Automatic Speed Control of 1-Ph Induction Motor

Automatic Speed Control of 1-Ph I.M.

CHAPTER-1

ABSTRACT:

In this automatic speed control of single phase induction motor, speed

control is done by successfully comparing actual speed with entered speed. We

know now days the scope of electric machines are growing rapidly. Speed control

of such an electrical machines to run it at desired value of speed is also essential

and microcontroller can done it in very finest way.

As we had surveyed speed of electrical machines is a need of today’s era

with healthy machines and increased efficiency, hence the machine can gives the

exact value of desired speed with anti- parallel thyristor based driving circuit. The

errorless proximity metal sensor forced to sense the pulse of revolution of motor

and give it to microcontroller and finally is getting displayed on the liquid crystal

display in revolution per second i.e. in RPS.

R.I.T., Sakharale 1


CHAPTER-2

INTRODUCTION:

The speed of induction motor can be reduced by decreasing stator voltage by an

amount which is sufficient for the speed control of some drives. While torque is

proportional to voltage squared, current is proportional to voltage therefore, as voltage is

reduced to reduce speed, for same current motor develops lower torque. Consequently,

method is suitable for application where torque demand reduces with speed, which points

towards its suitability for fan and pump drives.

Variable voltage for speed control is obtained using ac voltage controllers.

Industrial fans and pumps are usually driven by induction motors. Thyristors are

commonly used for controlling the voltage to control the speed of induction motor. Speed

control is obtained by varying conduction period of thyristors. For low power rating

machines, anti-paralleled thyristor pair is used.

Speed of the motor can be varied more or less uniformly in the range of 80% to

30% of synchronous speed of the motor by varying the voltage between 100% to 30%.

The stator voltage is controlled in these speed control systems by means of a power

electronic controller. Here two thyristors in anti parallel are connected between the line

and motor in a phase. Normally thyristors in phase control mode are used. It is also

possible to fire the thyristors for only a portion of the cycle, thus utilizing conduction

angle manipulation. This is useful in motor control.

The conduction of thyristor pair is controlled by changing firing angle of

thyristors through microcontroller.

R.I.T., Sakharale 2


CHAPTER-3

FUNCTIONAL SPECIFICATION:

3.1 Supply specification:

Type of Supply: Single Phase

Voltage: 230V

Frequency: 50Hz

3.2 Electronic circuit specification:

Type of Supply: DC

Voltage: +5V Regulated, Ground.

3.3 Motor Specification:

Voltage: 240v

Current: 0.3A

Hz: 50

RPM: 1360

WATTS: 9

HP: 1/83

INSULATION CLASS: A

RATING: CONT

3.4 Driver circuit specification:

UNISON SSR

Dc to ac solid state relay (back to back SCR)

801 RDA 48 25 00 (801 model single phase ac load)

Input: 4-32Vdc, 4-16mA

Output: 24-480Vac, 25A

(Back to back SCR-silicon control rectifier with heat sink & 35mm din rail

mounting.)

R.I.T., Sakharale 3


CHAPTER-4

BLOCK DIAGRAM & WORKING:

Fig.(A) Block diagram

R.I.T., Sakharale 4


Fig.(B) Working of driver circuit.

It is based upon the silicon controlled rectifier or ‘thyristor’. By pulsing a

thyristor, it switches from ‘off’ to ‘on’ until the current stops flowing through it, which

occurs every half cycle in an AC supply. By controlling electronically the thyristor turn

on point, it is possible to regulate the energy passing through it. By starting with a large

delay angle and gradually reducing it, the motor terminal voltage is increased from a low

value to full value, giving a smooth, step less start. In short, by carefully controlling the

motor voltage at starting with the help of thyristor, the speed can be controlled.

