POWER FACTOR CORRECTION OF A 3-PHASE 4- SWITCH INVERTER FED BLDC MOTOR

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CHAPTER 1
INTRODUCTION
1.1GENERAL
1.1.1 Brushless DC motors
Brushless DC motors also known as electronically commutated motors are
electric motors powered by direct-current (DC) electricity and having
electronic commutation systems, rather than mechanical commutator and
brushes. The current-to-torque and frequency-to-speed relationships of BLDC
motors are linear.
BLDC motors may be described as stepper motors, with fixed permanent
magnets and possibly more poles on the rotor than the stator, or reluctance
motors. The latter may be without permanent magnets, just poles that are
induced on the rotor then pulled into alignment by timed stator windings.
However, the term stepper motor tends to be used for motors that are
designed specifically to be operated in a mode where they are frequently
stopped with the rotor in a defined angular position; this page describes more
general BLDC motor principles, though there is overlap.
The maximum power that can be applied to a BLDC motor is
exceptionally high, limited almost exclusively by heat, which can weaken the
magnets. Magnets demagnetize at high temperatures, the Curie point, and for
neodymium-iron-boron magnets this temperature is lower than for other
types. A BLDC motor's main disadvantage is of higher cost, which arises
from two issues. First, BLDC motors require complex electronic speed
controllers to run. Brushed DC motors can be regulated by a comparatively
simple controller, such as a variable resistor.

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1.2 LITERATURE SURVEY
The selection of this project and its completion needs so many Surveys
from various books, technical papers and journals. The main idea using more
number of switches complexities of control, so that the 3-Phase 4-Switch
technology has been used, which reduces number of switches, and thereby
the switching losses can be minimized. Using PWM Boost Converter the line
harmonics is reduced and the line current becomes sinusoidal and will be in
phase with the applied voltage. The methodology of speed and power factor
control is modified to bring better output.
Power Factor Correction using Boost Converter reduces the line harmonics
and hence, the line current becomes sinusoidal in shape and will be in same
phase with the voltage. The efficiency of the utility system will be high so
that the total working of the system will get better and hence, the motor can
have better control.
The performance of the drive system was evaluated through digital
simulation by Mat lab/simulink, the electromagnetic torque characteristics,
rotor speed, PWM pulse but brushless D.C. motor is nonlinear function of the
phase current and rotor position. Obtaining the mathematical model is not an
easy task, because the magnetic circuit operates at varying level of saturation
under operating conditions. To reduce the complexity, the linearised models
have been used for designing for controller and performance analysis. A
brushless DC motor is simulated for the analysis. All simulations are
completely documented by their block diagram, corresponding special mat
lab functions & parameters.

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CHAPTER 2
BRUSHLESS DC MOTOR
2.1 INTRODUCTION TO BLDC MOTOR
The need for reliable electrical contact no brush sparking, no electrical
interference and a long working life spawned the aerospace industry to
develop the first brushless D.C. motors in the 1960s. While they have not
totally replaced the brushed type, the advantages of brushless D.C. motors are
apparent in terms of speed, response, reliability and power density.
The primary advantages of brushless D.C. motors are:
 Low Maintenance
 No Brush Sparking
 High Operating Speeds
 High Efficiency
 Compact Size
 Fast Response
But brushless D.C. motors are not without their drawbacks. They are more
expensive due to their complex control system, the use of rare earth magnets
and the need for rotor position sensors. Higher costs are overcome by a longer
life and lower maintenance costs. They are primarily used in fractional
horsepower applications; however, they have been used as drives in electric
vehicles up to 100KW.
Brushless D.C. motors are widely used in the fractional horsepower range
for disk or tape drives for computer peripherals as well as in CD/DVD
players, cooling fans, laser printers and photocopiers. In addition, they are

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often used as spindle drives in machine tools because they can be driven at
very high speeds with fast acceleration, deceleration and reversing responses.
The larger horsepower sizes have found application in electric vehicles. Since
they do not have brushes, hence, are not susceptible to arcing, brushless D.C
motors are safe for environments with flammable gases, such as in the
petrochemical industries.
2.2 CONSTRUCTION AND OPERATION OF BLDC MOTOR
2.2.1 Construction of BLDC MOTOR
Brushless D.C. motors are most commonly constructed with a radically
magnetized permanent magnet rotor, mounted on a steel cylinder, and phase
windings wound on a slotted, laminated, non-salient stator. There are usually
multiple phase windings; however, a single winding can be wound so that it’s
distributed over the stator core. This is the reverse of brushed D.C. motors
allows brushless D.C. motors to have less internal resistance and much better
heat dissipation in the stator coils resulting in higher operating efficiencies
since heat can more efficiently dissipate via the stationary motor housing.
Brushless D.C. motors do not use carbon brushes or a mechanical
commutator; rather, commutation is done via a complex electronic controller
used in conjunction with a rotor position sensor. This is the primary reason
why brushless D.C. motors are low maintenance and non-sparking. In
addition, without brushes or a mechanical commutator, they have less shaft
friction or inertia, less audible noise and much better torque to weight ratios
hence; they are much smaller in size than a comparable brushed D.C. motor.

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Figure 2.1 The four poles on the stator of a two-phase BLDC motor. This is part
of a computer cooling fan; the rotor has been removed.
BLDC motors can be constructed in several different physical
configurations: In the 'conventional' configuration, the permanent magnets are
part of the rotor. Three stator windings surround the rotor. In the 'out runner'
configuration, the radial-relationship between the coils and magnets is
reversed; the stator coils form the center of the motor, while the permanent
magnets spin within an overhanging rotor which surrounds the core. The flat
type, used where there are space or shape limitations, uses stator and rotor
plates, mounted face to face. Out runners typically have more poles, set up in
triplets to maintain the three groups of windings, and have a higher torque at
low RPMs. In all BLDC motors, the coils are stationary.
There are also two electrical configurations having to do with how the
wires from the windings are connected to each other. The delta configuration
connects the three windings to each other in a triangle-like circuit, and power
is applied at each of the connections. The wye ("Y"-shaped) configuration,
sometimes called a star winding, connects all the windings to a central point
and power is applied to the remaining end of each winding.

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A motor with windings in delta configuration gives low torque at low rpm,
but can give higher top rpm. Wye configuration gives high torque at low rpm,
but not as high top rpm. Although efficiency is greatly affected by the motor's
construction, the wye winding is normally more efficient. In delta-connected
windings, half voltage is applied across the windings adjacent to the undriven
lead, increasing resistive losses. In addition, windings can allow high-
frequency parasitic electrical currents to circulate entirely within the motor. A
wye-connected winding does not contain a closed loop in which parasitic
currents can flow, preventing such losses.
From a controller standpoint, the two styles of windings are treated exactly
the same, although some less expensive controllers are designed to read
voltage from the common center of the wye winding.
2.2.2 OPERATIONS OF BLDC MOTOR
Brushless D.C. motors operate in conjunction with an electronic controller
and a rotor position feedback sensor. Based upon the actual rotor position, the
controller sequentially energizes or switches “on” the stator’s phase windings
so that torque is continuously generated as the permanent magnet (PM) rotor
rotates. This switching action is called electronic commutation. To sense the
rotor’s angular position, position sensors are used. When the PM rotor passes
one set of phase windings, a signal from the position sensor is sent to the
controller which then sends a signal to switch “on” the next set of phase
windings so that the magnetic fields of the rotor and the stator’s phase
windings remain synchronized. The torque/speed characteristic of the motor
is determined by the magnitude of the signal and the switching rate of the
controller. For example, in a 2-phase motor, when the phase 1 winding is
energized, the PM rotor will rotate to align itself with magnetic field produced
by the phase 1 winding. When the phase 1 winding is turned “off”, the phase

