Mitsubishi Electric FR-D720S SC EC Instruction Manual page 186

Adjust the output torque (current) of the motor
Setting of stall prevention operation in high frequency range (Pr. 22, Pr. 23, Pr. 66)
During high-speed operation above the rated motor frequency, acceleration may not be made
because the motor current does not increase. If operation is performed in a high frequency
range, the current at motor lockup becomes smaller than the rated output current of the inverter,
and the protective function (OL) is not executed if the motor is at a stop.
To improve the operating characteristics of the motor in this case, the stall prevention level can
be reduced in the high frequency region. This function is effective for performing operation up
to the high-speed range on a centrifugal separator etc.
Pr. 23 sets the change in the current limiting in the frequency range starting at the frequency set
by Pr. 66. For example, if Pr. 66 is set to 75Hz the motor stall prevention operation level at an
output frequency of 150Hz will be reduced to 75% when Pr. 23 is set to 100%, and to 66% when
Pr. 23 is set to 50% (see the formula below). Generally Pr. 66 is set to 50Hz and Pr. 23 to 100%.
Fig. 6-6: Stall prevention operation level
Setting example
Formula for stall prevention operation level:
Stall prevention operation level [%]
where A
When Pr. 23 "Stall prevention operation level compensation factor at double speed" = 9999 (in-
itial value), the stall prevention operation level is kept constant at the Pr. 22 setting up to 400Hz.
6 - 36
Output frequency [Hz]
Pr. 22 = 150%
Pr. 23 = 100%
Pr. 66 = 50Hz
Output frequency [Hz]
×
Pr. 66 [Hz] Pr. 22 [%]
= ------------------------------------------------------------ - B
Output frequency [Hz]
Pr. 23 = 9999
Current limiting if the current limit was set at higher
frequency (Pr. 23).
Fig. 6-7:
Stall prevention operation level when
Pr. 22 = 150%, Pr. 23 = 100% and
Pr. 66 = 50Hz
–
Pr. 22 A
------------------------- -
×
A B
–
Pr. 22 B
×
Pr. 66 [Hz] Pr. 22 [%]
, = ------------------------------------------------------------ -
400Hz
–
Pr. 23 100
------------------------------- -
×
100
Parameter
I001900E
I001545C