Introduction To The Low Harmonic Drive; Working Principle; Ieee519 Compliance - Danfoss VLT AutomationDrive FC 300 Operating Instructions Manual

Introduction to the Low Har...

3 Introduction to the Low Harmonic Drive

3.1.1 Working Principle

The VLT Low Harmonic Drive is a VLT High Power
frequency converter with an integrated active filter. An
active filter is a device that actively monitors harmonic
Mains
Optional
Optional Optional
380 to
Manual
RFI
Fuses
500 VAC Disconnect
Illustration 3.1 Basic layout for the Low Harmonic Drive

3.1.2 IEEE519 Compliance

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 toughest harmonic standards and has a THiD of less
than 5% at full load for <3% pre-distortion on a 3%
unbalanced three-phased grid. The unit is designed to
meet IEEE519 recommendation for Isc/Il >20 for both
uneven and even individual harmonic levels. The filter
portion of the low harmonic drives has a progressive
switching frequency which leads to a wide frequency
spreads giving lower individual harmonic levels above the
50th.
VLT Automation Low Harmonic Drive Operating Instructions
Relay 12
Control & AUX
Feedback
HI Reactor
AC
Contactor
L
m
L
ac
L
m
L
ac
L
m
Relay 12
Control & AUX
L
ac C C
ef ef
Feedback
R R
ef
®
MG34O202 - VLT is a registered Danfoss trademark
distortion levels and injects compensative harmonic
current onto the line to cancel out the harmonics.
Soft-Charge
NC
Relay
Converter
Side Filter
L
I
c r
L I
c s
L I
c t
3
3
Capacitor
AF Current
Current Sensors
C
Sensors
ef
R
ef ef
Frequency converter
3
Main's CTs
10
9
8
7
6
I [%]
5
4
3
2
1
0
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50
Illustration 3.2 Typical harmonic frequency spectrum and THD
value at the mains terminals of the drive
n = harmonic order
⃟.....IEEE519 (Isc/IL>20) limits for individual harmonics
Power Stage
[n]
3 3
11