Mitsubishi Electric FR-A700 Technical Manual page 450

(3) Light motor load
If the load is extremely light as compared to the rated
torque of the motor used, the motor current is smaller
than the rated current. Hence, cost may be reduced
by using an inverter having a smaller rated capacity
than the motor capacity. In this case, the following
must be noted in determining the rated inverter
capacity:
An excitation current (no-load current), 30 to 50% of
the rated motor current, flows in a standard motor,
even if under no load. For this reason, an inverter
with extremely small rated capacity cannot be used.
Under a light load, the ripple factor of the current is
higher than that under a rated load even if the
effective current value is the same. Since the inverter
detects the instantaneous crest value of the motor
current to provide protection against overcurrent, the
current limit function may be activated at the crest
value due to a ripple even if the effective current
value is small.
For light-load operation, therefore, it is the best policy
to select the inverter capacity which corresponds to
the capacity of the motor used.
(4) Special motor (e.g.constant-torque motor
dedicated to inverter use)
Special motors are different in motor electrical circuit
constants from a standard motor. A motor dedicated
to inverter for increased torque at low frequency may
be more instable in motor characteristic or be larger
in current ripple especially in the low frequency range
(about 20Hz or less). When the inverter is used with
such a special motor (different in electrical design
from the standard motor), select the inverter capacity
after fully checking the motor characteristics, noting
the following:
1) Choose the inverter capacity one or two ranks
higher than the standard.
2) Match the V/F
characteristic using [Pr. 0] (torque boost).
(5) For selection of the Simple magnetic flux
vector control method
Select Simple magnetic flux vector control when
higher torque than V/F control is necessary in the low
speed range.
Simple magnetic flux vector control may be used
under the following conditions:
1) The number of motor poles should be any of 2, 4
and 6 poles.
2) Single-motor operation (one motor run by one
inverter) should be performed.
3) The wiring length from inverter to motor should be
within 30m.
(6) For selection of the General-purpose
magnetic flux vector control method
E700 D700
Select the General-purpose magnetic flux vector
control when you need a large starting torque (3Hz
200% torque (slip compensation is set for 3.7K or
common
pattern with the motor
F700
less)) for a small capacity or when it is desired to
shorten the acceleration time.
When choosing the General-purpose magnetic flux
vector control, set the capacity (kW) of the applied
motor. (For
E700
control method.)
When using a constant-torque motor, select a
constant-torque motor in [Pr. 71 (applied motor
selection)].
When using the General-purpose magnetic flux
vector control, there are the following restrictions:
1)Motor of which capacity is equal to or one rank
lower than the inverter capacity.
2)Single-motor operation (one motor is run by one
inverter).
3)The wiring length from the inverter to the motor
should be within 30m. (When the wiring length
exceeds 30m, perform offline auto tuning with wires
already in place.)
If any of the above conditions are not satisfied,
excellent operation characteristics may not be
provided.
(7) For selection of the Advanced magnetic
flux vector control method
Select the Advanced magnetic flux vector control for
a load which requires a large starting torque (0.5Hz
150% torque) or a load which requires a 130 to 140%
average acceleration
acceleration time.
Advanced magnetic flux vector control may be used
under the following conditions:
1) Motor to be used is either Mitsubishi standard
motor (SF-JR, SF-HR
pole 0.4kW or more) or Mitsubishi constant torque
motor (SF-JRCA, SF-HRCA four-pole 0.4kW to
55kW). When using a motor other than the above
(other manufacturer's motor, SF-JRC, etc.),
perform offline auto tuning without fail.
2) The motor capacity should be equal to or one rank
lower than the inverter capacity.
3) Single-motor operation (one motor run by one
inverter) should be performed.
4) The wiring length from inverter to motor should be
within 30m. (Perform offline auto tuning in the
state where wiring work is performed when the
wiring length exceeds 30m.)
(8) For selection of the Real sensorless
vector control
Select Real sensorless vector control for a load
which requires a quick response to the sudden load
fluctuation and torque limit during speed control
operation.
Real sensorless vector control may be used under
the following restriction, conditions.
1) Make sure to perform offline auto tuning before
performing Real sensorless vector control.
2) Torque control can not be performed in the low
speed regeneration range and at a low speed with
light load. In this case, select vector control.
484
SELECTION
, set number of motor poles and
A700 E700
torque to decrease
two-pole, four-pole, six-
A700
the