Danfoss FC 300 Design Manual page 33

FC 300 Design Guide
The following parameters are relevant for the speed control:
Parameter
Feedback Par. 7-00
Proportional Gain Par.
7-02
Integral
7-03
Differentiation
Par. 7-04
Differentiator
Limit Par. 7-05
Low-pass Filter Time
Par. 7-06
Below is given an example of how to program the speed control:
In this case, speed PID control is used to
maintain a constant motor speed regardless of
the changing load on the motor.
The required motor speed is set via a poten-
tiometer connected to terminal 53. The speed
range is 0 - 1,500, which corresponds to 0 -
10V over the potentiometer.
Starting and stopping is controlled by a switch
connected to terminal 18.
The speed PID monitors the actual RPM of the
motor by using a 24 V (HTL) incremental en-
coder as feedback. The feedback sensor is an
encoder (1024 pulses per revolution) connec-
ted to terminals 32 and 33.
Description of function
Select from which input the speed PID should get its feedback.
The higher the value, the quicker the control. However, too high value
may lead to oscillations.
Time Par. Eliminates steady state speed error. Lower value means quick reac-
tion. However, too high value may lead to oscillations.
Time Provides a gain proportional to the rate of change of the feedback. A
setting of zero disables the differentiator.
Gain If there are quick changes in reference or feedback in a given appli-
cation - which means that the error changes swiftly - the differentiator
may soon become too dominant. This is because it reacts to changes
in the error. The quicker the error changes, the stronger the differ-
entiator gain is. The differentiator gain can thus be limited to allow
setting of the reasonable differentiation time for slow changes and a
suitably quick gain for quick changes.
A low-pass filter that dampens oscillations on the feedback signal and
improves steady state performance. However, a filter time that is too
long will deteriorate the dynamic performance of the speed PID con-
trol.
Practical settings for Par 7-06 taken from the number of pulses per
revolution from the encoder (PPR):
Encoder PPR
512
1024
2048
4096
MG.33.B9.22 - VLT ® is a registered Danfoss trademark.
3. Introduction to FC 300
Par. 7-06
10 ms
5 ms
2 ms
1 ms
3
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