Danfoss VLT AutomationDrive FC 300 Design Manual page 33

Introduction
Parameter
7-00 Speed PID Feedback Source Select from which input the Speed PID should get its feedback.
30-83 Speed PID Proportional
Gain
7-03 Speed PID Integral Time
7-04 Speed PID Differentiation
Time
7-05 Speed PID Diff. Gain Limit
7-06 Speed PID Lowpass Filter
Time
Table 3.5 Relevant Parameters for Speed Control
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 potenti-
ometer connected to terminal 53. The speed range is 0 to
1500 RPM corresponding to 0 to 10 V over the potenti-
ometer. 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
encoder as feedback. The feedback sensor is an encoder
(1024 pulses per revolution) connected to terminals 32 and
33.
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VLT AutomationDrive FC 300 Design Guide, 0.25-75 kW
Description of function
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 differ-
entiator 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 parameter 7-06 taken from the number of pulses per revolution on from encoder
(PPR):
Encoder PPR 7-06 Speed PID Lowpass Filter Time
512 10 ms
1024 5 ms
2048 2 ms
4096 1 ms
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L1
L2
L3
N
PE
F1
12
91 92 93 95
37
L1 L2 L3 PE
18
50
53
55
39
20
U V W PE
32
33
96 97 98 99
M
24 Vdc
3
Illustration 3.20 Example - Speed Control Connections
3 3
31