In Vector control, the voltage and output frequency are calculated to control the motor so that the excitation 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.
Motor-generated torque (TM), slip angular velocity (ωs) and the motor's secondary magnetic flux (Φ2) can be found by the
TM Φ2 · iq
Φ2 = M · id
where, L2: secondary inductance
L2 = 2 + M
Vector control provides the following advantages:
• Vector control has excellent control characteristic compared to V/F control and other controls. The control characteristic of
the Vector control is equal to those of DC machines.
• It is applicable to fast response applications with which induction motors were previously regarded as difficult to use.
Applications requiring a wide variable-speed range from extremely low speed to high speed, frequent acceleration/
deceleration operations, continuous four-quadrant operations, etc.
• Torque control is enabled (when an induction motor is used).
• It allows servo-lock torque control which generates a torque in the motor shaft while stopped. (Not available under Real
sensorless vector control.)
motor current im
5.2 Control method