SPECIAL CHARACTERISTICS AFFECTING THE SELECTION
vacon • 13
24-hour s358 (0)201 212 575 • Email: [email protected]
3
Figure 11. DC+ to ground voltage. On the left U
dc
= 1200 V, on the right 800 V.
The battery system does not withstand unfiltered common mode voltage. Because PWM modulation
is a CM voltage source, the DC side of the energy storage system must be stabilized. This means
that there must be a flexible element in electrical system that is able to take this common mode
voltage fluctuation. This element is now a transformer star point (instead of a motor stator star
point) that shall not be grounded.
Figure 12. Transformer must be isolated from ground.
In the grid side filter, if LCL is used, the grounded capacitors cannot be kept connected to ground. If
transformer inductance is bigger or at least the same as proposed grid side inductance, it is
possible to use only an LC filter (sine) to avoid additional voltage drop in the grid side choke.
0
0.00
5
0.01
0.01
5
0.02
0.02
5
0.03
0.03
5
0.04
0
0.00
5
0.01
0.01
5
0.02
0.02
5
0.03
0.03
5
0.04
-1000
-500
0
500
1000
1500
Sampled waveform
time [s]
voltage [V]
voltage [V]
time [s]
-600
-400
-200
0
200
400
600
800
1000
1200
Sampled waveform
CM
Transformer
LCL-filter
AFE
(Active Front End)
DC-link
Summary of Contents for NX6
Page 1: ...vacon nx ac drives design guide hybridization ...
Page 2: ......
