2.7.25 Why use a Adjustable Frequency Drive for Controlling Fans and Pumps?
A Adjustable frequency drive takes advantage of the fact that centrifugal fans and pumps follow the laws of proportionality
for such fans and pumps. For further information, see the text and figure
The Laws of Proportionality
.
2.8 Control Structures
2.8.1 Control Principle
Inrush
R inr
Load sharing -
Load s
LC Filter -
(5A)
LC
(5A)
Brake
Resistor
130BA193.13
M
L2 92
L1 91
L3 93
89(+)
88(-)
R+
82
R-
81
U 96
V 97
W 98
P 14-50
Figure 2.21 Control structures.
The Adjustable frequency drive is a high performance unit for demanding applications. It can handle various kinds of motor
control principles such as U/f special motor mode and VVC
plus
and can handle normal squirrel cage asynchronous motors.
Short-circuit behavior on this Adjustable frequency drive depends on the three current transducers in the motor phases.
In
1-00 Configuration Mode
, it can be selected if open-loop or closed-loop is to be used
2.8.2 Control Structure Open-loop
130BB153.10
100%
0%
-100%
100%
P 3-13
Reference
site
Local
reference
scaled to
RPM or Hz
Auto mode
Hand mode
LCP Hand on,
off and auto
on keys
Linked to hand/auto
Local
Remote
Reference
Ramp
P 4-10
Motor speed
direction
To motor
control
Reference
handling
Remote
reference
P 4-13
Motor speed
high limit [RPM]
P 4-14
Motor speed
high limit [Hz]
P 4-11
Motor speed
low limit [RPM]
P 4-12
Motor speed
low limit [Hz]
P 3-4* Ramp 1
P 3-5* Ramp 2
Figure 2.22 Open-loop structure.
In the configuration shown in
Figure 2.22
,
1-00 Configuration Mode
is set to Open-loop [0]. The resulting reference from the
reference handling system or the local reference is received and fed through the ramp limitation and speed limitation
before being sent to the motor control.
The output from the motor control is then limited by the maximum frequency limit.
Introduction to VLT® HVAC D...
VLT
®
HVAC Drive Design Guide
MG11BB22 - VLT
®
is a registered Danfoss trademark
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