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2 winding is turned “on” and the rotor will continue to rotate to align itself
with the magnetic field of the phase 2 winding. This “on” and “off” switching
of the phase windings will maintain torque of the PM rotor.
Figure 2.2 BLDCs use electronic commutation to control the power distribution to
the motor, using Hall-effect sensors to measure the motor’s position.
The number of windings and the type of switching sequence determines
the phase winding utilization and the torque response of the motor. Fewer
windings and fewer switching pulses give the motor less winding utilization,
more inertia to overcome and a poorer torque response. The most common
configuration of a brushless D.C. motor is “three phase six pulse.” In this
configuration, the stator has three phase windings connected in a delta or star
configuration with no neutral. The windings are excited by 6 pulses
sequentially with each winding being switched by pulses of opposite polarity.
This delivers a linear torque speed characteristic, similar to a brushed D.C.
motor.
Figure 2.3 Schematic for delta and wye winding styles

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The BLDC motor is an AC synchronous motor with permanent magnets
on the rotor and windings on the stator. Permanent magnets create the
rotor flux and the energized stator windings create electromagnet poles.
The rotor is attracted by the energized stator phase. By using the
appropriate sequence to supply the stator phases, a rotating field on the
stator is created and maintained. This action of the rotor - chasing after
the electromagnet poles on the stator is the fundamental action used
in synchronous permanent magnet motors. The lead between the rotor
and the rotating field must be controlled to produce torque And this
synchronization implies knowledge of the rotor position. On the stator
side, three Phase motors are the most common.
Figure 2.4 A three-phase synchronous motor with a one permanent
magnet pair pole rotor
Permanent magnet synchronous motors can be classified in
many ways, one of these is that it is of Particular interest tous is that
depending on back emf profiles. BLDC and PMSM. This terminology
defines the shape of the back-emf of the synchronous motor. Both
BLDC and PMSM motors have permanent magnets on the rotor but
differ in the flux distributions and back-emf profiles. To get the best
performance out of the synchronous motor.

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2.2.3 BLDC Motor Control
The BLDC motor is characterized by a two phase ON operation to
control the inverter. In this control scheme, torque production follows
the principle that current should flow in only two of the three phases at
a time and that there should be no torque production in the region of
back EMF zero crossings. The following figure describes the electrical
wave forms in the BLDC motor in the two phases ON operation.
This control structure has several advantages
 Only one current at a time needs to be controlled.
 Only one current sensor is necessary or none for speed loop
only, as detailed in the next sections.
 The positioning of the current sensor allows the use of low
cost sensors.
We have seen that the principle of the BLDC motor is, at all times,
to energize the phase Pair which can produce the highest torque.
To optimize this effect the Back EMF shape is trapezoidal. The
combination of a DC current with a trapezoidal Back EMF makes
it theoretically possible to produce a constant torque. In practice,
the current cannot be established instantaneously in a motor phase;
as a consequence the torque ripple is present at each 60 degree
phase commutation.
2.2.4 Two Phase ON Operation
If the motor used has a sinusoidal Back EMF shape, this control can be
applied but the produced torque is:
Firstly, not constant can be made up from portions of a sine wave.

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This is due to its being the combination of a trapezoidal current
control strategy and of a sinusoidal Back EMF. Bear in mind that a
sinusoidal Back EMF shape motor controlled with a sine wave
strategy produces a constant torque.
Secondly, the torque value produced is weaker.
Figure 2.5 Electrical Waveforms in the Two Phase ON Operation and Torque Ripple
2.2.5 Torque Ripple in a Sinusoidal Motor Controlled as a
BLDC
Figure 2.6 Torque Ripple in a Sinusoidal Motor Controlled as a BLDC

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2.2.6 Transport
High power BLDC motors are found in electric vehicles and hybrid
vehicles. These motors are essentially AC synchronous motors with
permanent magnet rotors.
A number of electric bicycles use BLDC motors that are sometimes built
into the wheel hub itself, with the stator fixed solidly to the axle and the
magnets attached to and rotating with the wheel. The bicycle wheel hub is the
motor. This type of electric bicycle also has a standard bicycle transmission
with pedals, sprockets, and chain that can be pedaled along with, or without,
the use of the motor as need arises.
2.2.7 Heating and ventilation
There is a trend in the HVAC and refrigeration industries to use BLDC
motors instead of various types of AC motors. The most significant reason to
switch to a BLDC motor is the dramatic reduction in power required to
operate them versus a typical AC motor. While shaded-pole and permanent
split capacitor motors once dominated as the fan motor of choice, many fans
are now run using a BLDC motor. Some fans use BLDC motors also in order
to increase overall system efficiency.
In addition to the BLDC motor's higher efficiency, certain HVAC
systems use BLDC motors because the built-in microprocessor allows for
programmability, better control over airflow, and serial communication.

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2.2.8 Stepper motor
The stepper motor is used in microprocessor and microcontroller-based
and robotic equipment, as it consumes less power and provides accurate
movement of robotic arms. Semiconductor producers include Infineon
Technologies, Texas Instruments and Microchip. Infineon offers so-called
LIN stepper motors used in applications such as instrumentation and gauges,
CNC machining, multi-axis positioning, printers and surveillance equipment.
2.2.9 Applications
BLDC motors fulfill many functions originally performed by brushed DC
motors, but cost and control complexity prevents BLDC motors from
replacing brushed motors completely in the lowest-cost areas. Nevertheless,
DC motors have come to dominate many applications, particularly devices
such as computer hard drives and CD/DVD players. Small cooling fans in
electronic equipment are powered exclusively by BLDC motors. They can be
found in cordless power tools where the increased efficiency of the motor
leads to longer periods of use before the battery needs to be charged. Low
speed, low power BLDC motors are used in direct-drive turntables for
"analog" audio discs.

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CHAPTER 3
PROJECT DESCRIPTION
3.1 BLOCK DIAGRAM
The power factor correction circuit has been designed for a nominal mains
voltage of 230 Vrms, 50 - 60 Hz. Basically, the circuit consists of several
sections they are given bellow. Figure 1 shows the block diagram of the
circuit.
Figure 3.1 Block diagram of the proposed project

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3.1.1 POWER SUPPLY
It has unit which has to drive a circuit. It has basic unit for all electrical
circuits. The follings are required for construction of a power circuit.
Figure 3.2 power supply regulator
The linear supply
The component blocks of a linear supply are common to all variants,
and can be described as follows:
Input circuit
Conditions the input power and protects the unit, typically voltage
selector, fuse, on-off switching, filter and transient suppressor.
Transformer
Isolates the output circuitry from the ac input, and steps down or up the
voltage to the required operating level.
Rectifier and reservoir
Converts the ac transformer voltage to dc, reduces the ac ripple
component of the dc and determines the output hold-up time when the input is
interrupted.
Regulation
Stabilizes the output voltage against input and load fluctuations.

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3.2 CURRENT TRANSFORMER
In electrical engineering, a current transformer is used for measurement of
electric currents. Current transformers, together with voltage transformers, are
known as instrument transformers. When current in a circuit is too high to
directly apply to measuring instruments, a current transformer produces a
reduced current accurately proportional to the current in the circuit, which can
be conveniently connected to measuring and recording instruments. A current
transformer also isolates the measuring instruments from what may be very
high voltage in the monitored circuit. Current transformers are commonly
used in metering and protective relays in the electrical power industry.
Figure 3.3 current transformer coil
Current transformers used in metering equipment for three-phase 400
ampere electricity supply. Like any other transformer, a current transformer
has a primary winding, a magnetic core, and a secondary winding. The
alternating current flowing in the primary produces a magnetic field in the
core, which then induces a current in the secondary winding circuit.
Primary objective of current transformer design is to ensure that the primary
and secondary circuits are efficiently coupled, so that the secondary current
bears an accurate relationship to the primary current.
The most common design of CT consists of a length of wire wrapped
many times around a silicon steel ring passed over the circuit being measured.
The CT's primary circuit therefore consists of a single 'turn' of conductor,
with a secondary of many tens or hundreds of turns. The primary winding

