CHAPTER 1INTRODUCTION
1.1. INTRODUCTION
The buck, boost, buckboost, and Cuk converters are the four
basic dcdc nonisolating converters that have found wide
applications in industry. The buck converter can step down the dc
voltage, whereas the boost converter is capable to perform a
step-up function. In applications where both step-up and step-down
conversion ratios are required, the buckboost and Cuk converters
can be used. Simplicity and robustness are among the advantages of
the buckboost converter. However, the pulsating input and output
currents cause high conduction losses, and thus, impair the
efficiency of buckboost. Furthermore, the buckboost converter uses
the inductor to store the energy from the input source, and then,
release the stored energy to the output. For this reason, the
magnetic components of buckboost are subjected to a significant
stress. These disadvantages limit the applications of the buckboost
converter mainly to low power level. The isolated version of
buckboost, referred to as the flyback converter, can achieve
greater step-up or step-down conversion ratio utilizing a
transformer, possibly, with multiple outputs. As compared with the
buckboost converter, the Cuk converter has higher efficiency and
smaller ripples in input and output currents. A significant
improvement of the Cuk converter performance can be achieved by
applying the zero ripple concept. The Cuk converter can be found in
many high-performance power applications. In theory buck and boost
converters can generate almost any voltage, in practice, the output
voltage range is limited by component stresses that increase at the
extreme duty cycle. Consequently, buck converter losses mount at
low duty cycle, whereas boost converter efficiency deteriorates
when the duty cycle tends to unity. Accordingly, voltage conversion
range of the buck converter below 0.10.15 becomes impractical
whereas that of the boost converters is limited to below 810.
Additional problems associated with narrow duty cycle are caused by
MOSFET drivers rise and fall times as well as pulsewidth-modulated
(PWM) controllers that have maximum pulsewidth limitations. These
problems become even more severe at higher voltages and higher
frequencies. Introducing a transformer helps attaining large
step-up or step-down voltage conversion ratio. Transformers turn
ratio should be chosen as to provide the desired voltage gain while
keeping the duty cycle within a reasonable range for higher
efficiency. The transformer, however, brings in a whole new set of
problems associated with the magnetizing and leakage inductances,
which cause voltage spikes and ringing, increased core and copper
losses as well as increased volume and cost. Single-transistor
converter topologies, with quadratic conversion ratios, were
proposed and demonstrated large step-down conversion ratio. This
method has successfully achieved wide conversion range in the step
done direction. A different approach to obtain wide conversion
range utilizing coupled inductors was proposed. With only minor
modification of the tapped-inductor buck, shows low component count
and solves the gate-drive problem by exchanging the position of the
second winding and the top switch. The problem of a high turn-off
voltage spike on the top switch was solved by applying a lossless
clamp circuit. Due to the coupled inductor action, the converter
demonstrated high step-down dcdc conversion ratio, whereas the
converters efficiency was improved by the extended duty cycle. A
tapped-inductor buck with soft switching was introduced in. Another
modification of the tapped-buck converter was realized in for power
factor correction (PFC) application. With the addition of a
line-frequency-commutated switch and a diode, both flyback and buck
characteristics were achieved and large step-down was demonstrated.
Some applications, especially battery-operated equipment, require
high voltage boosting. To attain very large voltage step-up,
cascaded boost converters that implement the output voltage
increasing in geometric progression were introduced. These
converters effectively enhance the voltage transfer ratio, however,
their circuits are quite complex. In comparison, tapped-inductor
boost converters proposed and attain a comparable voltage step-up
preserving relative circuit simplicity. The boost converter output
terminal and flyback converter output terminal are connected in
series to increase the output voltage gain with the coupled
inductor. The boost converter also functions as an active clamp
circuit to recycle the snubber energy.This project proposes a new
wide-inputwide-output (WIWO) dcdc converter. The new converter is
an integration of buck and boost converters via a tapped inductor.
By applying proper control to the two active switches, the
converter exhibits both buck and boost features.The high step-up
dc-dc converters for these applications have the following common
features.1) High Step-up voltage gain. Generally, about a tenfold
step-up gain is required.2) High efficiency.3) No isolation is
required.
CHAPTER 2LITERATURE SURVEY2.1 Switching converter with wide dc
conversion range by D. Maksimovic and S. Cuk, Vol. 6, No.1, Jan.
1991.In dc-to-dc conversion applications that require a large range
of input and/or output voltages, conventional PWM converter
topologies must operate at extremely low duty ratios, which limits
the operation to lower switching frequencies because of the minimum
ON time of the transistor switch. This is eliminated in a new class
of single transistor PWM converters featuring voltage conversion
ratios with quadratic dependence on duty ratio. Practical circuit
examples operating at 0.5 MHz are described.
2.2 A Family of Buck-Type DC-DC Converters with Autotransformers
by Kaiwei Yao, Yuancheng Ren, Jia Wei, Ming Xu and Fred C. Lee,
Vol. 18, No. 1, Jan. 2003.It consists of a family of buck-type
DC-DC converters with autotransformers, including forward,
push-pull, half-bridge, and full-bridge topologies. Compared with
an isolated transformer, the autotransformer has a simpler winding
structure, and it only needs to transfer part of the input power,
resulting in a smaller secondary winding current. Analysis shows
that the autotransformer can also help to reduce the voltage stress
and current ratings of power devices in the DC-DC converters. For
some applications, a simple lossless passive clampCircuit can be
implemented to solve the transformer leakage problems, and the gate
drive is significantly improved with a simple self-adaptive
dead-time-controlled bootstrap gate driver. Simulation and
experimental results show that the proposed topologies are very
suitable for high-frequency applications.
