Mitsubishi Electric FR-A800, Instruction Manual

Page: 233 / 1042

Parameters Control method
FR-A800 5 - 53
5.2.1 Vector control and Real sensorless vector control
Vector control is one of the control techniques for driving an induction motor. To help explain vector
control, the fundamental equivalent circuit of an induction motor is shown below:
r1: Primary resistance
r2: Secondary resistance
l1: Primary leakage inductance
l2: 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 (ex-
citation current) for making a magnetic flux in the motor and a current iq (torque current) for causing
the motor to develop torque.
In vector control, the voltage and output frequency are calculated to control the motor so that the ex-
citation current and torque current flow to the optimum as described below:
●
The excitation current is controlled to place the internal magnetic flux of the motor in the optimum
status.
●
The torque command value is derived so that the difference between the motor speed command
and the actual speed (speed estimated value for Real sensorless vector control) obtained from the
encoder connected to the motor shaft is zero. Torque current is controlled so that torque as set in
the torque command is developed.
I002501E
Fig. 5-2: Equivalent circuit of an induction motor
Fig. 5-3: Motor current components
I001498E
1
im
r
1
r
2
S
M id iq
2
l1 l2
iq
To
rq
u
e
c
u
rr
e
n
t
Excitation current
id
Motor current
im