8
05.01
8.12 Induction motor operation
8-304
© Siemens AG 2008 All Rights Reserved
SIMODRIVE 611 Configuration Manual (PJU) – 05/2008 Edition
8.12 Induction motor operation
8.12.1 Operating several induction motors in parallel
Several motors can also be operated in parallel on a power module, for each
axis. When selecting the motor and drive module, several engineering guide-
lines must be observed.
When expanded to the maximum, a drive configuration for parallel operation
can comprise up to eight motors. Motors connected to a drive module in parallel
must have the same V/f characteristics. Further, we recommend that the motors
have the same number of poles. If more than two motors are connected to a
drive module, then these should essentially have the same power ratings.
For a 2–motor configuration, the difference between the power ratings of the
motors should not exceed a ratio of 1:10.
The following engineering guidelines must be carefully observed:
Selecting the size of the drive module
– Steady–state operation of the motors connected in parallel – namely in
the closed–loop controlled range (> n
min
1)
) and preferably in the rated
speed range:
Σ rated motor currents rated current of the drive module
– Operation of motors connected in parallel with dynamic load (where the
load condition changes quickly) and in the open–loop controlled range
require an additional dimensioning:
1.2 (Σ rated motor currents) rated current of the drive module
– The current limit of the drive module must be increased to 150% of the
rated current when commissioning the system.
The motors should not be subject to torques that exceed their rated torque.
For special high–speed induction motors, e.g. for woodworking, a series
reactor must always be located between the drive module and the motor
group:
Rated reactor current: rms current of the motor group
2)
When the above information and instructions are taken into consideration, the
individual motors are able to correct even for dynamic load and speed steps.
”Stable” operation without stalling – also for individual motors – is achieved
when following the dimensioning guidelines specified above. The speeds of the
individual motors depend on the load. The currently set speeds can drift apart
by several percent due to the closed–loop group slip control.
1) Standard motor: 2-pin > 600 RPM
4-pin > 300 RPM
6-pin > 200 RPM
8-pin > 150 RPM
Special motors: n
min
>
40 V • n
rated
>
U
rated
motor
600 RPM
No. of pole pairs
2) Σ Rated motor currents, or when taking into account the load duty cycles, the total rms current of the motor group.
8 Im
ortant Circuit Information 10.0402.07
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