Mini Project

MINIMINIMINIMINI PROJECTPROJECTPROJECTPROJECT

CLOSED LOOP SPEED CONTROL OF

BLDC MOTOR

SUBMITTED BY

NITHIL BABU N (B120004EE) SUBIN T (B120008EE)

SARATH SANKAR (B120095EE)

DEPARTMENT OF ELECTRICAL ENGINEERING

NATIONAL INSTITUTE OF TECHNOLOGY CALICUT

23 FEBRUARY 2015

CONTENTSCONTENTSCONTENTSCONTENTS

1.1.1.1. INTRODUCTIONINTRODUCTIONINTRODUCTIONINTRODUCTION

2.2.2.2. BLOCK DIAGRAMBLOCK DIAGRAMBLOCK DIAGRAMBLOCK DIAGRAM

3.3.3.3. POWER SUPPLYPOWER SUPPLYPOWER SUPPLYPOWER SUPPLY

4.4.4.4. CONTROL SECTIONCONTROL SECTIONCONTROL SECTIONCONTROL SECTION

5.5.5.5. BLDC MOTORBLDC MOTORBLDC MOTORBLDC MOTOR

6.6.6.6. ISOLATIONISOLATIONISOLATIONISOLATION

7.7.7.7. MOSFET AS SWITCHING DEVICEMOSFET AS SWITCHING DEVICEMOSFET AS SWITCHING DEVICEMOSFET AS SWITCHING DEVICE

8.8.8.8. FEEDBACK LOOPFEEDBACK LOOPFEEDBACK LOOPFEEDBACK LOOP

9.9.9.9. WORKING OF THE PROJECTWORKING OF THE PROJECTWORKING OF THE PROJECTWORKING OF THE PROJECT

1. INTRODUCTION :

The project is designed to Control the speed of a Brushless DC (BLDC)

Motor using Closed loop control technique. BLDC motor has various

application used in industries like in drilling, lathes, spinning, elevators, electric

bikes etc. The speed control of the DC motors is very essential. This proposed

system provides a very precise and effective speed control system. The user

can enter the desired speed using a keypad and the motor will run at that

exact speed.

Based on the principle of Pulse Width Modulation (PWM), speed can be

controlled. This is achieved by keeping BLDC motor on closed loop feedback by

giving RPM reference to the microcontroller using a IR reflection arrangement.

An LCD is duly interfaced to the microcontroller to display the running speed.

The desired speed in percentage of full speed is fed with the help of keypad.

The controller delivers desired pulse width to automatically adjust the DC

power to the motor for required speed. The above operation is carried out by

using one opto-isolator and a MOSFET for driving the BLDC motor with IR

sensing for getting the speed reference to the microcontroller.

The main parts of this project, between input and output, can be divided

into three :

1. Supply Section 2. Control Section 3. Isolation Section

2. BLOCK DIAGRAM 3. POWER SUPPLY:

K DIAGRAM:

POWER SUPPLY:

The 230V AC supply is first stepped down to 12V AC using

Transformer. This is then converted to DC using

four diodes. The AC ripples is filtered out by using a capacitor and

voltage near to 12V can be obtained. From this, two connections are made :

(i) The constant dc ouPower MOSFET, which drives BLDC motor.

(ii) The constant dc ouregulator 7805, for getting a constant 5V DC at its output for

Microcontroller and other components.

4. CONTROL SECTION

The speed of the BLDC motor is mainly controlled using a

(uC). It is a smaller computer

microcontroller which we are using in this project is

8051 family. It has the same architecture and instruction set as that of the

original Intel 8051, except

older version. The architecture of Microcontroller is shown below :

The 230V AC supply is first stepped down to 12V AC using

This is then converted to DC using Bridge rectifier

The AC ripples is filtered out by using a capacitor and

12V can be obtained. From this, two connections are made :

The constant dc output near to 12V from bridge rectifier

which drives BLDC motor.

