Mitsubishi Electric FR-A720-0.4K Instruction Manual page 216

(5) Magnetic flux decay output shutoff (Pr. 850 = "2")
⋅ Frequent starts/stops (inching) under Real sensorless vector control may cause an inverter failure or create a
difference in operation with the motor. The reason is that some magnetic flux is left in the motor at shutoff of the
inverter output. If this is the case, set Pr. 850 ="2" to select the magnetic flux decay output shutoff, and decay the
magnetic flux before shutting off the output at a stop.
⋅ Turning OFF the start command decelerates the speed. Then, when an estimated speed is lower than Pr. 10 DC
injection brake operation frequency, inverter starts the magnetic flux decay output shutoff function.
⋅ When using brake sequence, the inverter starts the magnetic flux decay output shutoff function at 0.5Hz or Pr. 13
Starting frequency (whichever is lower) during deceleration.
⋅ During magnetic flux decay output shutoff, the torque decreases. Set a mechanical brake to be activated during
magnetic flux decay output shutoff.
⋅ When the MC is provided on the inverter output side, open the MC after magnetic flux decay processing time (refer
to the following) has passed.
⋅ The magnetic flux decay output shutoff function is stopped at restart or when tuning ON the Pre-excitation signal
(LX)/External DC injection brake operation start signal (X13).
Inverter output voltage shutoff timing
Normal operation
Start command
(STF, STR)
Speed command
(rotation per
second)
Pr. 10 DC injection
brake operation
frequency
Magnetic flux decaying
Output voltage
RUN ON
RY2
Mechanical brake
MC on the output side
* The maximum time for magnetic flux decaying
Motor capacity (Pr. 80 setting)
Magnetic flux decay processing time
REMARKS
⋅ When some other factor affecting output shutoff (such as inverter fault or MRS signal ON) occurs during the magnetic flux
decay output shutoff function, the magnetic flux decay output shutoff function is immediately stopped and shuts off the output.
⋅ Regardless of the Pr. 850 setting, turning ON the X74 (magnetic flux decay output shutoff signal) starts the magnetic flux decay
output shutoff. To operate the magnetic flux decay output shutoff function by turning ON the X74 signal, set "74" in any of Pr. 178
to Pr. 189 (input terminal function selection) to assign the function. (Refer to page 231)
CAUTION
⋅ Voltage is output during magnetic flux decay processing. Take caution to avoid an electrical shock.
⋅ If the timing of mechanical brake opening is early, motor shaft may be forced to turn by a gravity drop or external force. If the
timing of mechanical brake opening is late, overcurrent, stall prevention operation or electronic thermal relay function may be
activated. Use output frequency detection signal (FU) or output current detection signal (Y12) to perform the mechanical brake
opening suitable for the machine.
ON
Magnetic flux decay
processing time*
ON
ON
ON
ON
Do not turn OFF MC
during this period
2.2kW or lower 3.7kW to 11kW 15kW to 30kW 37kW to 55kW 75kW or higher
250ms 500ms
Motor brake and stop operation
During brake sequence
Start command
(STF, STR)
Speed command
(rotation per
minute)
Pr. 13 Starting
frequency or 0.5Hz
(whichever is lower)
Magnetic flux decaying
Output voltage
RUN ON
RY2
Mechanical brake
MC on the output side
800ms
ON
Magnetic flux
decay
processing time*
ON
ON
ON
ON
Do not turn OFF MC
during this period
900ms 1100ms
205
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