Mitsubishi Electric FR-A700 Technical Manual page 114

1.5.5 Regenerative overvoltage protection (OV1 to OV3)
When the motor is decelerated by the inverter, the output
frequency falls according to the deceleration time set
value. When the load is light or inertia J (moment of inertia)
is large, the motor speed may exceed the synchronous
speed and enter the power regeneration range. At this
time, the regeneration energy of the load is converted
(regenerated) into electric energy and consumed by the
motor itself and in the inverter. The regeneration
overvoltage function is provided to prevent the built-in
capacitor terminal voltage from rising abnormally due to
large regenerative energy when motor slip has increased.
Braking torque of approximately 20% of the rated motor
torque is generated by the regenerative energy consumed
in the motor and inverter. When the brake unit is used,
braking torque of 100 to 150% of the rated torque is
generated by the electrical energy consumed by the
discharging resistor.
Deceleration start
1) Regenerative brake operation
(approximately 360VDC)
2) Regenerative brake duty excessive
3) Regenerative overvoltage shut-off
(200Vclass : approximately 400VDC)
400Vclass : approximately 800VDC
*1 Voltage where the function activates differ according to
the model. Refer to the below table.
A700
22K or 75K or
less more
200V
DC380V DC376V DC376V
class
400V
DC760V DC785V DC785V
class
BU mode
200V
DC360V
class
400V
DC740V
class
*2 Voltage where inverter trips differ according to the model.
*1
*2
F700 E700 D700
75K or
0.4K or more
more
DC390V
DC760V
FR-BU2 MT-BU5
mode mode
DC370V DC376V
DC740V DC784V
common
(common)
The regenerative energy of the transistorized inverter is not
returned to the commercial power supply. Install the power
supply regenerating converter (FR-CV) and high power
factor converter (FR-HC, MT-HC) options to return the
regenerative energy to the power supply.
If the regenerative energy from the motor has become
excessive and the regenerative brake torque (current) has
exceeded the specified value during motor deceleration,
the stall prevention (overvoltage) function stops the fall of
the output frequency to prevent regenerative overvoltage
shut-off from being activated. If the deceleration time is
extremely short or the load inertia J (moment of inertia) is
very large, the stall prevention (overvoltage) function may
not be enough to prevent regenerative overvoltage shut-
off.
The stall prevention function is not available for
regenerative overvoltage during constant-speed operation.
When working with a negative load (in descending
operation) which always is in the regenerative status, fit the
power supply regenerating converter option to avoid
regenerative overvoltage shut-off to activate. Also, to use
power supply regenerating converter, install a brake
register and inverter with sufficient heat capacities.
1) Regenerative brake operation
Switches ON the brake transistor to start current
in the brake discharge resistor.
2) Regenerative brake duty excessive
Stops use of the regenerative brake temporarily
if the regenerative brake duty value exceeds the
specified value.
regenerative brake when the brake discharge
resistor has cooled down.
3) Regenerative overvoltage shut-off
Instantly activates the protective circuit to shut
off the transistor gate.
Regenerative
brake voltage
Regenerative
brake operation
OFF ON OFF
Regenerative overvoltage stall activated
Operation of regenerative overvoltage stall prevention
107
SPECIFICATIONS
Resumes use of
Regenerative
overvoltage
Stall preven-
protection
tion voltage
voltage
(over voltage)
Time
ON
Regenerative
overvoltage
shut-off
Time
1
the