Mitsubishi Electric FR-A700 Technical Manual page 445

5) Real sensorless vector control
Real sensorless vector control is a control method
which estimates the motor speed from the motor
constants, voltage, and current without using an
encoder (with a standard motor without encoder).
The response and characteristics at nearly zero
speed are low as compared to vector control
using a motor with encoder.
Real sensorless vector control is the control
method which divides the inverter output current
into an excitation current and a torque current by
vector calculation, and improves low speed
torque, speed control range, and speed response
by controlling frequency and voltage optimally to
flow a motor current which meets the load torque,
achieving maximum of 200% (3.7kW or less) high
torque at 0.3Hz.
It responds to the load variation quickly (high
response) by torque current control, and torque
control is also enabled by giving torque command.
To help explain vector control, the fundamental
equivalent circuit of an induction motor is shown
below:
r
im 1
1
i d
r1:Primary resistance
r2:Secondary resistance
1:Primary leakage inductance
2:Secondary leakage inductance
M:Mutual inductance
S:Slip
id:Excitation current
iq:Torque current
im:Motor current
In the above diagram,
currents flowing in the
induction motor can be
classified into a current id
(excitation current) for
making a magnetic flux in
the motor and a current iq
(torque current) for
causing the motor to
develop a torque. With
Real sensorless vector
control, inverter controls
the motor so that the
excitation current and
torque current to flow to
the optimum by
calculating the voltage
and output frequency.
Control block diagram is
shown on the next page.
A700
2
r
M iq 2
S
Motor
current
Torque
current
479
Motor-generated torque TM, slip angular velocity
s and the motor's secondary magnetic flux
be found by the following calculation:
TM 2 iq
2 M id
s
where, L2 = secondary inductance
L2= 2 + M
Example of torque characteristic
Maximum torque for short time
(0.4K to 3.7K)
200
Maximum torque for short time
(5.5K to 500K)
150
Continuous torque
(0.4 to 3.7K)
100
95
70
50
0 0 . 3 1 6
60
Torque characteristic
For the motor SF-JR 4P (at 220V input)
Example of torque limit characteristic
Motor speed
Under torque limit
150
Motor generated torque
0
Example of torque limit characteristic
SF-JR 4P 3.7kW motor
Also, when the online auto tuning is selected, the
motor is tuned quickly when starting, allowing
high-accuracy operation unaffected by motor
temperatures and high-torque, stable operation
down to an ultra-low speed.
SELECTION
can
120
Output frequency(Hz)
1500
3
0