Siemens simovert masterdrives, Справочник

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06.2005 Engineering Information
Siemens AG 6SE7087-6QX70 (Version AE)
SIMOVERT MASTERDRIVES Compendium Motion Control
11-19
11.6 Selection of the rectifier unit for multi-axis drives
When multi-axis drives are used, several inverters are supplied with
power by a rectifier unit. When the rectifier unit is being selected, it
must be determined whether all the drives can work at the same time.
The criteria for making the selection are as follows:
♦
The maximum DC link current occurring must be smaller than the
maximum permissible output current of the rectifier unit. In the case
of a Compact PLUS rectifier unit, if three times the rated current is
utilized, this current must not flow for longer than 250 ms, otherwise
1.6 times the rated current is permissible for 30 s (see technical
data). If a Compact PLUS rectifier unit is not used, the maximum
output current must not exceed 1.36 times the rated current for a
time of 60 s (see technical data).
♦
The arithmetic mean value of the DC link current must be smaller
than the rated value of the DC link current of the rectifier unit when
the maximum cycle time is 300 s.
The second condition arises from the fact that the forward losses in the
rectifier are approximately proportional to the DC link current. The rms
value can also be calculated instead of the arithmetic mean value. One
is then more on the safe side, but it requires more calculation work.
The DC link current is calculated as follows:
I I
Link ct Link Inv Re
=
∑
I
P
U
Link Inv
Mot
Mot Inv Link
=
⋅ ⋅ η η
DC link current of an inverter in
motor operation
U U
Link Line
= ⋅
135 .
DC link voltage
P
M n
Mot
Mot Mot
=
⋅
9 55 .
Motor output in W
M
Mot
Motor torque in Nm
n
Mot
Motor speed in rpm
η
Mot
Motor efficiency
η
Inv
Inverter efficiency (
≈
0.98)
When the rectifier is being selected, only motor operation needs to be
considered. The maximum DC link current occurs when all the motors
connected to the inverters have to simultaneously produce the
maximum motor output. If this is not the case, the rectifier unit can be
smaller. The total number of connected inverters, however, must not be
too large because, otherwise, precharging of the rectifier unit can be
overloaded (see technical data).