Danfoss FC 300 Design Manual page 31

FC 300 Design Guide
The following parameters are relevant for the Speed Control:
Parameter
Speed PID Feedback
Par. 7-00
Source
Par. 7-02 Speed PID Proportional
Gain
Speed PID Integral Time
Par. 7-03
Speed PID Differentiation
Par. 7-04
Time
Speed PID Diff. Gain Limit
Par. 7-05
Speed PID Lowpass Filter
Par. 7-06
Time
Below is given an example of how to programme the Speed Control:
In this case the 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 potentiometer connected to terminal 53. The speed range is 0 - 1500 RPM corresponding 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 24V (HTL) incremental encoder as feedback. The feedback sensor is an encoder (1024
pulses per revolution) connected 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.
Eliminates steady state speed error. Lower value means quick reaction. However, too low value may lead to
oscillations.
Provides a gain proportional to the rate of change of the feedback. A setting of zero disables the differentiator.
If there are quick changes in reference or feedback in a given application - 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 differentiator 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, too large filter time will deteriorate the dynamic performance of the Speed PID control.
Practical settings of 7-06 taken from the number of pulses per revolution on from encoder (PPR):
Encoder PPR
512
1024
2048
4096
MG.33.BC.02 - VLT ® is a registered Danfoss trademark
3 Introduction to AutomationDrive FC 300
par. 7-06 Speed PID Lowpass
Filter Time
10 ms
5 ms
2 ms
1 ms
3
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