1

Abstract :

This project studies different ways of controlling induction motor speed and also

induction motor start , the new technology has development a batter ways to limit the

huge current of the induction motor when its begin to start , however this project will

show the design of the circuit and the analyses of the circuit for controlling the speed of

induction motor using modern equipment from power electronic device like thyristor

and other equipment . and will show the way and the result of the simulation

2
Electric Motors
One way of classifying electric motors is by the type of power they consume. Using this
approach, we may state that all electric motors fall into one or the other of the two
categories, AC or DC. AC motors are those that run on alternating current or AC power, and
DC motors are those that run on direct current, or DC power. AC motors work by setting up
a magnetic field pattern that rotates with respect to the stator and then employing
electromagnetic forces to entrain the rotor in the rotating magnetic field pattern.

Figure 1.1 Classification of electric motors[1]

3
1.1 Motor Selection
The motor may be selected according to Cost , Efficiency, Thermal capacity, Torque-speed
profile, Acceleration, Power density, volume of the motor, Peak torque capability,……etc.
Among all the existing motors on the market there are three classical motors: the DC motor
type, and two Alternative Current AC motors the synchronous motor type and the induction
motor type.

1.2 The Induction Motor

Induction motors are probably the most numerous in today’s economy. Induction machines
are simple, rugged and usually are cheap to produce. They dominate in applications at power
levels from fractional horsepower (a few hundred watts) to hundreds of horsepower (perhaps
half a megawatt) where rotational speeds required do not have to vary. Figure 1.4 shows
cartoon of induction motor. Most (but not all) machines have this structure.

Figure 1.2 Induction motor structure [2]

4
1.3.BAsic Construction
The AC induction motor comprises two electromagnetic parts:
• Stationary part called the stator
• Rotating part called the rotor, supported at each end on bearings

The stator and the rotor are each made up of:

• An electric circuit, usually made of insulated copper or aluminum, to
carry current.
• A magnetic circuit, usually made from laminated steel, to carry magnetic flux

In most electric motors, rotor and stator are made of highly magnetically permeable materials
- steel or iron. In many common motors, rotor and stator are made of thin sheets of silicon
steel (laminations). Punched into these sheets are slots which contain rotor and stator
conductors.

A - The Stator
The stator is the outer stationary part of the motor, which consists of:
The outer cylindrical frame of the motor, which is made either of welded sheet steel, cast
iron or cast aluminum alloy. This may include feet or a flange for mounting, The magnetic
path, which comprises a set of slotted steel laminations pressed into the cylindrical space
inside the outer frame. The magnetic path is laminated to reduce eddy currents, lower losses
and lower heating, and a set of insulated electrical windings, which are placed inside the
slots of the laminated magnetic path. The cross-sectional area of these windings must be
large enough for the power rating of the motor. For a 3-phase motor, 3 sets of windings are
required, one for each phase.

B - The Rotor
This is the rotating part of the motor. As with the stator above, the rotor consists of a set of
slotted steel laminations pressed together in the form of a cylindrical magnetic path and the
electrical circuit. The electrical circuit of the rotor can be either:

B.1 Wound Rotor Type

which comprises 3 sets of insulated windings with connections brought out to 3 sliprings
mounted on the shaft. The external connections to the rotating part are made via brushes onto
the sliprings. Consequently, this type of motor is often referred to as a slipring motor.

B.2 Squirrel Cage Rotor Type

Which comprises a set of copper or aluminum bars installed into the slots, which are
connected to an end-ring at each end of the rotor. The construction of these rotor windings
resembles a ‘squirrel cage’. Aluminum rotor bars are usually die-cast into the rotor slots,
which results in a very rugged construction. Even though the aluminum rotor bars are in

5
direct contact with the steel laminations, practically all the rotor current flows through the
aluminum bars and not in the laminations.

Figure 1.3 Stator and rotor laminations[2]

C - The Other Parts

The other parts, which are required to complete the induction motor, are:
• Two end-flanges to support the two bearings, one at the drive-end (DE) and the
other at the non drive-end (NDE)
• Two bearings to support the rotating shaft, at DE and NDE
• Steel shaft for transmitting the torque to the load
• Cooling fan located at the NDE to provide forced cooling for the stator and rotor
• Terminal box on top or either side to receive the external electrical connections

Figure 1.4 Assembly details of a typical AC induction motor[2]

6
Most widely spread induction motor is the squirrel cage motor because of its good self-
starting capability, more efficient, require lower maintenance, and rugged structure.

