Derating Function For Chassis Units - Siemens SINAMICS S120 Function Manual

Basic functions

6.26 Derating function for chassis units

6.26 Derating function for chassis units
An adapted derating function greatly reduces the noise produced by chassis format power
units (Motor Modules and Power Modules) and enables operation at a multiple of the rated
pulse frequency at nearly rated current. This is achieved by monitoring the temperature
difference between heat sink and chip using temperature sensors. When the operating
temperature threshold is exceeded, the pulse frequency or permitted current limit,
respectively, is automatically reduced.
This enables the maximum output current of the power unit to be achieved even at high
pulse frequencies. The derating curve becomes effective at a later point.
The derating function is effective for Motor Modules and Power Modules in the chassis
format. Units that are connected in parallel operate in the same manner as single units. The
dependency of the output current on the pulse frequency for the chassis power units is
described in the SINAMICS S120 Chassis Power Units Manual.
Operating principle
In order to optimize the use of the power unit also at temperatures below the maximum
permitted ambient temperature, the maximum output current is controlled as a function of the
operating temperature. This function also accounts for the dynamic response of the thermal
performance (rise and decay curves of the operating temperature).
An alarm threshold is calculated that is weighted with the current ambient temperature.
By weighting the alarm threshold with the current ambient temperature, the power unit can
output higher currents close to nominal current even at lower ambient temperatures.
Depending on the setting of parameter p0290 "Power unit overload response", the pulse
frequency or the current will be reduced, or no response will occur if the alarm threshold is
exceeded. An alarm (e.g. A07805 "Infeed: Power unit overload") is generated even if no
response is desired.
The following quantities can result in a response to thermal overload:
● Heat sink temperature via r0037[0]
● Chip temperature via r0037[1]
● Power unit overload after I2t calculation via r0036
Possible measures to avoid thermal overload:
● For servo control, reduce the output current (closed-loop speed/velocity or torque/force)
● Reduction of the output frequency for V/f control.
● Reduction of the pulse frequency for vector control.
Parameter r0293 "Power unit alarm threshold model temperature" indicates the temperature
alarm threshold for the difference between the chip and heat-sink temperatures.
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Function Manual, (FH1), 01/2013, 6SL3097-4AB00-0BP3
Drive functions