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may be a permanent part of the current transformer, with a heavy copper bar
to carry current through the magnetic core. Window-type current transformers
are also common, which can have circuit cables run through the middle of an
opening in the core to provide a single-turn primary winding. When
conductors passing through a CT are not centered in the circular opening,
slight inaccuracies may occur.
Shapes and sizes can vary depending on the end user or switchgear
manufacturer. Typical examples of low voltage single ratio metering current
transformers are either ring type or plastic molded case. High-voltage current
transformers are mounted on porcelain bushings to insulate them from
ground. Some CT configurations slip around the bushing of a high-voltage
transformer or circuit breaker, which automatically centers the conductor
inside the CT window. The primary circuit is largely unaffected by the
insertion of the CT. The rated secondary current is commonly standardized at
1 or 5 amperes. For example, a 4000:5 CT would provide an output current of
5 amperes when the primary is passing 4000 amperes. The secondary winding
can be single ratio or multi ratio, with five taps being common for multi ratio
CTs. The load, or burden, of the CT should be of low resistance. If the voltage
time integral area is higher than the core's design rating, the core goes into
saturation towards the end of each cycle, distorting the waveform and
affecting accuracy.
Figure 3.4 current transformer coil connection

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3.2.1 Usage
Current transformers are used extensively for measuring current and
monitoring the operation of the power grid. Along with voltage leads,
revenue-grade CTs drive the electrical utility's watt-hour meter on virtually
every building with three-phase service and single-phase services greater than
200 amps.
The CT is typically described by its current ratio from primary to
secondary. Often, multiple CTs are installed as a "stack" for various uses. For
example, protection devices and revenue metering may use separate CTs to
provide isolation between metering and protection circuits, and allows current
transformers with different characteristics to be used for the devices.
3.2.2 Safety precautions
Care must be taken that the secondary of a current transformer is not
disconnected from its load while current is flowing in the primary, as the
transformer secondary will attempt to continue driving current across the
effectively infinite impedance. This will produce a high voltage across the
open secondary, which may cause arcing.
3.2.3 Accuracy
Accuracy classes for various types of measurement are set out in IEC
60044-1, Classes 0.1, 0.2s, 0.2, 0.5, 0.5s, 1, and 3. The class designation is an
approximate measure of the CT's accuracy. The ratio error of a Class 1 CT is
1% at rated current; the ratio error of a Class 0.5 CT is 0.5% or less. Errors in
phase are also important especially in power measuring circuits and each class
has an allowable maximum phase error for specified load impedance. Current

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transformers used for protective relaying also have accuracy requirements at
overload currents in excess of the normal rating to ensure accurate
performance of relays during system faults
3.2.4 Knee-point voltage
The knee-point voltage of a current transformer is the magnitude of the
secondary voltage after which the output current ceases to follow linearly the
input current. This means that the one-to-one or proportional relationship
between the input and output is no longer within declared accuracy. In testing,
if a voltage is applied across the secondary terminals the magnetizing current
will increase in proportion to the applied voltage, up until the knee point.
The knee point is defined as the point at which an increase of applied
voltage of 10% results in an increase in magnetizing current of 50%. From the
knee point upwards, the magnetizing current increases abruptly even with
small increments in voltage across the secondary terminals. The knee-point
voltage is less applicable for metering current transformers as their accuracy
is generally much tighter but constrained within a very small bandwidth of the
current transformer rating, typically 1.2 to 1.5 times rated current. However,
the concept of knee point voltage is very pertinent to protection current.
3.2.5 Rating factor
Rating factor is a factor by which the nominal full load current of a CT
can be multiplied to determine its absolute maximum measurable primary
current. Conversely, the minimum primary current a CT can accurately
measure is light load. Most CTs have rating factors for 35 degrees Celsius and
55 degrees Celsius.

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It is important to be mindful of ambient temperatures and resultant rating
factors when CTs are installed inside pad-mounted transformers or poorly
ventilated mechanical rooms. Recently, manufacturers have been moving
towards.
3.3 POTENTIAL TRANSFORMER
Voltage transformers or potential transformers are another type of
instrument transformers used for metering and protection in high-voltage
circuits. They are designed to present negligible load to the supply being
measured and to have a precise voltage ratio to accurately step down high
voltages so that metering and protective relay equipment can be operated at a
lower potential. Typically the secondary of a voltage transformer is rated for
69 V or 120 V at rated primary voltage, to match the input ratings of
protective relays.
The transformer winding high-voltage connection points are typically
labeled as H1, H2 and X1, X2 and sometimes an X3 tap may be present.
Sometimes a second isolated winding (Y1, Y2, Y3) may also be available on
the same voltage transformer. The high side may be connected phase to
ground or phase to phase. The low side is usually phase to ground.
The terminal identifications are often referred to as polarity. This
applies to current transformers as well. At any instant terminals with the same
suffix numerals have the same polarity and phase. Correct identification of
terminals and wiring is essential for proper operation of metering and
protective relays. Some meters operate directly on the secondary service
voltages at or below 600 V. VTs are typically used for higher voltages, or
where isolation is desired between the meter and the measured circuit.

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3.4 RECTIFIER
Converts the ac transformer voltage to dc, reduces the ac ripple
component of the dc and determines the output hold-up time when the input is
interrupted.
3.4.1 Diodes
The diode is a two-terminal device whose function is to pass current in
one direction but not in the other. A conventional diode is formed from the
junction of p-type and n- type silicon. The ideal device has a “brick-wall” V-I
characteristic the practical silicon diode has an exponential characteristic
which approximates to the brick wall, if viewed.
3.4.2Diode Bridge
Figure 3.5 bridge rectifier
A diode bridge is an arrangement of four diodes in a bridge
circuit configuration that provides the same polarity of output for either
polarity of input. When used in its most common application, for conversion
of an alternating current input into direct current a DC output, it is known as
a bridge rectifier. A bridge rectifier provides full-wave rectification from a
two wire AC input, resulting in lower cost and weight as compared to a
rectifier with a 3-wire input from a transformer with a center
tapped secondary winding.
In the diagrams below, when the input connected to the left corner of
the diamond is positive, and the input connected to the right corner

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is negative, current flows from the upper supply terminal to the right along
the red positive path to the output, and returns to the lower supply terminal
via the blue negative path.
Figure 3.6 Positive half conduction
When the input connected to the left corner is negative, and the input
connected to the right corner is positive, current flows from the lower supply
terminal to the right along the red positive path to the output, and returns to
the upper supply terminal via the blue negative path.
Figure 3.7 Negative half conduction
In each case, the upper right output remains positive and lower right
output negative. Since this is true whether the input is AC or DC, this circuit
not only produces a DC output from an AC input, it can also provide what is
sometimes called "reverse polarity protection". That is, it permits normal
functioning of DC-powered equipment when batteries have been installed
backwards, or when the leads wires from a DC power source have been

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reversed, and protects the equipment from potential damage caused by reverse
polarity.
Figure 3.8 Bridge rectifier with load
The function of this capacitor, known as a reservoir capacitor is to
lessen the variation in the rectified AC output voltage waveform from the
bridge. There is still some variation, known as "ripple". One explanation of
'smoothing' is that the capacitor provides a low impedance path to the AC
component of the output, reducing the AC voltage across, and AC current
through, the resistive load. In less technical terms, any drop in the output
voltage and current of the bridge tends to be canceled by loss of charge in the
capacitor. This charge flows out as additional current through the load. Thus
the change of load current and voltage is reduced relative to what would occur
without the capacitor. Increases of voltage correspondingly store excess
charge in the capacitor, thus moderating the change in output voltage /
current.
The simplified circuit shown has a well-deserved reputation for being
dangerous, because, in some applications, the capacitor can retain
a lethal charge after the AC power source is removed. If supplying a
dangerous voltage, a practical circuit should include a reliable way to
discharge the capacitor safely. If the normal load cannot be guaranteed to
perform this function, perhaps because it can be disconnected, the circuit
should include a bleeder resistor connected as close as practical across the

