Mg.11.B4.22 - Vlt - Danfoss VLT Series Design Manual

2. Introduction to the VLT HVAC Drive
The following parameters are relevant for a simple PID control application:
Parameter
2
Feedback 1 Source par. 20-00 Select the source for Feedback 1. This is most commonly an
Reference/Feed-
back Unit
PID Normal/Inverse
Control
PID Proportional
Gain
PID Integral Time
This table summarizes the parameters that are needed to set up the drive's closed-loop controller
when a single feedback signal with no conversion is compared to a single setpoint. This is the
most common type of closed-loop controller.
2.8.2. Closed-loop Control Relevant Parameters
The drive's closed-loop controller is capable of handling more complex applications, such as sit-
uations where a conversion function is applied to the feedback signal or situations where multiple
feedback signals and/or setpoint references are used. The table below summarizes the additional
parameters that may be useful in such applications.
36
Description of function
analog input, but other sources are also available. Use the
scaling of this input to provide the appropriate values for this
signal. By default, Analog Input 54 is the default source for
Feedback 1.
par 20-12 Select the unit for the setpoint referenceand feedback for the
drive's closed-loop controller. Note: Because a conversion
can be applied to the feedback signal before it is used by the
closed-loop controller, the reference/feedback unit (par.
20-12) may not be the same as the feedback source unit
(par. 20-02, 20-05 and 20-08).
Normal
par. 20-81 Select [0] if the motor's speed should decrease when
the feedback is greater than the setpoint reference. Select
Inverse
[1] if the motor's speed should increase when the
feedback is greater than the setpoint reference.
par. 20-93 This parameter adjusts the output of the drive's closed-loop
control based on the error between the feedback and the
setpoint reference. Quick controller response is obtained
when this value is large. However, if a value that is too large
is used, the drive's output frequency may become unstable.
par. 20-94 Over time, the integrator adds (integrates) the error between
the feedback and the setpoint reference. This is required to
ensure that the error approaches zero. Quick controller re-
sponse is obtained when this value is small. However, if a
value that is too small is used, the drive's output frequency
may become unstable. A setting of 10,000 s disables the in-
tegrator.

MG.11.B4.22 - VLT

® is a registered Danfoss trademark.
VLT ® HVAC Drive Design Guide