Derating Function For Chassis Units - Siemens SINAMICS S120 Function Manual

11.8

Derating function for chassis units

Description
An adjusted 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
nominal pulse frequency at nearly nominal current. This is achieved by monitoring the
temperature increase between heat-sink and chip by means of 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 with Motor Modules (DC/AC units of chassis format) and
Power Modules (AC/AC units of chassis format). Units that are connected in parallel operate
in the same manner als single units. The dependency of the output current of the pulse
frequency for the chassis power units of the SINAMICS S120 is described in the S120
Function Manual, Chassis Power Units.
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 p290 "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 (r0037.0)
● Chip temperature (r0037.1)
● Power unit overload I2T (r0036)
Possible measures to avoid thermal overload:
● Reduce the output current (closed-loop speed/velocity or torque/force control) or the
● Reduce the pulse frequency (only for closed-loop vector control).
Parameter r293 "Power unit alarm threshold model temperature" indicates the temperature
alarm threshold for the difference between the chip and heat-sink temperatures.
Drive functions
Function Manual, (FH1), 10/2008, 6SL3097-2AB00-0BP5
output frequency (V/f control).
11.8 Derating function for chassis units
Applications
559