As shown in above fig the connection of anti-parallel thyristor in series with

induction motor having 230V, 50 Hz ac supply. In positive half cycle of ac supply the

thyristor T1 conducts, during that state thyristor T2 is in OFF condition and according to

firing angle of thyristor T1 the voltage appears across induction motor. As same, in the

negative half cycle of ac supply, the thyristor T2 conducts, during that state thyristor T1

is in OFF condition and according to firing angle of thyristor T2 the voltage appears

across induction motor. According to the variation of firing angle of both thyristor, the

respective voltage appears across induction motor. Because of this voltage stator flux will

gets changed, resulting in change in speed of induction motor.

R.I.T., Sakharale 5

G2

T1

T2230V50 Hz

G1

1-PhI.M.


CHAPTER-5

HARDWARE DETAILS:

5.1 POWER SUPPLY:

Circuit Diagram:

The dimmer is to be a self-contained unit and thus requires a power supply to

provide low voltage DC for its electronics from the AC power line. The microcontroller

need +5V DC, These specifications dictate the use of a low-cost, ubiquitous linear

regulator National Semiconductor LM7805. The LM7805 requires an input voltage of at

least 7.5V in order to guarantee regulation, so the unregulated power supply should

supply at least this voltage under worst-case current consumption, assumed to be about

200mA.

Because a full-wave rectifier will be used for efficiency (diodes D1-D2), we can

assume that about 1.4V will be lost across the bridge (0.7V per conducting diode). We

R.I.T., Sakharale 6


therefore need a transformer was selected as T1, which is of rating 9-0-9 secondary at

500 mA

Positive Voltage Regulator (IC 7805):

Voltage regulator is commonly weal for on card regulators and laboratory type.

Power supplies, at most all power supplies we some type of IC voltage regulator. Because

voltage regulators are simple to use, reliable, low in cost and above all available in

variety of voltage and current rating.

We use in our project fixed voltage regulator. The 7800 series are fixed voltage

regulator IC. Although these device do not require external components such components

can be used to obtain adjustable voltage and currents. This IC s also has internal thermal

overload protection and internal short circuit current limiting. Following are the

connection diagrams of IC 7805 which provide +5. The capacitors C in and Cout are used to

nullify inductance due to input wires and to improve the transient response.

R.I.T., Sakharale 7


5.2 ZERO CROSSING DETECTOR:

Circuit Diagram:

Input output Waveform:

R.I.T., Sakharale 8


In order for the thyristor pair to determine at which point on the AC cycle to turn

on invidiously, it needs a reference for the AC zero crossing. Zero crossing detector is

used to convert sine wave or other signal into square-wave, the output should be low if

the input is positive and high if the input if negative.

I contract to sine wave oscillators, square wave outputs are generated when the

op-amp is forced to operate in the saturated region. That is the output of op-amp is forced

to swing repetitively between positive saturation +Vsat (≈ +Vcc) and negative saturation

–Vsat (≈ -Vcc), resulting in square wave output.

LM339 Pinout:

As shown in figure above LM339 consists of four op-amp’s inside it. From which

one of the op-amp is used for zero crossing detection.

R.I.T., Sakharale 9


5.3 MICROCONTROLLER AT89S52:

5.3.1 MICROCONTROLLER AT 89S52 FEATURES:

Compatible with MCS 51 products

8k bytes of in system Re-programmable Flash Memory

Fully static operation : 0 Hz to 24 MHz

256 x 8 bit internal RAM

32 programmable I/O Lines

Three 16 bit Timer or Counters

8 Interrupt sources

Programmable serial channel

Low power Idle & power down modes

5.3.2 MICROCONTROLLER AT 89S52 DISCRIPTION:

R.I.T., Sakharale 10


The Microcontroller IC 89S52 has 256x8 bit internal RAM which is most important

feature for this application. Here eight to ten readings can be recorded in RAM after each

half an hour to achieve data logging.

The Timer/Counter application of 89S52 is used to count the pulses from proximity

sensor. The interrupt pin INTR0 is used to switch into different setting modes The serial

channel is used to get interface with pc for data logger application.

