Siemens Sinamics G120 CU240E, Operating Instructions Manual, Page: 121 / 238

Functions
5.8 Motor and inverter protection
Frequency inverter
Operating Instructions, 08.10. 2008, t.b.d.
121
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
DCmax
controller prevents – as far as is technically possible – the DC link voltage from
reaching critical levels.
The V
DCmax
controller is not suitable for applications in which the motor is permanently in the
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 V
DCmax
controller parameters
Parameter Description
P0003 = 3 User access level
3: Expert
P1240 = … Enables the V
DCmax
controller
1: Enables the V
DCmax
controller
3: Enables the V
DCmax
controller with kinetic buffering
r1242 Shows the value of the DC link voltage above which the V
DCmax
controller is active
P1243 = … Defines the extent to which the V
DCmax
controller responds to excessively high DC link
voltages
P1250 = … Proportional gain of the V
DCmax
controller
P1251 = … Integral time of the V
DCmax
controller
P1252 = … Derivative time of the V
DCmax
controller
P1253 = … Limits the output of the V
DCmax
controller
P1254 = … Activates or deactivates automatic detection of the switch-on levels of the V
DCmax
controller
For more information about this function, see function diagram 4600 in the List Manual.