Design a Highly Efficient Push-Pull converter for Photovoltaic Applications

Design a Highly Efficient Push-Pull converter for
Photovoltaic Applications
Umesh Kumar1,a)
Navtej Swaroop Singh1,b)
Department of EEE Department of EEE
BKBIET, Pilani, India BKBIET, Pilani , India
umesh.pilani@gmail.com navtej631@gmail.com
Eklavya Sharma2
Bavessh Raina3
Department of EE Department of CS
BKBIET,Pilani,India. BKBIET,Pilani,India3
.
Abstract
Renewable energy source plays an important role in
energy co-generation and distribution. A traditional solar-
based inverter system has two stages cascaded, which has
simpler controller but low efficiency. A new solar-based
single-stage grid-connected inverter system can achieve
higher efficiency by reducing the power semiconductor
switching loss and output stable and synchronizing sinusoidal
current into the utility grid.
The need for renewable energy sources is on the rise
because of the acute energy crisis in the world today. India
plans to produce 20 Giga-watts Solar power by the year
2020, whereas we have only realized less than half a Giga-
watt of our potential as of March 2010. Solar energy is a vital
untapped resource in a tropical country like ours. The main
hindrance for the penetration and reach of solar PV
systems is their low efficiency and high capital cost.
PVs are used in order to convert solar energy into
electric power. They make use of solar cells to produce direct
current so as to power equipment or to recharge a battery. An
inverter whose efficiency is about 95% is necessary in order to
convert the DC current produced by PVs to AC. Solar cells
must be protected from damages so most of the times are
closely packed behind a sheet made of glass. The power which
is required is usually much bigger than that a single solar cell
can deliver, thus cells are electrically connected together to
make solar panels - solar modules. The solar panel is then
used in a larger photovoltaic system as a component. We
create then a linked connection of solar panels to create a
photovoltaic array. In a PV array now the PV panels are
firstly connected in series in order to obtain the required
voltage and then the 'individual strings' are connected in
parallel so as to provide the desired current to our system.
The building integrated PV systems are particularly materials
which are used to replace the ordinary construction materials
in certain regions of a building such as roof and windows.
They are available in several forms like flat roofs, pitched
roofs, facades and glazing. These PV materials are used more
and more nowadays as they can provide the new buildings
with sufficient electrical power, while they can be positioned
also to existing buildings. PVs are an opportunity for making
an aesthetically appealing and attractive building. It is very
important also that they don't produce noise. BIPVs can serve
as thermal insulation materials because of their sandwich
construction (the modules themselves, the layer of air within
the modules, the ray absorption by the crystalline silicon)
meaning we have a diminishing heat loss from the interior of
the building to the exterior environment. They are used as a
basic or additional source of power. If the building is at a
small distance from the existing grid, the optimum usage of the
PVs is applicable; they can cover the building's needs and sell
then the superfluity to the grid, having a specific feed-in tariff.
In this thesis, we examine a schematic to extract
maximum obtainable solar power from a PV module and use
the energy for a DC application. This project investigates in
detail the concept of Maximum Power Point Tracking
(MPPT) which significantly increases the efficiency of the
solar photovoltaic system.
Keywords— Maximum Power Point Tracking-
MPPT ,Capture Compare PWM -CCP, Standard wire
Gage-SWG ,Timer Register of Controller –TGC,
Modulation Index -Ma
Introduction
As of 2012, these state industries accounted for over
18,591 full-time equivalent employees across 1,100 businesses
accounting for $3.7 billion in annual gross revenues. This
growth is especially noteworthy in the solar industry. Total
registered capacity has increased from less than 1 megawatt
(MW) in 2006 to 632 MW in 2012, which amounts to an
average annual growth rate of 1,243%. Powered by over 500
state businesses working in the solar space,3 this trajectory
ranks North Carolina as the 3rd most active state in the nation
in terms of new solar additions in 2013 Q3. Geothermal
(ground-source) heat pumps have grown in popularity globally
with annual increases of approximately 10% in many areas.5
Growth in North Carolina’s renewable energy and energy
efficiency sectors is driven by many factors, including the
falling price of installation, rising electricity prices, and the
predictability of state renewable energy incentives. The price
of solar panels has fallen 60% since 2011,6 and it is expected
that, for the majority of electricity ratepayers, utility scale and
commercial scale solar PV systems in North Carolina will

deliver at grid parity without any solar subsidies within the
next five years. Residential scale solar PV systems will deliver
at grid parity around the year 2020.
