Danfoss VLT AQUA Drive FC 200 Programming Manual page 138

Parameter Description
3.17.4 20-7* PID autotuning
The adjustable frequency drive PID Closed-loop controller
(parameter group 20-**, FC Drive Closed-loop) can be auto-
3 3
tuned, simplifying and saving time during commissioning,
while ensuring accurate PID control adjustment. To use
auto-tuning, it is necessary for the adjustable frequency
drive to be configured for closed-loop in 1-00 Configuration
Mode.
A Graphical Local Control Panel (LCP) must be used in
order to react to messages during the auto-tuning
sequence.
Enabling 20-79 PID Autotuning, puts the adjustable
frequency drive into auto-tuning mode. The LCP then
directs the user with on-screen instructions.
The fan/pump is started by pressing [Auto On] and
applying a start signal. The speed is adjusted manually by
▲
pressing [ ] or [
the system setpoint.
NOTICE!
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 auto-tuning.
PID auto-tuning functions by introducing step changes
whilst 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 displayed 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 auto-tuning mode is disabled in 20-79 PID Autotuning.
Depending on the system being controlled, the time
required to carry out auto-tuning 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 auto-tuning. If PID
auto-tuning is carried out with slow ramp times, the auto-
tuned 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 auto-tuning. In
3-112
VLT
▼
] to a level where the feedback is around
MG20O622 - VLT
®
AQUA Drive Programming Guide
order to obtain the most accurate controller parameters, it
is advisable 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:
[0] Auto
[1] Fast Pressure
[2] Slow Pressure
[3] Fast Temperature
[4] Slow Temperature
20-71 PID Performance
Option:
[0] Normal Normal setting of this parameter will be suitable for
[1] Fast
20-72 PID Output Change
Range:
0.10 [0.01 -
*
0.50 ]
®
is a registered Danfoss trademark
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
autotuning. The setting has no impact on
the value of the tuned parameters and is
used only for the autotuning sequence.
Function:
pressure control in fan systems.
Fast setting would generally be used in pumping
systems, where a faster control response is desirable.
Function:
This parameter sets the magnitude of step
change during auto-tuning. 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 50 Hz, 0.10 is 10% of 50 Hz, which is 5
Hz. This parameter should be set to a value
resulting in feedback changes of between 10%
and 20% for best tuning accuracy.