FACULTY OF ENGINEERING(INDUSTRIAL ELECTRONIC AND CONTROL)

DC Motor Speed Controllerby PWM technique

KGK 1500011Khairi A. M. Elrmali

outline• Introduction to pwm technique• Generate PWM signal in MATLAB Simulink

1. Varying Frequency modulation ratio2. varying amplitude modulation ratio

• PWM Spectral Modelling and Characteristics Bipolar Double-Edge Modulation &single-Edge Modulation unipolar Double-Edge Modulation & single-Edge Modulation

• DC motor speed control circuit– switch charactristic

• simulate model by proteus8• Pulse Width Modulator Motor Speed Control kit• CONCLUSION

Introduction to pwm technique• PWM (Pulse Width Modulation) is an efficient way to

vary the speed and power of electric DC motors.

Period (T)

Duty Cycle (D)VL

VH

On Off

%100Period

TimeOnCycleDuty

LHavg VDVDV 1

Duty Cycle is determined by:

Average signal can be found as:

Usually, VL is taken as zero volts for simplicity.

Generate PWM signal in MATLAB Simulink

A.Varying Frequency modulation ratio

sinffm tri

f

The binary PWM output can be mathematically written as

tctrtb pwm sgn

Bipolar& Unipolar pwm genetartor B. varying amplitude modulation ratio

tria V

Vm sin

PWM Spectral Modelling and Characteristics

the harmonic at frequency f = mfc + nf1 is zero if m + n is evenCarrier frequency and its harmonics, at frequencies f = mfc, m = 1, 2,...,+∞.Sideband harmonics of the carrier and its harmonics, at frequencies f = mfc +nf1, n = ±1,±2,...,±∞

single single singledouble double double

single , double edge

PWM Spectral Models

Bipolar Double-Edge Modulation Bipolar trailing-edge modulation

more attractive for AC–DC and DC–AC converter application

PWM Spectral Models unipolar single-Edge Modulation unipolar Double-Edge Modulation

DC motor speed control circuit

• “To explain working of the PWM circuit.”• BASIC BLOCK DIAGRAM

As shown in block diagram there are mainly three blocks: Astable Multivibrator, Driving Circuit and dc motor

The Basic Blocks are explained below:

(5) 1

(4) 244.1

(3) 2

(2) 69.0(1) 69.0

21

21

21

2

21

FT

CRRF

RRRR

TTTD

CRTCRRT

OFFON

ON

OFF

ON

• Multivibrator: This block produces square pulses of variable

frequencies. The frequency of output pulse can be varied by changing the value of resistor shown in figure. These pulses are fed to the driving circuit.

• GENERAL formulae for using 555 as

astable multivibrator:

switch charactristic driving Circuit: 1) A theoretically the switching frequency

must be much higher than 1/Ta where Ta = L/R is the electric time constant of the motor.

2) Usually a frequency around 20 kHz is used. This also avoids noise from the motor in the audio range.

3) The maximum output of the 555 IC is 200mA ,this can increased by BD139 transistor up to 1A ,For high current appication other transistor like BD 139,BD679,TIP31,2N3055 ,MOSFET IRF520,IRF540 .

4) the transistor may be become hot during the operation therefor it is essential to use a suitable heatsink

5) A diode, Di, has been added to reroute inductive motor spikes. A 1N914 or 1N4001, 1N4007 is okay for smaller motors, but prefer a 1N5817.

mAII cb 5

5001

min

The desired collector current is 1A

desire a base current of 10mAcalculate R_b as follows:

4401010

6.053

b

bebb I

VVR

simulate model by proteus8

R4

DC 7

Q 3

GN

D1

VC

C8

TR2 TH 6

CV5

U1

555

U1(VCC)

C15nF

R11k

C25nF

D1

1N4148

D2

1N4148

7%

RV1

10k

R2

440

D31N4001

Q1TIP31

• Description:

• 100% brand new and high quality• Control the speed of a DC motor with this

controller.• High efficiency, high torque, low heat

generating.• With reverse polarity protection, high

current protection.

• Specification:• Model: CCM6C• Input voltage: 6V/12V /24V DC• Control Power: 24V, within 200W; 12V ,

within 200W; 6V , within 60W• Current: Sustained current maximum

20A, suggest use within 10A• PWM Duty Cycle:5% -100%• PWM Frequency:21khz

Pulse Width Modulator Motor Speed Control kit

CONCLUSION

• From the project work, following points can be concluded.

• The motor responds to the average value of the pulses and not to the individual pulses as the chopper works at high frequency.

• Changing the duty-cycle of the pulse by changing the speed of regulator changes the average voltage level.