SENSORLESS BLDC MOTOR CONTROL IN MATLAB SIMULINK

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Available Online At www.ijpret.com

INTERNATIONAL JOURNAL OF PURE AND

APPLIED RESEARCH IN ENGINEERING AND

TECHNOLOGY

A PATH FOR HORIZING YOUR INNOVATIVE WORK

SENSORLESS BLDC MOTOR CONTROL IN MATLAB SIMULINK

ANKITA A KANEKAR, V. K. JOSEPH

Electronics and Telecommunication Engg. Goa College of Engineering Farmagudi, Goa.

Accepted Date:

27/02/2013

Publish Date:

01/04/2013

Keywords

Brushless DC Motor,

Back EMF ZCD,

Sensorlesscontrol,

Trapezoidal emf.

Corresponding Author Ms. Ankita A Kanekar

Abstract

Brushless DC Motor drives have made a successful entrance into various sectors of industry such as aerospace, automotive and home appliances due to its simple structure. The accurate knowledge of the rotor position is required for good performance of brushless DC motors the need for the rotor angle information in BLDC has been satisfied by use of some form of rotor position sensor. The position sensor used in BLDC drives have the

disadvantages of additional cost, electrical connections,

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INTRODUCTION

During the last two decades, a lot of

research on sensor less control technique

for BLDC motor has been conducted. Using

of Permanent Magnet in electrical machines

have so many benefits and advantages then

electromagnetic excitation machines these

are zero excitation losses result in high

efficiency, simple construction, low cost less

maintenance and high torque or high

output power per unit volume. Due to high

power to weight ratio, high torque, good

dynamic control for variable speed

applications, absence of brushes and

commutator make Brushless dc (BLDC)

motor, bestchoice for high performance

applications. Due to the absence of brushes

and commutator there is no problem of

mechanical wear of the moving parts.

As well, better heat dissipation property

and ability to operate at high speeds make

them superior to the conventional dc

machine. However, the BLDC motor

constitutes a more difficult problem than its

brushed counterpart in terms of modelling

and control system design due to its

multi-input nature and coupled nonlinear

dynamics. Due to the simplicity in their

control, Permanent-magnet brushless dc

motors are more accepted used in

high-performance applications. In many of these

applications, the production of ripple-free

torque is of primary concern. Therefore, if

the waveforms of the phase back EMF and

phase current are perfectly matched,

torque ripple is minimized. In this paper

finally closed loop speed control is done by

using PID controller under various loading

conditions.

PRINCIPLE OF OPERATION

In conventional BLDC motor during bipolar

operation, at any time across DC bus, two

phases come in series. Only half of the DC

bus voltage is applied to each phase,

resulting in addition of torque constant on

both phases there by achieving high starting

torque. But speed will be limited. To get

higher speed, full DC bus voltage is to be

applied to each phase. This can be achieved

in unipolar operation, where each phase

conducts only in one direction which in turn

reduces the starting torque. order to get

high torque, motor should operate in

bipolar mode and to get high speed motor

should operate in unipolar mode. Shifting of

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Available Online At www.ijpret.com operation is achieved based on speed

requirement. In bipolar operation first 3

legs are active and the 4th leg is inactive.

By switching on Q1 and Q4, phase A

conducts in positive direction and phase B

conducts in negative direction. By switching

off Q4 and switching on Q6, a free-wheeling

path is established through phase B, diode

D3, switch Q1 and Phase A as shown in

Figure-1.

By switching off Q1 and switching on Q3

and Q6, the free-wheeling energy in

positive conducting phase A flows through

resistor Rs, D2, phase A, phase C, and Q6, as

shown in Figure2.

SENSORLESS CONTROL OF BLDC MOTOR

Brushless dc (BLDC) motors, with their

trapezoidal electromotive force (EMF)

profile, requires six discrete rotor position

information for the inverter operation.

These are typically generated by Hall- effect

switch sensors placed within the motor.

