Danfoss VLT HVAC Series Programming Manual page 205

VLT ® HVAC Drive Programming Guide
20-94 PID Integral Time
Range:
20.00 s* [0.01 - 10000.00 s]
20-95 PID Differentiation Time
Range:
0.00 s* [0.00 - 10.00 s]
20-96 PID Diff. Gain Limit
Range:
5.0 N/A* [1.0 - 50.0 N/A]
Function:
Over time, the integrator accumulates a contribution to the output from the PID controller as long
as there is a deviation between the reference/setpoint and feedback signals. The contribution is
proportional to the size of the deviation. This ensures that the deviation (error) approaches zero.
Quick response on any deviation is obtained when the integral time is set to a low value. Setting it
too low, however, may cause the control to become unstable.
The value set, is the time needed for the integrator to add the same contribution as the proportional
part for a certain deviation.
If the value is set to 10,000, the controller will act as a pure proportional controller with a P-band
based on the value set in par.20-93
from the proportional controller will be 0.
Function:
The differentiator monitors the rate of change of the feedback. If the feedback is changing quickly,
it will adjust the output of the PID controller to reduce the rate of change of the feedback. Quick
PID controller response is obtained when this value is large. However, if too large of a value is used,
the adjustable frequency drive's output frequency may become unstable.
Differentiation time is useful in situations where extremely fast adjustable frequency drive response
and precise speed control are required. It can be difficult to adjust this for proper system control.
Differentiation time is not commonly used in VLT HVAC Drive applications. Therefore, it is generally
best to leave this parameter at 0 or OFF.
Function:
The differentiator of a PID controller responds to the rate of change of the feedback. As a result,
an abrupt change in the feedback can cause the differentiator to make a very large change in the
PID controller's output. This parameter limits the maximum effect that the PID controller's differ-
entiator can produce. A smaller value reduces the maximum effect of the PID controller's differen-
tiator.
This parameter is only active when par.20-95
MG.11.C6.22 - VLT ® is a registered Danfoss trademark
3 Parameter Description
PID Proportional Gain . When no deviation is present, the output
PID Differentiation Time
is not set to OFF (0 s).
3
3-181