The AT89C52 provides the following standard features: 8Kbytes of Flash, 256 bytes

of RAM, 32 I/O lines, three 16-bittimer/counters, a six-vector two-level interrupt

architecture, a full duplex serial port, on-chip oscillator, and clock circuitry. In addition,

the AT89C52 is designed with static logic for operation down to zero frequency and

supports two software selectable power saving modes.

The Idle Mode stops the CPU while allowing the RAM, timer/counters, serial port,

and interrupt system to continue functioning. The Power down Mode saves the RAM

contents but freezes the oscillator, disabling all other chip functions until the next

hardware reset.



5.3.3 AT 89S52 PINOUT:



Port 0

Port 0 is an 8-bit open drain bidirectional I/O port. As an output port, each pin can

sink eight TTL inputs. When 1s are written to port 0 pins, the pins can be used as high

impedance inputs. Port 0 can also be configured to be the multiplexed low order

address/data bus during accesses to external program and data memory. In this mode, P0

has internal pull-ups. Here port 0 is used as Data lines to LCD.

Port 1

Port 1 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 1 output

buffers can sink/source four TTL inputs. When 1s are written to Port 1 pins, they are

pulled high by the internal pull-ups and can be used as inputs. In addition, P1.0 and P1.1

can be configured to be the timer/counter 2 external count input (P1.0/T2) and the

timer/counter 2 trigger input (P1.1/T2EX). Here Port 1 is used Data lines to the ADC and

simultaneously by using Buffer they are used for addressing of mode selection switches.

Port 2

Port 2 is an 8-bit bidirectional I/O port with internal pullups. The Port 2 output


pulled high by the internal pull-ups and can be used as inputs. As inputs, Port 2 pins that

are externally being pulled low will source current (IIL) because of the internal pull-ups.

Here Port 2 is used for different functions as, P2.0-2 for channel selection of ADC.

P2.3 for accepting Start of Conversion signal from ADC.

Port 3

Port 3 is an 8-bit bidirectional I/O port with internal pull-ups. The Port 3 output


pulled high by the internal pull-ups and can be used as inputs. Port 3 also serves the

functions of various special features of the AT89S52, as shown in following table. Here

Port 3 pins are used for many different functions.





Timer Control (TCON) Special Function Register:

Symbol Position Function

TF1 TCON.0 Timer 1 over flow flag.

TR1 TCON.1 Timer 1 run control bit.

TF0 TCON.2 Timer 0 over flow flag.

TR0 TCON.3 Timer 0 run control bit.

IE1 TCON.4 External Interrupt 1 Edge flag.

IT1 TCON.5 External Interrupt 1 signal type control bit

IE0 TCON.6 External Interrupt 0 Edge flag.

IT0 TCON.7 External Interrupt 0 signal type control bit.


TF1 IT0TR1 TF0 IE0IT1TR0 IE1


Timer Mode Control (TMOD) Special Function Register:


Gate D7/3 OR gate enable bit which controls RUN/STOP

Of Timer 1/0

C/Tbar D6/2 Set to 1 by program to make timer 1/0 act as timer /

Counter.

M1 D5/1 Timer/ Counter operating mode select bit 1.

M0 D4/0 Timer/ Counter operating mode select bit 0.

Mode selection:

M1 M0 Mode

0 0 0

0 1 1

1 0 2

1 1 3


Gate M0C/Tbar M1 M1C/TbarM0 Gate


Serial Port Control (SCON) Special Function Register:


SM0 SCON.0 Serial port mode bit 0. Set / cleared to select

Mode.

SM1 SCON.1 Serial port mode bit 1. Set / cleared to select

Mode.

