Danfoss VLT FC 103, Руководство по конструкции

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2.4 Control Structures
2.4.1 Control Structure Open Loop
When operating in open-loop mode, the frequency
converter responds to input commands manually via the
LCP keys or remotely via the analog/digital inputs or serial
bus.
In the configuration shown in Illustration 2.8 , the frequency
converter operates in open-loop mode. It receives input
from either the LCP ( Hand mode) or via a remote signal
( Auto mode). The signal (speed reference) is received and
conditioned with the following:
•
Programmed minimum and maximum motor
speed limits (in RPM and Hz).
•
Ramp-up and ramp-down times.
•
Motor rotation direction.
The reference is then passed on to control the motor.
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
Illustration 2.8 Block Diagram of Open-loop Mode
2.4.2 Control Structure Closed Loop
In closed-loop mode, an internal PID controller allows the
frequency converter to process system reference and
feedback signals to act as an independent control unit. The
frequency converter can provide status and alarm
messages, along with many other programmable options,
for external system monitoring while operating
independently in closed loop.
P 20-81
PID Normal/Inverse
Control
PID
Ref.
Handling
Feedback
Handling
Scale to
speed
P 4-10
Motor speed
direction
To motor
control
(Illustra-
tion)
(Illustra-
tion)
130BA359.12

100%
0%
-100%
100%
*[-1]
_
+
Illustration 2.9 Block Diagram of Closed-loop Controller
For example, consider a pump application in which the
speed of a pump is controlled so that the static pressure in
a pipe is constant (see
Illustration 2.9 ). The frequency
converter receives a feedback signal from a sensor in the
system. It compares this feedback to a setpoint reference
value and determines the error, if any, between these 2
signals. It then adjusts the speed of the motor to correct
this error.
The static pressure setpoint is the reference signal to the
frequency converter. A static pressure sensor measures the
actual static pressure in the pipe and provides this
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