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CHAPTER 1

INTRODUCTION

1.1 GENERAL

A Permanent Magnet Brushless DC motor (PMBLDCM) consists

of a permanent magnet rotor and a three-phase stator winding. PMBLDC

motors are electronically commutated, and do not use the brushes for

commutation. Three hall sensors detect the rotor position, and commutation

is based on these sensor inputs. The permanent magnet of the motor rotates

and the three phase stator windings remain static. The brush-commutator

assembly is replaced by an electronic controller. With rapid development in

the field of microelectronics and power switches, the most adjustable speed

drives are realized with AC machines.

The Permanent Magnet Synchronous Motor with the sinusoidal

back-EMF, and the PMBLDC motor with the trapezoidal back EMF, are

widely used because of their distinct advantages. They have a large torque to

inertia ratio, high power density, high efficiency and better controllability.

Of these two motors, the preferred choice is the PMBLDC motor for

industries like Automotive, Aerospace, Consumer, Medical, Industrial

Automation equipment and Instrumentation, because of its high torque, high

efficiency, simplicity of control, and less maintenance.

1.2 LITERATURE SURVEY

An improvement of the power factor in an electronic system was

traditionally made by a PFC circuit, designed and placed in the front end of

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the system and interfaced with the load. This circuit may be an independent

unit followed by a DC-DC converter, or one incorporated in the power supply

of the load, as an inseparable part of the circuit. They were the two-stage

PFC power supply and the single-stage PFC power supply respectively. The

basic idea of the PFC circuit is to force the current flow in the line, to follow

the waveform of the voltage, as the line voltage is normally near sinusoidal

and not distorted.

The conventional boost converters concerned themselves with the

volume and weight of the inductor and losses in power devices; these factors

influenced the cost of the converter, the power density and efficiency.

Zhang et al (1995) proposed a three-level boost converter that had a much

smaller inductor and lower voltage devices for the single-phase PFC. It

yielded high power density, high efficiency and less cost. Low device voltage

rating is very important in high voltage applications. This three-level volume

and weight boost converter was very useful in high power applications, since

two active switches were used.

Wei et al (2000) stated that excellent line regulation capability can

be had in a single-stage, single-switch PFC converter with electrical isolation,

and it makes the converter suitable for universal input application. Its

simplified power stage and control circuit makes for better efficiency and

high reliability.

The primary requirement of any power supply is to regulate the

output voltage which is often combined with the PFC. Tse (2003) discusses

the circuit theory aspects of PFC in switching converter circuits. The paper

presents 16 minimal configurations, each consisting of two basic switching

converters. The comparative study of their efficiency leads to the concept of

reduced redundant power processing. This is useful in designing efficient

power supplies, which provide both output regulation and the PFC.

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A technique was proposed by Swami (2005) for three phase PFC,

which uses a three phase line side active front-end converter, and simplifies

the PFC algorithm to a great extent. This results in reduced sampling time

and improved switching frequency. This also does away with both forward

and backward d-q reference frame transformations, and the presetting of two

orthogonal references.

In the universal-input PFC application providing both step-up and

step-down conversion was attractive, since the output DC voltage can be set

to any value. However, single-switch buck-boost topologies have a high

degree of component stresses and component sizes comparable to those of

boost converters. Jing quan et al (2006) proposed a two-switch topology,

boost-interleaved buck-boost converter, offers significant performance

improvements over the single-switch buck-boost converters, or other two-

switch buck-boost converters in the universal-input PFC applications.

To avoid electromagnetic interference in high power and high

voltage applications, the current, operation frequency and bandwidth of the

three level PFC converters must be limited. Lock & Silva (2007) presented a

fixed frequency hysteresis current control for three level single-phase, double

boost PFC converters. This paper alone proposes hysteresis current control

with adaptive band error, to constrain switching frequency for a given range.

It results in fast response, relatively small bandwidth and reduced harmonic

content. This method also eliminates the problem of coupling output voltage,

by compensating the current reference.

