What Is Vector Control - Mitsubishi Electric FR-A700 Instruction Manual

Control mode
6.2.1

What is 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
(excitation current) for making a magnetic flux in the motor and a current iq (torque current) for
causing the motor to develop a torque.
● In vector control, the voltage and output frequency are calculated to control the motor so
that the excitation current and torque current (as shown in the left figure) 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. Derive the torque command value so that the difference between the motor speed com-
mand 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.
6 - 66
l1 l2
Motor current im
iq
Excitation current
Fig. 6-1:
Equivalent circuit of an induction motor
Fig. 6-2:
Motor current components
id
Parameter
I001497E
I001498E