SIEMENS
5/7
Siemens D 15.1 · 2017
Engineering Information
Output voltage and current
5
■
Function
Output voltage characteristics
Output voltage
Harmonic voltage factor as a function of the number of
750 V cells (6SR4... drive types)
Harmonic voltage factor as a function of the number of
690 V cells (6SR3... drive types)
Output current
Output voltage capability
Speed reduction as a result of an undervoltage condition at the
input
The drive limits are described in more detail below in the event
that the input voltage falls below 90 %.
When the input line voltage drops below 90 % of its rated value,
the drive limits the amount of power (and hence the torque) that
can be delivered to the load. The maximum permissible drive
power as a function of line voltage is shown in the diagram be-
low. At 66 % input voltage, the maximum drive power is limited
to 50 %, and is quickly reduced to a slightly negative value ("re-
gen limit") at 65 %. This limit forces the drive to absorb power
from the motor and maintain the (power cell) DC bus voltages in
case the input voltage recovers during MV ride-through. The limit
is implemented as an inverse function of speed in order to main-
tain constant power flow to the (cell) DC bus.
Drive power (
P
max
) as a function of input voltage imbalance (
E
rms
)
Quantity
Value
Distortion at rated voltage
(as a % of rated output voltage)
without overmodulation:
2 %
(for the first 20 harmonics)
with overmodulation:
3 %
1)
(for the first 20 harmonics)
Imbalance
(as a % of rated output voltage)
1 %
dv/dt
2)
< 1000 V/μs for 6SR3... drives
< 3000 V/μs for 6SR4... drives
Harmonic voltage factor (HVF)
3)
< 0.02 for drives with number of
cells
9
< 0.035 for drives with number of
cells = 6
Number of cells
Output voltage
kV
HVF
9
4.16
4)
0.019
15
6.00
0.008
15
6.60
0.007
18
7.20
0.006
18
8.00
0.005
21
9.20
0.004
24
10.00
0.004
Number of cells
Output voltage
kV
HVF
9
2.40
0.019
9
3.30
0.017
12
4.16
0.009
12
4.80
0.010
15
6.00
0.007
18
6.90
0.005
Quantity
Value
DC component
(as % of the rated output current)
1 %
Distortion or THD
5) 6)
(as % of the rated output current; when
motor and drive ratings are equal and the
motor leakage reactance is 16 % or
higher)
without overmodulation:
3 %
with overmodulation:
4.5 %
1)
Also see footnote 4) of the following table
.
2)
Although output dv/dt values are high, the control ensures that only one
cell switches at a particular instant. The magnitude of voltage steps
applied to the motor are thus smaller than the rated voltage (and equal to
the DC bus voltage of a single cell), which limits the stress on the insulation
of the first few turns (of the motor winding).
3)
NEMA MG 1, Part 30, recommends that no motor derating is required when
the inverter voltage waveform has an HVF value that is less than 0.03. HVF
is defined as:
where
V
n
is the harmonic amplitude referred to the rated quantity, and n is
the harmonic order (= ratio of harmonic frequency to fundamental
frequency).
SINAMICS PERFECT HARMONY GH180 drives (with 9 cells or more) meet
this requirement. Therefore, any temperature rise due to switching
harmonics is negligible and no motor derating is needed.
4)
Note:
Although overmodulation is allowed for all drives with article number
6SR4..., only those with this cell count and this rated output voltage can
operate in overmodulation in the 95 to 100 % speed range. Higher output
voltage and current harmonics are present for the 5th and 7th harmonic
frequencies. This is reflected in the THD and torque pulsation values.
5)
The maximum output current distortion limit of 3 % is valid for drives with
number of cells
9 and no overmodulation. As the number of cells
increases, the current distortion decreases to below 2 % for 18 cell drives
with a typical motor.
6)
Most motors have a leakage reactance that is greater than 16 %. Output
current distortion is inversely proportional to motor leakage reactance, i.e.
as motor leakage reactance decreases, output current distortion
increases.
HVF =
V
2
n
n
±
²
±
n
≥ 5
%
%
105
100
50
65
66
90
0
P
max
E
rms max
Regen limit
G_D015_EN_00012
© Siemens AG 2017