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capacitor. This resistor should consume a current large enough to discharge
the capacitor in a reasonable time, but small enough to minimize unnecessary
power waste.
The capacitor and the load resistance have a typical time constant
τ = RC
Where C and R are the capacitance and load resistance respectively.
As long as the load resistor is large enough so that this time constant is
much longer than the time of one ripple cycle, the above configuration will
produce a smoothed DC voltage across the load.
When the capacitor is connected directly to the bridge, as shown,
current flows in only a small portion of each cycle, which may be undesirable.
The transformer and bridge diodes must be sized to withstand the current
surge that occurs when the power is turned on at the peak of the AC voltage
and the capacitor is fully discharged. Sometimes a small series resistor is
included before the capacitor to limit this current, though in most applications
the power supply transformer's resistance is already sufficient. Adding a
resistor, or better yet, an inductor, between the bridge and capacitor can
ensure that current is drawn over a large portion of each cycle and a large
current surge does not occur.
In older times, this crude power supply was often followed by passive
filters to reduce the ripple further. When an inductor is used this way it is
often called a choke. The choke tends to keep the current more constant.
Although the inductor gives the best performance, usually the resistor is
chosen for cost reasons.
The idealized waveforms shown above are seen for both voltage and
current when the load on the bridge is resistive. When the load includes
a smoothing capacitor, both the voltage and the current waveforms will be

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greatly changed. While the voltage is smoothed, as described above, current
will flow through the bridge only during the time when the input voltage is
greater than the capacitor voltage. For example, if the load draws an average
current of n Amps, and the diodes conduct for 10% of the time, the average
diode current during conduction must be 10n Amps. This non-
sinusoidal current leads to harmonic distortion and a poor power factor in the
AC supply.
Some early console radios created the speaker's constant field with the current
from the high voltage power supply, which was then routed to the consuming
circuits to create the speaker's constant magnetic field. The speaker field coil
thus performed 2 jobs in one: it acted as a choke, filtering the power supply,
and it produced the magnetic field to operate the speaker.
3.4.3 Poly Phase Bridge
The diode bridge can be generalized to rectify poly phase AC inputs.
For example, for a three phase AC input, a half-wave rectifier consists
of three diodes, but a full wave bridge rectifier consists of six diodes.
Figure 3.9 Six diodes bridge rectifier

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RECTIFIED OUTPUT WAVEFORM
Figure 3.10 Three phase AC input waveform (top), half wave rectified waveform
(center), and wave of rectified waveform (bottom)

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3.5 DC-TO-DC CONVERTER
Figure 3.11 Regulator IC
DC to DC converters are important in portable electronic devices such
as cellular phones and laptop computers, which are supplied with power from
batteries primarily. Such electronic devices often contain several sub-circuits,
each with its own voltage level requirement different from that supplied by
the battery or an external supply. Additionally, the battery voltage declines as
its stored power is drained. Switched DC to DC converters offer a method to
increase voltage from a partially lowered battery voltage thereby saving space
instead of using multiple batteries to accomplish the same thing.
Most DC to DC converters also regulate the output. Some exceptions
include high-efficiency LED power sources, which are a kind of DC to DC
converter that regulates the current through the LEDs, and simple charge
pumps which double or triple the input voltage.
3.5.1 CONVERSION METHODS
3.5.1 Linear method
Linear regulators can only output at lower voltages from the input.
They are very inefficient when the voltage drop is large and the current is
high as they dissipate heat equal to the product of the output current and the

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voltage drop; consequently they are not normally used for large-drop high-
current applications.
The inefficiency wastes power and requires higher-rated, and
consequently more expensive and larger, components. The heat dissipated by
high-power supplies is a problem in itself as it must be removed from the
circuitry to prevent unacceptable temperature rises.
Linear regulators are inexpensive, reliable if good heat sinking is
used and much simpler than switching regulators. As part of a power supply
they may require a transformer, which is larger for a given power level than
that required by a switch-mode power supply. Linear regulators can provide a
very low-noise output voltage, and are very suitable for powering noise-
sensitive low-power analog and radio frequency circuits. A popular design
approach is to use a Low Drop-out Regulator that provides a local "point of
load" DC supply to a low power circuit.
3.5.2 Switched-mode conversion
Electronic switch-mode DC to DC converters convert one DC voltage
level to another, by storing the input energy temporarily and then releasing
that energy to the output at a different voltage. The storage may be in either
magnetic field storage components. This conversion method is more power
efficient than linear voltage regulation. This efficiency is beneficial to
increasing the running time of battery operated devices, which incur more
switching losses and require a more complicated drive circuit. Another
important innovation in DC-DC converters is the use of synchronous
rectification replacing the flywheel diode with a power FET with low "On"
resistance, thereby reducing switching losses.

28
Most DC to DC converters are designed to move power in only one
direction, from the input to the output. However, all switching regulator
topologies can be made bi-directional by replacing all diodes with
independently controlled active rectification. A bi-directional converter can
move power in either direction, which is useful in applications requiring
regenerative braking.
Drawbacks of switching converters include complexity, electronic noise
and to some extent cost, although this has come down with advances in chip
design, DC to DC converters are now available as integrated circuits needing
minimal additional components. DC to DC converters are also available as a
complete hybrid circuit component, ready for use within an electronic
assembly.
3.5.3 Magnetic
In these DC to DC converters, energy is periodically stored into and
released from a magnetic field in an inductor or a transformer, typically in the
range from 300 kHz to 10 MHz By adjusting the duty cycle of the charging
voltage, the amount of power transferred can be controlled. Usually, this is
applied to control the output voltage, though it could be applied to control the
input current, the output current, or maintain a constant power. Transformer-
based converters may provide isolation between the input and the output. In
general, the term "DC to DC converter" refers to one of these switching
converters. These circuits are the heart of a switched-mode power supply.
Many topologies exist. This table shows the most common.
 Hard switched - transistors switch quickly while exposed to both full
voltage and full current

29
 Resonant - an LC circuit shapes the voltage across the transistor and
current through it so that the transistor switches when either the voltage
or the current is zero
Magnetic DC to DC converters may be operated in two modes, according to
the current in its main magnetic component
 Continuous - the current fluctuates but never goes down to zero
 Discontinuous - the current fluctuates during the cycle, going down to
zero at or before the end of each cycle
The Half bridge and Fly back topologies are similar in that energy stored
in the magnetic core needs to be dissipated so that the core does not saturate.
Power transmission in a fly back circuit is limited by the amount of energy
that can be stored in the core, while forward circuits are usually limited by the
I/V characteristics of the switches. MOSFET switches can tolerate
simultaneous full current and voltage; bipolar switches generally can't so
require the use of a snubber.
3.5.4 Capacitive
Switched capacitor converters rely on alternately connecting capacitors to
the input and output in differing topologies. For example, a switched-
capacitor reducing converter might charge two capacitors in series and then
discharge them in parallel. This would produce an output voltage of half the
input voltage, but at twice the current. Because they operate on discrete
quantities of charge, these are also sometimes referred to as charge pump
converters. They are typically used in applications requiring relatively small
amounts of current, as at higher current loads the increased efficiency and
smaller size of switch-mode converters makes them a better choice.

30
3.5.5 Electrochemical
A further means of DC to DC conversion in the kilowatt to many
Megawatts range is presented by using redox flow batteries such as the
vanadium redox battery, although this technique has not been applied
commercially to date.
3.5.6 Terminology:
Step-down–A converter where output voltage is lower than the input voltage.
Like a Buck converter.
Step-up–A converter that outputs a voltage higher than the input voltage. Like
a Boost converter.
Continuous Current Mode–Current and thus the magnetic field in the
inductive energy storage never reach zero.
Discontinuous Current Mode–Current and thus the magnetic field in the
inductive energy storage may reach or cross zero.
Noise - Since all properly designed DC to DC converters are completely
inaudible, "noise" in discussing them always refers to unwanted electrical and
electromagnetic signal noise.
Output noise - The output of a DC to DC converter is designed to have a flat,
constant output voltage. Unfortunately, all real DC to DC converters produce
an output that constantly varies up and down from the nominal designed
output voltage. This varying voltage on the output is the output noise. All DC
to DC converters, including linear regulators, have some thermal output noise.
Switching converters have, in addition, switching noise at the switching
frequency and its harmonics. Some sensitive radio frequency and analog
circuits require a power supply with so little noise that it can only be provided
by a linear regulator.