2.3 High-Efficiency, High Step-Up DCDC Converters, Qun Zhao and
Fred C. Lee, Vol. 18, No. 1, Jan. 2003.Many applications call for
high step-up dcdc converters that do not require isolation. Some
dcdc converters can provide high step-up voltage gain, but with the
penalty of either an extreme duty ratio or a large amount of
circulating energy. DCDC converters with coupled inductors can
provide high voltage gain, but their efficiency is degraded by the
losses associated with leakage inductors. Converters with active
clamps recycle the leakage energy at the price of increasing
topology complexity. A family of high-efficiency, high step-up dcdc
converters with simple topologies is proposed in this paper. The
proposed converters, which use diodes and coupled windings instead
of active switches to realize functions similar to those of active
clamps, perform better than their active-clamp counterparts. High
efficiency is achieved because the leakage energy is recycled and
the output rectifier reverse-recovery problem is alleviated.
2.4 Tapped-Inductor Buck Converter for High-Step-Down DCDC
Conversion, Kaiwei Yao, Mao Ye, Member, Ming Xu and Fred C. Lee,
Vol. 20, No. 4, July 2005.The narrow duty cycle in the buck
converter limits its application for high-step-down dcdc
conversion. With a simple structure, the tapped-inductor buck
converter shows promise for extending the duty cycle. However, the
leakage inductance causes a huge turn-off voltage spike across the
top switch. Also, the gate drive for the top switch is not simple
due to its floating source connection. This paper solves all these
problems by modifying the tapped-inductor structure. A simple
lossless clamp circuit can effectively clamp the switch turn-off
voltage spike and totally recover the leakage energy.
2.5 A Novel Tapped-Inductor Buck Converter for Divided Power
Distribution System, K. Nishijima, K. Abe, D. Ishida, T. Nakano, T.
Nabeshima T. Sato and K. Harada, June 2006.A novel tapped-inductor
converter which has similar characteristics to a typical buck
converter is proposed. A high step-down conversion ratio is
achieved, and the magnetic core size of the tapped-inductor is
minimized. The high side switch is easily driven by a usual driver
IC without a pulse transformer. The over voltage load protection is
inherently realized without any additional components. Furthermore
a divided power distribution system with the
proposedTapped-inductor converter is discussed for supplying the
power to the digital applications.
CHAPTER 3DC-DC CONVERTERS
3.1 INTRODUCTIONA dc converter can be considered as dc
equivalent to an ac transformer with a continuously variable turns
ratio. Like a transformer it is used to step down or step up a dc
voltage source. There are various dc-dc converters such as buck,
boost, buck-boost and cuk converters. The basic buck and boost
converters can be transformed into a number of new topologies by
bringing in the tapped inductor.3.2 BUCK CONVERTERThe buck
converter is widely adopted for step-down dc-dc conversion when
there is no isolation requirement. For output levels with high
currents and low voltages, a synchronous MOSFET can replace the
freewheeling diode in order to reduce the conduction loss. Fig.3.1
shows a synchronous buck converter. A simple bootstrap gate driver
can drive both the top and bottom switches (Q1 and Q2). Because of
its simple structure and very low cost, the buck converter
dominates the power supply market in the telecom and data com
fields.For a dc-dc converter, is defined as the voltage gain, as
follows: *High-step-down conversion means a very small value
for.*The duty cycle of the buck converter in continuous-current
mode (CCM) which is completely determined by the voltage gain.*For
high-step-down dc-dc conversion, the duty cycle becomes very small.
Consequently, the regulation period is very short, which is much
worse in high-frequency applications.
Fig.3.1 Synchronous buck converter
Thus the buck-derived converters with tapped inductors is shown
in the fig.3.2, with their corresponding voltage conversion ratios
plotted in fig. 3.3.
Fig 3.2 Buck derived converters with tapped inductor
In fig 3.3, D is the duty ratio of switch S, M is the voltage
conversion ratio, and n is the turn ratio of the tapped inductors,
which is defined as n = n2: n1. As the turn ratio n tends to
infinity, the conversion ratio of the buck-derived converters
approach the characteristic of a basic buck topology.
Fig 3.3 Voltage conversion ratio of buck derived converters with
tapped inductors
3.3 BOOST CONVERTERThe boost converter converts an input voltage
to a higher output voltage. The boost converter is also called a
step-up converter. Boost converters are used in battery powered
devices, where the electronic circuit requires a higher operating
voltage than the battery can supply, e.g. notebooks, mobile phones
and camera-flashes.
Fig.3.4 Circuit diagram of Boost converter
Thus the buck-derived converters with tapped inductors is shown
in the fig.3.5, with their corresponding voltage conversion ratios
plotted in fig. 3.6.
Fig 3.5 Boost derived converters with tapped inductor
In fig 3.6, D is the duty ratio of switch S, M is the voltage
conversion ratio, and n is the turn ratio of the tapped inductors,
which is defined as n = n2: n1. As the turn ratio n tends to zero,
the conversion ratio of the buck-derived converters approach the
characteristic of a basic boost topology.
