WEG CFW700, Programming And Troubleshooting Manual

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9
Scalar Control (V/f)
CFW700 | 9-9
9.4 V/f DC VOLTAGE LIMITATION
There are two functions in the inverter for limiting the DC link voltage during the motor braking. They act limiting
the braking torque and power, avoiding therefore the tripping of the inverter by overvoltage (F022).
The overvoltage on the DC link is more common when a load with high inertia is driven or when a short
deceleration time is programmed.
NOTE!
When using the dynamic braking the function “Ramp Hold” or “Ramp Acceleration” must be disabled.
Refer to the P0151 description.
In the V/f mode, there are two types of function to limit the DC link voltage:
1 - “Ramp Hold”:
It is effective only during the deceleration.
Working: When the DC link voltage reaches the level adjusted in P0151, a command is sent to the “ramp” block,
which inhibits the motor speed variation (“ramp hold”). Refer to the
figures 9.9 and 9.10 .
With this function an optimized deceleration time (minimum possible) for the driven load is obtained.
The use is recommended for loads running with high inertia moment referenced to the motor shaft, or loads
with medium inertia, which require short deceleration ramps.
Error < 0: Ramp Hold = inactive
Error ≥ 0: Ramp Hold = active
Ramp Hold
Output
Acceleration/Deceleration Ramp
Dc link
Voltage (U
d
)
Error
Input
P0151
Figure 9.9: Limitation of the DC link voltage using Ramp Acceleration function block diagram