Mitsubishi Electric FR-A700 Technical Manual page 448

Block diagram of vector control
Magnetic
φ 2
ω
*
+
-
ω FB
ω FB
By detecting the motor speed with an encoder and
computing the motor slip, the magnitude of the load can be
found.
With the magnitude of the load found, the inverter output
current is divided into an excitation current (current
required to generate magnetic flux) and torque current
(current proportional to the load torque) by vector
operation, and frequency and voltage are controlled
optimally to flow a current necessary for each.
Since vector control has a current control loop, necessary
excitation current and torque current can be calculated
separately.
[Speed control]
Speed control operation is performed to zero the
difference between the speed command
rotation detection value
time, the motor load is found and its result is transferred
to the torque current controller as a torque current
command iq * .
[Torque current control]
A voltage Vq is calculated to start a current iq which is
identical to the torque current command iq
speed controller.
id
*
+
flux
control
-
id
iq *
Speed +
control
iq
ω 0
+
+
ω s
iq
Slip
calculation
φ 2
Magnetic
calculation
* and actual
FB by the encoder. At this
found by
*
Excitation
Vd
current
control
Torque
Vq
current
-
control
id
flux
[Magnetic flux control]
The magnetic flux
excitation current id. An excitation current command
(id*) is calculated for the motor magnetic flux
the predetermined magnetic flux.
[Excitation current control]
A voltage (Vd) is calculated to start a current id
is identical to the excitation current command (id*)
found by magnetic flux control.
[Output frequency calculation]
Motor slip
current value iq and magnetic flux
frequency
feedback
The above results are used to make PWM modulation and
run the motor.
482
PWM
modulation
Output
voltage
conversion
ω 0
id
Current
iq
conversion
2 of the motor is derived from the
s is calculated on the basis of the torque
0 is found by adding that slip
FB found by a feedback from the encoder.
SELECTION
IM
Encoder
2 to be
* which
2. The output
s to the