoint is greater than
the feedback signal. If it is necessary to run inverse
regulation, in which the speed is reduced when the
reference/setpoint is greater than the feedback signal,
parameter 437
PID normal/inverted control
must be
programmed at
Inverted
.
Anti Windup
In the factory the process regulator is preset with an
active anti windup function. This function means that
when either a frequency limit, a current limit or a volt-
age limit is reached, the integrator is initialised at a
frequency corresponding to the present output fre-
quency. This is a means of avoiding the integration of
a variance between the reference and the process's
actual mode that cannot be deregulated by means of
a change of speed. This function can be deselected in
parameter 438
Process PID anti windup
.
Starting conditions
In some applications the optimal setting of the process
regulator will mean that a relatively long period of time
will pass before the required process condition is ach-
ieved. In these applications it can be a good idea to
define an output frequency to which the frequency
converter must run the motor before the process reg-
ulator is activated. This is done by programming a start
frequency in parameter 439
Process PID start frequen-
cy
.
Handling of feedback
Feedback handling is depicted in this flowchart.
The flowchart shows which parameters can affect the
handling of feedback and how. A choice can be made
between voltage, current and pulse feedback signals.
= factory setting, () = display text, [] = value for use in communication via serial communication port
MG.27.E2.02 - VLT is a registered Danfoss trademark
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