Danfoss VLT FC 100 Series Programming Manual page 147

Parameter Description
Enabling 20-79 PID Autotuning puts the Adjustable
frequency drive into auto-tuning mode. The LCP then
directs the user with on-screen instructions.
3 3
The fan/pump is started by pressing [Auto On] button on
the LCP and applying a start signal. The speed is adjusted
manually by pressing the [
LCP to a level where the feedback is around the system
setpoint.
NOTE!
It is not possible to run the motor at maximum or
minimum speed when manually adjusting the motor
speed, due to the need to give the motor a step in the
speed during autotuning.
PID autotuning functions by introducing step changes
while operating at a steady state and then monitoring the
feedback. From the feedback response, the required values
for 20-93 PID Proportional Gain and 20-94 PID Integral Time
are calculated. 20-95 PID Differentiation Time is set to value
0 (zero). 20-81 PID Normal/ Inverse Control is determined
during the tuning process.
These calculated values are presented on the LCP and the
user can decide whether to accept or reject them. Once
accepted, the values are written to the relevant parameters
and autotuning mode is disabled in 20-79 PID Autotuning.
Depending on the system being controlled, the time
required to carry out autotuning could be several minutes.
It is advised to set the ramp times in 3-41 Ramp 1 Ramp-up
Time, 3-42 Ramp 1 Ramp-down Time or 3-51 Ramp 2 Ramp-
up Time and 3-52 Ramp 2 Ramp-down Time according to
the load inertia before carrying out PID autotuning. If PID
autotuning is carried out with slow ramp times, the
autotuned parameters will typically result in very slow
control. Excessive feedback sensor noise should be
removed using the input filter (parameter groups 6-**, 5-5*
and 26-**, Terminal 53/54 Filter Time Constant/Pulse Filter
Time Constant #29/33) before activating PID autotuning. In
order to obtain the most accurate controller parameters, it
is advised to carry out PID autotuning, when the
application is running in typical operation, i.e. with a
typical load.
20-70 Closed-loop Type
Option:
3-120
®
VLT HVAC Drive Programming Guide
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] or [ ] navigation keys on the
Function:
This parameter defines the application
response. The default mode should be
sufficient for most applications. If the
application response speed is known, it
can be selected here. This will decrease
the time needed for carrying out PID
MG11CD22 - VLT
20-70 Closed-loop Type
Option:
[0] Auto
*
[1] Fast Pressure
[2] Slow Pressure
[3] Fast Temperature
[4] Slow Temperature
20-71 PID Performance
Option: Function:
[0] Normal Normal setting of this parameter will be suitable
*
for pressure control in fan systems.
[1] Fast Fast setting would generally be used in pumping
systems, where a faster control response is
desirable.
20-72 PID Output Change
Range: Function:
0.10 [0.01 - This parameter sets the magnitude of step
*
0.50 ] change during autotuning. The value is a
percentage of full speed, i.e., if maximum
output frequency in 4-13 Motor Speed High
Limit [RPM]/4-14 Motor Speed High Limit [Hz] is
set to 50Hz, 0.10 is 10% of 50Hz, which is 5Hz.
This parameter should be set to a value
resulting in feedback changes of between 10%
and 20% for best tuning accuracy.
20-73 Minimum Feedback Level
Range:
-999999.000 [
ProcessCtrlUnit par. 20-74
*
ProcessCtrlUnit]
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Function:
autotuning. The setting has no impact
on the value of the tuned parameters
and is used only for the autotuning
sequence.
Function:
-999999.999 - The minimum allowable
feedback level should be
entered here in user units
as defined in
20-12 Reference/Feedback
Unit. If the level falls below
20-73 Minimum Feedback
Level, autotuning is
aborted and an error
message will appear on
the LCP.