In recent times, the demand for improvement in the power quality

of the AC system has been of great concern, because of the rapidly increasing

number of electronic equipment coming into use. Various PFC converters

were developed to reduce the harmonics in power lines and improve the

transmission efficiency. The PFC circuits have become mandatory in single-

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phase power supplies, as more stringent power quality regulations and strict

limits on the THD of the input current, were imposed. Huber et al (2007)

presented a systematic review of bridgeless boost rectifiers, and a

performance comparison between a conventional PFC boost rectifier and a

bridgeless PFC boost rectifier. It was found that bridgeless boost rectifiers

have reduced conduction losses since they have reduced number of

semiconductor components in the path of the line current.

Martinez & Gomez (2007) presented the successful use of fuzzy

logic to derive a practical control scheme for boost converter with PFC. The

new controller performed well during transient conditions because of its

robustness and power factor correction as it used only two input variables. As

fuzzy rules can be assigned to different operation area, the new controller can

work under voltage regulation and at the same time providing dynamic

performance and active power factor correction.

A novel bridgeless single-phase AC-DC converter with an

automatic power factor correction proposed by Ismail (2008) was based on

the single-ended primary inductor converter (SEPIC) topology. It utilizes a

bidirectional switch and two fast diodes. The absence of an input diode and

the presence of only one diode in the current path on each switching cycle

resulted in less conduction loss and improved thermal management compared

to the existing PFC circuits.

Singh & Singh (2010) presented a single ended primary inductor

converter (SEPIC) as a power factor correction (PFC) converter which is

operated in voltage control mode for the speed control of a permanent magnet

brushless DC motor driven air-conditioner. The proposed converter combines

the PFC and DC link voltage control in single stage and uses only one

controller.

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Sahid & Yatim (2008) deals with comparison of full-bridge

topology with two DC/DC converters and a full-bridge topology with one

DC/DC converter and a bridgeless converter. The focus of this study is on the

energy efficiency at low power up to 300W with various topologies.

Bridgeless topology has been found to be efficient when it is followed by a

full bridge with one DC/DC converter. Reduction in components improved

its efficiency by 8% to 10%.

Though a bridge converter is simple, it has many drawbacks like

poor harmonics and reduced efficiency. To enhance its power factor

correction capability, a simple zero-current switching (ZCS) circuit based on

a passive circuit without any complicated switch control was developed and

applied to the boost diode. This circuit operated in the continuous conduction

mode, increasing efficiency and reducing electromagnetic inferences claimed

Hwu et al (2008).

Meng Tao et al (2009) came up with a three-phase single-stage

boost power factor correction converter topology which operates in the

discontinuous conduction mode. Compared with single switch three phase

PFC, this can bring about electrical isolation between the input and output

sides, output DC voltage regulation and achieve zero-current switching for the

lagging-leg switches. A single-switch cannot by itself achieve soft-switching

and hence a full-bridge circuit replaces it. A high frequency transformer was

adopted to achieve electrical isolation and output voltage regulation. The

compensating circuit comprising of six switches and resistors was used to get

rid of the dead zone.

Digitally controlled boost PFC rectifiers operating in continuous

conduction mode can be provided with a robust auto-tuning technique to

bring about the desired crossover frequencies and phase margins for a wide

range of operating conditions and power-stage parameters through simple

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compensator gain adjustments as proposed by Moon et al (2010). This

approach perturbs the PFC current and the voltage control loops, through the

injection of digital perturbation signals. A precise estimation of the filter

inductance and the capacitance values through the tuning process also

provides useful information for any digital current-programmed control

technique.

Swamy (1996) designed and developed a simple low cost prototype

controller without current and position sensors for the PMBLDC motor. In

remote villages where electric supply was either not available or reliable

MOSFET based current controlled VSI coupled with PMBLDC motor, in

water pumping application operated by PV array is an efficient alternative

energy source. The water pump is powered by the PV array through a filter

and an inverter. The magnitude of the PV-array current depends on the

intensity of sunlight and this current is fed to the VSI which supplies the

necessary power to the motor. As the PV array itself controls the current up

to its maximum value there is no need for a current controller. Position

estimation has been carried out by sensing back-EMF.

