Mitsubishi Electric FR-E800, Instruction Manual

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4. Control Method
4.1 Vector control and Real sensorless vector control
4.1
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.
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 torque.
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 ( ω s) and the motor's secondary magnetic flux ( Φ 2) can be found by the
following calculation:
TM
Φ 2 · iq
Φ 2 = M · id
ω s =
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.
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
1
im
r
1
r
2
S
M id iq
2
torque current
iq
motor current im
excitation current
id
L2
r2
id
iq