6.2.20.2 Current-dependent derating
With the current-dependent derating it can be selected if the switching frequency
should be reduced automatically on exceeding the short-time limiting currents in
order to avoid an OL2 error. In the same way, if a power unit-dependent tempera-
ture value is exceeded, the switching frequency can be reduced in order to reduce
the internal losses of the inverter. The reduction of the switching frequency can be
configured with this parameter.
The switching frequency is not changed current-dependent
Lower limit for switching frequency reduction
The min. switching frequency is never fallen below (independent of the adjust-
ment). The minimum switching frequency is e.g. defined by sinus
filt.min.switch.freq. dr53 or limited by the power unit (=> installation instructions
power unit).
If the value of is16 is higher or equal to is10, there is also no "derating“.
The switching frequency is increased when the current is once again within the
permissible range (limit – hysteresis).
The actual switching frequency of the inverter is displayed in ru72 act.switch.freq
(kHz).
Like is10, is16 is also dependent on the used switching frequency group.
6.2.20.3 Temperature-dependent derating
Additionally to the current-dependent derating, a temperature-dependent derating
can be activated with parameter is15 temp dep.
Temperature-dependent derating deactivated
Additionally to the current-dependent derating, also the temperature-dependent derat-
ing is activated with corresponding setting of is16
The lower limit for the temperature-dependent derating is the rated switching fre-
quency of the inverter (de33), if the lower limit is not set to a higher value via other
parameters (sinusfilter min. switch. freq. dr53 or min. derating frequency is16).
There are 3 temperature values for each inverter:
▪ Temperature for switching frequency reduction TDR
▪ Temperature for switching frequency increase TUR
▪ Temperature for change-over to rated switching frequency TEM
These values are dependent on the inverter and can be taken from the installation
manual for the respective power unit.
If the heatsink temperature (ru25 SubIdx 1 heatsink temperature 1) exceeds the
temperature for switching frequency reduction while the switching frequency is
higher than the derating lower limit, then the switching frequency is reduced to the
next lower stage.
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