Though PID controllers were very common, their performance

deteriorates with changes in system operating conditions. A hybrid controller,

a combination of fuzzy logic and conventional controller was given by Singh

et al (2000) for the PMBLDC drive. This controller uses the fuzzy rules based

on eliminating overshoots and provides compensation for overshoots and

oscillations. Adjusting only an additional parameter, the manual tuning time

of the controller can be significantly reduced. The controller was robust

enough to withstand external disturbances.

The PMBLDC motor equipped with an artificial neural network

based reference commutation signal generator for the speed control of

PMBLDC motor was implemented. Whereas the transient method was based

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on the torque balance aspect, models based on the transient analysis design

explicitly furnished the relation between the input average voltage and actual

speed and hence this model was superior claimed Singh & Rai (2005). This

type of system was found to be ideal for variable torque drive and is capable

of driving multiple motors. Hence it was found suitable for designing of

autonomous robots with automated assembly lines in textile industries.

Kumar (2006) came up with a fuzzy pre-compensated PI speed

controller for the PMBLDC motor drives. The conventional PI controllers are

very sensitive to the variations of system parameters and also require an

accurate mathematical model of the drive system for tuning PI gains. But the

rectifier and inverter combination that feeds power to the drive system makes

it more complex and difficult to model. When precise mathematical modeling

of the system was not feasible, the fuzzy logic based controllers were

preferred. It was found that fuzzy pre-compensated PI controller was superior

to conventional controllers.

The speed controller for the PMBLDC motor can be made more

robust and accurate by using a phase-locked-loop (PLL) assisted internal

method. Since it is proper to integrate the motor current sensing scheme with

the PWM control the hardware implementation of the PMBLDC motor drive

will be more compact and cheaper. Pan & Fang (2008) claimed that both the

steady state and fast transient responses can be achieved with this method.

Enabling online tuning of the controller gains depending on

operating points the fuzzy based gain scheduled PI controller eliminates the

problem of fixed gain PI speed controller. Srinivas & Rajagopal (2009)

described the automated tuning technology for controllers which provide

better, steady and dynamic state speed response compared with conventional

PI controllers.

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Iizuka et al (1985) proposed a microcomputer control brushless

motor without a shaft position sensor. The rotor position was sensed by the

back EMF induced in the stator windings. The motor voltage was cut by

commutator transistors to alter motor speed. This control system consists of a

4-bit single-chip microcomputer and two-quadrant comparators.

PMBLDC motor exhibits nonlinear behavior due to its friction,

inertial variation, saturation and nonlinear coupling between motor current

and rotor speed. Such uncertain system dynamics entitle auto tuning speed

control strategy for PMBLDC motor. Thirusakthimurugan & Dananjayan

(2006) designed and implemented a novel auto tuning controller which is

robust against load and inertial variations.

Hao & Toliyat (2003) proposed a full range speed control and the

topology developed was similar to field oriented controls for sinusoidal PM

motors taking into consideration the fifth and the seventh harmonics

variables. This proposed method brought about an increase in the torque

developed. Controllability is the same as it is in the sinusoidal PM motor

over flux weakening operations compared to the conventional six-step BLDC

drive system.

Sayed et al (2007) presented a control structure for the PMBLDC

drive system describing the dynamics of the BLDC drive system with

classical PI controller and Fuzzy-Logic Speed controllers as also an account

of its performance analysis. The dynamic behaviours of the drive system with

both controllers were presented and compared for a wide range of speed

range. Step changes in reference speed, load torque and speed reversal were

also studied. It was proved that for such a complicated and nonlinear control

system, the Fuzzy Logic Controller ensured much better dynamic properties

and robust to systems with parameter changes.

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The boost converter topology is highly effective in power factor

correction applications, provided the DC output voltage is close to, but

slightly greater than, the peak AC line voltage ( Erickson 2001).