Fig 3.6 Voltage conversion ratio of boost derived converters
with tapped inductors
Inspection of the conversion ratio plots, as given in Fig.
3.2(a), reveals that the proposed buck-derived converter achieves
wider voltage step down than a basic buck converter. Also, by
examining Fig. 3.5(a), it becomes evident that the suggested
boost-derived converter attains a wider voltage step-up than a
basic boost converter.The idea proposed here is that these two
topologies may be combined to form a new two-switch topology, with
an extended conversion range.
3.4 BUCK-BOOST CONVERTER*The main application of a buck-boost
converter is in regulated dc power supplies, where a negative
polarity output may be desired, and the output voltage can be
either higher or lower than the input voltage.*A buck-boost
converter can be obtained by the cascade connection of the two
basic converters: buck converter and boost converter.
The buck-boost converter is a type of DC-to-DC converter that
has an output voltage magnitude that is either greater than or less
than the input voltage magnitude.
Fig. 3.7 Circuit diagram of buck-boost converterWhen Switch is
ON, inductor stored energy. Diode isolates input from the output.
Capacitor supplies the load. When the switch is OFF, the inductor
stored energy charges the capacitor and supplies the load through
the diode. As the inductance polarity is reversed when it transfers
power, the output has a reverse polarity compared to the input.When
the switch is closed, (3.1)
(3.2)
ON (3.3)
When the switch is OFF, (3.4)
OFF (3.5)
Therefore, (3.6) Where, Vin =input voltage L = inductor di/dt
=rate of change of current Ton =on time Toff =off time D =duty
ratio. Two different topologies are called buck-boost converter.
Both of them can produce a range of output voltages, from an output
voltage much larger (in absolute magnitude) than the input voltage,
down to almost zero.
44
CHAPTER 4WIWO DC-DC CONVERTER4.1 GENERALWIWO can operate either
in step-down or the buck mode or in step-up or in boost mode. The
buck will reduce voltage until 15%, Boost will increase the voltage
until 800-1000%, and buck-boost will be in between. To have higher
range we will go for fly back converter. But the leakage and
magnetizing inductance will cause spike and ringing. To have a
range between all these range and above we are going for WIWO.
4.2 PROPOSED WIWO DC-DC CONVERTER TOPOLOGYThe proposed WIWO
DC-DC converter is illustrated in Fig 4.1Fig 4.1 WIWO DC-DC
converterThe converter is comprised of two active switches S1 and
S2, tapped inductors L1 and L2 with turns ratio n = n2 : n1 , diode
D, and capacitive output filter C the tapped inductor is
reconfigured into a pair of coupled inductors in Fig. 4.1. Being
equivalent electrically, this reconfiguration is beneficial from a
practical point of view. In Fig. 4.1, S1 and S2 are connected to a
common junction or midpoint. The midpoint is periodically switched
by S1 to ground, which allows recharging the bootstrap power supply
and reliable operation of the flying driver of the top switch S2.
Consequently, a standard half-bridge driver chip can be used with
the low-side driver operating the bottom switchS1 and the bootstrap
high-side driver activating the top switch S2. WIWO can operate
either in the step-down or the buck mode or in the step-up or the
boost mode. To operate the WIWO in the buck mode, the switch S1 is
assigned a high-frequency switching signal with a predetermined
duty cycle D, whereas S2 is switched complementarily to S1. The
diode D is kept ON by the inductor L2 current, which is assumed to
be continuous. To operate WIWO in the boost mode, the controller
keeps S2 switch continuously ON and issues the required duty cycle
signal for the S1 switch. Thus, the diode D is forced to switch on
and off complementarily to S1. In both modes, the capacitor C
filters the pulsating current and provides a smoothed output
voltage for the load R.
4.3 CONTROL SCHEMEFor the proper operation of WIWO, a modified
PWM control circuitry is required. This PWM is generated using a
microcontroller and the process for generating switching pulses for
the mosfet switches are defined in the microcontroller. The
microcontroller generates a PWM signal in the form of pulses whose
voltage is low compared to the switching pulses of the switch,
there the signal generated is not directly given to the switch
since there is no use. It requires an intermediate circuit to drive
the pulses and amplify the pulses. This process is done by means of
driver circuit. The generated pulse from the controller is boosted
up and given to the switches.
4.4 OPERATING PRINCIPLE OF WIWO CONVERTERThe steady-state
operation of the proposed WIWO converter is described. The analysis
is performed assuming that the circuit is comprised of ideal
components. The coupling coefficient of the tapped inductor is
assumed to be unity. Under continuous inductor current (CCM)
condition, the proposed WIWO converter exhibits four topological
states, as shown in Fig. 4.2.
Fig 4.2 (a) Buck mode charging state, (b) Buck mode discharging
state, (c) Boost mode charging state, (d) Boost mode discharging
state
4.4.1 BUCK MODE:STATE 1 (t0 t < t1)It is the buck-mode
charging state [see Figs. 4.2(a) and 4.5(a)]. Here, the switch S2
is turned on and S1 is turned off. The diode D conducts and the
coupled inductors L1 and L2 are charged. The energy is also
transferred from dc source to load.
