Permissible Motor-Converter Combinations; Drives With Permanent-Magnet Three-Phase Synchronous Motors - Siemens SINAMICS G130 Engineering Manual

Drive Dimensioning
Engineering Information

Permissible motor-converter combinations

Rated motor current higher than the rated current of the converter or Motor Module
If the motor used has a higher rated current than the rated current of the converter or Motor Module, the motor will
only be able to operate under partial load. The following limit applies:
The maximum possible short-time current of the converter or Motor Module (short-time current = 1.5 • base load
current) should be greater than or equal to the rated current of the connected motor.
It is important to observe this guideline, as very high, modulation-related current spikes caused by the low leakage
inductance of large motors could otherwise occur. These can lead either to shutdown on over-current or, if the total
RMS value of the motor current increases too far due to the high "current ripple", to a continuous reduction in output
power as a result of limits imposed by internal protection mechanisms (overload reaction triggered by I
or thermal monitoring model).
Rated motor current significantly lower than the rated current of the converter or Motor Module
In typical applications with vector control (with or without speed encoder), the rated motor current should equal at
least 25 % of the rated current of the converter or Motor Module. The greater the difference between the rated
currents of motor and converter, the less accurate will be the actual current sensing circuit and the lower the quality
of the vector control. For applications with very high control requirements which use a speed encoder and demand a
very accurate vector control, it is advisable to select a motor rated current which equals at least 50 % of the rated
current of the converter or Motor Module.
No restrictions of this type apply to V/f control mode. Motors with very low rated currents can operate on the
converter. This applies, for example, to roller drive applications in which up to 100 small motors are supplied by a
single converter in extreme cases.

Drives with permanent-magnet three-phase synchronous motors

With SINAMICS converters permanent-magnet, three-phase synchronous motors can also be used alongside three-
phase asynchronous motors. These motors are available as motor series HT-direct 1FW4 as high-torque motors with
high number of poles. They are designed for use with SINAMICS converters as low-speed direct drives and can
replace favorably conventional motor-gearbox combinations. In addition to the motors of series HT-direct 1FW4,
permanent-magnet synchronous motors made by other manufacturers can also be used with SINAMICS converters.
Closed-loop control of permanent-magnet synchronous motors
SINAMICS converters of type G130, G150, S120 and S150 have a closed-loop control function for permanent-
magnet synchronous motors implemented in their firmware.
•
SINAMICS G130 and G150 are designed for sensorless vector control. With these converters, regenerative
energy cannot be returned to the supply system. For this reason, these drives are suitable only for standard
applications with low requirements regarding dynamic performance and accuracy. If the drive has to be
capable of flying restart, i.e. switching onto a rotating motor, a Voltage Sensing Module (VSM) must be
integrated in the converter instead of an encoder module.
•
SINAMICS S120 and S150 are designed for both, sensorless vector control and vector control with speed
encoders. In addition, the servo control mode is available. With these converters, regenerative energy can
be returned to the supply system. These drives are therefore suitable for use with demanding applications
with the highest requirements in terms of dynamic performance and accuracy. Sensorless vector control is
possible for simple, standard applications. Vector control with speed encoder is always required when high
dynamic performance and accuracy are needed. The highest dynamic performance is achieved using the
servo control mode.
Important current derating factors applicable to the converter
Pulse frequency derating
It is essential that SINAMICS converters, when used with permanent-magnet synchronous motors, must be operated
with relatively high pulse frequency due to the eddy current losses in the magnets. Therefore, the factory-set pulse
frequency of 1.25 kHz resp. 2.0 kHz must be increased, which causes a derating of the output current. The derating
factors can be found in the corresponding tables of the unit-specific chapters.
Synchronous motors of the series HT-direct 1FW4 require a pulse frequency of at least 2.5 kHz. Synchronous motors
produced by other manufacturers often require even higher pulse frequencies of up to 4 kHz.
SINAMICS Engineering Manual – May 2008
314/396
© Siemens AG
2
t monitoring