Mitsubishi Electric FR-A700 Technical Manual page 453

3.1.5 Acceleration/deceleration time of the motor
To suppress the motor starting current within the overload
capacity of the inverter, start the motor at a low frequency
(initial value 0.5Hz) and increase the frequency gradually.
When the motor is decreased from the set frequency,
gradually decrease the frequency to prevent the DC bus
voltage from being increased
regenerative energy from the motor. For these reasons,
when the motor is accelerated and decelerated by the
inverter, the acceleration time and deceleration time
between zero and the maximum frequency must be set in
advance.
(1) Setting the acceleration
deceleration time
common
The acceleration time and deceleration time must be
set longer than those found from the torque
generated by the inverter-driven motor, the load
torque, and the motor and load inertia (J (moment of
inertia)).
If the acceleration time setting is too short, the
overcurrent protective function (OC1) is activated to
stop the inverter. If the deceleration time setting is too
short, the overcurrent protective function (OC3) or
regenerative overvoltage protective function (OV3) is
activated to stop the inverter.
On the contrary, if the acceleration time is too long
when the lift is descending, the overcurrent protective
function (OC1) or overvoltage protective function
(OV1) may be activated.
The acceleration or deceleration time ([Pr. 7] or [Pr. 8])
value set from the operation panel (parameter unit) is
the length of time between zero and the acceleration/
deceleration reference frequency ([Pr. 20]).
The time required to reach the set frequency can be
calculated by proportion as indicated in [Example 1].
The frequency is found from the operating speed and
the number of motor poles by using the formula
below, with slip ignored:
Speed [r/min]
Frequency [Hz] =
excessively by the
time and
number of poles
120
487
common
(common)
[Example 1]
When a four-pole motor is accelerated from 500 to 1000 r/min in
10 seconds, acceleration time setting is as follows (assuming that
the acceleration/deceleration reference frequency is the factory
setting of 60Hz)
1800r/min
t =
(1000 - 500)r/min
Hence, the acceleration time (Pr. 7) is set to 36 seconds.
Acceleration/deceleration
reference frequency [Pr. 20]
1800r/min
(60Hz)
1000r/min
500r/min
0r/min
10s
t seconds (acceleration time setting)
Acceleration Time Setting
Note : When the acceleration time or deceleration time is set without
enough examination, set a long time and check during
operation that the OL display on the parameter unit is not lit.
When this display is not lit, reduce the set value and make the
test again. Repeat this operation until the optimum acceleration
or deceleration time is obtained.
(2) Calculation of acceleration and deceleration
time
common
N
1
Speed
N
2
ta td
Acceleration Deceleration
time time
Acceleration/deceleration operation pattern
For full information
acceleration and deceleration times, refer to any
of the following manuals according to the
operation pattern:
• Technical note No.30: Capacity selection II
(data part)
• Technical note No.31: Capacity selection II
(selection part)
SELECTION
10s = 36s
Time
on how to calculate
3