Siemens A1 User Manual
Advanced Applications
International English
50
MICROMASTER Applications Handbook
8.2.2
Braking and Stopping with an Inverter
Ramping Down and Braking
As stated above, if the inverter reduces the output frequency (i.e. Ramps down) the
motor and load will slow down. If the load and motor inertia is high, regeneration
will occur. In many cases there is insufficient regeneration to cause excessive
voltage; in fact very fast ramp down rates can often be used in certain processes
without problems. In many cases the energy is absorbed by other losses, such as
gearbox or rolling friction. The ramp down time, controlled by the inverter allows
predictable deceleration and stopping times.
motor and load will slow down. If the load and motor inertia is high, regeneration
will occur. In many cases there is insufficient regeneration to cause excessive
voltage; in fact very fast ramp down rates can often be used in certain processes
without problems. In many cases the energy is absorbed by other losses, such as
gearbox or rolling friction. The ramp down time, controlled by the inverter allows
predictable deceleration and stopping times.
Where regeneration does cause trips, several solutions are possible. An external
brake, DC braking or Compound braking may be used. These are described in
section 8.2.2.
brake, DC braking or Compound braking may be used. These are described in
section 8.2.2.
However, a simple solution is to connect a resistor across the DC link of the
inverter to dissipate the regenerated energy.
inverter to dissipate the regenerated energy.
Some inverters incorporate a controller which switches the resistor on and off to
maintain the DC link voltage at a constant level.
maintain the DC link voltage at a constant level.
The MICROMASTER MM420 has no controller and the use of an external
controller or resistor is not possible.
controller or resistor is not possible.
+
-
Motor
External Optional Resistor
Resistive Brake Controller (built in on some Controllers)
Figure 8-3
Absorbing Regenerated Current
DC Braking.
If a controlled DC voltage is applied to the motor, a braking and holding torque is
produced in the rotor. During DC braking the stored energy of the motor and load
is dissipated in the rotor itself, so there is no regeneration back to the inverter.
However, because no frequency is applied, there is no control over motor speed,
and it is not possible to predict the stopping time of the motor and load. The torque
on the rotor is maintained even at standstill, so DC braking can be used to hold the
rotor and load for short periods if required.
produced in the rotor. During DC braking the stored energy of the motor and load
is dissipated in the rotor itself, so there is no regeneration back to the inverter.
However, because no frequency is applied, there is no control over motor speed,
and it is not possible to predict the stopping time of the motor and load. The torque
on the rotor is maintained even at standstill, so DC braking can be used to hold the
rotor and load for short periods if required.
Parameter P1232 sets the level of DC Braking current, and braking will be applied
for the time set in P1233 irrespective of the motor speed. The parameter value
for the time set in P1233 irrespective of the motor speed. The parameter value