SPEED CONTROL OF INDUCTION
MOTOR USING CONTROL VECTOR
1-Abstract:
. AC induction motors, which contain a cage, are very popular in variable speed drives. In many industries, we need to speed control of AC induction motor allows vector control of the AC induction motor running in a closed loop with the speed/position sensor coupled to the shaft PWM modules are the hybrid controller’s key features enabling motor control.
.The AC induction motor is a rotating electric machine designed to operate from a 3-phase source of alternating voltage. For variable speed drives, the source is normally an inverter that use power switches to produce approximately sinusoidal voltages and currents of controllable magnitude and frequency.
. The fast torque response obtained using vector control is achieved by estimating, measuring, calculating the magnitude and position of the motor flux in the machine. If this flux is known, the stator current phasor can be aligned to maintain the field at the desired level and to produce torque as desired. A reference a frame conversion is used to transform the three- phase stator currents into two orthogonal components, one to control the flux magnitude and the other current to control the developed torque. FIG .(1.1).
2-Introduction:
MACHINES: 
Widely used machine in fixed-speed applications due to reasons of cost, size, weight, reliability, ruggedness, simplicity, efficiency and ease of manufacture. Complexity arises because of variable frequency power supply ; ac signals processing and complex dynamics of ac machine. Requires more expensive higher inverters. 
VECTROL CONTROL: Fast torque response obtained using this method is achieved by estimating , calculating , magnitude and position of motor flux in machine. There are two methods to detect rotor flux position
1. Direct vector control method .
2. Indirect vector method .
3-Ac induction motor specifications:
P=100 Hp
Vline=420V
Frequency=50 Hz
Poles 4
Ns=1500rpm
Lm=0.01664H
Lr=0.017H
Rs= 0.03957ohm
Rr=0.02215 ohm
4-To perform vector control:
follow these steps: show that in fig (1.2)
ü Measure the motor quantities (phase voltages and currents) .
ü Transform them to the 2-phase system X,Y using a Clarke transformation.
ü Calculate the rotor flux space vector magnitude and position angle.
ü Transform stator currents to the d-q coordinate system using a Park transformation.
ü The stator current torque- (isq) and flux- (isd) producing components are separately controlled.
ü The output stator voltage space vector is calculated using the decoupling block.
5-Forward and Inverse Clarke Transformation (a,b,c to
α,β and backwards)
The forward Clarke transformation converts a
3-phase system (a, b, c) to a 2-phase coordinate system (α, β). Figure (1.3)
shows graphical construction of the space vector and projection of the space
vector to the quadrature-phase components α, β.
6-DESIGN CONCEPT OF ACIM VECTOR CONTROL:
System outline:
The system is designed to drive a 3-phase ac induction motor (ACIM). The
application has the following specifications:
Vector control technique used for ACIM
control Speed control loop of the ACIM Runs on 3-phase ac induction motor control
development platform at a variable line voltage of 400/420v The control technique incorporates:
ü speed control loop with an in q axis stator
current loop
ü rotor flux control loop with an inner d
axis stator current loop
ü field weakening technique
ü stator phase current measurement method
ü ac induction flux model calculation in an
x, y –stationary reference frame
ü D-q establishment allows transformation
from the stationary reference frame to the rotating reference frame
ü space vector modulation(SVM)
motor mode maximum speed of 1500 rpm at input power
line 420v ac
NOTES
ý The inverter converts DC power to AC power
at the required frequency and amplitude.
ý consists of three half-bridge units where
the upper and lower switch are controlled complimentarily, meaning when the
upper one is turned on, the lower one must be turned off, and vice versa.
ý As the power device’s turn-off time is
longer than its turn- on time, some dead time must be inserted between the time
one transistor of the half-bridge is turned off and its complementary device is
turned on.
ý The output voltage is created by PWM
technique.
An inverse Park transformation transforms
the stator voltage space vector back from the d-q Coordinate system to the
2-phase system fixed with the stator. Using the space vector modulation, the
output 3-phase voltage is generated. The flux reference is calculated. Speed reference is calculated by using
torque, Id and Iq. The rotor position (teta) is calculated for
ABC to dq conversion. The constant speed is assumed 80 rad/sec. The reference torque is assumed to 120 Nm. Apply the inverter in put voltage is
Vdc=420V. Id* is calculate by using reference flux. Iq* is calculate by using the Te* and flux.
7- Digital Control of an AC Induction Motor:
The combination of ON / OFF states of the power stage switches for each
voltage vector is coded in Fig. (1.4).by the three-digit number in parenthesis.
Each digit represents one phase. For each phase, a value of one means that the
upper switch is ON and the bottom switch is OFF. A value of zero means that the
upper switch is OFF
and the bottom switch is ON. These states, together with the resulting
instantaneous output line-to-line voltages, phase voltages and voltage vectors.
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