18 Special Functions
The configurable functions of the corresponding control methods enable another field
of application of the frequency
inverters. The integration in the application is made
easier by special functions.
18.1 Pulse Width Modulation
The motor noises can be reduced by changing over the parameter Switching fre-
quency 400. A reduction
of the switching frequency should be up to a maximum
ratio of 1:10 to the frequency of the output signal for a sine-
shaped output signal.
The maximum possible switching frequency depends on the drive output and the
ambient conditions. For the required tech
nical data refer to the corresponding table
and the device type diagrams.
Parameter Settings
400 Switching frequency 2 kHz 16 kHz
The factory setting of parameter
400 depends on the setting of param-
eter
Configuration 30:
1)
configurations 1xx
2)
configurations 2xx / 4xx/ 5xx
The heat losses increase proportionally to the load point of the frequency inverter
and the switching frequency. The automatic reduction adjusts the switching frequen-
cy to the current operating state of the frequency inverter in order to provide the
output performance required for the drive task at the greatest possible dynamics and
a low noise level.
The switching frequency is adapted between the limits which can be set with the pa-
rameters
Switching frequency 400 and Min. switching frequency 401. If the Min.
switching frequency
401 is larger than or equal to the Switching frequency 400
, the
automatic reduction is deactivated.
The change of the switching frequency depends on the heat sink temperature switch-
off limit and the output current. The temperature limit to be exceeded so that the
switching frequency is reduced can be set via parameter
Reduction limit heat sink
temp. 580. If the heat sink tempe
rature falls below the threshold set via parameter
Reduction limit heat sink temp. Ti/Tk 580 by 5 °C, the switching frequency is in-
creased again step by step.
Parameter Settings
The limit for the switching frequency reduction is influenced by the intelligent current
limits depending on the selected
Operation mode 573
and the output current. If they
have been switched off or provide the full overload current, the switching frequency is
reduced when the output current exceeds the limit of 87.5% of the long
-
term overload
current (60s). The switching frequency is increase
d if the output cur
rent drops below
the reference current of the next highest switching frequency.
240 Operating Instructions ACU 06/13
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