31
Input noise - If the converter loads the input with sharp load edges. Electrical
noise can be emitted from the supplying power lines as RF noise. This should
be prevented with proper filtering in the input stage of the converter.
RF noise - Switching converters inherently emit radio waves at the switching
frequency and its harmonics. Switching converters that produce triangular
switching current, such as the Split-Pi or Ćuk converter in continuous current
mode, produce less harmonic noise than other switching converters. Linear
converters produce practically no RF noise. Too much RF noise causes
electromagnetic interference.
3.6 INVERTOR
An invertor is an electrical device that converts direct current to alternating
current. The converted AC can be at any required voltage and frequency with
the use of appropriate transformer, switching, and control circuit.
Solid-state inverters have no moving parts and are used in a wide range of
applications, from small switching power supplies in computers, to large
electric utility high-voltage direct current applications that transport bulk
power. Inverters are commonly used to supply AC power from DC sources
such as solar panels or batteries.
3.6.1 Types
1. Modified sine wave
The output of a modified sine wave inverter is similar to a square wave
output except that the output goes to zero volts for a time before switching
positive or negative. It is simple and low cost and is compatible with most
electronic devices, except for sensitive or specialized equipment, for example
certain laser printers, fluorescent lighting, and audio equipment.

32
2. Pure sine wave
A pure sine wave inverter produces a nearly perfect sine wave output
that is essentially the same as utility-supplied grid power. Thus it is
compatible with all AC electronic devices. This is the type used in grid-tie
inverters. Its design is more complex, and costs more per unit power. The
electrical inverter is a high-power electronic oscillator. It is so named because
early mechanical AC to DC converters was made to work in reverse, and thus
was "inverted", to convert DC to AC.
3. Uninterruptible power supplies
An uninterruptible power supply (UPS) uses batteries and an inverter to
supply AC power when main power is not available.
3.6.2 Applications
 Induction heating
 Inverters convert low frequency main AC power to higher frequency
for use in induction heating. To do this, AC power is first rectified to
provide DC power. The inverter then changes the DC power to high
frequency AC power.
 HVDC power transmission
 With HVDC power transmission, AC power is rectified and high
 Voltage DC power is transmitted to another location. At the receiving
location, an inverter in an inverter plant converts the power back to AC.
 Variable-frequency drives
 A variable-frequency drive controls the operating speed of an AC
motor by controlling the frequency and voltage of the power supplied
to the motor. An inverter provides the controlled power.

33
3.7 PULSE WIDTH MODULATION
Pulse-width modulation or pulse duration modulation is a commonly
used technique for controlling power to inertial electrical devices, made
practical by modern electronic power switches. The switch is ON compared
to the OFF periods, the higher the power supplied to the load is the average
value of voltage and current fed to the load is controlled by turning the switch
between supply and load ON and OFF at a fast pace.
The term duty cycle describes the proportion of 'on' time to the regular
interval or 'period' of time; a low duty cycle corresponds to low power,
because the power is off for most of the time. Duty cycle is expressed in
percent, 100% being fully on. The main advantage of PWM is that power loss
in the switching devices is very low.
When a switch is off there is practically no current, and when it is on,
there is almost no voltage drop across the switch. Power loss, being the
product of voltage and current, is thus in both cases close to zero. PWM also
works well with digital controls, which, because of their on/off nature, can
easily set the needed duty cycle.
3.7.1 Working Principle
Pulse width modulation uses a rectangular pulse we whose pulse width
is modulated resulting in the variation of the average value of the waveform.
If we consider a pulse waveform f(t) with a low value ymin, a high value ymax
and a duty cycle D, the average value of the waveform is given by:

34
Figure 3.12 Rectangular square pulses
3.7.2 Generate PWM Pulse
Figure 3.13 PWM pulse signal
The signal here the red sine wave is compared with a saw tooth waveform
blue. When the latter is less than the former, the PWM signal magenta is in

35
high state 1. Otherwise it is in the low state 0.The simplest way to generate a
PWM signal is the introspective method, which requires only a saw tooth or a
triangle waveform easily generated using a simple oscillator and a
comparator. When the value of the reference signal the red sine wave in is
more than the modulation waveform blue, the PWM signal magenta is in the
high state, otherwise it is in the low state.
3.7.3 Delta Modulation
In the use of delta modulation for PWM control, the output signal is
integrated, and the result is compared with limits, which correspond to a
reference signal offset by a constant. Every time the integral of the output
signal reaches one of the limits, the PWM signal changes state.
Figure 3.14 Delta modulation waveform
The Principle of the delta PWM output signal is compared with the
limits. These limits correspond to the reference signal offset by a given value.
Every time the output signal reaches one of the limits, the PWM signal
changes state.

36
3.7.4 Direct Torque Control
Direct torque control is a method used to control AC motors. It is
closely related with the delta modulation. Motor torque and magnetic flux are
estimated and these are controlled to stay within their hysteresis bands by
turning on new combination of the device's semiconductor switches each time
either of the signal tries to deviate out of the band.
3.7.5 Types of Pulse-Width Modulation
1. The pulse center may be fixed in the center of the time window and
both edges of the pulse moved to compress or expand the width.
2. The lead edge can be held at the lead edge of the window and the tail
edge modulated.
3. The tail edge can be fixed and the lead edge modulated.
Figure 3.15 Pulse-Width Modulations

37
3.8 ATMEGA 8 MICROCONTROLLER
3.8.1 Features
High-performance, Low-power AVR 8-bit Microcontroller
-Advanced RISC Architecture
–130 Powerful Instructions
– Most Single-clock Cycle Execution
– 32 x 8 General Purpose Working Registers
– Fully Static Operation
– Up to 16 MIPS Throughput at 16 MHz
– On-chip 2-cycle Multiplier
High Endurance Non-volatile Memory segments
– 8K Bytes of In-System Self-programmable Flash program memory
– 512 Bytes EEPROM
– 1K Byte Internal SRAM
– Write/Erase Cycles: 10,000 Flash/100,000 EEPROM
– Data retention: 20 years at 85°C/100 years at 25°C
– Optional Boot Code Section with Independent Lock Bits
In-System Programming by On-chip Boot Program
– Programming Lock for Software Security
3.8.2 Peripheral Features
– Two 8-bit Timer/Counters with Separate Presale, one Compare Mode
– One 16-bit Timer/Counter
– Real Time Counter with Separate Oscillator
– Three PWM Channels
– 8-channel ADC in TQFP and QFN/MLF package Eight Channels 10-bit
Accuracy
– 6-channel ADC in PDIP package
Six Channels 10-bit Accuracy

38
– Byte-oriented Two-wire Serial Interface
– Programmable Serial USART
– Master/Slave SPI Serial Interface
– Programmable Watchdog Timer with Separate On-chip Oscillator
– On-chip Analog Comparator
3.8.3 Special Microcontroller Features
– Power-on Reset and Programmable Brown-out Detection
– Internal Calibrated RC Oscillator
– External and Internal Interrupt Sources
– Five Sleep Modes: Idle, ADC Noise Reduction, Power-save, Power-
down, an Standby I/O and Packages
– 23 Programmable I/O Lines
Operating Voltages
– 2.7 - 5.5V (ATmega8L)
– 4.5 - 5.5V (ATmega8)
Speed Grades
– 0 - 8 MHz (ATmega8L)
– 0 - 16 MHz (ATmega8)
Power Consumption at 4 MHz, 3V, 25°C
– Active: 3.6 mA
– Idle Mode: 1.0 mA
– Power-down Mode: 0.5
3.8.4 Overview
The ATmega8 is a low-power CMOS 8-bit microcontroller based
on the AVR RISC architecture. By executing powerful instructions in a single
clock cycle, the ATmega8 achieves throughputs approaching 1 MIPS per
MHz, allowing the system designed to optimize power consumption versus
processing speed.

