Vdc Max Controller; Compound Braking - Siemens MICROMASTER 420 Reference Manual

2.9.3

Vdc Max Controller

The MICROMASTER 420 has a controller to limit the DC voltage ( Vdc Max
controller). When braking a load faster than would normally be possible, excess
energy has to be dissipated. This energy is unable to go back into the input supply
so the result is that the DC link voltage rises. If this voltage rises too high, the trip
level will be reached and the output pulses disabled to prevent damage to the
inverter. The Vdc Max controller automatically increases the frequency and
extends the ramp down period so that the braking is not as fast, thus reducing the
risk of an overvoltage trip and keeping the system running. This means that the
system will ramp down on the voltage limit until a standstill or a new setpoint is
reached. (Refer to parameter P1240 for configuration details).
2.9.4

Compound Braking

When Compound braking is used, the energy is dissipated in the motor instead of
coming back into the DC link. This has the advantage that the braking
performance of the inverter can be increased, without tripping the inverter and
without the use of a braking resistor.
Compound braking combines the braking power of DC braking with the control
offered by a ramp down. When using Compound braking, the ramp-down time is
defined and the level of current to be used in Compound braking is defined using
P1236.
Figure 2-13
MICROMASTER 420 Reference Manual
Issue A1
Compound Braking
21