However, it is a well-known fact that these

sensors have a number of drawbacks. They

increase the cost of the motor and need

special mechanical arrangements to be

mounted. Further, Hall sensors are

temperature sensitive, and hence limit the

operation of the motor. They could reduce

system reliability because of the extra

components and wiring. sosensorless

method is the reliable method used in harsh

environments.There are three independent

methods for determining the Hall

configuration.The selection of which

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information provided. 1. Hall Based

Commutation Sequence Provided. 2. Back

EMF Waveforms.

1: Hall Based Commutation Sequence

Provided

Either method conveys adequate

information about driving the motor phases

based on Hall Effect sensor states. The

relationship between the Hall Effect sensors

themselves is always consistent. In other

words the Hall Effect sensor sequence seen

in can be found in all motors with

120-degree Hall Effect sensors when the motor

rotates. However, the direction of rotation,

CW or CCW, necessary to produce this

relationship can vary across different

motors. Very often the binary state of the

three Hall Effect sensors will be combined to

create a 3-bit binary word. The mapping

between the Hall states and the three-bit

word. Below the binary word representation

in is tables that represent the states of the

MOSFETs of the half-bridges.

A+ = Phase A high side MOSFET closed

A- = Phase A low side MOSFET closed

B- = Phase B high side MOSFET closed

C- = Phase B low side MOSFET closed

C+ = Phase C high side MOSFET closed

D- = Phase C low side MOSFET closed

If the state of a MOSFET for a particular

Hall state is not defined then it is assumed

to be 0pen. For example during Hall state

1-0-1, MOSFETs A-, B+, C+ and C- are all open.

Below the table of MOSFET states in is a

diagram of the relative voltages through

each motor phase based on the Hall states

(and subsequent MOSFET states). For

instance in Hall state 1- 0-1, the path of the

current begins at the voltage source, flows

through the high side MOSFET of phase A,

through motor winding A, through motor

winding B, through the low side MOSFET of

phase B, and finally to the ground plane.

2 :Back EMF

When a BLDC motor rotates, each winding

generates a voltage known as back

electromotive Force or back EMF, which

opposes the main voltage supplied to the

windings according to Lenz‟s Law. The

commutation time is determined by the

rotor position. Since the shape of back EMF

indicates the rotor position, it is possible to

determine the commutation timing if the

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Available Online At www.ijpret.com phase with the phase back EMF. If the zero

crossing of the phase back EMF can be

measured, we will know when to

commutate the current. As mentioned

before, at one time instant, since only two

phases are conducting current, the third

winding is open. This opens a window to

detect the back EMF in the floating winding.

The proposed back emf detection

method describes that, instead of detecting

the zero-crossing point (ZCP) of the

non-excited motor back electromagnetic force

(EMF)or the average motor terminal to

neutral voltage, the true zero-crossing

points of back EMF are extracted directly

from the supply with simple RC circuits and

comparators. In contrast to conventional

methods, the neutral voltage is not needed

and the diode freewheeling currents in the

non-conducted phase are eliminated

completely; therefore, the commutation

signals are more accurate and insensitive to

the common-mode noise. As a result, the

proposed method makes it possible to

achieve good motor performance over a

wide speed range and to simplify the

starting procedure.

A power supply is given to the inverter.

The three phase output of the inverter is

applied to the motors stator windings. From

the supply, voltage divider is connected,

with the RC low pass filter and a zero

crossing detector circuit to produce the back

EMF for three phases. Low pass filter is a

filter that passes low frequency signals but

attenuates higher frequency signals. The

actual amount of attenuation for each

frequency varies from filter to filter. The

Back EMF signals are send to the zero

crossing detector the positional pulse are

produced. A voltage divider (also known as a

potential divider) is a simple linear circuit

that produces an output voltage (Out) that

is a fraction of its input voltage (Vin).

