VLT® 5000 Crane
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Control Principle
A frequency converter rectifies AC voltage from mains
into DC voltage. This DC voltage is then converted into
a AC voltage with a variable amplitude and frequency.
The motor is thus supplied with variable voltage and
frequency, which enables infinitely variable speed
control of three-phased, standard AC motors.
1. Mains voltage
3 x 400 - 500 V AC, 50 / 60 Hz.
2. Rectifier
A three-phase rectifier bridge that rectifies AC
voltage into DC voltage.
3. Intermediate circuit
4. Intermediate circuit coils
Smooth the intermediate circuitcurrent and limit the
load on mains and components (mains transformer,
wires, fuses and contactors).
5. Intermediate circuit capacitors
Smooth the intermediate circuit voltage.
6. Inverter
Converts DC voltage into variable AC voltage
with a variable frequency.
7. Motor voltage
Variable AC voltage, 0-100% of mains supply voltage.
Variable frequency: 0 - 300 Hz.
8. Control circuit
On basis of parameters, reference settings and input
signals, pulse patterns are generated for forming
the variable motor voltage and frequency.
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Flux Vector Control Principle
The aim of developing the Flux Vector control
principle has been to obtain a robust motor control
that is tolerant to different motor characteristics
without motor derating being required.
The current is split into magnetising and
torque-generating parts and provides for much
better and quicker estimation of the actual motor
loads. It is now possible to compensate for rapid
load changes. Full torque as well as extremely
accurate speed control can now be obtained even
at low speeds or even at standstill.
Good torque control properties and smooth transitions
to and from current limit operation are ensured.
Advantages of the Flux Vector control system:
-
Accurate speed control down to 0 speed
-
Quick response from received signal to
full motor shaft torque
-
Good compensation for step loads
-
Controlled transition from normal operation to
current limit operation (and vice versa)
-
Torque control, comprising control of both
the torque-generating and the magnetising
component of the current
-
Full holding torque
Programmable signal outputs
VLT 5000 Crane uses a digital technique which makes
it possible to program the signal outputs.
For the user, it is easy to program the desired functions
by means of the control panel on VLT 5000 Crane
or the RS 485/RS 232 user interfaces.
Protection against mains interference
VLT 5000 Crane is protected against the transients
that occur in the mains supply, eg. when switching
power factor correction or when fuses blow.
The rated motor voltage and full torque can be
maintained all the way down to 10% undervoltage
in the mains supply.
MG.50.N4.02 - VLT is a registered Danfoss trademark
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