Speed Control system for BLDC motor without position sensor ...

38 Page 38-47 © MANTECH PUBLICATIONS 2020. All Rights Reserved

International Journal of Research in Electrical, Electronics and Communication

Engineering

Volume 5 Issue 1

Speed Control System for BLDC motor without Position Sensor

using MSP430 Controller and back EMF Method

Mahesh Dattatraya Bhambure

Assistant Professor

Department of Electronics and Telecommunication

Adarsh Institute of Technology and Research Center, vita

Dr. Babasaheb Ambedkar Technical University, Lonere, Maharastra, India

Corresponding Author’s email id: [email protected]

DOI:- http://doi.org/10.5281/zenodo.3766074

Abstract

Use of BLDC Motors are huge in human life for industrial applications, in

medical field, in home appliances etc., Speed control of BLDC motors require

for this applications. BLDC motor speed control using position sensor to

identify rotor position makes configuration more complex and costly. In this

paper we are using Back E.M.F. zero crossing detection method and

electronic commutation circuitry to identify rotor position and speed control

of BLDC Motors, this helps to reduce cost and make controlling BLDC motor

flexible with more simplicity.

Keywords: - Brushless DC motor, Back EMF, sensor less control, electronic

commutation, Zero crossing detection

INTRODUCTION

The most important feature of Brushless

DC motor is the mechanical commutation

configuration constituted by commutator

and brushes are replaced by electronic

commutation circuitry. It solves drawbacks

caused by mechanical commutation.

BLDC motors have less maintenance due

to absence of brushes, enables operation at

all speeds with rated load. Provide high

efficiency, reduced size, and reduced

maintenance and gives higher speed range;

hence BLDC motors are use for large

number of applications such as in medical

field, fans, drones, transportation field,

Electric vehicles, Electric ship,



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Volume 5 Issue 1

Automobile, Automation. In specialized

fields such as when in high temperature

position sensors does not work, this

system plays important role. Brushless DC

motors such as fans are smaller in size and

weight than AC fans using shaded pole or

universal motors. BLDC motors can work

with the low voltage sources such as 24V

or 12V DC supply, due to which BLDC

motors can use for small fans, in electronic

equipment, spindle drives, mobile

equipments, it have high efficiency and

ability to reverse rapidly. Brushless DC

motors in the fractional horsepower range

have been used in various types of

actuators in advanced aircraft and satellite

systems. BLDC motors mainly consist

three phases which are controlled and

driven by full bridge transistor circuits.

Forces produced due to interaction of

magnetic fields and shafts starts to rotate.

One magnetic field is of permanent

magnet and one magnetic field is due to

excitation. This system uses a MSP430

microcontroller and a rectified power

supply, optocoupler is connected to trigger

the MOSFET for driving BLDC. A BLDC

motor of 12V DC is used to which control

signals receives from controller through

MOSFET circuit. A Back EMF circuit

provides feedback and by using zero

crossing detector rotor position can be

detected. A speed command circuit can

help to get variable frequency, variable

speed system based on microcontroller

MSP430, which provide a compact,

flexible speed control for brushless DC

motor using Back EMF and zero crossing

detector without using position sensor at

low cost. It consist A. Power circuit B.

Control circuit C. Command circuit D.

Display circuit.

A. Power circuit

Power circuit of this system consist two

12V fixed DC power supply which consist

a transformer which convert 230V AC

supply in to 12V AC, Bridge rectifier of

four diodes to convert that 12V AC into

12V DC supply and RC filters to filter it.

This 12V DC power supply is given to

MOSFET module, display circuit,

command circuit and control circuit.

MOSFET module consist six MOSFET of

IRF Z44N having fast switching and low

on-resistance per silicon area. It provides

the highest power capability and the

lowest possible on-resistance in any

existing surface mount package.

B. Control Circuit

The control circuit of this system is

composed by MSP430G2253

microcontroller, Back EMF zero crossing

detection circuit, MSP430G2253 consist of

several devices featuring different sets of

40 8-47 © MANTECH PUBLICATIONS 2020. All Rights Reserved


Engineering

Volume 5 Issue 1

peripherals targeted for various

applications. It contains 16 RISC CPU, 16

bit registers and constant generator,

digitally controlled oscillator(DCO),

which change microcontroller from low

power modes to active mode, 16 bit timers.