Samaranayake et al (2002) described the theoretical background

and implementation of a real-time speed control scheme for a BLDC motor

set-up, via Ethernet network and studied the Hard Real-Time capability of

Ethernet within the scope of TCP/IP. It was found that delays in connection

establishment and connection termination phases of TCP sessions are

constants and the value depends on the configuration and the direction of the

traffic flow. Observed controller to actuator delays agrees with the theoretical

delay values. But the sensor to controller delay values deviate to a certain

amount, missing a continuous set of samples, resulting poor performance in

the network connected operation with both switch and Hub. Therefore it was

concluded that either the speed controller must be robust enough to handle the

cases of unacceptable delays and missing samples or the TCP/IP protocol has

to be modified to the communication deterministic.

Wang et al (2009) have employed Y connected three-phase full

bridge drive mode control scheme for a BLDC motor. It had a microchip

TMS320F2812 as the controller and IPM as the driver. In this method the

PID algorithm was combined with the mathematical model of the BLDC

motor to present a sort of modularization design for the drive control system.

ASIC (Application Specific IC) was often used for sensorless

control PMBLDC motor. This IC integrates the terminal voltage of unexcited

winding containing back EMF and uses PLL to determine the proper

commutation sequence for the BLDC motor. Voltage was distorted by

voltage pulses because of free wheeling diode conduction. The ASIC

integrates these pulses which results in retardation of commutation. Shen &

Iwasaki (2006) suggested that ASIC should integrate the third harmonic back

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EMF instead of the terminal voltage to reduce the commutation retarding and

to improve the motor performance.

Ozturk et al (2010) have used four-switch inverter in the constant

torque region and present a direct torque control technique for the BLDC

motors with non-sinusoidal back EMF. The desired quasi-square current

waveforms can be had by properly selecting the inverter voltage space vectors

from a simple look up table at a predefined sampling time. The torque

response was hence faster and the desired torque characteristics were realized.

Further low-frequency torque oscillations were eliminated by the direct

control of voltage space vectors.

The speed and position of the rotor of a PMBLDC motor is

controlled in a conventional cascade structure. The inner current control loop

runs at a larger bandwidth than the outer speed control loop to achieve

effective cascade control. Thirusakthimurugan & Dananjayan (2007)

proposed a multirate based general predictive control (GPC) law for the

conventional cascaded PI-PI scheme. Both speed and torque tracking

objectives were achieved in matched and mismatched parameter cases. The

inner loop used an adaptive based model predictive controller, exploiting

information conveyed by accessible disturbances, while the outer loop used a

GPC to restrain the error from nonlinear identification of the generalized

system. The measured and unmeasured disturbances get rejected effectively

so that the motor could run at the desired speed at constant load. Non-

minimum phase characteristics and system constraints can also be effectively

handled by the proposed GPC algorithm. This strategy resulted in better

performance, satisfactory system output and smooth feasible control actions.

Back EMF was used to detect rotor position. Since back EMF is

very small at the time of starting, getting the rotor position efficiently is very

difficult. Zeng & Zicheng (2010) proposed a re-setting method wherein a

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current loop was used for high speeds and safety at the start of the motor. A

closed loop system was designed using voltage and current loops. The rotor

position can be estimated by back EMF detection and the speed of the drive

was estimated by speed algorithm calculated by the use of a DSP chip

TMS320LF2407. This makes the system simple and reliable, since several

advanced peripherals, optimized for digital motors and motion control

applications have been integrated to provide a true single chip DSP controller.

Friction, inertial variation, saturation and non-linear coupling

between the rotor speed and the motor current result in the nonlinear behavior

of a PMBLDC motor. The self-tuning speed control of the PMBLDC motor

was subjected to stringent tests because the usual controllers were not robust

enough to cope with the inertial and load variations. Thirusakthimurugan &

Dananjayan (2006) designed and implemented a novel auto tuning controller

which stood up to the load and inertial variations. Departing from the usual

approach of tuning the outer and inner loops in strict sequence, the proposed

approach carried out the entire tuning process in one experiment. This

method was claimed to be economical.