39
The resulting architecture is more code efficient while achieving
throughputs up to ten times faster than conventional CISC microcontrollers.
The device is manufactured using Atmel’s high density non-volatile memory
technology. The Flash Program memory can be reprogrammed In-System
through an SPI serial interface, by a conventional non-volatile memory
programmer, or by an On-chip boot program running on the AVR core. The
boot program can use any interface to download the application program in
the Application Flash memory. Software in the Boot Flash Section will
continue to run while the Application Flash Section is updated, providing true
Read While Write operation.
3.8.5 Pin Configurations
Figure 3.16 Pin details

40
3.8.6 Pin Descriptions
VCC: 5v dc supply voltage.
GND: Ground.
Port B: is an 8-bit bi-directional I/O port with internal pull-up
XTAL1/XTAL2/TOSC1/ Port B output buffers have symmetrical drive
Oscillator amplifier. If the Internal Calibrated RC Oscillator is used as chip
clock
input for the Asynchronous Timer/Counter2 if the AS2 bit in The various
special
features of Port B are elaborated in “Al 58 and “System Clock and Clock
Options”
Port C (PC5-PC0): Port C is an7-bit bi-directional I/O port with internal pull-
up
Port C output buffers have symmetrical drive character is capability. As
inputs, Port C pins that are externally pulled resistors are activated. The Port
C pins are tri-stated when even if the clock is not running. PC6/RESET If the
RSTDISBL
Port If the RSTDISBL Fuse is un programmed, generate a Reset. The various
Special features of Port C are elaborated on Port D .
Port D (PD7-PD0): is an 8-bit bidirectional I/O port with internal pull-up
Port D output buffers has symmetrical drive characters capability. As inputs,
Port
3.8.7 General Purpose
The Register File is optimized for the AVR Enhanced RISC instruction
set. In order to achieve Register File the required performance and flexibility,
the following input/output schemes are supported by the file.
Register File

41
One 8-bit output operand and one 8-bit result input.
Two 8-bit output operands and one 8-bit result input.
Two 8-bit output operands and one 16-bit result input.
One 16-bit output operand and one 16-bit result input.
3.9 ANALOG-TO-DIGITAL CONVERTER
An analog-to-digital converter is a device that converts a continuous
quantity to a discrete time digital representation. An ADC may also provide
an isolated measurement. The reverse operation is performed by a converter.
Typically, an ADC is an electronic device that converts an input analog
voltage or current to a digital number proportional to the magnitude of the
voltage or current. However, some non-electronic or only partially electronic
devices, such as rotary encoders, can also be considered ADCs.
3.9.1 8-level ADC
The resolution of the converter indicates the number of discrete
values it can produce over the range of analog values. The values are usually
stored electronically in binary form, so the resolution is usually expressed in
bits. In consequence, the number of discrete values available, or "levels", is a
power of two. For example, an ADC with a resolution of 8 bits can encode an
analog input to one in 256 different levels, since 28
= 256. The values can
represent the ranges from 0 to 255.

42
Resolution can also be defined electrically, and expressed in volts.
The minimum change in voltage required to guarantee a change in the output
code level is called the least significant bit voltage. The resolution Q of the
ADC is equal to the LSB voltage. The voltage resolution of an ADC is equal
to its overall voltage measurement range divided by the number of discrete
voltage intervals:
Where, N is the number of voltage intervals and EFSR is the full scale
voltage range. EFSR is given by
Where VRefHi and VRefLow are the upper and lower extremes,
respectively, of the voltages that can be coded.
Normally, the number of voltage intervals is given by
Where, M is the ADC's resolution in bits.
3.9.2 Response type
Most ADCs are linear types. The term linear implies that the range of
input values has a linear relationship with the output value. Some early
converters had a logarithmic response to directly implement A-law or µ-law
coding. These encodings are now achieved by using a higher-resolution linear
ADC and mapping its output to the 8-bit coded values.

43
1. Accuracy
An ADC has several sources of errors. Quantization error and non-
linearity are intrinsic to any analog-to-digital conversion. There is also a so-
called aperture error which is due to a clock jitter and is revealed when
digitizing a time-variant signal. These errors are measured in a unit called the
least significant bit. In the above example of an eight-bit ADC, an error of
one LSB is 1/256 of the full signal range, or about 0.4%.
2. Quantization error
Quantization error is the difference between the original signal and the
digitized signal. Hence, the magnitude of the quantization error at the
sampling instant is between zero and half of one LSB. Quantization error is
due to the finite resolution of the digital representation of the signal, and is an
unavoidable imperfection in all types of ADCs.
3. Non-linearity
All ADCs suffer from non-linearity errors caused by their physical
imperfections, causing their output to deviate from a linear function of their
input. These errors can sometimes be mitigated by calibration, or prevented
by testing. Important parameters for linearity are integral non-linearity and
differential non-linearity. These nonlinearities reduce the dynamic range of
the signals that can be digitized by the ADC, also reducing the effective
resolution of the ADC.
4. Sampling rate
The analog signal is continuous in time and it is necessary to convert
this to a flow of digital values. It is therefore required to define the rate at

44
which new digital values are sampled from the analog signal. The rate of new
values is called the sampling rate or sampling frequency of the converter.
A continuously varying band limited signal can be sampled and then the
original signal can be exactly reproduced from the discrete-time values by an
interpolation formula. The accuracy is limited by quantization error.
However, this faithful reproduction is only possible if the sampling rate is
higher than twice the highest frequency of the signal. This is essentially what
is embodied in the Shannon-Nyquist sampling theorem.
5. Aliasing
All ADCs work by sampling their input at discrete intervals of time.
Their output is therefore an incomplete picture of the behavior of the input.
There is no way of knowing, by looking at the output, what the input was
doing between one sampling instant and the next. If the input is known to be
changing slowly compared to the sampling rate, then it can be assumed that
the value of the signal between two sample instants was somewhere between
the two sampled values. If, however, the input signal is changing rapidly
compared to the sample rate, then this assumption is not valid.
If the digital values produced by the ADC are, at some later stage in the
system, converted back to analog values by a digital to analog converter or
DAC, it is desirable that the output of the DAC be a faithful representation of
the original signal. If the input signal is changing much faster than the sample
rate, then this will not be the case, and spurious signals called aliases will be
produced at the output of the DAC. The frequency of the aliased signal is the
difference between the signal frequency and the sampling rate. For example, a
2 kHz sine wave being sampled at 1.5 kHz would be reconstructed as a
500 Hz sine wave. This problem is called aliasing.

45
6. Dither
In A-to-D converters, performance can usually be improved using
dither. This is a very small amount of random noise, which is added to the
input before conversion. Its effect is to cause the state of the LSB to randomly
oscillate between 0 and 1 in the presence of very low levels of input, rather
than sticking at a fixed value. Rather than the signal simply getting cut off
altogether at this low level, it extends the effective range of signals that the A-
to-D converter can convert at the expense of a slight increase in noise
effectively the quantization error is diffused across a series of noise values
which is far less objectionable than a hard cutoff. The result is an accurate
representation of the signal over time. A suitable filter at the output of the
system can thus recover this small signal variation.
7. Oversampling
Usually, signals are sampled at the minimum rate required, for
economy, with the result that the quantization noise introduced is white noise
spread over the whole pass band of the converter. If a signal is sampled at a
rate much higher than the Nyquist frequency and then digitally filtered to
limit it to the signal bandwidth and effective resolution larger than that
provided by the converter alone to improvement in SNR is 3 dB per octave of
oversampling which is not sufficient for many applications. Therefore,
oversampling is usually coupled with noise shaping. With noise shaping, the
improvement is 6L+3 dB per octave where L is the order of loop filter used
for noise shaping.

