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3.16 DC Injection braking [dbF. dbu. db/: ]
While a motor is undergoing a decelerating stop, a dynamic injection braking may be engaged.
When the DC injection braking function is activated, the message" db " appears on the inverter'
s monitor display. This DC injection braking function may used for precise positioning ("inching")
of the motor-driven equipment.
The DC injection braking start frequency [ dbF ] can be set within a range of from OHz to 10Hz.
The DC injection braking voltage [ dbu ] can be set within a range of from 0% to 20%. The DC
injection braking time [ db/: ] can be set within a range from 0 seconds to 5 seconds.
Figure 3.27 shows an example operation of DC injection braking.
When the inverter's F switch is thrown off, deceleraiton will begin by regenerative braking in
accordance with a deceleration time setting made at rheostat dEC, and DC injection braking is
activated according to the DC injection braking start frequency preset at rheostat dBF.
output
frequency
output
frequency ,
;
DC injection braking stop
n"~'""
I
' T i m e
: a
DC injection braking start
-- ---------
--~----
frequency (dbF)
Time
Output
frequency
,
DC braking time (dbt)
Ili,~'i"
••••••••••••••••••••••
t
Across ST
-CC
J:
L
Across
F-CC
J
a)
DC braked stop
When the dbu has been set at 0, a coasting stop will be activated if the inverter's output
frequency below db/C.
b)
If the ST switch is thrown off before the start of DC braking, a coasting stop will result.
Figure 3.27 Timing chart showing an example of a DC injection braking operation
*
Because DC injection braking forces the motor to stop running, do not set excessive braking
voltage ( dbu ) or braking times ( db/: ). This is necessary to avoid straining the motor.
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