Somanathan et al (2006) came out with the modeling and

simulation of sensor less control of PMBLDC motors using zero-crossing

back EMF technique. Line back EMF information was considered, is the

neutral point of the star connected machine had a tendency to float and not

accessible to detect zero-crossing points. In the paper various waveforms

like line back EMF, phase currents, rotor position, speed, torque with respect

to time at varying loads were presented. Initially the stator windings of the

motor were excited by an inverter which operates in 120° mode conduction

for a threshold period. When the minimum speed was reached, the control

was transferred to zero crossing detection circuit. A closed loop operation

followed wherein a pair of stator windings was excited by the logical inverter.

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The Sensor less operation can be easily implemented in this method, without

the neutral point. At any load, as the delay angle increases, the speed,

frequency and back EMF decrease and speed ripple, current and torque ripple

also increase. The torque pulsations were found to be uniform for no-delay

and non-uniform.

The design of a precise speed and current controller for PMBLDC

motors was a tedious task because of the magnetic saturation of the rotor and

non-linearity present in the developed torque. Thirusakthimurugan &

Dananjayan (2006) presented a new control scheme for the PMBLDC motor

to improve control system robustness via complete decoupling of the design

and performance of the control loops. This decoupling control scheme

minimized the mutual influence among speed and the current control loops. It

was applicable to both the static and dynamic aspects. This method proved to

enhance the robustness of load variations apart from ensuring good

performance in nominal conditions. The most important feature of this speed

control scheme is that the outer speed controller is free from wind up and

saturation of the inner loop which considerably simplifies the overall control

sequence. The proposed controller is found to be very stable for the

PMBLDC motors irrespective of load variations and disturbances.

Shao et al (2002) proposed a novel EMF detection method for

sensor less BLDC motor drives without motor neutral point voltage

information. The back EMF can be detected during the OFF time of PWM,

because the terminal voltage of the motor was directly proportional to the

phase back EMF during this interval. The true back EMF signal can be

directly obtained from the motor terminal voltage by properly choosing the

PWM and the sensing strategy. This makes the proposed method insensitive

to switching noise, frees it from filtering requirements and leads to improved

motor performance over a wide speed range. Hence it is suitable for high and

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low voltage as well as high speed or low speed applications. Quick motor

starting is also possible with this proposed system.

For robust position control of the PMBLDC motor a method of

single neuron PID control was addressed by Wang & Liu (2010). A

disturbance observer was designed to increase the system robustness of the

PMBLDC motor. A state feedback controller intended for this purpose using

a single neuron and a disturbance observer included in the design of the speed

loop effectively suppress the external disturbances. It was found that the

proposed controller was insensitive to load changes and parameter variation

and could increase the response time of the system.

Miao & Yanpeng (2009) have introduced a speed regulating system

for the PMBLDC motor using the digital signal processor ADMCF328 as the

core of the control system. The use of this DSP reduces the hardware circuit

and its high data processing capacity makes the control convenient and exact.

A Voltage controlled scheme with extended speed range was

presented by Sue & Wu (2008), for the PMBLDC motor. This scheme

combines low speed PWM control and high speed phase advance

commutation to attain extended speed range drive feature. Speed transition

was smooth from the low speed region to the high speed region because the

PWM control was saturated as the applied voltage amplitude was at the same

level as the saturated voltage amplitude of the PWM control. A proper phase

advance angle was determined by the proposed control in the field weakening

region. Further as it does not have the current control loop it eliminates the

need for current sensors in the drive. An indirect over current limitation

method was used to limit the DC link current at any overload operation. The

developed scheme was claimed to be more efficient over wide speed ranges

since the operational criterion was based on the minimum current amplitude

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control of a Vector Controlled Permanent magnet Synchronous Motor

(PMSM) drive.

Zhang & Zhou (2009) presented a control without a position sensor

for brushless DC motor based on a commercial application-specific integrated

circuit (ASIC) ML4425. The position detection scheme was based on the

controller function of ML4425 and terminal voltage sensing which includes

the complete circuit for the sensor less control of the BLDC motor. The

peripheral circuit of ML4425 is very simple. A few isolation components,

such as resistor and capacitor are only needed. Hence this control system

provides very reliable and economical operation.