Figure 1.5 The squirrel cage motor type[2]

1.4 Principles Of Operation

The three-phase stator is supplied by balanced three-phase voltage that drives an ac
magnetizing current through each phase winding. The magnetizing current in each phase
generates a pulsating ac flux. The flux amplitude varies sinusoidally and the direction of the
flux is perpendicular to the phase winding. The three fluxes generated by the phase windings
are separated by 120° in space and in time for a two-pole motor .The total flux in the
machine is the sum of the three fluxes. The summation of the three ac fluxes results in a
rotating flux, which turns with constant speed and has constant amplitude. The rotating flux
induces a voltage in the short circuited bars of the rotor. This voltage drives current through
the bars. The induced voltage is proportional with the difference of motor and synchronous
speed. Consequently the motor speed is less than the synchronous speed. The interaction of
the rotating flux and the rotor current generates a force that drives the motor. The force is
proportional with the flux density and the rotor bar current.

7
1.5 The Equivalent Circuit
To understand the performance of an AC induction motor it is useful to electrically represent
the motor by an equivalent circuit. This clarifies what happens in the motor when stator
voltage and frequency are changed or when the load torque and slip are changed. There are
many different versions of the equivalent circuit, which depend on the level of detail and
complexity.

Figure 1.6 The equivalent circuit of an AC induction motor[2]

Where
V = Stator supply voltage RS = Stator resistance
ES = Stator induced voltage XS = Stator leakage reactance at 50 Hz
ER = Rotor induced voltage RR = Rotor resistance
NS = Stator turns XR = Rotor leakage reactance
NR = Rotor turns XM = Magnetizing inductance
IS = Stator current RC = Core losses
IR = Rotor current
IM = Magnetizing current
The main components of the motor electrical equivalent circuit are:
• Resistances represent the resistive losses in an induction motor
• Inductances represent the leakage reactance. These are associated with the fact that not all
the flux produced by the stator windings cross the air-gap to link with the rotor windings and
not all of the rotor flux enters the air-gap to produce torque.

8
The equivalent circuit can be re-arranged and simplified as shown in the figure 1.8 below.

Figure 1.7 The simplified equivalent circuit of an AC induction motor[2]

Where
X'R = N2 × XR
R'R = N2 × RR
N = NS/NR, the stator/rotor turns ratio

In contrast with a DC motor, the AC induction motor does not have separate field windings.
As shown in the equivalent circuit, the stator current therefore serves a double purpose:
• It carries the current (IM) which provides the rotating magnetic field
• It carries the current (IR) which is transferred to the rotor to provide shaft torque

9
Control circuit design and simulation

10
Objective :

To control the speed of the three phase induction motor using power electronic
component

Theory:
Th snober circuit:
It is essential for diode used in switching it can save the diode from over voltage peaks avery
common snubeer circuit for power diode consist from capacitor and resistor connected in
parallel with diode .

Diode:

It is the most common device used in power system it is circuit very simple its consist of tow
part and cathode if the anode terminal has higher potential than the cathode it well be
forward and also the current well be forward in this case small voltage drop will happen
almost less than one if the diode reversed it well not conduct

Thyristor: the thyristor called silicon control rectifier it is four layer three junction it has
three terminals :anode cathode and gate its on when we apply the pulls on the gate but as the
device on the gate cannot switched off aging. The device can turned off by applying reveres
gate an anode and cathode ,there are tow calcification for this device, converter gate and
inverter gate the low turn off time for latter

11
Zero crossing point :

shows the logic used in zero crossing detector-block. The zero crossing is detected by simple
logic circuit and an external analog comparator. Zero crossing comparator output is a square
waveform has a +V value with the positive half cycle of phase voltage and 0 with the
negative half cycle of phase voltage as shown in Fig.(2)The required signal for the control
system has two pulses for each period one when the comparator output changes from 0 to +V
and the other when it changes from +V to 0.. Comparing any two successive samples of
comparator output using XOR logic function will generate the pulses whenever the
comparator output changed as shown in Fig.(2). Comparator output is sampled using a single
bit register, and the register input and output are applied to XOR logic gate as shown in
Fig.(1). The AND gate and the inverter1) are used to disable the zero crossing pulse
generation whenever a global system reset is applied. Each phase has a separate zero-
crossing detector block to synchronize the saw-tooth

12
Equipment used :

1) Three power triacs (Part # BT139) has a 600V Repetitive peak off-state voltage and
16 A on-state current.