Fig 4.3 Switched circuit models (a) Buck mode when charging
STATE 2 (t1 t t2)
It is the buck-mode discharging state [see Figs. 4.2(b) and
4.5(a)]. Here, the switch S2 is turned off also cutting off the
current in the L1 winding, whereas S1 is turned on and the diode D
conducts L2 current to the load.
Fig 4.3 Switched circuit models (b) Buck mode when
discharging
4.4.2 BOOST MODE:STATE 3 (t0 t < t1)
It is the boost-mode charging state [see Figs. 4.2(c) and
4.5(b)]. Here, the switches S1 and S2 are turned on charging the L1
inductor. The diode D is cut off by the negative voltage induced in
L2 winding. The output voltage is supported by the capacitor C.
Fig 4.3 Switched circuit models (c) Boost mode when charging
STATE 4 (t1 t < t2)It is the boost-mode charging state [see
Figs. 4.2(c) and 4.5(b)]. Here, the switch S2 is still ON whereas
S1 is turned off. Both windings L1 and L2 conduct through the diode
D and discharge the stored energy to the output.
Fig 4.3 Switched circuit models (d) Boost mode when
discharging
4.5 STEADY STATE ANALYSISThe steady-state models of the proposed
WIWO converter are shown in Fig. 4.2. These models preserve the
tapped-inductor symbol. More suitable for analysis purposes,
however, are the models of Fig. 4.3. Here, the role of the
magnetizing inductance Lm is clearly shown. The detailed analysis
was carried out in using state-space averaging technique.
Fig 4.4 Voltage transfer characteristic M (n,m) of the WIWO
DC-DC converter.
WIWO voltage conversion ratio, output voltage ripple, voltage
stresses, etc., were obtained. WIWO voltage transfer
characteristics M (n, m) are plotted in Fig. 4.4. Clearly, for n =
1, the voltage transfer ratio is smooth at the vicinity of the buck
to boost switchover point m = 1, whereas for other values of n, the
curves exhibit a slope change. This statement can be verified
analytically by calculating the derivatives of M (m) atm=1. Using
the expressions for voltage conversion ratio, the result is ((n +
1)/n) for the buck mode and (n + 1) for the boost mode. Obviously,
the slope of WIWO dcdc characteristic becomes continuous for n =
1.
The small-signal transfer functions of the WIWO converter were
derived by linearizing the state-space equations around the
operating point. The line-to-output and control-to-output transfer
functions reveal strong dependence on the operating point and a
right-half-plane (RHP) zero. Here the large output filter capacitor
is replaced by an ideal voltage source. The waveforms and timing
diagram of WIWO for both buck and boost modes are illustrated in
Fig 4.5.
Fig 4.5 Waveforms of the DC-DC converter. (a) Buck mode (b)
Boost mode.CHAPTER 5BLOCK DIAGRAM DESCRIPTION OF PROPOSED SYSTEM5.1
BLOCK DIAGRAM DESCRIPTION:The Block diagram of the proposed
converter is shown in Fig.5.1. It consists of DC source, proposed
converter, driver circuit, micro controller and load.
Fig.5.1 Block Diagram of wide input wide output dc-dc
converter5.1.1 POWER SUPPLY CIRCUIT The main purpose of the power
supply circuit is the conversion of AC voltage to required DC
voltage. The rated AC voltage is first stepped down to the required
AC voltage by using a step down transformer. Then this AC voltage
is given to a bridge rectifier consists of 4 diodes for the
conversion of AC to DC voltage. Due to this conversion, ripples are
present in the obtained DC voltage. To avoid this, a capacitive
filter is used. A smoothed output voltage is provided for resistive
load.
5.1.2 POWER CIRCUIT The converter is comprised of two active
switches S1 & S2, tapped inductors L1 & L2 with turns ratio
n= n2:n1, diode D and capacitive output filter C. S1 & S2 are
connected to common junction or midpoint. The midpoint is
periodically switched by S1 to ground, which allows recharging the
bootstrap power supply and reliable operation of the flying driver
of top switch S2. A bridge rectifier chip can be used with low side
driver operation the bottom switch S1 & bootstrap high-side
driver activating the top switch S2. To operate WIWO in buck mode,
the switch S1 is assigned a high frequency switching signal with a
predetermined duty cycle D, whereas S2 is switched complementary to
S1. The diode D is kept ON by inductor L2 current. In boost mode,
the controller keeps S2 switch continuously ON and issues the
required duty cycle signal for S1 switch. Thus, the diode D is
forced switch ON & OFF complementary to S1. C used to provide a
smoothed output voltage for load R.
5.1.3 DRIVER CIRCUIT The main purpose of driver circuit is To
enhance the switching voltage for the mosfet or any switching
device. To isolate the power circuit from the microcontroller
circuit, because the power circuit must not enter into the
microcontroller circuit. An opto-coupler will be connected as the
buffer which receives pulse signals of 5 V from microcontroller to
the driver circuit, opto-coupler isolates the power circuit with
microcontroller circuit. After it gets the signal from the
microcontroller it will get enhanced using a NPN transistor to
higher level of voltage. This voltage gets regulated by the use of
Darlington pair (PNP-NPN transistor pair).5.1.4 CONTROL CIRCUIT The
control circuit is used to provide the required gate pulses to the
switches in the power circuit. It is provided by means of
developing a PWM signal using a microcontroller. The developed
signal is given to the driver circuit for amplification and then
provided to the switch.5.2 COUPLED INDUCTORSMutual inductance
occurs when the change in current in one inductor induces a voltage
in another nearby inductor. It is important as the mechanism by
which transformers work, but it can also cause unwanted coupling
between conductors in a circuit.The mutual inductance, M, is also
measure of the coupling between two inductors. The mutual
inductance by circuit i on circuit j is given by the double
integral Neumann formula,The mutual inductance also has the
relationship:M21N1N2P21 (5.1)WhereM21 is the mutual inductance, and
the subscript specifies the relationship of the voltage induced in
coil 2 due to the current in coil 1,N1 is the number of turns in
coil 1,N2 is the number of turns in coil 2,P21 is the permeance of
the space occupied by the flux.
