Danfoss VLT AQUA Drive Design Manual page 24

2. Introduction to the VLT AQUA Drive
2.9.2. 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 where multiple feedback
2
signals and/or setpoint references are used. The table below summarizes the additional parame-
ters that may be useful in such applications.
Parameter
Feedback 2 Source
Feedback 3 Source
Feedback 1 Conversion
Feedback 2 Conversion
Feedback 3 Conversion
Reference Feedback
Feedback Function
Setpoint 1
Setpoint 2
Setpoint 3
Setpoint Adjustment Factor
PID Start Speed [RPM]
PID Start Speed [Hz]
On Reference Bandwidth
PID Anti Windup
PID Differentiation Time
PID Diff. Gain Limit
Flow Compensation
Square-linear Curve Approximation
Work Point Calculation
Speed at No-Flow [RPM]
Speed at No-Flow [Hz]
Speed at Design Point [RPM]
Speed at Design Point [Hz]
Pressure at No-Flow Speed
Pressure at Rated Speed
Flow at Design Point
Flow at Rated Speed
Low-pass Filter Time:
Analog Input 53
Analog Input 54
Digital (pulse) input 29
Digital (pulse) input 33
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Par. No. Description of function
20-03 Select the source, if any, for Feedback 2 or 3. This is most commonly a
20-06 drive analog input, but other sources are also available. Par. 20-20 deter-
mines how multiple feedback signals will be processed by the drive's
closed-loop controller. By default, these are set to
20-01 These are used to convert the feedback signal from one type to another,
20-04 such as from pressure to flow, for example.
Flow Pressure
=
20-07
20-12 For setting the unit used for setpoint reference and feedback.
20-20 When multiple feedbacks or setpoints are used, this determines how they
will be processed by the drive's closed-loop controller.
20-21 These setpoints can be used to provide a setpoint reference to the drive's
20-22 closed-loop controller. Par. 20-20 determines how multiple setpoint refer-
20-23 ences will be processed. Any other references that are activated in par.
20-29 group 3-1* will add to these values.
Par. 20-29 can be used to reduce the setpoint at low flow benefiting from
a reduced pipe resistance at reduced flow.
20-82 The parameter that is visible will depend on the setting of par. 0-02, Motor
20-83 Speed Unit. In some applications, and after a start command, it is important
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.
20-84 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
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 correct
the error. This allows the controller to respond more quickly once it can
again control the system.
function stay active continuously.
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 a fast controller re-
sponse, such a response is seldom needed in water systems. The default
value for this parameter is Off, or 0.00 s.
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
controller. This is used to limit the maximum effect of the differentiator.
This is not active when par. 20-95 is set to Off.
22-80 It is sometimes the case that it is not possible for a pressure transducer to
22-81 be placed at a remote point in the system, and it can only be located close
22-82 to the fan/pump outlet. Flow compensation operates by adjusting the set-
22-83 point according to the output frequency, which is almost proportional to
22-84 flow, thus compensating for higher losses at higher flow rates.
22-85 These parameters are used for setting up flow compensation.
22-86
22-87
22-88
22-89
22-90
6-16 This is used to filter out high frequency noise from the feedback signal. The
6-26 value entered here is the time constant for the low-pass filter. The cut-off
5-54 frequency in Hz can be calculated as follows:
5-59
F cut
=
off
−
Variations in the feedback signal whose frequency is below F
used by the drive's closed-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.20.N2.22 - VLT ® is a registered Danfoss trademark.
VLT ® AQUA Drive Design Guide
No function
[0].
Off
[0] disables this function, making the integral
1
T low−pass
2π
cut-off
will be