46
3.9.3 ADC types
These are the most common ways of implementing an electronic ADC.
A direct-conversion ADC or flash ADC has a bank of comparators sampling
the input signal in parallel, each firing for their decoded voltage range. The
comparator bank feeds a logic circuit that generates a code for each voltage
range. Direct conversion is very fast, capable of gigahertz sampling rates, but
usually has only 8 bits of resolution or fewer, since the number of
comparators needed, 2N
- 1, doubles with each additional bit, requiring a
large, expensive circuit. ADCs of this type have a large die size, a high input
capacitance, high power dissipation, and are prone to produce glitches at the
output. Scaling to newer submicron meters technologies does not help as the
device mismatch is the dominant design limitation. They are often used for
video, wideband communications or other fast signals in optical storage.
1. Successive-Approximation DC
Uses a comparator to reject ranges of voltages, eventually settling on a
final voltage range. Successive approximation works by constantly comparing
the input voltage to the output of an internal digital to analog converter until
the best approximation is achieved. At each step in this process, a binary
value of the approximation is stored in a successive approximation register.
The SAR uses a reference voltage for comparisons. For example if the input
voltage is 60 V and the reference voltage is 100 V, in the 1st clock cycle, 60
V is compared to 50 V, and the voltage from the comparator is positive. At
this point the first binary digit is set to a '1'. In the 2nd clock cycle the input
voltage is compared to 75 V because 60 V is less than 75 V, the comparator
output is now negative. The second binary digit is therefore set to a '0'. In the
3rd clock cycle, the input voltage is compared with 62.5 V. The output of the

47
comparator is negative or '0' so the third binary digit is set to a 0. The fourth
clock cycle similarly results in the fourth digit being a '1'. The result of this
would be in the binary form 1001. This is also called bit-weighting
conversion, and is similar to a binary search. The analogue value is rounded
to the nearest binary value below, meaning this converter type is mid-rise.
Because the approximations are successive, the conversion takes one clock-
cycle for each bit of resolution desired. The clock frequency must be equal to
the sampling frequency multiplied by the number of bits of resolution desired.
2. Ramp Type ADC
Produces a saw-tooth signal that ramps up or down then quickly returns
to zero. When the ramp starts, a timer starts counting. When the ramp voltage
matches the input, a comparator fires, and the timer's value is recorded. Timed
ramp converters require the least number of transistors. The ramp time is
sensitive to temperature because the circuit generating the ramp is often just
some simple oscillator. There are two solutions: use a clocked counter driving
a DAC and then use the comparator to preserve the counter's value, or
calibrate the timed ramp. A special advantage of the ramp-compare system is
that comparing a second signal just requires another comparator, and another
register to store the voltage value.
4. Integrating ADC
Applies the unknown input voltage to the input of an integrator and allows
the voltage to ramp for a fixed time period. Then a known reference voltage
of opposite polarity is applied to the integrator and is allowed to ramp until
the integrator output returns to zero. The input voltage is computed as a
function of the reference voltage, the constant run-up time period, and the
measured run-down time period.

48
3.9.4 Pipeline ADC
Uses two or more steps of sub ranging. First, a coarse conversion is done
Analog to digital converter. This difference is then converted finer,
and the results are combined in a last step. This can be considered a
refinement of the successive-approximation ADC wherein the feedback
reference signal consists of the interim conversion of a whole range of bits
rather than just the next-most-significant bit.
3.10 LIQUID CRYSTAL DISPLAYS
Figure 3.17 LCD Display
3.10.1 General
Craft data BC1602A
An LCD is a small low cost display. It is easy to interface with a micro-
controller Because of an embedded controller.
This controller is standard across many displays (HD 44780) which means
many Micro-controllers have libraries that make displaying
3.10.2 Testing
Testing your LCD with an Adriano is really simple. Wire up your
display using the schematic or breadboard layout sheet.

49
CHAPTER 4
IMPLEMENTION OF PROPOSED PROJECT
4.1 Schematic Circuit Diagram
Figure 4.1 Circuit diagram

50
4.1.1 Power Supply
A transformer is a static device that transfers electrical energy from one
circuit to another through inductively coupled conductors the transformer's
coils. A varying current in the first or primary winding creates a varying
magnetic flux in the transformer's core and thus a varying magnetic field
through the secondary winding. This varying magnetic field induces a varying
electromotive force (EMF) or "voltage" in the secondary winding. This effect
is called mutual induction.
If a load is connected to the secondary, an electric current will flow in
the secondary winding and electrical energy will be transferred from the
primary circuit through the transformer to the load. In an ideal transformer,
the induced voltage in the secondary winding (Vs) is in proportion to the
primary voltage (Vp), and is given by the ratio of the number of turns in the
secondary (Ns) to the number of turns in the primary (Np) as follows:
Primary coil changes the magnetic flux that is developed.
The changing magnetic flux induces a voltage in the secondary coil by
appropriate selection of the ratio of turns, a transformer thus allows an
alternating current (AC) voltage to be "stepped up" by making Ns greater than
Np, or "stepped down" by making Ns less than Np.
In the vast majority of transformers, the windings are coils wound around a
ferromagnetic core, air-core transformers being a notable exception.
Transformers range in size from a thumbnail-sized coupling
transformer hidden inside a stage microphone to huge units weighing
hundreds of tons used to interconnect portions of power grids. All operate

51
with the same basic principles, although the range of designs is wide. While
new technologies have eliminated the need for transformers in some
electronic circuits, transformers are still found in nearly all electronic devices
designed for household voltage. Transformers are essential for high-voltage
electric power transmission, which makes long-distance transmission
economically practical.
The transformer is based on two principles: first, that an electric current
can produce a magnetic field, second that a changing magnetic field within a
coil of wire induces a voltage across the ends of the coil.
Figure 4.2 step down transformer coil
An ideal transformer is shown in the adjacent figure. Current passing
through the primary coil creates a magnetic field. The primary and secondary
coils are wrapped around a core of very high magnetic permeability, such as
iron, so that most of the magnetic flux passes through both the primary and
secondary coils.

52
4.1.2 Diodes
The diode is a two-terminal device whose function is to pass current in
one direction but not in the other. A conventional diode is formed from the
junction of p-type and n- type silicon. The ideal device has a “brick-wall” V-I
characteristic: the practical silicon diode has an exponential characteristic
which approximates to the brick wall, if viewed
Forward bias:
The first thing to notice is that the forward voltage V is not constant,
nor is it zero. It has two determinants, forward current I and temperature T.
They are related by the
I = I [exp (V · q/kT) - 1]
Reverse bias:
So far we have only considered the forward characteristic that is for
positive applied voltage. An ideal diode would block all current flow in the
reverse direction. There are two main reverse characteristics, reverse leakage
current I and reverse breakdown voltage VBR. The diode equation holds good
in the reverse direction until VBR is approached; in the low-voltage region IR
is almost equal to IS.
Breakdown VBR is that voltage at which the reverse-biased junction
can no longer withstand the applied electric field. At this point, avalanche
breakdown occurs and a current limited mainly by the external source
impedance will flow. If the device maximum power dissipation is exceeded
the junction will be destroyed. Diodes operated conventionally, as opposed to
Zener diodes to which we will return shortly, are always run at reverse
voltages lower than VBR.