SM2 SCON.2 Multiprocessor communications bit

REN SCON.3 Receive enable bit

TB8 SCON.4 Transmitted bit 8

RB8 SCON.5 Received bit 8

TI SCON.6 Transmit Interrupt flag

RI SCON.7 Receive Interrupt flag

Mode selection:

SM0 SM1 SM2 Description

0 0 0 Shift register, baud = f/12

0 1 1 8 bit UART, baud = variable

1 0 2 9 bit UART, baud = f/32 or f/64

1 1 3 9 bit UART, baud = variable


SM0 RISM1 SM2 TIRB8REN TB8


INTERRUPTS:

The AT89C52 has a total of six interrupt vectors: two external interrupts (INT0

and INT1), three timer interrupts (Timers 0, 1, and 2), and the serial port interrupt. Each

of these interrupt sources can be individually enabled or disabled by setting or clearing a

bit in Special Function Register IE. IE also contains a global disable bit, EA, which

disables all interrupts at once.

In the AT89S52, bit position IE.5 is also unimplemented. User software should

not write 1s to these bit positions, since they may be used in future AT89 products.

Timer 2 interrupt is generated by the logical OR of bits TF2 and EXF2 in register

T2CON. Neither of these flags is cleared by hardware when the service routine is

vectored to. In fact, the service routine may have to determine whether it was TF2 or

EXF2 that generated the interrupt, and that bit will have to be cleared in software.

The Timer 0 and Timer 1 flags, TF0 and TF1, are set at S5P2 of the cycle in which the

timers overflow. The values are then polled by the circuitry in the next cycle. However,

the Timer 2 flag, TF2, is set at S2P2 and is polled in the same cycle in which the timer

overflows.



Interrupt Enable (IE) Register:


EA IE.7 Disables all interrupts. If EA = 0, no interrupt is

acknowledged. If EA = 1, each interrupt source is individually enabled or disabled

by setting or clearing its enable bit.

— IE.6 Reserved.

ET2 IE.5 Timer 2 interrupt enable bit.

ES IE.4 Serial Port interrupt enable bit.


EX1 IE.2 External interrupt 1 enable bit.


EX0 IE.0 External interrupt 0 enable bit.

5.3.4 BUFFER IC 74LS245:



These octal bus transceivers are designed for asynchronous two-way

communication between data buses. The device allows data transmission from the A bus

to B bus or from the B bus to A bus depending upon the logic level at the direction

control (DIR) input. The enable input can be used to disable the devices so that the buses

are effectively isolated.

74LS245 Pinout:

Features:

Bi- directional bus transceiver in a high density 20 pin package.

Tri-state outputs drive bus lines directly.

PNP inputs reduce DC loading on bus lines.

Hysteresis at Bus inputs improves Noise margins.

Typical propagation delay times port to port 8ns.

Typical enable or disable times 17ms.

5.4 16X2 LCD:



LCD indicates different mode settings & set point adjustment. Also 16 char are

divided to indicate speed output. The LCD Display used here is 16 character by 2 line

display. The 16 characters in both lines are equally divided to indicate commands and

speed. In sub routines ‘Enter Speed’ and ‘Current Speed’ message, set Speed value is

indicated on screen.

In our project LCD is interfaced with the port-0 (D0-D7) i.e. from pin number 32

to pin number 39. In other words the data-bus D0-D7 is connected to port-0 of IC 89s52.

Pin RS is directly connected to Pin11 of controller and one more another important pin

EN (LCD enable) is directly connected to pin 14 of the controller. On the other hand pin

R/W of LCD is connected to ground. The LCD interfacing is done here for indicating

various display messages for the user.

The interfacing is given in detail which is as follows:-

In this equipment the LCD which is used is 16X2 type. i.e. 16 characters per rows

and two rows. The function of LCD is to display the status of events performed by the

respective circuit or to display those resulting parameters which have to be displayed on

the screen as per user requirement.

5.4.1 Basics of LCD:



LCD has 8 Bit data (D0-D7). Basically LCD requires three control signals which

are-

1. R/W: - Read/Write signal when low it is configuring as write function.

2. RS : - The display contains two internal byte-wide registers, one for commands

(RS=0) and the second for characters to be displayed (RS=1).