In light of these trends, the purpose of this Paper is to
assess the financial, personal, and policy drivers that have
influenced residential owners of solar PV and geothermal
systems in North Carolina to make these investments. In
January 2012, the NC Sustainable Energy Association and the
University of North Carolina at Chapel Hill Kenan-Flagler
Business School conducted a survey of 1,323 solar PV owners
and 1,023 geothermal system owners to assess the motivations
behind their decision to purchase a renewable energy system,
challenges faced in the process, energy efficiency behaviors in
which they engage, energy efficiency products and design they
have chosen, and characteristics of these consumers.
Among other objectives, the results of this study can be
used for the following:
 To assess which policies and incentives are
working and need to be reinforced,
 To understand which incentives require greater
education to enable their full effect,
 To expand residential and commercial solar PV
and geothermal adoption in North Carolina and
other states, and
 To inform outreach messaging that encourages
individuals to adopt energy efficient technologies
and energy-saving behaviors.
Literature Survey
1. Cost and Lifespan study
This project presents the results of electrical
performance measurements of 204 crystalline silicon-wafer
based photovoltaic modules following long-term continuous
outdoor exposure. The modules comprise a set of 53 module
types originating from 20 different producers, all of which
were originally characterized at the European Solar Test
Installation (ESTI), over the period 1982-1986. The modules
represent diverse generations of PV technologies, different
encapsulation and substrate materials. The modules electrical
performance was determined according to the standards IEC
60891 and the IEC 60904 series, electrical insulation tests
were performed according to the recent IEC 61215 edition 2.
Many manufacturers currently give a double power warranty
for their products, typically 90% of the initial maximum
power after 10 years and 80% of the original maximum power
after 25 years. Applying the same criteria (taking into account
modules electrical performance only and assuming 2•5%
measurement uncertainty of a testing lab) only 17•6% of
modules failed (35 modules out of 204 tested). Remarkably
even if we consider the initial warranty period i.e. 10% of
Pmax after 10 years, more than 65•7% of modules exposed for
20 years exceed this criteria. The definition of life time is a
difficult task as there does not yet appear to be a fixed
catastrophic failure point in module ageing but more of a
gradual degradation. Therefore, if a system continues to
produce energy which satisfies the user need it has not yet
reached its end of life. If we consider this level arbitrarily to
be the 80% of initial power then all indications from the
measurements and observations made in this paper are that the
useful lifetime of solar modules is not limited to the
commonly assumed 20 year.
2. Rate Calculation
As the solar photovoltaic (PV) matures, the economic
feasibility of PV projects is increasingly being evaluated
using the levelized cost of electricity (LCOE) generation
in order to be compared to other electricity generation
technologies. Unfortunately, there is lack of clarity of
reporting assumptions, justifications and degree of
completeness in LCOE calculations, which produces
widely varying and contradictory results. This paper
reviews the methodology of properly calculating the
LCOE for solar PV, correcting the misconceptions made
in the assumptions found throughout the literature. Then a
template is provided for better reporting of LCOE results
for PV needed to influence policy mandates or make
invest decisions. A numerical example is provided with
variable ranges to test sensitivity, allowing for
conclusions to be drawn on the most important variables.
Grid parity is considered when the LCOE of solar PV is
comparable with grid electrical prices of conventional
technologies and is the industry target for cost-
effectiveness.
3. Carbon Emission
The challenge of stabilizing global carbon emissions over the
next 50 years has been framed in the context of finding seven
1.0 G ton C/year carbon reduction wedges. Solar PV could
provide at least one carbon wedge, but will require significant
growth in PV manufacturing capacity. The actual amount of
installed PV capacity required to reach wedge-level carbon
reductions will vary greatly depending on the mix of avoided
fuels and the additional emissions from manufacturing PV
capacity. In this work, we find that the US could reduce its
carbon emissions by 0.25 Gton C/year, equal to the fraction of
a global carbon wedge proportional to its current domestic
electricity use, by installing 792–811 GW of PV capacity. We
evaluate a series of PV growth scenarios and find that wedge-
level reductions could be met by increasing PV manufacturing
capacity and annual installations by 0.95 GW/year/year each
year from 2009 to 2050 or by increasing up to 4 GW/year/year

for a period of 4–17 years for early and late growth scenarios.
This challenge of increasing PV manufacturing capacity and
market demand is significant but not out of line with the recent
rapid growth in both the global and US PV industry. We find
that the rapid growth in PV manufacturing capacity leads to a
short term increase in carbon emissions from the US electric
sector. However, this increase is small, contributing less than
an additional 0.3% to electric sector emissions for less than
4.5 years, alleviating recent concern regarding carbon
emissions from rapid PV growth scenarios.
