6.2.26.3.4 DC braking: start at DEC (Bit 9…11)
With start at DEC = 512: on, the DC braking is started as soon as the ramp state
DEC is active. If DC braking shall be started below a speed level, the setting 1024:
speed level must be selected. During operation in the torque limit, the ramp state
DEC may have been left and changed to state "CONST“ before the speed level
ds62[7] braking speed level [%Nn] is fallen below. Therefore the mode "1024:
speed level“ monitors whether both the target speed (ru05 set value display) and
the actual speed (ru08 actual value) are below the level. The condition is that the
actual speed has been once above the level ds62[7] braking speed level [%Nn].
6.2.26.3.5 Start after switched on (Bit 12, 13)
The DC braking is activated at the change from st12 state machine display 4:
switched on to 11: start operation activ
If Speed Search (dd16) is activated, this function runs first.
If the identified speed is less than 5% of the rated motor speed for encoderless
drives, it is evaluated as "ZERO". In this case, mode "Start after switched on“ is
carried out.
6.2.26.4 DC braking Timing
6.2.26.4.1 Motor de-exitation time (Bit 0…2)
Before DC braking can be started, the flux of the asynchronous machine must be
reduced in order to reduce current peaks when switching to DC voltage.
Cause: The DC voltage reacts against the output voltage of the motor which de-
pends on the speed * motor flux.
Depending on the selected control mode cs00 there are different methods for flux
reduction.
6.2.26.4.1.1 Motor de-excitation time in v/f operation
In v/f mode, the modulation is switched off for an inverter-dependent constant time
(minimum switch-off time).
If ru08 actual value at the start of the DC braking is less than 5% of the rated motor
speed, the minimum switch-off time is omitted and the DC voltage is immediately
switched to the motor.
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