Control Structures - Danfoss VLT HVAC Drive FC 100 Series Design Manual

Introduction to VLT® HVAC D...
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
L1 91
L2 92
L3 93
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
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
Reference
handling
Remote
reference
Auto mode
Linked to hand/auto
Hand mode
Local
reference
scaled to
RPM or Hz
LCP Hand on,
o and auto
on keys
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.
®
VLT HVAC Drive Design Guide
Load sharing +
89(+)
R inr Inrush
88(-)
Load sharing -
plus
P 4-13
Motor speed
high limit [RPM]
P 4-14
Motor speed
high limit [Hz]
Remote
Reference
Local
P 4-11
Motor speed
low limit [RPM]
P 3-13
Reference
P 4-12
site Motor speed
low limit [Hz]
MG11BB22 - VLT ® is a registered Danfoss trademark
LC Filter +
(5A)
LC Filter -
(5A)
and can handle normal squirrel cage asynchronous motors.
100%
P 3-4* Ramp 1
P 3-5* Ramp 2
0%
Ramp
100%
-100%
2
R+ Brake
Resistor
82
R-
81
U 96
V 97
M
W 98
To motor
control
P 4-10
Motor speed
direction
2-23
2