Limiting The Maximum Dc Link Voltage - Siemens Sinamics G120 CU240E Operating Instructions Manual

5.8.3

Limiting the maximum DC link voltage

How does the motor generate overvoltage?
An induction motor can operate as a generator if it is driven by the connected load, whereby
the motor converts mechanical energy to electrical energy. The motor feeds the regenerative
energy back to the inverter.
As a consequence, the DC link voltage is increased. The frequency inverter can only reduce
the increased DC link voltage if it is capable of regenerative feedback into the line supply or
is equipped with a braking resistor.
Without being capable of regenerating into the line supply, only extremely low or brief
regenerative loads – relative to the frequency inverter power – are possible because the
frequency inverter may be damaged if the DC link voltage reaches critical levels. Before the
voltage can reach critical levels, however, the inverter shuts down with the fault message
"DC link overvoltage".
Protecting the motor and inverter against overvoltage
The V
reaching critical levels.
The V
regenerative mode, e.g. in hoisting gear or when large flywheel masses are subject to
braking. For applications such as these, you must select an inverter that is equipped with a
braking resistor or that can feed energy back into the line supply (e.g. PM250 and PM260)
Table 5- 30
Parameter
P0003 = 3
P1240 = ...
r1242
P1243 = ...
P1250 = ...
P1251 = ...
P1252 = ...
P1253 = ...
P1254 = ...
For more information about this function, see function diagram 4600 in the List Manual.
Frequency inverter
Operating Instructions, 08.10. 2008, t.b.d.
controller prevents – as far as is technically possible – the DC link voltage from
DCmax
controller is not suitable for applications in which the motor is permanently in the
DCmax
V controller parameters
DCmax
Description
User access level
3: Expert
Enables the V
DCmax
1: Enables the V
3: Enables the V
Shows the value of the DC link voltage above which the V
Defines the extent to which the V
voltages
Proportional gain of the V
Integral time of the V
Derivative time of the V
Limits the output of the V
Activates or deactivates automatic detection of the switch-on levels of the V
controller
controller
controller
DCmax
controller with kinetic buffering
DCmax
controller responds to excessively high DC link
DCmax
controller
DCmax
controller
DCmax
controller
DCmax
controller
DCmax
5.8 Motor and inverter protection
controller is active
DCmax
Functions
DCmax
121