Line Drop-Out; Built-In Pid Controllers - Danfoss VLT AQUA Drive FC 202 Design Manual

Product Overview
2 2
•
Mechanical thermal switch (Klixon type) on a DI.
•
Via the built-in electronic thermal relay (ETR) for
asynchronous motors.
ETR calculates motor temperature by measuring current,
frequency, and operating time. The adjustable frequency
drive displays the thermal load on the motor in percentage
and can issue a warning at a programmable overload
setpoint.
Programmable options at the overload allow the adjustable
frequency drive to stop the motor, reduce output, or
ignore the condition. Even at low speeds, the adjustable
frequency drive meets I2t Class 20 electronic motor
overload standards.
t [s]
2000
1000
600
500
400
300
200
100
60
50
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10
1.0
Figure 2.18 ETR Characteristics
The X-axis in Figure 2.18 shows the ratio between I
I nominal. The Y-axis shows the time in seconds before
motor
the ETR cuts off and trips the adjustable frequency drive.
The curves show the characteristic nominal speed, at twice
the nominal speed and at 0.2 x the nominal speed.
At lower speed, the ETR cuts off at lower heat due to less
cooling of the motor. In that way, the motor is protected
from being overheated even at low speed. The ETR feature
calculates the motor temperature based on actual current
and speed. The calculated temperature is visible as a
readout parameter in 16-18 Motor Thermal.
30
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PTC thermistor input on VLT
Tthermistor Card MCB 112 (ATEX
approved).
1.2 1.4 1.6 1.8 2.0
Danfoss A/S © 09/2014 All rights reserved.
®
VLT AQUA Drive FC 202
®
PTC

2.6.3 Line Drop-out

During a line drop-out, the adjustable frequency drive
keeps running until the intermediate circuit voltage drops
below the minimum stop level, which is typically 15%
below the lowest rated supply voltage. The AC line voltage
before the drop-out and the motor load determines how
long it takes for the adjustable frequency drive to coast.
The adjustable frequency drive can be configured
(14-10 Line Failure) to different types of behavior during
line drop-out,
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•
•
•
Flying start
This selection makes it possible to catch a motor that is
spinning freely due to a line drop-out. This option is
relevant for centrifuges and fans.
Kinetic backup
This selection ensures that the adjustable frequency drive
fOUT = 1 x f M,N
runs as long as there is energy in the system. For short line
fOUT = 2 x f M,N
power drop-out, the operation is restored upon line return,
fOUT = 0.2 x f M,N
without bringing the application to a stop or losing control
at any time. Several variants of kinetic backup can be
selected.
IM
Configure the behavior of the adjustable frequency drive
IMN
at line drop-out, in 14-10 Line Failure and 1-73 Flying Start.

2.6.4 Built-in PID Controllers

and
motor
The four built-in proportional, integral, derivative (PID)
controllers eliminate the need for auxiliary control devices.
One of the PID controllers maintains constant control of
closed-loop systems where regulated pressure, flow,
temperature, or other system requirements must be
maintained. The adjustable frequency drive can provide
self-reliant control of the motor speed in response to
feedback signals from remote sensors. The adjustable
frequency drive accommodates two feedback signals from
two different devices. This feature allows regulating a
system with different feedback requirements. The
adjustable frequency drive makes control decisions by
comparing the two signals to optimize system
performance.
Trip Lock once the DC link is exhausted.
Coast with flying start whenever line power
return (1-73 Flying Start).
Kinetic backup.
Controlled ramp-down.
MG20N622