Technical data

Drive functions
7.2 Basic functions
Function Manual
Function Manual, 06/2012, 6SL3097-4AB10-0BP4
191
7.2.4 Armature short-circuit brake, DC brake
Features
● For permanent-magnet synchronous motors:
– Controlling an external armature short-circuit configuration
● For induction motors:
– Activation of DC brake
● Assignment as fault response
Description
Armature short-circuit braking is only supported for permanent-magnet synchronous motors.
It is mainly required when braking in a hazardous situation if controlled braking using the
frequency converter is no longer possible (e.g. in the event of a power failure, emergency
shutdown, etc.). The motor's stator windings are short-circuited by means of a contactor
circuit (possibly using external braking resistors). The resistance in the motor circuit
suppresses the motor's kinetic energy.
In order for the CU305 to be able to maintain this function in the event of a power failure, an
uninterruptible 24 V power supply (UPS) must be used. High-speed permanent-magnet
spindle drives for machine tools are a typical application for armature short-circuit braking.
With the external armature short-circuit brake, the slow contactor response causes a
response in the range of > 60 ms.
DC braking is only supported for induction motors. It can be used most effectively to bring
the rotor to a safe standstill in the event of the loss of the encoder signal. In order to achieve
this, a constant DC current is injected in the stator to decelerate the rotor to standstill and
hold it there.
The functions can be triggered by applying a "1" signal to binector input p1230 or in
response to a fault (see the description of p0491 or p2100/p2101).
External armature short-circuit braking
The external armature short-circuit is activated by setting p1231 = 1 (with contactor feedback
signal) or p1231 = 2 (without contactor feedback signal). It can be triggered via an input
signal p1230 (signal = 1) or a fault response. Triggering takes place once the pulses have
been suppressed or the circuit breaker has been inhibited.
This function uses output terminals to control an external contactor, which can short-circuit
the motor terminals via external resistors, for example. An armature short-circuit brake has
the advantage of a higher braking effect than a mechanical brake at the start of braking (at a
high speed). However, since the braking effect fades away as the speed drops, we
recommend a combination of armature and mechanical braking.