Siemens SINAMICS G120 Operating Instructions Manual page 259

Above a critical DC-link voltage both the inverter and the motor will be damaged. Before
harmful voltages occur, the inverter switches off the connected motor with the fault
"DC-link overvoltage".
Protecting the motor and inverter against overvoltage
To the extent the application permits, the Vdc_max control prevents the DC-link voltage from
reaching critical levels. The Vdc_max control increases the ramp-down time of the motor
during braking, so that the motor feeds back only as little power to the inverter as is covered
by the losses in the inverter.
The Vdc_max control is not suitable for applications where the motor is continuously in the
generator mode. This includes, for example, cranes or applications involving braking large
moments of inertia. Further information on inverter braking methods can be found in Section
Braking functions of the inverter (Page 267).
There are two different groups of parameters for the Vdc_max control, depending on whether
the motor is being operated with U/f control or vector control.
Parameter for
V/f control
p1280 = 1
r1282
p1283
p1290
p1291
p1292
p1294
p0210
For more information about this function, see the List Manual (function diagrams 6320 and
6220).
Converter with the CU250S-2 Control Unit (vector)
Operating Instructions, 06/2013, FW V4.6, A5E31759476B AB
Parameter for Description
vector control
p1240 = 1 Vdc_max control Vdc monitoring configuration (factory setting:
1)
1: Enable Vdc_max control
r1242 Vdc_max control activation level
Shows the value of the DC link voltage above which the
Vdc_max control is active
p1243 Vdc_max control dynamic factor (factory setting: 100 %)
Scaling control parameters p1290, p1291 and p1292
p1250 Vdc_max control proportional gain (factory setting: 1)
p1251 Vdc_max control integral time (factory setting p1291: 40 ms,
factory setting p1251: 0 ms)
p1252 Vdc_max control rate time (factory setting p1292: 10 ms, factory
setting p1252: 0 ms)
p1254 Vdc_max control automatic sensing ON level (factory setting
p1294: 0, factory setting p1254: PM330/PM240 = 1, PM230 = 0)
Activates or deactivates automatic detection of the switch-on
levels of the Vdc_max control.
0: Automatic detection disabled
1: Automatic detection enabled
p0210 Unit supply voltage
If p1254 or p1294 = 0, the inverter uses this parameter to
calculate the switch-in thresholds of the Vdc_max control.
Set this parameter to the actual value of the input voltage.
Setting functions
8.6 Protection functions
259