Regenerative Power; Common Dc Capacitance - ABB ACSM1 System Manual

Regenerative power

Regenerative power is fed by motor to DC link, when that motor is producing
negative torque and is then braking. This is typical, when motor is
decelerating or motor is in so called generator mode (e.g. unwinder). If the
other drive modules are not taking at the same time enough active power
from the DC link, the braking energy is stored in DC link capacitors and the
DC link voltage will increase. Low amounts of regenerative energy can be
handled within common DC capacitors, if the DC link voltage stays below trip
limit.
The regenerative energy should be taken away from system, if the energy
capacity of common DC system is not enough. This can be done by braking
resistors or feeding the excess energy back to the supply network.
At the moment only resistor braking can be used with ACSM1 drive
modules. However, it is also possible to use a suitable external supply unit,
which can feed the energy back to network (so called regenerative supply
unit).

Common DC capacitance

Many acceleration and deceleration processes are typical for applications
with high performance machinery drives. It is useful for such applications to
connect those drives into common DC link to utilize also the DC link energy
storage behavior. In the common DC system all the capacitor banks of the
individual drive modules are connected in parallel and acting as a common
energy storage. This provides the following advantages:
•
•
The need for the braking resistor in the drive system may be eliminated.
The heat dissipation in the control cabinet is considerably reduced.
The energy stored in the DC bus capacitors during the regenerating can
be used after that for the motoring power. The energy demand from the
supply is then reduced.
21