A novel and simple approach to achieve low frequency torque

ripple free direct torque control with maximum efficiency based on a d-q

reference frame similar to PMSM was presented by Ozturk & Toliyat (2008).

The electrical rotor position was estimated by using winding inductance,

stationary reference frame stator flux linkages and the current. This method

directly controls the torque and stator flux amplitude indirectly using d-axis

current. Flux weakening operation is possible since stator flux is controllable.

This method also provides regulated varying signals. A simple voltage vector

selection look-up table was designed to obtain the fast torque and flux

control,. Two actual and easily available line-to-line back EMF constants

related to the rotor position were obtained, which help to eliminate low-

frequency torque oscillations. These constants are obtained offline and

converted to d-q frame equivalents using the new line-to-line Park

Transformation and these were set up in the look-up table for torque

estimation.

Direct back-EMF sensing scheme used in a PMBLDC motor

requires a minimum PWM off time to sample the back-EMF signal, which

results in limiting the duty cycle to something less than 100%. Shao (2006)

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proposed an improved direct back-EMF detection scheme that samples the

motor back-EMF synchronously during either the PWM on time or the PWM

off time.

A simple mode of controlling the BLDC motor for electric vehicle

applications is by the sensorless method which needs on the rotor position of

the PMBLDC motor. Dixon et al (2002) presented a simple solution to

determine the commutation sequence of a BLDC motor with sinusoidal flux

distribution. This method is based on two phase current sensing and the

determination of the back EMF. For trapezoidal flux distributions the solution

could be implemented with some minor changes. The proposed solution

makes use of the information contained in the back EMF, calculating the six

commutation points required. This method is applicable only when the

current is sensed; hence it needs to be compensated by a starting method.

This system was implemented with a fast digital signal processor

(TMS320F241) programmed with a closed loop PI current controller for the

motor to produce constant torque. Also a fiber optic link was used between

the controller and the inverter to minimize noise production and the

possibilities of error on commutations.

Hall-ICs or a sensorless algorithm can provide rotor position

information of a PMBLDC motor. Since sensorless algorithm is not suitable

for complicated operational conditions of the drive, Hall-ICs are set up in the

motor to detect main flux from the rotor. Yong et al (2004) used only two

Hall-ICs instead of three Hall-ICs and encoder for rotor position and speed

position feedback signals. They also made use of a 16bit microcontroller

(80C196KC) with a three phase slotless PMBLDC motor. The 2 Hall-ICs

were placed on the end-plate of 120° phase difference. With this information

the other phase was estimated in sequence through a revolving rotor. A rotor

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position signal synthesizer using a PLL, based on two Hall-ICs was proposed

to improve the speed range.

The sensorless BLDC motor encountered chronic problems because

of operations at low speed. Kim et al (2003) proposed a novel sensorless

technique which overcame this problem and ensured highly accurate, robust

sensorless operation from near zero to high speed. For this purpose a speed-

independent function, based on a new flux linkage function was used. The

capability of position detection at around 1% of the rated speed makes starting

procedure much simpler than the conventional methods.

Kaliappan et al (2010) dealt with direct torque control of a

PMBLDC motor using a hybrid controller to reduce torque ripple. This

controller uses GA and Fuzzy logic. The conventional controller though

common in practice, is not satisfactory under nonlinear conditions and

parametric variations. This hybrid controller also controls the flux linkage

angle of the PMBLDC motor. Torque error and the flux linkage angle of the

motor were fuzzified and it was auto tuned by GA to improve dynamic

characteristics.

Keshri et al (2011) proposed four possible switching patterns by

modulating only the upper/lower switches and the incoming/outgoing phase

switches. The adoption of different possible switching patterns/ schemes

affect transient behaviors such as phase current and torque of a PMBLDC

motor. Dummy hall sensor signals are generated for variable speed reference

with the help of a micro-controller to analyze inverter voltages. Provision has

also been made to bypass the generated dummy hall sensor signal with actual

hall sensor signals from the motor for control purposes.