53
Positive Voltage Regulator:
A monolithic regulator IC includes the voltage reference on-chip, along
with other circuitry and the series pass element. This means that the reference
is subject to a thermal shift when the power dissipation of the series pass
element changes. This gives rise to a separate longer term component of
regulation, called thermal regulation, defined as the change in output voltage
caused by a change in dissipated power for a specified time. Provided the chip
has been well-designed, thermal regulation is not a significant factor for most
purposes, but it is rarely specified in data sheets and for some precision
applications may render monolithic regulators unsuitable.
4.1.3 Rectifier
In the diagrams below, when the input connected to the left corner of
the diamond is positive, and the input connected to the right corner
is negative, current flows from the upper supply terminal to the right along
the red positive path to the output, and returns to the lower supply terminal
via the blue negative path.
When the input connected to the left corner is negative, and the input
connected to the right corner is positive, current flows from the lower supply
terminal to the right along the red positive path to the output, and returns to
the upper supply terminal via the blue negative path.
In each case, the upper right output remains positive and lower right
output negative. Since this is true whether the input is AC or DC, this circuit
not only produces a DC output from an AC input, it can also provide what is
sometimes called "reverse polarity protection". That is, it permits normal
functioning of DC-powered equipment when batteries have been installed
backwards.

54
4.1.4 Boost circuit
Electronic switch-mode DC to DC converters convert one DC voltage
level to another, by storing the input energy temporarily and then releasing
that energy to the output at a different voltage. The storage may be in either
magnetic field storage components. This conversion method is more power
efficient than linear voltage regulation. This efficiency is beneficial to
increasing the running time of battery operated devices.
4.1.5 ADC
An analog-to-digital converter is a device that converts a continuous
quantity to a discrete time digital representation. An ADC may also provide
an isolated measurement. The reverse operation is performed by a digital-to-
analog converter. Typically, an ADC is an electronic device that converts an
input analog voltage or current to a digital number proportional to the
magnitude of the voltage or current. However, some non-electronic or only
partially electronic devices, such as rotary encoders, can also be considered
ADCs. The digital output may use different coding schemes. Typically the
digital output will be a two's complement binary number that is proportional
to the input, but there are other possibilities. An encoder, for example, might
output a Gray code.
4.1.6 Pulse width modulation
Pulse width modulation uses a rectangular pulse we whose pulse width
is modulated resulting in the variation of the average value of the waveform.
If we consider a pulse waveform f(t) with a low value ymin, a high value ymax
and a duty cycle D

55
Figure 4.3 PWM signal
4.1.7 Three Phase Inverter
The BLDC motor control consists of generating DC currents in the
motor phases. This control is subdivided into two independent operations:
stator and rotor flux synchronization and control of the current value. Both
operations are realized through the three phase inverter depicted in the
following scheme.
Figure 4.4 Three Phase Inverter

56
The flux synchronization is derived from the position information coming
from sensors, or from sensor less techniques. From the position, the controller
determines the appropriate pair of transistors which must be driven. The
regulation of the current to a fixed 60 degrees reference can be realized in
either of the two different modes:
4.1.8 BLDC Motor
Brushless D.C. motors operate in conjunction with an electronic
controller and a rotor position feedback sensor. Based upon the actual rotor
position, the controller sequentially energizes or switches “on” the stator’s
phase windings so that torque is continuously generated as the permanent
magnet (PM) rotor rotates. This switching action is called electronic
commutation. To sense the rotor’s angular position, position sensors are used.
When the PM rotor passes one set of phase windings, a signal from the
position sensor is sent to the controller which then sends a signal to switch
“on” the next set of phase windings so that the magnetic fields of the rotor
and the stator’s phase windings remain synchronized.
The torque/speed characteristic of the motor is determined by the
magnitude of the signal and the switching rate of the controller. For example,
in a 2-phase motor, when the phase 1 winding is energized, the PM rotor will
rotate to align itself with magnetic field produced by the phase 1 winding.
When the phase 1 winding is turned “off”, the phase 2 winding is turned “on”
and the rotor will continue to rotate to align itself with the magnetic field of
the phase 2 winding. This “on” and “off” switching of the phase windings
will maintain torque of the PM rotor.

57
CHAPTER 5
SIMULATION IMPLEMENTATION
5.1 SIMULATION CIRCUIT DIAGRAM
Figure 5.1 simulation circuit diagram

58
5.2 SIMULATION OUTPUT SPEED WAVEFORM
Figure 5.2 speed waveform
5.3 TORQUE WAVEFORM
Figure 5.3 torque waveform

59
5.4 PULSE WITH MODULATION SIMULATION OUTPUT WAVEFORM
Figure 5.4 PWM waveform

60
5.5 POWER FACTOR SIMULATION OUTPUT
Figure 5.5 power factor waveform
5.6 STATOR CURRENT SHAPING SIMULATION
Figure 5.6 Stator current waveform

61
CHAPTER 6
CONCLUSION
Power Factor correction of a 3-phase Four Switch Inverter fed
BLDC Motor with PI control is analyzed. Design of Boost Converter, 3-
phase Four Switch Inverter, programing processor, LCD display, hall sensor
feedback control, and PMBLDC Motor etc. are done. Hardware for the
topology with machine design is implemented.
Power Factor Correction using Boost Converter reduces the line
harmonics
and hence, the line current becomes sinusoidal in shape and will be in same
phase with the voltage.
The efficiency of the utility system will be high so that the total working
of the system get better motor control. 3-Phase 4-Switch technology has been
used number of switches, switching losses; cost, complexity etc. can be
reduced.
THD is reduced to 3% in simulation and achieve the same in hardware.
The cost off the drive is reduced from Rs- 2800 to less than Rs- 1000.

62
REFERENCES
1. Atef, S.O. and Al-Mashakbeh, 2009. “Proportional Integral and derivative
control of brushless DC motor”.Eur. J. Sci. Res., 35(2): 198-203c.
2. A. Monti, D. Patterson, E. Santi, F. Ponci, J. Bastos, D. Franzoni, W.
Jiang, D. Kovuri, S. Krooswyk, S. Lentijo, D. Li, T. Lovett, B. Lu, L.
Lu, J. Mcclanahan, K. Patel, A. Smith, K. Veturi, X. Wu, "An
innovative low-cost drive for permanent magnet motors: a Future
Energy Challenge experience," Proc. IEEE Applied Power Electronics
Conference (APEC'04), pp. 1137-1142, 2004
3. Krishnan, R., 2003. “A Text Book on Electric Motor Drives, Modelling,
Analysis and Control”. Prentice Hall of India Pvt Ltd., New Delhi.
4. Byoung-Kuk, L., K. Tae-Hyung and J. Mehrdad Ehsani, 2001. “On the
feasibility of four-switch three phase BLDC motor drives for low cost
commercial applications topology and control”. IEEE Tran. Power Electron.
APEC, 18(1): 428-433.
5. R. W. Erickson, D. Maksimovic, “Fundamentals of Power
Electronics,” Kluwer Academic Publishers, Second Edition, 2001
6. F. Blaabjerg, D. O. Neacsu and J. K. Pedersen, “Adaptive SVM to
Compensate Dc-Link Voltage Ripple for Four-Switch, Three-Phase Voltage
Source Inverter”, IEEE Trans. on Power Electronics, Vol. 14, No. 4, July
1999, pp.743-751.

63
7. G. Spiazzi, “Analysis of Buck converters used as power factor
preregulators,” Power Electronics Specialists Conference, vol.1, pp.
564 – 570, 1997
8. K.M. Smedley, S. Cuk, “One-cycle control of switching converters,”
IEEE Transactions on Power Electronics, Volume 10, Issue 6, Nov.
1995 pp. 625 – 633
9. W. Tang, F.C. Lee, R.B. Ridley, I. Cohen, “Charge control: modeling,
analysis, and design,” IEEE Transactions on Power Electronics,
Volume 8, Issue 4, Oct. 1993 pp. 396 – 403
10 . J. Skinner, T.A. Lipo, “Input current shaping in brushless DC motor
drives utilizing inverter current control,” Fifth International
Conference on Electrical Machines and Drives, 1991, 11-13 Sep 1991
pp. 121 – 125

POWER FACTOR CORRECTION OF A 3-PHASE 4- SWITCH INVERTER FED BLDC MOTOR

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