Danfoss VLT Series Design Manual page 38

2. Introduction to the VLT HVAC Drive
Parameter
Custom Refrigerant A1
Custom Refrigerant A2
2 Custom Refrigerant A3
PID Start Speed [RPM]
PID Start Speed [Hz]
On Reference Bandwidth par. 20-84
PID Anti Windup
PID Differentiation Time
PID Diff. Gain Limit
Low-pass Filter Time:
Analog Input 53
Analog Input 54
Digital (pulse) input 29
Digital (pulse) input 33
38
Description of function
par. 20-31 When par. 20-30 is set to
par. 20-32 parameters are used to define the value of coeffi-
par. 20-33 cients A1, A2 and A3 in the conversion equation:
Temperature
par. 20-82 The parameter that is visible will depend on the
par. 20-83 setting of par. 0-02, Motor Speed Unit. In some
applications, and after a start command, it is im-
portant to quickly ramp the motor up to a pre-
determined speed before activating the drive's
closed-loop controller. This parameter defines that
starting speed.
This determines how close the feedback must be
to the setpoint reference for the drive to indicate
that the feedback is equal to the setpoint.
On
par. 20-91 [1] effectively disables the closed-loop
controller's integral function when it is not possible
to adjust the output frequency of the drive to cor-
rect the error. This allows the controller to respond
more quickly once it can again control the system.
Off
[0] disables this function, making the integral
function stay active continuously.
par. 20-95 This controls the output of the drive's closed-loop
controller based on the rate of change of feedback.
While this can provide fast controller response,
such response is seldom needed in HVAC systems.
The default value for this parameter is Off, or 0.00
s.
par. 20-96 Because the differentiator responds to the rate of
change of the feedback, a rapid change can cause
a large, undesired change in the output of the con-
troller. This is used to limit the maximum effect of
the differentiator. This is not active when par.
20-95 is set to Off.
par. 6-16 This is used to filter out high frequency noise from
par. 6-26 the feedback signal. The value entered here is the
par. 5-54 time constant for the low-pass filter. The cut-off
par. 5-59 frequency in Hz can be calculated as follows:
F =
cut off
−
Variations in the feedback signal whose frequency
is below F
cut-off
loop controller, while variations at a higher fre-
quency are considered to be noise and will be
attenuated. Large values of Low-pass Filter Time
will provide more filtering, but may cause the con-
troller to not respond to actual variations in the
feedback signal.
MG.11.B4.22 - VLT ® is a registered Danfoss trademark.
VLT ® HVAC Drive Design Guide
User defined
[7], these
A 2
=
( ( + 1 ) − 1 )
ln pressure A
1
T
2π
low− pass
will be used by the drive's closed-
A
− 3