Praveen et al (2010) presented the design and analysis of a novel

family of slotless PMBLDC motors for the precision and positioning of

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applications in spacecraft. Estimations of initial design, selection of major

parameters and air gap magnetic flux density were done using the analytical

model of the machine. This novel machine topology was found to deliver

high torque density, high efficiency, zero cogging torque, better positional

stability and high torque to inertia ratio. The machine also provides uniform

air gap flux density along the radius, thus avoiding circulating currents in

stator conductors and reducing torque ripple.

Rizwan & Doss (2011) proposed a routine for the reduction of

cogging torque with reduced stator tooth width and bifurcated active surface

area using Finite Element Analysis. Variation in flux density, distribution in

the air gap, cogging torque and reluctance torque ripple were determined for

the proposed change in the motor design.

Singh & Singh (2010) presented a single ended primary inductor

converter (SEPIC) as a power factor correction (PFC) converter which is

operated in voltage control mode for the speed control of a permanent magnet

brushless DC motor driven air-conditioner. The proposed converter combines

the PFC and DC link voltage control in single stage and uses only one

controller. Its performance has been evaluated under speed control with

varying input AC voltage which has demonstrated nearly unity power factor

in wide range of speed and input AC voltage. The proposed drive has also

demonstrated smooth seed control proportional to the DC link voltage while

maintaining the power quality indices well within the limits of an

international standard IEC 61000-3-2.

Govindan et al (2011) presented method of controlling the speed of

a PMBLDC motor using TMS320F2812 DSP controller. This mode has

specific peripherals dedicated to digital motor control applications. Control

algorithms used for speed control have been implemented through the

programming of the assembly language in the DSP controller.

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Varatharaju et al (2010) described a procedure for deriving a model

for a brushless DC motor with 120-degree inverter system and its variation on

the MATLAB/Simulink platform.

Varatharaju et al (2011) presented a tuning methodology suitable

for the parameters of an adaptive speed controller in a BLDC motor and drive

system. They analyzed the design of the closed loop drive system employing

the adaptive-network based fuzzy interference system (ANFIS) based on the

mathematical model of the BLDC drive system. The simulated

electromagnetic torque and rotor speed signify the superiority of the proposed

technique over the classical method.

Bansal et al (2011) proposed an algorithm using fuzzy logic to

estimate the speed and position of the BLDC motor from back EMF for

sensorless BLDC motor drives. This improves the performance of

conventional sensorless drives. This algorithm makes robust control for the

reversal of reference speed and continuously calculates the position of the

rotor at the transient as well as at the steady state.

Praveen et al (2010) came up with an optimal design of a surface

mounted PMBLDC motor meant for spacecraft applications. Performance of

two types of machine configurations like slotted and slotless PMBLDC motor

with Halbach array was compared by analytical and finite element analysis. It

was found that unlike a slotted PMBLDC motor, the slotless types with

Halbach array could develop zero cogging torque without reduction in the

developed torque.

Chang et al (2010) proposed a new module structure of phase

locked loop speed controller for the PMBLDC motor drives to achieve both

fast response and high accuracy. This standard module renders controller

design simple and straightforward. A phase current sensing scheme was

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adopted for proper integration with the PWM control of a PLL controller to

reduce the drive cost.

Sue et al (2009) proposed a phase advanced commutation scheme

for IPM-BLDC motor drives. To utilize the torque capability of an IPM-

BLDC motor as much possible for a low cost and information limited drive,

the inverter gating time is advanced such that the phase angle of the stator

current can lead that of the corresponding back-EMF. To determine the

advanced angle instead of look up table method or complicated evaluation

scheme electric parameters of the motor , rotor speed and inverter switching

duty cycle are used.

Saxena et al (2010) used soft computing technique for the

performance simulation of the BLDC motor. With the help of user friendly

approach of PSIM, the models were constructed easily.

Reljic et al (2012) analyses phase shifting technique for harmonic

mitigation. The proposed technique improves power factor and reduces

harmonics at the same time.

