The Pulse Frequency And Its Influence On Key System Properties - Siemens SINAMICS G130 Engineering Manual

The pulse frequency and its influence on key system properties

The pulse frequency of the inverter is an important parameter which has a crucial influence on various properties of
the drive system. It can be varied within certain given limits. In order to reduce the motor noise, reach very high
output frequencies or in the event that sinus filters are to be used at the converter output, it is sensible, or rather
necessary, to increase the pulse frequency.
The following aspects of the pulse frequency are described briefly below:
•
The pulse frequency factory settings
•
The limits within which the pulse frequency can be adjusted
•
The effect of the pulse frequency on various properties of the drive system
•
When it is advisable or even essential to change the pulse frequency
•
What needs to be noted in connection with motor-side options (motor reactor, motor filter).
Factory settings and pulse frequency setting ranges
The pulse frequency of the motor-side inverter on SINAMICS G130, G150, S150, S120 (Chassis and Cabinet
Modules) operating in vector control mode is preset at the factory to 2.0 kHz or 1.25 kHz as specified in the table
below.
Line supply voltage Power
≤ 250 kW
380 V to 480 V 3AC
≥ 315 kW
500 V to 600 V 3AC All power ratings
660 V to 690 V 3AC All power ratings
Converter-dependent factory setting of pulse frequency for SINAMICS G130, G150, S150
and for SINAMICS S120 Motor Modules, Chassis and Cabinet Modules
The pulse frequency can be varied in discrete steps. Possible settings correspond to twice the factory setting value in
each case as well as whole multiples thereof. Depending on the unit type, the pulse frequency can therefore be
increased to 8 kHz (when factory setting is 2 kHz) or to 7.5 kHz (when factory setting is 1.25 kHz). Switching between
integer multiples of the pulse frequency is also possible when the drive is in operation.
With introduction of firmware version V2.4 in the summer of 2006 intermediate values can also be parameterized,
allowing the pulse frequency to be set in relatively fine increments. This setting of intermediate values is only possible
when the drive is not in operation.
Influence of the pulse frequency on the inverter output current
The pulse frequency factory setting of either 2.0 kHz or 1.25 kHz is relatively low to generate low inverter switching
losses. If the pulse frequency would be increased, and this can be done at any time by adjustment of the parameter
settings, the switching losses in the inverter and thus the overall losses in the converter would increase accordingly.
The result would be overheating of the power unit if the inverter would operate at full capacity. For this reason, the
conducting losses must be lowered in order to compensate for the increase of the switching losses. This can be
achieved by reducing the permissible output current (current derating). The pulse-frequency-dependent current
derating is specific to individual units. This has to be taken into account when dimensioning a converter. The derating
factors for integer multiples of factory settings can be found in the chapters on specific unit types. The derating
factors for intermediate values can be ascertained through linear interpolation between the corresponding table
values.
Influence of the pulse frequency on losses and efficiency of inverter and motor
With the factory set pulse frequency of 2.0 kHz or 1.25 kHz, the motor current is already close to sinusoidal. The
stray losses in the motor caused by harmonic currents are low, but not negligible. Commercially available standard
motors for 50 Hz or 60 Hz and utilized according to temperature class B in mains operation can be partially utilized
according to temperature class F at the nominal working point up to rated torque when operated on a converter. The
winding temperature rise is then between 80 and 100 K.
Raising the pulse frequency on standard motors for 50 Hz or 60 Hz reduces the motor stray losses only slightly, but
results in a considerable increase in the converter switching losses. The efficiency of the overall system (converter
and motor) deteriorates as a result.
Fundamental Principles and System Description
Rated output current
≤ 490 A
≥ 605 A
All currents
All currents
Engineering Information
Pulse frequency factory
setting
2.00 kHz
1.25 kHz
1.25 kHz
1.25 kHz
SINAMICS Engineering Manual - May 2008
© Siemens AG
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