Danfoss VLT HVAC Series, Programming Manual, Page: 202 / 338

NOTE!
It is not possible to run the motor at maximum or minimum speed, when manually adjusting the motor speed due to the need of giving
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 par.20-93
PID Proportional Gain and par.20-94 PID Integral Time are calculated. par.20-95 PID Differentiation Time is set to value
0 (zero). par.20-81 PID Normal/ Inverse Control is determined during 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 par.20-79
PID Auto Tuning . 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 par.3-41
Ramp 1 Ramp-up Time , par.3-42 Ramp 1 Ramp-down Time or par.3-51 Ramp 2 Ramp-up Time and par.
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: 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.
[0] * Auto
[1] Fast Pressure
[2] Slow Pressure
[3] Fast Temperature
[4] Slow Temperature
20-71 Tuning Mode
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 de-
sirable.
20-72 PID Output Change
Range: Function:
0.10 N/A* [0.01 - 0.50 N/A] This parameter sets the magnitude of step change during autotuning. The value is a percentage of
full speed. This means that if the maximum output frequency inpar.4-13
Motor Speed High Limit
[RPM]
/par.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.
3 Parameter Description VLT ® HVAC Drive Programming Guide
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MG.11.C6.22 - VLT ® is a registered Danfoss trademark
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