Akhila & Nikhil (2012) made a comparative study of the sensor

and sensorless control of four-switch inverter fed PMBLDC drives simulating

a model using the transfer function of the drive. Hardware implementation

was with DSP processor TMS 320LF2407.

Chun et al (2013) proposed a single stage light emitting diode

(LED) driver with interleaving PFC feature for street –lighting applications.

The circuit integrates an interleaved boost PFC converter with a half-bridge-

type LLC resonant converter into a single-stage power converter. The AC-DC

resonant converter uses interleaving methods to achieve input-current

shaping, and possess soft switching functions on two active power switches to

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reduce their switching losses in order to increase the circuit efficiency. It also

features low levels of input-current ripple, reduced switching losses, high

power factor, low THD of input current and a reduced component count.

Roedgaard et al (2013) proposed a new forward conduction mode

control method for piezoelectric transformer based power converter. The

drive utilizes an inductorless half-bridge topology. A piezoelectric transformer

based PFC was developed, utilizing and validating the forward conduction

mode control method. For circuit minimization and simplicity, it has no load

regulation and has a 100-Hz output modulation. The proposed method ensures

that the piezoelectric transformer is operated at its optimal operation

frequency, which ensures soft-switching operation and a constant gain.

Nikolic et al (2013) presented the analysis, design and

implementation of a cost-effective control technique for a six switch three-

phase inverter brushless DC motor drive using single current sensor for

current control. Various parameters defined optimization path for target drive

solution.

The literature reviewed above does not deal with the comparison of

PFC converters for the control of PMBLDC motor drives. Converters like

Bridgeless Boost, Buck- boost, Cuk and Zeta Converters are not used at the

input side for power factor correction. This work proposes Zeta Converter

and Cuk Converter at the input side of PMBLDC drive system. It also aims at

finding the best PFC converter for the control of PMBLDC drives.

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1.3 OBJECTIVES OF THE RESEARCH

The objectives of the work carried out can be summarized as

follows:

To improve the power quality by increasing the power factor

at the input side of a PMBLDC motor.

To model a closed loop controlled power factor correction

converter fed PMBLDC motor drive, with buck-boost, Cuk,

bridgeless and Zeta Converters.

To compare the PFC converter fed PMBLDC drives

employing the above mentioned converters.

In order to validate the analysis and design of the above converters

in power factor correction, and to verify the effectiveness of the control

technique, MATLAB/ SIMULINK software was used. The PIC 16F877

microcontroller was used to ascertain the effectiveness of the control

techniques in real time.

1.4 ORGANISATION OF THE THESIS

The study has been presented in seven chapters and they have been

organized as follows:

The first chapter gives the general introduction to the problem, and

previous studies are reported in the literature. It includes the statement of the

problem and objectives of the present work.

The second chapter analyzes the working and operation of the

various configurations of the PFC Converters. Simulation circuits and the

corresponding results are presented.

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The modeling, simulation and implementation of the VSI fed

PMBLDC motor with bridgeless boost converter are presented in the third

chapter. The performances of the VSI fed PMBLDC motor with L and T

filters are presented.

The modeling and simulation of the performance of the closed loop

control and its implementation in a PMBLDC motor fed by PFC buck-boost

Converter are presented in chapter four.

Chapter five describes the closed loop control of the PMBLDC

Motor, fed by the Zeta Converter, which naturally has an isolated structure.

The Zeta PFC converter based PMBLDCM drive is designed, modeled and

simulated using MATLAB- SimuLink environment. The hardware

implementation is also presented.

The closed loop control of the PMBLDC Motor, fed by the

bridgeless Cuk Converter is described in chapter six. It behaves as an

automatic current wave shaper with no current control. The Simulink model

of the Cuk converter fed PMBLDC drive is explained in detail. The hardware

results are also presented.

Chapter seven is the concluding chapter in which the summary,

conclusions and scope for further research are given.

1.5 CONCLUSION

The literature review, objectives and the organization of the thesis

are presented in this chapter.