Mitsubishi Electric FR-A700 Technical Manual page 444

4) Advanced magnetic
A700 E700
The output current of the inverter is divided into an
excitation current and a torque current by vector
operation, then the voltage drop causing torque
decrease is compensated for and the speed is
automatically compensated (slip compensation) to
the optimum so that the speed will not change.
The output current of the inverter is divided into an
excitation current and a torque current by vector
operation and the frequency and voltage are
compensated for to flow a motor current which
meets a load torque, thereby improving a low
speed torque and speed accuracy. This method
provides a high (150%) torque at 0.5Hz.
The output current (motor
current) of the inverter is
divided into an excitation
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)
200
100
0
50 100 150 200
-100
-200
Speed (r/min)
Speed-torque characteristic example for Advanced magnetic flux vector control
(online auto tuning selected, inverter used with 3.7kW 4-pole motor)
flux vector control
Motor
current
Torque
current
200
100
6Hz
0
200
Expanded
-100
-200
The actual motor speed is estimated from the
torque current and the output frequency is
compensated
achieve the preset speed. (slip compensation)
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 excitation current.
This voltage drop is found from the motor and
primary wiring constants of the motor and torque
current magnitude, and the output voltage of the
inverter
decreased) to keep the primary magnetic flux of
the motor constant.
Also, when the online auto tuning is selected in
, the motor is tuned quickly when starting,
A700
allowing high-accuracy operation unaffected by
motor temperatures and high-torque, stable
operation down to an ultra-low speed.
The motor
characteristic example is shown below.
320
Speed: with tuning
310
300
290
Speed: without tuning
280
270
260
250
Motor temperature
240
0 10
Motor temperature-speed fluctuation characteristic
(when the motor SF-JR 4P 3.7kW is used)
(Online auto tuning selected, repeated operation at
30Hz
400 600 800 1000
Speed (r/min)
478
SELECTION
for (increased/decreased)
is compensated for
temperature-speed
20 30 40 50 60
Elapsed time [min.]
example
90% duty)
60Hz
1200 1400 1600 1800
to
(increased/
fluctuation
160
140
120
100
80
60
40
20
0
70
2000