Mitsubishi Electric FR-A720-0.4K Instruction Manual page 512

If torque is required in a low-speed range (less than 1/10 of the rated motor frequency), set Pr.791 Acceleration time in
low-speed range and Pr.792 Deceleration time in low-speed range settings higher than the Pr.7 Acceleration time and Pr.8
Deceleration time settings so that the mild acceleration/deceleration is performed in the low-speed range. (For an
operation with second acceleration/deceleration times, set the acceleration/deceleration times longer than the second
acceleration/deceleration times.)
Acceleration time
in low-speed range
Slope set by Pr. 791
REMARKS
 Set Pr.791 higher than Pr.7, and Pr.792 higher than Pr.8. If set as Pr.791 < Pr.7, the operation is performed as Pr.791 = Pr.7. If
set as Pr.792 < Pr.8, the operation is performed as Pr.792 = Pr.8.
 Refer to page 6 for the rated motor frequency of MM-CF.
1.8 DC injection brake of the PM sensorless vector control
DC injection brake under PM sensorless vector control is performed as below.
<High frequency superposition control (Pr.788 = "9999 (initial value)")>
When Pr.11
Commanded speed
DC injection brake applied
when:
The commanded speed = 0Hz
The calculated speed
<Current synchronization operation Pr.788 = "0">
When Pr.11
DC injection brake applied when
the commanded and calculated
speeds are 0Hz
REMARKS
 The X13 signal is disabled during PM sensorless vector control.
Acceleration time
Slope set by Pr.7
"0"
Calculated speed
Pr.10
Time
Pr.10
Time
Pr.11
"0"
Time
Time
Pr.11
Low-speed range
(rated motor frequency/10)
Time
Deceleration time
Slope set by Pr.8
When Pr.11 = "0"
Commanded speed
Motor coasting when:
The commanded speed
The calculated speed
When Pr.11 = "0"
Commanded
speed
Motor coasting when:
The commanded speed
The calculated speed
15/24
Deceleration time
in low-speed range
Slope set by Pr.792
P M P M P M
Calculated speed
Pr.10
Time
Pr.10
Pr.10
Calculated speed
Pr.10
Time
Pr.10
Pr.10
BCN-C22005-634