Electrically Braking The Motor - Siemens sinamics G120 Operating Instructions Manual

6.7.3

Electrically braking the motor

Braking with the motor in generating mode
If the motor brakes the connected load electrically, it will convert the kinetic energy of the
motor to electrical energy. The electrical energy E released on braking the load is
proportional to the moment of inertia J of the motor and load and to the square of the speed
n. The motor attempts to pass the energy on to the inverter.
Main features of the braking functions
DC braking
DC braking prevents the motor from transferring braking energy
to the inverter. The inverter impresses a DC current into the mo-
tor, therefore braking the motor. The motor converts braking
energy E of the load into heat.
Advantage:
•
having to process regenerative power.
Disadvantages:
•
no defined braking characteristics; no constant braking
torque; no braking torque at standstill; braking energy is lost
as heat; does not function when the power fails
Compound braking
One version of DC braking. The inverter brakes the motor with a
defined ramp-down time and superimposes a DC current on the
output current.
Dynamic braking
Using a braking resistor, the inverter converts the electrical en-
ergy into heat.
Advantages:
•
does not increase any further; constant braking torque
Disadvantages:
•
lost in the form of heat
Converter with CU250S-2 Control Unit
Operating Instructions, 01/2016, FW V4.7 SP6, A5E31759476B AE
The motor brakes the load without the inverter
significant increase in the motor temperature;
defined braking response; motor temperature
Braking resistor required; braking energy E is
Advanced commissioning
6.7 Application-specific functions
271