CHAPTER 1 INTRODUCTION -...
Transcript of CHAPTER 1 INTRODUCTION -...
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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.