These microcontrollers have 24 I/O

capacitive touch enabled pins, a versatile

analog comparator and built in

communication capacity using the

universal serial communication interface,

10 bit analog to digital convertor. This

microcontroller works on 1.8V to 3.6V,

having ultra low power consumption.

Controller operates with its software

“Energia” which is based on c language.

Controlled Signals to 12V BLDC motor

getting from microcontroller. Controlled

Signals are in pulse width modulated form.

MOSFET module works as three phase

inverter it’s three phase output terminal

voltages corresponds to ground act as

terminal voltage, this terminal voltage is

feed to controller trough Back- EMF zero

crossing detector circuit. Pulse width

modulation is employed to achieve varying

voltage conveniently, reduce torque ripples

also helps in enlarging speed controlling

range. PWM mode we can set

independently only if the value in the

period registerer is constant, via changing

the value in the compare registerers can

modulate the width of the PWM output

signals. By varying delay time we can

change speed of motor for this time delay

and speed calculation obtained from

microcontroller.

Fig. 1 Control circuit of BLDCM



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BI. Three Phase Inverter

The BLDC motor control consists of

generating DC currents in the motor

phases. This control is subdivided into two

independent operations: first, stator flux

synchronization, then control through the

three phase inverter in the following

scheme. The flux synchronization is

derived from sensorless techniques, that is

by back E.M.F. and zero crossing

detection the position of stator and rotor

identifies, from position of stator and rotor

the controller defines the appropriate pair

of transistors which must be driven.

BII. Design Control Strategy without

Position Sensor

MSP430 controller generates six

independent PWM signals through opto-

isolated signals acting on control terminals

of three phase inverter circuit. In three

phase inverter circuit phase shift of 120

degree are used to drive the BLDCM via

changing each phase output average

voltage amplitude, variable frequency and

variable speed of motor is attained.

The inverters three phase output terminal

voltages related to negative pole are sent to

three capture ports of MSP430 controller

through Back-EMF zero crossing detection

circuit. According to that six MOSFETS in

inverter circuit conduct PWM used for

inverter control. A terminal voltage varies

with control torque ripples. The inverters

three phase output terminal sent to

controller through Back EMF zero

crossing circuit.

There are only two phase conducting at

time, each phase winding continues

conduction for the full 120 degree angle

whether in negative or positive direction,

the Back-EMF in each phase stator

winding has two zero crossing points, each

leads its phase commutation instant 30

degree angle, so via detecting the Back-

EMF zero crossing point rotor and stator

position can identify and according to that,

three phase inverter generates motor

terminal voltage and according to that

motor operates.

This terminal voltages detect by zero

crossing detection point that can obtained

indirectly through dealing with the signals

and the conducting instants of the power

devices in the inverter are attained at the

same time.



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Figure:-2 Waveforms with Back-EMF control method in ideal condition

The Back-EMF wave shape of BLDCM in

trapezoidal shape is shown in Fig.2 where

Ea, Eb, Ec represents the motor three-

phase winding Back-EMF respectively and

ia, ib, ic donates the three-phase winding

phase current respectively. In order to get

the biggest torque output, there should be

positive current conducted, so the motor

torque output is larger while the torque

ripple is small.

C. Command Circuit

Command circuit provides signals to

controller. It consist touch pad with push

buttons, by pressing push buttons we can

increment or decrement values of

parameters that is we can increase or

decrease angle or speed level. Command

circuit gets power from fixed 12 volt D.C.

power supply. Command circuit is

electronic circuit which we can keep

separate from system or can use with the

system.

D. Display Circuit

Display circuit interfaced with controller,

Speed level of motor can see in display

attached to system through controller. It

consist seven segment LCD display to

which gets power from fixed 12 volt D.C.

power supply and display signals through

controller.



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SOFTWARE DESIGN

The whole control system software is

composed by the main program and the

interrupt service subsystem, while the

main program is composed by system

initialize program, motor start program.

