Siemens SINAMICS G120 Operating Instructions Manual page 253

Compound braking prevents the DC-link voltage increasing above a critical value. The
inverter activates compound braking depending on the DC-link voltage. Above a DC-link
voltage threshold (r1282), the inverter adds a DC current to the motor current. The DC
current brakes the motor and prevents an excessive increase in the DC-link voltage.
Note
Compound braking is possible only with the U/f control.
Compound braking does not operate in the following cases:
• The "flying restart" function is active
• DC braking is active
• Vector control is selected
Setting and enabling compound braking
Parameter
p3856
r3859.0
NOTICE
Motor damage from overheating with compound braking
The motor will overheat if braking lasts too long or the motor is braked too often. This may
damage the motor.
Monitor the motor temperature. If the motor gets too hot during operation you must select
another braking method or give the motor more time to cool down.
Converter with CU230P-2 Control Units
Operating Instructions, 04/2015, FW V4.7 SP3, A5E34257946B AB
Description
Compound braking current (%)
With the compound braking current, the magnitude of the DC current is defined, which
is additionally generated when stopping the motor for operation with U/f control to in-
crease the braking effect.
p3856 = 0
Compound braking locked
p3856 = 1 ... 250
Current level of the DC braking current as a % of the rated motor current (p0305)
Recommendation: p3856 < 100% × (r0209 - r0331) / p0305 / 2
Compound-braking status word
r3859.0 = 1: Compound braking is active
Advanced commissioning
6.7 Application-specific functions
253