Danfoss VLT FCD 303 Operating Instructions Manual page 6

Control principle
A frequency converter rectifies AC voltage from
the mains supply into DC voltage, following which
it changes this voltage to an AC voltage with
variable amplitude and frequency.
The motor thus recei v es a variable voltage and
frequency, which enables infinitely variable speed
control of three-phase, standard AC motors.
1. Mains voltage
3 x 380 - 480 V AC, 50 / 60 Hz.
2. Rectifier
Three-phase rectifier bridge which rectifies AC
voltage into DC voltage.
3. Intermediate circuit
√2 x mains voltage [V].
DC voltage
4. Intermediate circuit coils
Evens out the intermediate circuit current and
limits the load on mains and components (mains
transformer, cables, fuses and contactors).
5. Intermediate circuit capacitor
Evens out the intermediate circuit voltage.
6. Inverter
Converts DC voltage into a variable AC voltage
with a variable frequency.
7. Motor voltage
Variable AC voltage depending on supply voltage.
Variable frequency: 0.2 - 132 / 1 - 1000 Hz.
8. Control card
Here is the computer that controls the inverter
which generates the pulse pattern by which
the DC voltage is converted into variable AC
voltage with a variable frequency.
6
®
VLT FCD Series
MG.04.B7.02 - VLT is a registered Danfoss trademark