Controlling An Induction Motor Using Vector Control - YASKAWA VS-626M5 Instruction Manual

N : Rotator speed (min
r
Also, switching to 3-phase alternating current will reverse the order of the phases, causing the rotation
magnetic field to rotate in reverse, so the motor will rotate in reverse.
In this way, the squirrel cage induction motor changes slip to meet the required torque, generates the re-
quired primary current, and functions as an energy converter that converts electric power (electrical ener-
gy) to to torque and speed (mechanical energy). Differing from the DC motor, however, there is the prob-
lem that the magnetic flux of the rotation magnetic field and the secondary current cannot be controlled
directly, so careful planning for the control is required.

15.1.4 Controlling an Induction Motor Using Vector Control

Vector control permits controls equivalent to the DC motor in a squirrel cage induction motor. This control
method is called slip frequency control, it requires a speed detector, and it performs control taking the de-
tected speed as a standard. Nearly all vector control inverters in use employ this method.
Vector control uses applies the torque generation principle of the squirrel cage induction motor to inverter
control. Primary current I
distributed to secondary current I
performs control so that the required torque is generated.
The VS-626M5 control block is shown in Fig. 15.6.
The speed controller performs control so that there is no difference in speed reference value ω
detection value ω
I * using a secondary current reference limiter. Rated speed settings and speed adjustment parameters are
2
used to standardize the signals. The speed controller gain and integral time can be selected to suit the con-
trol mode.
The magnetic flux reference part inputs the speed detection value ω
ence value φ* to control fixed outputs.
The vector controller develops the torque generation principle. Primary current reference value I
its frequency and phases, are generated from secondary current reference value I
ence value φ*, and speed detection value ω
the motor model.
Current flows through the current controller according to primary current reference vector
forms control to generate the required torque.
Speed control
Torque limiter
Speed controller
Speed
* +
ω
refer-
r
−
ence
φ*
Magnetic flux
reference
ω
r
Fig 15.6
−1
), f: Power supply frequency (Hz), P: No. of motor poles
, which is supplied to the induction motor in line with the torque references, is
1
and magnetized current I
2
according to the speed detector signal, and outputs secondary current reference value
r
Vector control
*
*
I
I
1
2
*
I
1

= * 2 * 2
I + I
2 m
Current
reference
*
1 +
θ
I
m
*
I
θ=
M
2
+
−1
tan
m
I
2
R
2
s
ω
+
s
ω
+
r
VS-626M5 Control Block
15 -5
as per the set value inside the motor, and
m
and outputs the magnetic flux refer-
r
Use the motor codes to select the parameters depending upon
r.
Current control
Current controller
S *
*
S
V
+
1
I
1
−
θ
1
PWM
control
S
I
1
dt
15.1 Inverter Drive Basics
speed
and
r*
*, and
1
*, magnetic flux refer-
2
S
*
, and per-
I
1
VS-656MR5
Converter
VS-626M5
Inverter
CT
M
Induction motor
E Encoder
15