Siemens SINAMICS G130 Engineering Manual page 515

If the converter trips during operation in the field-weakening range, the reactive current I in the stator, which weakens
the rotor field, is no longer present and therefore also the voltage drop ΔV. The voltage V at the motor terminals and
at the converter output thus increases within a few 10 ms to the value of the EMF depending on the field-weakening
speed of the motor. As a result, the DC link is charged via the free-wheeling diodes of the inverter to the amplitude of
the EMF of the motor.
Protection measures in the field-weakening range
In order that the maximum permissible DC link voltage is not exceeded and the DC link capacitors are not damaged
in the event of a trip of the converter during operation in the field-weakening range, either the motor speed must be
limited, or other suitable measures must be taken to ensure that the maximum permissible DC link voltage is not
exceeded, e.g. by the use of a appropriate dimensioned Braking Module.
1. Limitation of the speed in the field-weakening range
With SINAMICS G130, G150, S120 (Chassis and Cabinet Modules) and S150 operating in vector control mode, the
speed in the field-weakening range is limited to the value n
Key to abbreviations:
·
n Maximum permissible speed in the field-weakening range for the protection of the converter
max
·
n Rated motor speed
Rated
·
I Rated motor current
Rated
·
P Rated motor output power
Rated
·
U Maximum permissible DC link voltage of the converter or inverter in dependency on the
DC max
line supply voltage:
- 820 V for units with a line supply voltage of 380 V – 480 V 3AC
- 1022 V for units with a line supply voltage of 500 V – 600 V 3AC
- 1220 V for units with a line supply voltage of 660 V – 690 V 3AC
With 1FW4 synchronous motors from the SIMOTICS HT series HT-direct range, the maximum permissible field-
weakening speed is limited to 1.2 times the rated speed. Thus it lies within the limit defined in the given formula. With
synchronous motors of other manufacturers, often much higher field-weakening speeds are permissible.
2. Use of a Braking Module
The speed limit can be parameterized to a higher setting. However, the essential requirement for this is that the drive
is equipped with an appropriate dimensioned Braking Module in order to limit the DC link voltage in the event of a trip
of the drive. With the implementation of this measure, field-weakening speeds up to 2.5 times higher than the rated
speed can be achieved.
Protection concept
Since permanent-magnet synchronous motors with a rotating rotor are an active voltage source generating a voltage
in proportion to the speed, it is not safe simply to disconnect the converter from the supply system and wait for the
DC link to discharge before starting with maintenance or repair work. Additional measures must be taken to ensure
that the rotating synchronous motor is not generating any voltage at the converter output. This can be achieved either
by blocking the motor mechanically or, in cases where the type of application means that rotary movement of the
motor cannot be completely precluded, by disconnecting the converter from the motor by a switch at the output side
of the converter.
It is generally not safe to perform any maintenance or repair work on the motor terminal box or the motor cable, until
measures have been taken to preclude any risk of rotor movement, the supplying converter is reliably disconnected
from the supply system and the converter DC link is discharged.
max
V
3
= × ×
DC max
n n
max Rated
2 P
SINAMICS Engineering Manual – November 2015
Drive Dimensioning
Engineering Information
by factory settings, in order to protect the converter.
×
I
Rated
.
Rated
515/528
Ó Siemens AG