Fig. 5.2 Coupled Inductor
The mutual inductance also has a relationship with the coupling
coefficient. The coupling coefficient is always between 1 and 0,
and is a convenient way to specify the relationship between a
certain orientations of inductor with arbitrary inductance:
(5.2)Wherek is the coupling coefficient and 0 k 1,L1 is the
inductance of the first coil, andL2 is the inductance of the second
coil. (5.3) WhereVs is the voltage across the secondary inductor,Vp
is the voltage across the primary inductor (the one connected to a
power source)Ns is the number of turns in the secondary inductor,
andNp is the number of turns in the primary inductor.
CHAPTER 6DESIGN AND SIMULATION OF CIRCUITS6.1 DESIGNVin=12 V,
Vout=5-20 V, Io=2 A, s=50 kHz.
DUTY RATIO
INDUCTOR SELECTION
CAPACITANCE SELECTION
6.2 GENERALSimulation has become a very powerful tool on the
industry application as well as in academics, nowadays. It is now
essential for an electrical engineer to understand the concept of
simulation and learn its use in various applications. Simulation is
osne of the best ways to study the system or circuit behavior
without damaging it. The tools for doing the simulation in various
fields are available in the market for engineering professionals.
Many industries are spending a considerable amount of time and
money in doing simulation before manufacturing their product. In
most of the research and development (R&D) work, the simulation
plays a very important role. Without simulation it is quiet
impossible to proceed further. It should be noted that in power
electronics, computer simulation and a proof of concept hardware
prototype in the laboratory are complimentary to each other.
However computer simulation must not be considered as a substitute
for hardware prototype. The objective of this chapter is to
describe simulation of impedance source inverter with R, R-L and
RLE loads using MATLAB tool.
6.2.1 INTRODUCTION TO MATLABMATLAB is a high-performance
language for technical computing. It integrates computation,
visualization, and programming in an easy-to-use environment where
problems and solutions are expressed in familiar mathematical
notation. Typical uses includes,1. Math and computation2. Algorithm
development3. Data acquisition4. Modeling, simulation and
prototyping5. Data analysis, exploration and visualization6.
Scientific and engineering graphics7. Application development,
including graphical user interface buildingMATLAB is an interactive
system whose basic data element is an array that does not require
dimensioning. This allows you to solve many technical computing
problems, especially those with matrix and vector formulations, in
a fraction of the time it would take to write a program in a scalar
non interactive language such as C or FORTRAN. Areas in which
toolboxes are available include signal processing, control systems,
neural networks, fuzzy logic, wavelets, simulation and many
others.Electrical Power systems are combinations of electrical
circuits and electro mechanical devices like motors and generators.
Sim Power System is a modern design tool that allows scientists and
engineers to rapidly and easily build models that simulate power
systems. Sim Power Systems uses the Simulink environment, allowing
you to build a model using simple click and drag procedures. Since
Simulink environment, allowing you to build a model using simple
click and drag procedures. Since Simulink uses MATLAB as its
computational engine, designers can also use MATLAB toolboxes and
Simulink block sets. Sim Power Systems and Sim Mechanics share a
special Physical Modeling blocks and connection line interface.
6.2.2 SIM POWER SYSTEM LIBRARIESSim Power Systems can be made to
work. The libraries contain models of typical power equipment such
as transformers, lines, machines and power electronics as shown in
Fig.5.1. These models are proven ones coming from textbooks and
their validity is based on the experience of the Power Systems
Testing and Simulation Laboratory of Hydro-Quebec, a large North
American utility located in Canada. The capabilities of Sim Power
Systems for modeling a typical electrical system are illustrated in
demonstration files.
6.3 SIMULATION RESULTSimulations are carried for proposed
converter in both open and closed loops.6.3.1 PROPOSED METHOD WIWO
OPEN LOOP SYSTEMThe Simulation circuit of the proposed coupled
inductor WIWO converter open loop is shown in the Fig.6.1.
Fig 6.1 Simulation circuit of coupled inductor WIWO converter-
Open Loop.The output voltage of open loop in buck mode is shown in
the Fig.6.2.
Fig.6.2 Output voltage of open loop in buck modeBy performing
simulation with the help of MATLAB 13. It is observed that by
giving an input voltage of 12 V and the output is 4.33 V.
The output voltage of open loop in boost mode is shown in the
Fig.6.3.
Fig.6.3 Output voltage of open loop in boost modeBy performing
simulation with the help of MATLAB 13. It is observed that by
giving an input voltage of 12 V and the output is 19.68 V.6.3.2
PROPOSED METHOD-WIWO CLOSED LOOP SYSTEM
Fig 6.4 Simulation circuit of WIWO dc-dc converter- closed
loopThus the WIWO dc-dc converter subsystem output in buck and
boost mode is shown in fig 6.5 and 6.6
Fig 6.5 Output voltage of closed loop in buck modeBy performing
simulation with the help of MATLAB 13. It is observed that by
giving an input voltage of 12 V and the output is 4.65 V.