2) Three opto-coplers (Part # TLP3022).

3) Group of current limiting resistors between the triacs and optocopler.

4) One dc power supplies +5/-5V to feed the comparators required for zero crossing.

5)A group of capacitor with different farad

6)Pored made from cupper

7) Three step down transformers to feed the phase voltages to the three comparators

8)three op amps

8) Aluminum bar to hold the power triacs

9) Group of wires

Programs used :

1) Pcp express version 5

2) Psim version 5

13
14
 he design of the circuit using the pcp exxpress :
*Th

15
Simulation of the Circuit Using Psim Program :

16
*Computer Simulation:

The figure above is designed by using the PSIM (5) , it is content of three phase supply

Feeding three phase induction motor active as load , the name plate for the induction

Motor is

1 kW, 380 V, star connections, 3.0A, 4-pole, 60 Hz, Rs = 0.0583 pu, pu, X s = 0.125pu,
R r = 0 .0417

X r = 0 .018 pu, and X m =1.05 pu.

The simulation designed and used to show and calculate different operation to study

Variation between the different parameter the figures next how the different variation

And different relationships between different parameter as follow .

**the variation of the thee phase current under induction motor load with different has

Only show three type of modes (0\2 & 0\2\3 & 2\3) with different values of α (degree)

*the first mode is (2\3)

That is mean only two of the current will operate while the third off or the all three
current will operate to gathers

17
*the second mode is even no current flow or tow current flow or three current
flow(0\2\3)

The third mode is (0\2)

18
 speed (pu)vs α
1.2

0.8

0.6

0.4

0.2

0
0 10 20 30 40 50 60 70 80 90

Speed versus α at .5 pu constant torque

pf vsα
0.6

0.5

0.4

0.3
pf vsα
0.2

0.1

0
0 20 40 60 80 100

Power factor versus α at .5 pu torque

19
 phase voltage vs α
1.2

0.8

0.6
phase voltage vs α

0.4

0.2

0
0 20 40 60 80 100

Phase voltage versus α at 1.3 pu torque

THD vs α
120

100

80

60
THD vs α
40

20

0
0 20 40 60 80 100

THD versus α at no load

20
 η vsα
100

90

80

70

60

50
η vsα
40

30

20

10

0
0 20 40 60 80 100 120

Momtor η(%) versus α at .8 pu torque

PF vS SPEED
0.8

0.7

0.6

0.5

0.4
PF vS SPEED
0.3

0.2

0.1

0
0 0.2 0.4 0.6 0.8 1 1.2

Power factor vesus speed (pu) at .6 pu torque

21
 η VS SPEED
90
80
70
60
50
40
30
20
10
0
0 0.2 0.4 0.6 0.8 1 1.2

Motor η versus speed (pu) at α=80

Conclusions:

Three-phase ac voltage controller has been used to start and control the speed of induction
motor by controlling the stator voltage. Computer simulation using PSIM a software has
been carried out to configure the performance of the motor in each mode. From simulation
results there are three modes of operations depending on the shape of supply currents. These
modes namely 0/2 , 0/2/3, and 2/3. The variation of speed with firing angle is different in
each mode. The control system detects the mode of operation to provide the switches with
the correct firing angle. The operating limits have been determined from the simulation
results using PSIM computer program.

22
 Content:
topic Page number

Abstract 1

Introduction 2

Control circuit and design 10

Equipment used 13

Program used 14

The designed circuit 15

Simulation of the circuit 16

Result 19

References 23

23
References :

[1] ABB research 'three phase induction motor ' 2004

[2] eng pasil project ,eygebt ,2007.

[3] Dubey, G. K., Doradla, S. R., Hoshi, A. and Sinha, R. M.,

"Thyristorized Power Controllers", Book, John Wiley & Sons,
India, 1986.

[5] Hamed, S. and Chalmers, B., " Analysis of variable-voltage

thyristor controlled induction motors" IEE Proc., Vol. 137(3), Pt.
B, pp. 184-193, May 1990.

[6] Morters et. al. "Control system for regulating the speed of an
electric motor" U.S. Patent 4093898, June 1978.

[7] Kamaike, H. "Elevator speed control system" U.S. Patent

4052651, Oct. 1977.

[8] Rowan, T. M., Merrison, J. C. "Electric motor speed control

apparatus and Method" U.S. Patent 4996470, Feb. 1991.

[9] Delange, R. J. " Electric motor control apparatus and

Method" U.S. Patent 5187419, Feb. 1993.

24