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Functions, monitoring and protective functions
9.5 Monitoring functions and protective functions
9.5.2
Thermal monitoring and overload responses
Description
The thermal power unit monitor is responsible for identifying critical situations. Possible
reactions can be assigned and used when alarm thresholds are exceeded to enable
continued operation (e.g., with reduced power) and prevent immediate shutdown. The
parameterization options, however, only enable intervention below the shutdown thresholds,
which cannot be changed by the user.
The following thermal monitoring options are available:
● I²t monitoring – A07805 – F30005
i²t monitoring is used to protect components that have a high thermal time constant
compared with semiconductors. Overload with regard to i²t is present when the converter
load (r0036) is greater than 100% (load as a % of rated operation).
● Heat sink temperature – A05000 – F30004
Used to monitor the temperature r0037[0] of the heat sinks on the power semiconductors
(IGBT).
● Chip temperature – A05001 – F30025
Significant temperature differences can occur between the barrier layer of the IGBT and
the heat sink. The calculated barrier junction temperature is displayed in r0037[13...18];
the monitoring ensures that the specified maximum barrier junction temperature is not
exceeded.
If an overload occurs with respect to any of these three monitoring functions, an alarm is first
output. The alarm threshold p0294 (i²t monitoring) can be parameterized relative to the
shutdown (trip) values.
Overload responses
To reduce thermal stress and thus losses in the power unit, the following methods and
overload responses are available.
● Reducing the pulse frequency
Reducing the pulse frequency is an effective procedure for reducing losses in the power
unit. This is due to the fact that the switching losses make up a very large portion of the
total losses. In many applications, a temporary reduction in pulse frequency is tolerable.
Disadvantage:
Reducing the pulse frequency increases the current ripple. At a small moment of inertia,
this may cause an increase in the torque ripple on the motor shaft and a noise level
increase. We recommend using the overload response with pulse frequency reduction for
applications that are not critical from a control-related perspective (e.g. for pump and fan
drives).
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Operating Instructions, 12/2018, A5E36652151A
Enclosed Drives
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