Limiting The Maximum Dc Link Voltage - Siemens SINAMICS G120C Operating Instructions Manual

6.6.4

Limiting the maximum DC link voltage

How does the motor generate overvoltage?
An induction motor operates as a generator if it is driven by the connected load. A generator
converts mechanical energy into electrical energy. The electrical energy flows back into the
inverter. If the inverter cannot dissipate the electrical energy, for example in a braking
resistor, then the DC link voltage Vdc increases in the inverter.
Above a critical DC-link voltage both the inverter and the motor will be damaged. Before the
voltage can reach critical levels, however, the inverter switches the motor off with the fault
message "DC-link overvoltage".
Protecting the motor and inverter against overvoltage
The Vdc_max control avoids an excessively high DC link voltage, assuming that the
application permits this. The Vdc_max control increases the ramp-down time of the motor
when braking, so that the motor feeds back only as little energy 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
Electrically braking the motor (Page 229).
Table 6- 35
Parameter for
U/f control
p1280 = 1
r1282
p1283
p1294
p0210
For more information about this function, see the List Manual (function diagrams 6320 and
6220).
SINAMICS G120C converter
Operating Instructions, 07/2015, FW V4.7 SP3, A5E34263257B AC
V controller parameters
DCmax
Parameter for Description
vector control
p1240 = 1 V
DC
1)1: Enable V
r1242 V
DCmax
Shows the value of the DC-link voltage above which the V
controller is active
p1243 V
DCmax
of the control parameters P1290, P1291 and P1292
p1254 V
DCmax
setting p1294: 0, factory setting p1254: 1)Activates or deac-
tivates automatic detection of the switch-on levels of the V
controller.
0: Automatic detection disabled
1: Automatic detection enabled
p0210 Unit supply voltage
If p1254 or p1294 = 0, the inverter uses this parameter to calcu-
late the intervention thresholds of the V
Set this parameter to the actual value of the input voltage.
controller or V monitoring configuration(factory setting:
DC
controller
DCmax
controller switch-on level
controller dynamic factor (factory setting: 100 %) scaling
controller automatic recording ON-signal level(factory
-
Advanced commissioning
6.6 Protection functions
DCmax
DCmax-
controller.
DCmax
221