Working Principle - Danfoss VLT AQUA Drive FC 202 Operating Instructions Manual

Introduction

1.3.2 Working Principle

The VLT Low Harmonic Drive is a high-power frequency converter with an integrated active filter. An active filter is a device
that actively monitors harmonic distortion levels and injects compensative harmonic current onto the line to cancel the
harmonics.
Mains
Optional
Optional Optional
380 to
Manual
RFI Fuses
Disconnect
500 VAC
Illustration 1.1 Basic Layout for the Low Harmonic Drive
Low Harmonic Drives are designed to draw an ideal sinusoidal current waveform from the supply grid with a power factor
of 1. Where traditional non-linear load draws pulse-shaped currents, the Low Harmonic Drive compensates that via the
parallel filter path, lowering the stress on the supply grid. The Low Harmonic Drive meets the highest harmonic standards
with a THiD less than 5% at full load for <3% pre-distortion on a 3% unbalanced 3-phase grid.
MG21B202
Operating Instructions
HI Reactor
AC
Contactor
L
m
L
ac
L
m
L
ac
L
m
Relay 12
Control & AUX
L
ac C
ef
Feedback
R
ef
Danfoss A/S © Rev. 2014-01-22 All rights reserved.
Relay 12
Control & AUX
Feedback
Soft-Charge
NC
Relay
Converter
Side Filter
L I
c r
L I
c s
L I
c t
3
Capacitor
AF Current
Current Sensors
C C
Sensors
ef ef
R R
ef ef
Frequency converter
3
Main's CTs
Power Stage
3
5
1 1