The constant dc output near to 12V is given to the inpu

, for getting a constant 5V DC at its output for

Microcontroller and other components.

CONTROL SECTION :

The speed of the BLDC motor is mainly controlled using a

It is a smaller computer. It has on-chip RAM, ROM, I/O ports, ADC etc.

microcontroller which we are using in this project is ATMEL AT89S52

he same architecture and instruction set as that of the

except that it has a Flash memory opposed to EEPROM in

The architecture of Microcontroller is shown below :

The 230V AC supply is first stepped down to 12V AC using a Step down

ridge rectifier formed using

The AC ripples is filtered out by using a capacitor and a constant

12V can be obtained. From this, two connections are made :

rectifier is given to

given to the input pin of Voltage

, for getting a constant 5V DC at its output for

The speed of the BLDC motor is mainly controlled using a Microcontroller

p RAM, ROM, I/O ports, ADC etc. The

ATMEL AT89S52 from

he same architecture and instruction set as that of the

opposed to EEPROM in

The architecture of Microcontroller is shown below :

PIN DIAGRAM OF AT89S52

5. BRUSHLESS DC MOTOR (BLDC) :

Standard DC motor : Magnetic field is stationary in stator, rotor poles switch polarity due to commutation to provide constant rotation.

Brushless DC motor : Magnetic field of rotor is fixed. Magnetic field in stator poles is electronically commutated, provides rotating magnetic field.

Motor contains internal position encoder to provide position feedback to

the control system.

Applications of BLDC Motors:

- CPU cooling fans

- CD/DVD Players

- Electric automobiles

Advantages over brushed DC Motors:

-Higher efficiency

- Longer lifespan, low maintenance

- Clean, fast, no sparking/issues with brushed contacts.

Disadvantages over brushed DC Motors:

- Higher cost

- More complex circuitry and requires a controller.

BLDC used in this project for speed control is a CPU Cooling Fan rated at 12V.

6. ISOLATION:

Opto-coupler or Opto-isolator is used to isolate low Power side

(Microcontrollers and other ICs ) from high Power Side ( MOSFET and BLDC

Motor). Opto coupler is a 6 pin IC. It is a combination of 1 LED and a

transistor.

When logic zero is given as input then the light doesnt fall on transistor so it doesnt conduct which gives logic one as output.

When logic 1 is given as input then light falls on transistor so that it conducts, that makes transistor switched ON and it forms short circuit. This

makes the output a logic zero as collector of transistor is connected to

ground.

7. MOSFET AS SWITCHING DEVICE:

The MOSFET (Metal Oxide Semiconductor Field Effect Transistor) is a

Voltage controlled device. This means that a voltage at the gate control the

current flows from the drain to the source. There are three terminals: Gate(G)

, Source(S) and Drain(D). The Voltage across Gate and Source controls the state

of the device.

Power MOSFETs are used in the circuit for switching purpose. Using

PWM in microcontroller, MOSFET is switched on and off via Opto-isolator,

which controls the output to the BLDC motor.

8. FEEDBACK :

A feedback is taken from the BLDC motor as speed (RPM) using IR LED

and Photodiode. IR LED transmits IR signals and Photodiode receive these

signals and convert them into voltage or current corresponding to the Current

Speed. This speed is then compared with the Reference speed (User Input

Speed), and necessary control is provided through Microcontroller.

9. WORKING OF THE PROJECT:

BLDC Motor, which is a cooling fan, is initially kept rotating at a Specific

speed (Full Speed). The speed of the motor is sensed by an IR pair (IR LED and

Photodiode) and is displayed on LCD and is also fed to the Microcontroller. The

motor is interfaced to the MC through an Opto-coupler & a MOSFET, which

drives the motor.

The required speed is entered using a keypad which is interfaced with

microcontroller. According to the entered required speed, PWM pulses are

generated from microcontroller and fed to MOSFET and then Motor. Thus,

motor is adjusted to that speed and maintained at that speed.