Working Principle - Danfoss VLT AutomationDrive FC 302 Installation Manual

Introduction
1 1

1.3.2 Working Principle

The 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
380 to
RFI
500 VAC
Figure 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
THDi less than 5% at full load for <3% pre-distortion on a 3% unbalanced 3-phase grid.
6
VLT
132–630 kW
HI Reactor
L
m
L
ac
L
Optional
m
Optional
Manual
Fuses
Disconnect
L
ac
L
m
L
ac
Danfoss A/S © Rev. 04/2015 All rights reserved.
®
AutomationDrive FC 302 Low Harmonic Drive
Soft-Charge
Resistor
AC
Contactor
Relay 12
Control & AUX
Feedback C C C
ef ef ef
R R R
ef ef ef
Main's
Converter Side
Filter
L I
c r
L I
c s
L I
c t
3
3
Capacitor
Current Sensors
AF Current
Sensors
VLT Drive
3
CTs
Power Stage
MG37A322