Danfoss VLT Decentral FCD 300 Operating Instructions Manual page 11

1 Introduction to FCD 300
1.3.3 Control Principle
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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 receives 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
DC voltage ≅ √2 x mains voltage [V].
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.
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MG.04.B8.02 - VLT is a registered Danfoss trademark
VLT® Decentral FCD