Fig 6.6 Output voltage of closed loop in boost mode
By performing simulation with the help of MATLAB 13. It is
observed that by giving an input voltage of 12 V and the output is
21.68 V.
CHAPTER 7HARDWARE DESCRIPTION7.1 PROPOSED WIDE INPUT WIDE OUTPUT
DC-DC CONVERTERThe Circuit diagram of the proposed converter
consists of Power Supply circuit, proposed wide input wide output
converter, driver circuit, Microcontroller and load.7.2 POWER
SUPPLY7.2.1 CIRCUIT DESCRIPTION
Fig.7.1 Circuit diagram of the power supplyThe power circuit is
used for the conversion of 230 V ac to 12 V and 5 V dc. It
comprises of a step down transformer which is used for the
conversion of 230 V ac to 12 V ac. A bridge rectifier is used for
the conversion of ac to dc. During this conversion there will be a
formation of ripples in the dc, therefore a filter capacitor is
implemented and the pulsated dc is converted into dc by means of
regulator. The regulator determines the amount of output voltage
based on its value, the regulators used here are 7805 and 7812 for
outputs 5 V and 12 V.
7.3 DRIVER CIRCUITThe main purpose of driver circuit is we have
to enhance the switching voltage for the mosfet or any switching
device. And also we have to isolate the power circuit from the
microcontroller circuit. Because the power circuit current must not
enter into the microcontroller circuit. MCT2E is the opt coupler
which will be connected to the buffer CD4050 which send pulse
signals of 5v from microcontroller to the driver circuit.
Fig.7.2 Circuit Diagram of Driver CircuitMCT2E is the device
which isolates the power circuit with the microcontroller circuit.
After it gets the signal from the microcontroller it will get
enhanced using the 2N2222 transistor to higher level of voltage.
After this voltage get regulated by the use of Darlington pair. The
Darlington is made of 2N2222 (NPN) and CK100 (PNP) transistor. In
the driver circuit the following values are used IRFP460, Diode
IN4007, and Capacitors, 1000F/25V, Opto-coupler MCT2E, Transistors
2N2222 CK100, Resisters 1k, 100 ohm and Transformers 230V/50.
7.4 OPTO COUPLER ISOLATION7.4.1 OPTO ISOLATOR:In electronics, an
opto-isolator (or optical isolator, opto-coupler or photo coupler)
is a device that uses a short optical transmission path to transfer
signal between elements of a circuit, typically a transmitter and a
receiver, while keeping them electrically isolate since the signal
goes from an electrical signal to an optical signal back to an
electrical signal, electrical contact along the path is broken.
A common implementation involves an LED and a light sensor,
separated so that light may travel across a barrier but electrical
current may not. When an electrical signal is applied to the input
of the opto-isolator, its LED lights, its light sensor then
activates and a corresponding electrical signal is generated at the
output. With a photodiode as the detector, the output current is
proportional to the amount of incident light supplied by the
emitter. The diode can be used in a photovoltaic mode or a
photoconductive mode. In photovoltaic mode, the diode acts like a
current source in parallel with a forward-biased diode. The output
current and voltage re dependent on the load impedance and light
intensity.
Fig.7.3 Schematic Diagram of Opto-couplerIn photoconductive
mode, the diode is connected to a supply voltage, and the magnitude
of the current conducted is directly proportional to the intensity
of light. An opto-isolator can also be constructed using a small
incandescent lamp in place of the LED such a device, because the
lamp has a much slower response time than an LED, will filter out
noise or half-wave power in the input signal. It has the further
disadvantage, of course, (an overwhelming disadvantage in most
applications) that incandescent lampshade finite life spans. The
transmitting and receiving elements of an optical isolator may be
contained within a single compact module, for mounting, for
example, on a circuit board, in this case, the module is often
called an opto-isolator or opto-isolator.7.5 POWER CIRCUIT
Fig 7.4 Circuit diagram of Power circuitThe power circuit
comprises of coupled inductors L1 and L2, mosfet switches IRF840 S1
and S2, capacitor C1, diode D1 and resistor R1. It is the main
circuit of the whole system in which the buck boost converter is
implemented for WIWO operation. A predetermined duty cycle D is
provided to switches S1 and S2 by means of control and Driver
circuit. The main circuit comprises of following ratings 230/12V,
1A step down transformer, bridge Rectifier 5 amp, Toroidal core,
Inductor copper coil (1mm thickness) , Mosfet Switches IRF840,
Capacitor 25V, 4700uf, Power Resistors 10W.
7.6 METAL OXIDE FIELD EFFECT TRANSISTOR (MOSFET)The
metal-oxide-semiconductor field-effect transistor (MOSFET, MOS-FET,
or MOSFET) is a transistor used for amplifying or switching
electronic signals. Although the MOSFET is a four-terminal device
with source(S), gate (G), drain (D), and body (B) terminals, the
body (or substrate) of the MOSFET.It often is connected to the
source terminal, making it a three-terminal device like other
field. When two terminals are connected to each other
(short-circuited) only three terminals appear in electrical
diagrams.The MOSFET is by far the most common transistor in both
digital and analog circuits, though the bipolar junction transistor
was at one time much more common.
