Thermal Monitoring Of The Power Unit; Operation Of Converters At Increased Pulse Frequency - Siemens SINAMICS G130 Engineering Manual

1.13.4

Thermal monitoring of the power unit

In both continuous operation and load duty cycle mode, the power unit of the SINAMICS converters G130, G150,
S150 and S120 Motor Modules (Chassis and Cabinet Modules) is thermally monitored by three different methods:
·
The output current is monitored by an I
·
The heatsink temperature is monitored by direct temperature measurements.
·
The chip temperature of the IGBTs is monitored by the thermal model which can calculate the exact
temperature of the IGBT chips on the basis of the heatsink temperature measurement plus other electrical
quantities such as pulse frequency, DC link voltage and output current.
1
If a power unit overload is detected by these monitoring functions, an "overload reaction" defined by the setting in
parameter p0290 is triggered. The following overload reactions can be parameterized in p0290:
0: Reduce output current or output frequency.
1: No reduction / shutdown (trip) when the overload threshold is reached.
2: Reduce output current or output frequency and pulse frequency (not by I
3: Reduce pulse frequency (not by I
With many applications, the parameterizable overload reaction makes it possible to prevent instantaneous shutdown
when the power unit is overloaded briefly. For example, it is perfectly tolerable with most pump and fan applications
for the flow rate to drop briefly when the output current is reduced. If the drive is operating on a higher pulse
frequency than the factory setting in order to achieve a reduction in motor noise, for example, a possible overload
reaction would be to reduce the pulse frequency and thus maintain the flow rate.
If the parameterized overload reaction cannot reduce the overload sufficiently, then the drive will always shut down in
order to protect the power unit. This means that the risk of irreparable damage to the power unit as a result of
excessive IGBT temperatures is absolutely eliminated in all operating modes.
These protection mechanisms implemented in the SINAMICS units do, however, demand precise configuring of the
converter in relation to its load profile so that the drive can perform all the required functions without being interrupted
by overload reactions.
1.13.5

Operation of converters at increased pulse frequency

The technical data in the catalogs and operating instructions, in particular
·
the rated output current I
·
the base load currents I
definitions,
·
the maximum output current I
·
and the specified output power ratings
always refer to converter or inverter operation at the factory-set pulse frequency.
If the pulse frequency is increased above the factory-set value on G130, G150 and S150 converters or S120
inverters (Chassis and Cabinet Modules), the switching losses in the inverter rise in proportion to the pulse frequency
which generally results in thermal overloading of the power unit when the inverter is operating at full capacity.
Various strategies can be used to prevent the power unit from overheating when the pulse frequency is increased.
These depend on the overload reaction setting in parameter p0290 and they are described below.
It must be noted that the current derating factors k
sections on specific unit types are generally omitted from the I
inverter. This means that all currents, i.e. the rated output current I
maximum output current I
frequencies. This means basically that the inverter can be utilized with respect to current limits as if it were operating
at the factory-set pulse frequency.
For thermal reasons, however, this is true only on the condition that the unit is operated at the relevant currents for
only brief periods or that the values of the influencing parameters described further below, such as ambient
temperature, are favorable enough.
Since the current derating factors k
monitoring the utilization of the inverter, the inverter is practically protected in operation at increased pulse frequency
only by the monitoring systems for the heat sink temperature and chip temperature of the IGBTs.
Fundamental Principles and System Description
2
t calculation.
2
t).
,
rated
and I and their associated short-time currents according to the load duty cycle
L H
,
max
Pulse
remain unchanged and can thus be utilized in the first instance at increased pulse
max
for increased pulse frequencies are omitted from the I
Pulse
Engineering Information
for increased pulse frequencies which are specified in the
2
t calculation for monitoring the utilization of the
, the base load currents I
rated
SINAMICS Engineering Manual – November 2015
2
t).
and I , and the
L H
2
t calculation for
179/528
Ó Siemens AG