3 Introduction to VLT
®
Micro Drive
3.1 Control Structures
In
1-00 Configuration Mode
it can be selected if open or
closed loop is to be used.
3.1.1 Control Structure Open Loop
130BB892.10
100%
0%
-100%
100%
Local
reference
scaled to
Hz
Auto mode
Hand mode
LCP Hand on,
off and auto
on keys
Local
Remote
Reference
Ramp
P 4-10
Motor speed
direction
To motor
control
Reference
handling
Remote
reference
P 4-14
Motor speed
high limit [Hz]
P 4-12
Motor speed
low limit [Hz]
P 3-4* Ramp 1
P 3-5* Ramp 2
Illustration 3.1 Open Loop Structure
In the configuration shown in
Illustration 3.1
,
1-00 Configu-
ration Mode
is set to
[0] Open loop
. 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.
3.1.2 Local (Hand On) and Remote (Auto
On) Control
The frequency converter can be operated manually via the
local control panel (LCP) or remotely via analog/digital
inputs or serial bus. If allowed in
0-40 [Hand on] Key on
LCP
,
0-44 [Off/Reset] Key on LCP
, and
0-42 [Auto on] Key on
LCP
, it is possible to start and stop the frequency converter
by LCP using the [Hand On] and [Off/Reset] keys. Alarms
can be reset via the [Off/Reset] key. After pressing the
[Hand On] key, the frequency converter goes into Hand
Mode and follows (as default) the local reference set by
using the LCP potentiometer (LCP 12) or [
▲
]/[
▼
] (LCP 11).
The potentiometer can be disabled by parameter P6-80. If
potentiometer is disabled, arrow keys can be used for
adjusting reference.
After pressing the [Auto On] key, the frequency converter
goes into Auto mode and follows (as default) the remote
reference. In this mode, it is possible to control the
frequency converter via the digital inputs and RS-485. See
more about starting, stopping, changing ramps and
parameter set-ups etc. in parameter group 5-1* (Digital
Inputs) or parameter group 8-5* (Serial Communication).
Hand
On
Off
Reset
Auto
On
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Illustration 3.2
Local reference forces the configuration mode to open
loop, independent on the setting of
1-00 Configuration
Mode
.
Local Reference is restored at power-down.
3.1.3 Control Structure Closed Loop
The internal controller allows the frequency converter to
become an integral part of the controlled system. The
frequency converter receives a feedback signal from a
sensor in the system. It then compares this feedback to a
set-point reference value and determines the error, if any,
Introduction to VLT® Micro ...
VLT
®
Micro Drive FC 51 Design Guide
18
MG02K202 - VLT
®
is a registered Danfoss trademark
3
3
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