Mitsubishi Electric FR-A700 Series, Technical Manual

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477
SELECTION
S
E
LECTION
3
2) Simple magnetic flux vector control
This control method divides inverter output current
by vector calculation, and compensates for
amount of voltage drop which causes torque
decrease. Comparing with V/F control, higher
torque at low speed range is available.
To compensate the speed variation, use slip
compensation ([
Pr. 245 to Pr. 247
]).
3) General-purpose magnetic flux vector control
The output current of the inverter is divided into an
exciting current and a torque current by vector
operation and the voltage is compensated for to
flow a motor current which meets the load torque,
thereby improving the low-speed torque. This
control method provides a high torque of 200%
(3.7K or more) at 6Hz.
If the motor constants vary slightly (when the
inverter is used with the another manufacturers
motor, for example), this system provides a stable,
large, low-speed torque without specific motor
constant setting or tuning, achieving high
versatility. (Offline auto tuning can be performed
to run the motor with the optimum characteristic.)
When the motor current varies due to load
fluctuation, the voltage drop of the motor's primary
side (including the wiring) also changes, affecting
the magnitude of the exciting current.
This voltage drop is found from the motor and
primary wiring constants and torque current
magnitude, and the output voltage of the inverter
is compensated for (increased/decreased) to
keep the primary magnetic flux of the motor
constant.
Also, the motor speed varies with load fluctuation.
You can choose the slip compensation function
([
Pr. 245 to 247
]) which estimates the motor slip
from the output current of the inverter to keep the
motor speed constant. (The control method is
different from Advanced magnetic flux vector
control.)
At this time, the torque characteristic is as shown
on the below.
Speed-Torque Characteristic Example for General-Purpose Magnetic Flux Vector Control
(use of inverter with 0.75kW 4-pole motor)
F700
E700 D700
The output current (motor
current) of the inverter is
divided into an exciting
current (current required to
generate a magnetic flux)
and a torque current
(current proportional to load
torque) by vector operation
according to each phase of
the current relative to the
output voltage. (Refer to the
figure on the right.)
Motor
current
Excitation current
Torque
current
300
200
100
0
㧙
100
㧙 200
600 900 1200 1500 1800
Load torque (%)
Speed
(r/min)
300 180 30
90
Speed-Torque Characteristic Example for General-
Purpose Magnetic Flux Vector Control when Slip
Compensation Is Selected
(Use of inverter with 0.75kW 4-pole motor)
(a) General-purpose magnetic flux vector control
300
200
100
0
㧙
100
㧙 200
300 600 900 1200 1500 1800 90 180
300
200
100
0
㧙 100
㧙
200
90 300 900 1500 1800
150
㧙 150
Load torque (%)
Load torque (%)
Speed
(r/min) Speed
(r/min)
(b) V/F control