Fig.7.5 Structure of MOSFET
In enhancement mode MOSFETs, a voltage drop across the oxide
induces a conducting channel between the source and drain contacts
via the field effect. The term enhancement mode refers to the
increase of conductivity with increase in oxide field that adds
carriers to the channel, also referred to as the inversion layer.
The channel can contain electrons (called an nMOSFET or Nmos), or
holes (called a pMOSFET or pMOS), opposite in type to the
substrate, so nMOS is made with a p-type substrate, and pMOS with
an n-type substrate (see article on semiconductor devices)
7.6.1 RATINGSThe ratings of MOSFET IRF840 values are VDS = 500
V, ID (cont) = 20 A, RDS (on) = 0.85ohm. For some low power devices
(few hundred watts) may go up to MHZ range. Turning on and off is
very simple. Gate drive circuit is simple.
To turn on: VGS =+10V Circuit protection-Built-in overheating
protection shuts down output when regulator IC gets too hot.7.6.2
FEATURES Repetitive avalanche energy rated Fast switching times Low
RDS (on) HDMOSTM process Rugged polysilicon gate cell structure
High Commutating dv/dt Rating
7.7 CONTROL CIRCUIT
Fig 7.6 Circuit diagram of control circuitThe main circuit of
control circuit is to provide switching pulses to the mosfet. It is
generated as PWM pulses by using microcontroller. The
microcontroller requires VDD of 5 V and is given from the power
supply circuit. In hardware we used PIC16F877A microcontroller, ac
socket, bridge rectifier 1 amps, capacitor 470microfrad/25v,
voltage regulator LM7805, LED resistor 330 ohm, reset switch,
resistor 100 ohm.7.7.1 MICRO CONTROLLER (PIC16F877A)DESCRIPTIONThe
PIC16F877A is a low power, high performance CMOS 8-bit
microcomputer with 8k of flash programmable memory and 256 bytes of
EEPROM. It comprises of high performance RISC CPU with Only 35
single word instructions to learn All single cycle instructions
except for program branches which are two cycle Operating speed: DC
- 20 MHz clock input DC - 200 ns instruction cycle Up to 8K x 14
words of FLASH Program Memory, Up to 368 x 8 bytes of Data Memory
(RAM) Up to 256 x 8 bytes of EEPROM Data Memory Pin out compatible
to the PIC16C73B/74B/76/77 Interrupt capability (up to 14 sources)
Eight level deep hardware stack Direct, indirect and relative
addressing modes Power-on Reset (POR) Power-up Timer (PWRT) and
Oscillator Start-up Timer (OST) Watchdog Timer (WDT) with its own
on-chip RC oscillator for reliable peration Programmable code
protection Power saving SLEEP mode Selectable oscillator options
Low power, high speed CMOS FLASH/EEPROM technology Fully static
design In-Circuit Serial Programming (ICSP) via two pins Single 5V
In-Circuit Serial Programming capability In-Circuit Debugging via
two pins Processor read/write access to program memory Wide
operating voltage range: 2.0V to 5.5V High Sink/Source Current: 25
mA Commercial, Industrial and Extended temperature ranges Low-power
consumptionPIN DIAGRAM
Fig.7.7 Pin Diagram of PIC16F877A
PIN DESCRIPTIONI/O PORTSSome pins for these I/O ports are
multiplexed with an alternate function for the peripheral features
on the device. In general, when a peripheral is enabled, that pin
may not be used as a general purpose I/O pin. PORTA and the TRISA
RegisterPORTA is a 6-bit wide, bi-directional port. The
corresponding data direction register is TRISA. Setting a TRISA bit
(= 1) will make the corresponding PORTA pin an input (i.e., put the
corresponding output driver in a Hi-Impedance mode). Clearing a
TRISA bit (= 0) will make the corresponding PORTA pin an output
(i.e., put the contents of the output latch on the selected pin).
Reading the PORTA register reads the status of the pins, whereas
writing to it will write to the port latch. All write operations
are read-modify-write operations. Therefore, a write to a port
implies that the port pins are read; the value is modified and then
written to the port data latch. Pin RA4 is multiplexed with the
Timer0 module clock input to become the RA4/T0CKI pin. The
RA4/T0CKI pin is a Schmitt Trigger input and an open drain output.
All other PORTA pins have TTL input levels and full CMOS output
drivers. Other PORTA pins are multiplexed with analog inputs and
analog VREF input. The operation of each pin is selected by
clearing/setting the control bits in the ADCON1 register (A/D
Control Register1).PORTB and the TRISB RegisterPORTB is an 8-bit
wide, bi-directional port. The corresponding data direction
register is TRISB. Setting a TRISB bit (= 1) will make the
corresponding PORTB pin an input (i.e., put the corresponding
output driver in a Hi-Impedance mode). Clearing a TRISB bit (= 0)
will make the corresponding PORTB pin an output (i.e., put the
contents of the output latch on the selected pin). Three pins of
PORTB are multiplexed with the Low Voltage Programming function:
RB3/PGM, RB6/PGC and RB7/PGD. The alternate functions of these pins
are described in the Special Features Section. Each of the PORTB
pins has a weak internal pull-up. ASingle control bit can turn on
all the pull-ups. This is performed by clearing bit RBPU
(OPTION_REG). The weak pull-up is automatically turned off when the
port pin is configured as an output. The pull-ups are disabled on a
Power-on Reset.Four of the PORTB pins, RB7:RB4, have an interrupt
on- change feature. Only pins configured as inputs can cause this
interrupt to occur (i.e., any RB7:RB4 pin configured as an output
is excluded from the interrupt on- change comparison). The input
pins (of RB7:RB4) are compared with the old value latched on the
last read of PORTB. The mismatch outputs of RB7:RB4 are ORed
together to generate the RB Port Change Interrupt with flag bit
RBIF (INTCON).PORT CPORTC is an 8-bit wide, bi-directional port.
