Mitsubishi Electric FR-A820-00046 Instruction Manual page 327

Parameters Speed control under Real sensorless vector control, vector control, PM sensorless vector control
Speed limit (Pr. 873)
● This function prevents overrunning even when the setting value for the number of encoder pulses
and the value of the actual number of pulses are different. When the setting value for the number
of encoder pulses is lower than the actual number of pulses, because the motor may increase
speed, the output frequency is limited with the frequency of (set frequency + Pr. 873).
Fig. 5-34:
NOTES When the automatic restart after instantaneous power failure function is selected (Pr. 57 "Restart
coasting time" ≠ "9999") and the setting value for the number of encoder pulses is lower than the
actual number of pulses, the output speed is limited with the synchronous speed of the value of
Pr. 1 "Maximum frequency" + Pr. 873.
When a regenerative driving torque limit is applied and the speed limit function activates, the out-
put torque may drop suddenly. Also, when the speed limit function activates during pre-excitation
operation, output phase loss (E.LF) may occur.
If the setting for the number of encoder pulses is confirmed as correct, it is recommended that
Pr. 873 be set to the maximum value (400 Hz).
Even if the set frequency is lowered after inverter operation, the speed limit value is not lowered.
During deceleration, the speed is limited at frequency command value + Pr. 873.
Deceleration check (Pr. 690)
● When performing a deceleration stop on the motor, accidental acceleration can cause the inverter
to trip. This can prevent a malfunction due to an incorrect encoder pulse setting, when the motor
has stopped.
● When the difference between the actual motor speed and the speed command value exceeds
2 Hz after the start signal (STF, STR) is OFF, the deceleration check will start.
● If the motor has not decelerated in the time period between the start signal (STF, STR) OFF and
the Pr.690 setting, the protective function (E.OSD) is activated to trip the inverter.
Fig. 5-35:
FR-A800
Set speed + Pr. 873 value
Actual speed at
error occurrence
Speed limit
Motor speed
Start signal
ON
(STF, STR)
Fault output
(ALM)
Deceleration check time
Motor coasting
Pr. 690
Time
ON
E.OSD
Value of Pr. 873
Set speed
Speed during
normal operation
I001519E
I002816E
5 - 125