1. Command: -

Commands are such as Character size, rows and columns, cursor movement, blink

cursor etc.

Basically LCD can be configured in the two modes which are nothing but Slave

mode and Handshake mode. In the slave mode a command is transferred to LCD and wait

for some delay for the specific time which is normally 6msec. On the other hand i.e. in

the handshake mode the ‘D7’ bit is used. After the completion of the task the D7 bit is set

high by the display.

5.4.2 16X2 LCD INTERFACING:



Circuit Diagram:

5.5 4X4 KEYPAD:



The 4x4 Keypad has 16 keys and requires a single PORT or 8 I/O lines. Port 3

has been designed to handle keypad, LCD Data Bus D7-D0 is connected to PORT 1,

while (Enable) EN is connected to P2.0 (Register Select – Command or Data Register)

RS is connected to P2.1 (Read/Write) RW is connected to P2.2.

Working:

To check for the keystroke, a polling method has been used.

PORT 1.0 Key 1 Key 2 Key 3 Key 4




PORT 1.4 PORT 1.5 PORT 1.6 PORT 1.7

The connections are similar as shown over here. Now consider this, if I select the

first column only, it has 4 keys, 1, 5,9,13. If a change of value (i.e. Binary 1 or 0) is made

any one of these keys, it can be decoded and suitable message is displayed on the LCD.

This is exactly what happens. Initially all the I/O lines are pulled high, then during Key

Scan, every column linked is held low for a little time. If during that time a Key is



pressed in that column a row I/O lines is also held low, thus the keystroke can be

captured.

The answer is simple, the microcontroller runs quite fast, even a convention 89s52

in which the internal frequency= external frequency clock/12 can achieve 2 MIPS at

24MHz. That is 2 Million instructions Per Second. This method is not foolproof, it has a

drawback, while the Key Scan, It cannot perform other cumbersome operations which

may take time and a Key Stroke could be missed. The program will work very well for

small operations like activating a small relay or LED when a Key is pressed, but for

people who want their systems to be near to perfect they may utilize other method.

5.5.1 4X4 KEYPAD SCHEMATIC:



Circuit Diagram:

5.6 SENSOR:



Proximity Sensor:

Features:

Stainless steel face and barrel for high strength.

Available with abrasion resistant, fire retardant ToughLink cable.

Electrical protections against short circuits, overload, transient noise, false pulses

and reverse polarity (DC models) to help reduce downtime and maintenance costs

Extended range models available.



The proximity sensor used in our project is of inductive type which senses the

proximity up to 5mm distance. When the metal strip mounted on the fan belt comes

ahead of sensor a high to low pulse gets generated approximately of 3v magnitude and is

counted by the counter.

The sensor is engineered for enhanced toughness and flexibility, the latest flat

pack offers one of the longest sensing distances in the industry. This increased sensing

distance reduces target-to-sensor collisions by allowing the sensor to be mounted at a

safer distance from the target area. The durable one-piece housing provides superior

resistance to the elements.

Superior LED visibility and complementary outputs on standard models add even

more appeal to this feature-rich inductive proximity sensor.



5.7 DRIVER CIRCUIT:

5.7.1 SSR (Solid State Relay):

5.7.2 Supply Voltage Vs SSR Output:


Specifications:

UNISON SSRDC TO AC SOLID STATE RELAY (BACK TO BACK SCR) 801 RDA 48 25 00 (801 MODEL Single Phase AC load)INPUT: 4-32VDC, 4-16mAOUTPUT: 24-480VAC, 25Amp(BACK TO BACK SCR-silicon control rectifier)With Heat Sink & 35mm Din Rail Mounting.


5.7.3 Advantages of SSR:

No contact arcing, high surge capability

High resistance to shock and vibration

High resistance to aggressive chemicals and dust

No electromechanical noise

Logic compatibility

Fast switching

Low coupling capacitance

Long Life and high reliability more than 1010 cycle operations

Increases system temperature accuracy

Unique Input & Output LED indication gives heater failure status & increases

surge current / voltage capacity.