The A/D conversion to the speed

command is finished in the main program.

Capture interrupt subprogram and timer

compare interrupt service subprogram are

the main composed parts of the interrupt

service subprogram. The main function of

capture interrupt is to get three-phase

Back-EMF zero-crossing instants and read

the time interval between twice capture, so

to calculate timer internal corresponding to

the 30° angle. While the compare interrupt

of the timer is used to set commutation

instant and send value to the three compare

registers, the value is got from the

calculated pulse width corresponding to

speed command.

TIME DELAY AND ROTATE SPEED

CALCULATION

In the control system, time delay and

rotating speed calculation are both

obtained indirectly from the capture ports

of MSP430 microcontroller. The capture

port can be used to measure the time T

consumed by rotor for rotating 180° angle.

If divided by 6, the relating average time

to 30° angle can be obtained. The average

time is used as the time delay between the

lower half period zero-crossing point and

the related commutation point, then the

real speed of the motor can be calculated

from n = 30 / T.

MOTOR START SCHEME

Motor start scheme is important in this

speed control system of brushless DC

motor without Back-EMF and position

sensor because the Back-EMF is zero or

very little when the BLDCM operates at

static or lower speed state, it is useless to

estimate the rotor position at these times.

Therefore, Back-EMF scheme requires

special start technology. The usual way

employed is to accelerate the motor from

static state to sufficient speed using

separate-controlled motor, and then

converts to DC brushless operation mode.

In this mode contains three states, rotor

position dictated, accelerating and

switching stages. Rotor position dictated is

to give current to two of the three phases

while closing the other phase. Till the rotor

magnetic pole rotates to the direction of

stator integrated magnetic motive force,

then the rotor initial position can be

dictated. In accelerating stage, according

to motor rotating direction commutation

sequence, the corresponding winding is

conducted by control program to start the

motor. Switching process is that the open-



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loop commutation process lasts after one

commutation period, the motor speed and

the amplitude of Back-EMF have achieved

some extent, and when the Back-EMF can

be measured via detecting circuit, program

can jump out of open-loop commutation

program and enters into the self-control

operation state controlled by Back-EMF

detecting signal.

RESULT

In proper condition, for proper inputs

motor runs properly and get good motor

speed control. Gives efficiency of 95% for

a 20 Watt input overall cost of the

hardware is less than other BLDC motor

control.

Fig. 3 and Fig. 4 shows terminal voltage

waveform for continuous rotation

programme of motor. As we increase

speed of motor by pressing push buttons

on speed command circuit. Terminal

voltage and terminal current increases due

to which speed of motor increases in motor

speed control for rotation in particular

degree also, as terminal voltage and

terminal current increases motor rotation

speed increases but rotation done for

particular angle.

Fig.3Terminal voltage waveform



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Fig.4Terminal voltage waveform

SCOPE OF THE STUDY

Due to sensor less configuration system

can use in high temperature area. By

adding extra digital hardware we can

monitor motor current, voltage. By using

SCADA, we can control many motors at a

time. In future this system will help in

transportation field, for electric bikes and

cars. In automation and robotics this

system can help for fast and accurate

motors speed control.

OBJECTIVES OF STUDY

The main objective of this study is to

provide fast and accurate speed control

to permanent magnet D.C. motors.

To increase performance of BLDC

motors so that they can use for large

applications.

To reduce cost and make controlling of

BLDC motors flexible with more

simplicity.

CONCLUSIONS

This is variable speed, variable frequency

control system of non-position sensor

brushless DC Motor. This system is based

on intelligent power module and

microcontroller. Non-position sensor

configuration makes whole system

configuration compact and gives flexible

control capable of regulating speed

without observer. System failure chances



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Volume 5 Issue 1

are less due to Non –position sensor

configuration.

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Engineering

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Cite this Article as

Mahesh Dattatraya Bhambure (2020)

“Speed Control System for BLDC

motor without Position Sensor using

MSP430 Controller and back EMF

Method” International Journal of

Research in Electrical, Electronics and

Communication Engineering, 5 (1), 38- 47

http://doi.org/10.5281/zenodo.3766074

Speed Control system for BLDC motor without position sensor ...

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