The corresponding data direction register is TRISC. Setting a TRISC
bit (= 1) will make the corresponding PORTC pin an input (i.e., put
the corresponding output driver in a Hi-Impedance mode). Clearing a
TRISC bit (= 0) will make the corresponding PORTC pin an output
(i.e., put the contents of the output latch on the selected pin).
PORTC is multiplexed with several peripheral functions (Table 3-5).
PORTC pins have Schmitt Trigger input buffers. When the I2C module
is enabled, the PORTC pins can be configured with normal I2C levels
or with SMBus levels by using the CKE bit (SSPSTAT). When enabling
peripheral functions, care should be taken in defining TRIS bits
for each PORTC pin. Some peripherals override the TRIS bit to make
a pin an output, while other peripherals override the TRIS bit to
make a pin an input. Since the TRIS bit override is in effect while
the peripheral is enabled, read-modify write instructions (BSF,
BCF, and XORWF) with TRISC as destination, should be avoided. The
user should refer to the corresponding peripheral section for the
correct TRIS bit settings.PORTD and TRISD RegistersPORTD and TRISD
are not implemented on the PIC16F873 or PIC16F876. PORTD is an
8-bit port with Schmitt Trigger input buffers. Each pin is
individually configurable as an input or output. PORTD can be
configured as an 8-bit wide microprocessor port (parallel slave
port) by setting control bit PSPMODE (TRISE). In this mode, the
input buffers are TTL.TIMER0 MODULEThe Timer0 module timer/counter
has the following features: 8-bit timer/counter Readable and
writable 8-bit software programmable prescaler Internal or external
clock select Interrupt on overflow from FFh to 00h Edge select for
external clockTimer mode is selected by clearing bit T0CS
(OPTION_REG). In Timer mode, the Timer0 module will increment every
instruction cycle (without prescaler). If the TMR0 register is
written, the increment is inhibited for the following two
instruction cycles. The user can work around this by writing an
adjusted value to the TMR0 registerTIMER1 MODULEThe Timer1 module
is a 16-bit timer/counter consisting of two 8-bit registers (TMR1H
and TMR1L), which are readable and writable. The TMR1 Register pair
(TMR1H:TMR1L) increments from 0000h to FFFFh and rolls over to
0000h. The TMR1 Interrupt, if enabled, is generated on overflow,
which is latched in interrupt flag bit TMR1IF (PIR1). This
interrupt can be enabled/disabled by setting/clearing TMR1
interrupt enable bit TMR1IE (PIE1). Timer1 can operate in one of
two modes: As a timer As a counterThe operating mode is determined
by the clock select bit, TMR1CS (T1CON).TIMER2 MODULETimer2 is an
8-bit timer with a prescaler and a postscaler. It can be used as
the PWM time-base for the PWM mode of the CCP module(s). The TMR2
register is readable and writable, and is cleared on any device
RESET. The input clock (FOSC/4) has a prescale option of 1:1,1:4,
or 1:16, selected by control bitsT2CKPS1:T2CKPS0 (T2CON). The
Timer2 module has an 8-bit period register, PR2. A Timer2 increment
from 00h until it matches PR2 and then resets to 00h on the next
increment cycle. PR2 is a readable and writable register. The PR2
register is initialized to FFh upon RESET. The match output of TMR2
goes through a 4-bit postscaler (which gives a 1:1 to 1:16 scaling
inclusive) to generate a TMR2 interrupt (latched in flag bit
TMR2IF, (PIR1)). Timer2 can be shut-off by clearing control bit
TMR2ON (T2CON), to minimize power consumption.
CHAPTER 8HARDWARE IMPLEMENTATION8.1 HARDWARE SETUP
Fig.8.1 Experimental Setup of WIWO DC-DC Converter
8.2 OUTPUT WAVEFORMS:The output terminals are connected to the
CRO and the following waveforms are obtained,
Fig 8.2 Output voltage waveform of WIWO in Buck mode
Fig 8.3 Output voltage waveform of WIWO in Boost mode
CHAPTER 9CONCLUSION
A new WIWO dc-dc converter, which is an integration of buck and
boost converters with coupled inductors. The new converter topology
has several advantages. The WIWO retains the features of both the
buck and the boost converters however, it achieves wider step-up
and wider step-down dc-dc conversion range. By replacing the
inductor with coupled inductors, the new converter not only retains
the functions of both converters, but also extends the conversion
range. Therefore, wide-step-up and wide-step-down dc-dc conversions
can be achieved. Based on the Simulation results hardware setup is
designed and implemented, it yield a output voltage of 5-20V for an
input voltage of 12V.
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