5.7.4 Limitations of SSR:

Contact voltage drop

Do not have potential free contacts

Do not have multiple contacts in one module

Having Leakage currents

Heat sink is must for heat dissipation for current more than 3Amp

Possibility of false switching due to voltage transients.



5.8 PCB DESIGN:

5.8.1 PCB Layout:



CHAPTER-6

SOFTWARE DETAILS:

6.1 PRILIMANARY FLOW CHART:



CHAPTER-7

ADVANTAGES:

Smooth & step less speed control over wide range.

User friendly.

Efficiency is high due to Small power loss in power electronic devices i.e. driver

circuitry.

Fully automatic speed control.

Continuous speed indication.

Compact size.

Accuracy is high.

Simultaneous speed control of number of motors can be achieved.

E.g.:- Paper Industries, Textile Industries.

CHAPTER-8



DISADVANTAGES:

Rotor heating is more due to high rotor losses.

Sensitive to voltage fluctuations.

For lower speed efficiency lowers.

Harmonics are generated due to change in supply voltage by power electronic

devices.

Low torque.

CHAPTER-9



COSTING OF MATERIAL:

CHAPTER-10

APPLICATIONS:


Sr. No. Components Quantity Cost

1. Microcontroller (AT89S52) 1 85.00

2. LCD Display (16X2) 1 450.00

3. Keypad (4x4) 1 180.00

4. PCB(including general purpose) 4 1000.00

5. Induction motor 1 900.00

6. Proximity Sensor 1 750.00

7. Solid State Relay 1 850.00

8. Regulator (IC 7805) 2 50.00

9. Buffer ( IC 74LS245) 1 15.00

10. Crystal (11.0859MHz) 1 25.00

11. Transistors 2 30.00

12. Capacitors 1.1000µf …………4 2.10 µf …………1 3.33pf …………2

7 130.00

13. Registers 14 20.00

14. Resister Array 1 05.00

15. LED 1 05.00

16. Diodes(IN 4007) 8 40.00

17. IC LM339 1 40.00

18. Transformer(230V/9-0-9V) 2 85.00

19. Zener diode(IN 914) 1 20.00

20. Variable Resistance 1 10.00

Total cost = 4690.00


Industrial fan speed control.

For industrial pump drives

Transformer coil winding machine.

To wound bobbin of fabrics in textile industry.

For intermittent duty loads.

CHAPTER-11

FUTURE SCOPE:



In this automatic speed control of single phase induction motor, speed control is

done successfully by comparing actual speed with entered speed. The protective features

can be added later as follows-

Microcontroller can directly provide over current protection to the drive

motor. Simply by adding the preset value of current in the programming the

motor can be protected from the abnormal conditions.

For the speed control, stator voltage control method is used. In this method

when voltage decreases below certain level rotor losses increases resulting to

rotor heating. Therefore advanced temperature sensors can be used to detect

rotor heating which can further be operated the better cooling system for the

motor.

Simultaneous speed control of number of motors can be achieved by

providing number of channels from the microcontroller.

CHAPTER-12

CONCLUSION:



Finally we come to the result that, the speed of Induction Motor is controlled over

wide range with the help of stator voltage control technique. This project is applicable

where the speed required at any specific value. The theory of stator voltage control

method for speed control of induction motor gives the maximum efficiency will be

achieved in specific region of speed i.e. 30% to 80% of synchronous speed for the

voltage 30% to 100.

CHAPTER-13

REFERENCES:



1) Kenneth J. Ayala., “8051 Microcontroller”,

2) Mohammed Ali Mazadi., “8051 Microcontroller”,

3) Vaibhav Tarate., “Electronic System Design”

4) Ramakant Gaikwad., “Linear Integrated Circuits”

5) National Semiconductor Manual.


Automatic Speed Control of 1-Ph Induction Motor

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