SIMULATION RESULTS

Here simulation is carried out for four cases.

A. Case-1: BLDC with open loop control

When the motor is in standstill conditions

the back EMF will be zero, so rotor Position

cannot be determined by sensorless

method. So initially the motor is started by

applying external gate pulses to the Mosfets

in inverter circuit in proper commutation

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Available Online At www.ijpret.com unidirectional torque. The speed of a BLDC

motor is proportional to the voltage applied

to the motor. When using digital control, a

pulse-width modulated (PWM) signal is used

to generate an average voltage.

Figure3 : open loop control for loaded

condition

Figure4 : Table of conclusion

Figure5:open loop speed and torque at

25hz frequency

B. Case-2: BLDC with closed loop PID

control on no

Load Sensorless Method

Figure6 : circuit for close loop control

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Available Online At www.ijpret.com Figure7 Output waveforms of the speed of

the motor.

Figure-8.Back EMF of the BLDC motor.

Figure-9 Output waveform of the torque of

the motor.

Figure 10.Output waveforms of the

currents.

C. Case-3: BLDC with closed loop PID

control for

Increasing load

Here reference speed is taken as 1500 rpm

the motor reaches the reference speed very

quickly with PID control. Here load torque is

increasing from 0 to 5 N-m at time t = 0.15

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Available Online At www.ijpret.com Figure-11 Output waveforms of the speed

of the motor

Figure-12.Back EMF of the BLDC motor.

the motor.

Figure-14 Output waveforms of the

currents.

D. Case-4: BLDC with closed loop PID

control for decreasing load

Figure-15Output waveforms of the speed of

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Available Online At www.ijpret.com Figure-16 Output waveform of the torque of

themotor.

the motor.

CONCLUSIONS

A simple technique to detect back EMF

using RC filter and comparator is defined.

This method provides an amplified version

of the back EMF. Detection of Rotor Position

is determined using Back EMF ZCD.

Simulation results are shown which validate

the suitability of the proposed method.

Simulation of the proposed method is done

by using MATLAB/SIMULINK. The

performance evaluation results show that

this modeling is very useful in studying the

high performance drive before taking up the

dedicated controller design concept for

evaluation of dynamic performance of the

motor. Simulation results are shown for

various loading conditions.

REFERENCES

1. Anand Sathyan, Nikola Milivojevic,

Young-Joo Lee, Mahesh Krishnamurthy, Ali

Emadi,"An FPGA-Based Novel Digital PWM

Control Scheme for BLDC Motor

Drives",IEEE TRANSACTIONS ON

INDUSTRIAL ELECTRONICS,VOL.56, NO. 8,

AUGUST 2009.

2. Cheng-Tsung Lin, Chung-Wen Hung, and

Chih-Wen Liu, Senior

Member,IEEE."Position Sensorless Control

for Four Switch Three-Phase Brushless DC

Motor Drives",IEEE TRANSACTIONS ON

POWER ELECTRONICS, VOL. 23, NO. 1,

JANUARY 2008.

3. Meenal K,K Sobana,A Vanisri.Dr

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Available Online At www.ijpret.com POSITION DETECTION AND SPEED CONTROL

OF PMBLDC MOTOR USING VIRUTAL

INSTRUMENTATION",International Journal

of Communications and Engineering

Volume 03 No.3, Issue: 01 March2012.

4. S. Joshuwa, E Sathishkumar, S.

Ramsankar ," Advanced Rotor Position

Detection Technique For Sensorless Bldc

Motor Control ".

5. A.Purna Chandra Rao, Y. P. Obulesh and

Ch. Sai Babu IEEEDepartment, PVPSIT,

Vijayawada, Andhra Pradesh, India IEEE

Department, LBRCE, Maylavaram, India IEEE

Department, JNTUK, Kakinada, Andhra

Pradesh, India, ," Mathematical modeling of

BLDC Motor with closed loop speed control

using PID controller under various loading