Mitsubishi Electric FR-A800 Series Instruction Manual page 271

• When the difference (absolute value) between the speed command value and actual rotation speed in speed control under
Vector control is equal to or higher than the setting value in Pr.285 Speed deviation excess detection frequency for a
continuous time equal to or longer than the setting value in Pr.853 Speed deviation time, the speed deviation excess
detection (E.OSD) activates to shut off the inverter output.
Fault output
(ALM)
 Speed limit (Pr.873)
• This function prevents overrunning even when the setting value for 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).
Actual speed
at error occurrence
NOTE
• 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 output 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)
• This function can stop the inverter output when the motor is accelerated accidentally during rotation. This prevents a
malfunction due to incorrect encoder pulse settings.
• The function is activated when the difference between the actual motor speed and the speed command value exceeds 2
Hz.
• If the motor does not decelerate within the time period set in Pr.690, the speed deviation excess detection (E.OSD) is
activated to shut off the inverter output.
Motor speed
Speed command
Fault output
(ALM)
270
5. PARAMETERS
5.3 Speed control under Real sensorless vector control, vector control, PM sensorless vector control
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Set frequency
Pr.285
Actual speed
Time
Pr.853
OFF ON
Speed deviation
excessive fault activated
(E. OSD)
Set speed + Pr. 873 value
2Hz
Pr.690
ON
E.OSD
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Value of Pr. 873
Set speed
Speed during
normal operation
Motor coasting
Time