4. Connecting To the Grid
In this work, we examine some of the limits to
large-scale deployment of solar photovoltaics (PV) in
traditional electric power systems. Specifically, we
evaluate the ability of PV to provide a large fraction (up
to 50%) of a utility system's energy by comparing hourly
output of a simulated large PV system to the amount of
electricity actually usable. The simulations use hourly
recorded solar insolation and load data for Texas in the
year 2000 and consider the constraints of traditional
electricity generation plants to reduce output and
accommodate intermittent PV generation. We find that
under high penetration levels and existing grid-operation
procedures and rules, the system will have excess PV
generation during certain periods of the year. Several
metrics are developed to examine this excess PV
generation and resulting costs as a function of PV
penetration at different levels of system flexibility. The
limited flexibility of base load generators produces
increasingly large amounts of unusable PV generation
when PV provides perhaps 10–20% of a system's energy.
Measures to increase PV penetration beyond this range
will be discussed and quantified in a follow-up analysis..
5. Plant Design
The development of newer technologies in concentrating
solar power (CSP) plants, particularly plants using dish
Stirling systems, as well as changes in the design of
photovoltaic (PV) inverters is creating new challenges in
the design of low- and medium-voltage collector systems
for large solar power plants. Furthermore, interconnect
requirements for reactive power, voltage, and ramp rate
control and the characteristics of solar power require
unique solutions for optimal plant design.
Problem Statement
While PV systems have no moving parts (compared
to wind and micro hydro systems) and can be extremely
reliable, it does not mean they do not have potential
performance problems, which can stem from external and
internal issues.
External issues such as shade from growing trees
and module soiling (dust or soot from local air pollution), are
common problems that can reduce energy output significantly.
Studies on module soiling show an average annual energy loss
of 5% for arrays that are not periodically cleaned. These types
of problems are usually easily solved by intermittently
trimming vegetation and cleaning arrays. Impact to PV
systems from critters is another external issue, but one that
takes a little more consideration to fix. Wires might be
damaged by rodents chewing on them; modules soiled by
birds pooping on them; or cells shaded by weeds sprouting
between the module frames from dirt and/or bird “fertilizer”
beneath the array. The fix-it for stopping critters in their tracks
is to install rodent barriers and/or bird spikes. Many installers
are tackling this problem pre-emptively, including some kind
of screen or wire that keeps critters out but allows air to flow
beneath the array.
Internal Issues such as module/cell damage, can
also reduce system output. Sometimes these problems are easy
to spot, but often they are not. Visually inspecting the PV
array once a year is a good idea. Look for cracks in the glass,
brown/burn spots on both the front and the back of the
modules, burnt solder joints on the cell “grid,” and signs of
delamination and cell damage.
Objective of Project
In this project main focus to study grid connected
distributed generation system having solar energy, fuel
cell as an energy sources and minimise the losses of DC-
DC converter with design an effective control system.
Microgrid
Microgrid is a new type of power systems consisting
of generation sources, loads and energy storages. In another
words, it is an association of a small modular generation
system, a low voltage distribution network and load units
interfaced by means of fast acting power electronics.
Microgrids are determined usually in accordance with a few
definitive functions. They are usually used in small urban
areas or in small industry. The most common power range for
microgrids is from 25 to 100 kW.
The components of the microgrid system are
recognized in accordance with their function.The grid forming
units are able to control the voltage and frequency of the grid

by balancing the power of the loads and generators. Among
the grid forming units are the diesel generators and battery
inverters. The grid supporting units are simple control units.
Their active and reactive power simply depends on the voltage
and frequency characteristics of the systems.
PV modelling
A PV array consists of several photovoltaic cells in series and
parallel connections. Seriesconnections are responsible for
increasing the voltage of the module whereas the
parallelconnection is responsible for increasing the current in
the array.Typically a solar cell can be modeled by a current
source and an inverted diode connected inparallel to it. It has
its own series and parallel resistance. Series resistance is due
to hindrance inthe path of flow of electrons from n to p
junction and parallel resistance is due to the leakagecurrent.
In this model we consider a current source (I) along with a
diode and series resistance (Rs). Theshunt resistance (RSH) in
parallel is very high, has a negligible effect and can be
neglected /The output current from the photovoltaic array
is I=Isc – Id
Id= Io (eqVd/kT - 1)
where Io is the reverse saturation current of the diode,
q is the electron charge, Vd is the voltage across the diode,
k is Boltzmann constant (1.38 * 10-19 J/K) and T is the
junction temperature inKelvin (K)
From equations above
. Figure No. 1: Single diode model of a PV cell
Using suitable approximations,
I = Isc – Io (eq((V+IRs)/nkT) - 1)
where, I is the photovoltaic cell current, V is the PV cell
voltage, T is the temperature (in Kelvin)and n is the diode
ideality factor.
In order to model the solar panel accurately we
can use two diode model but in our project ourscope of study
is limited to the single diode model. Also, the shunt resistance
is very high andcan be neglected during the course of our
study.
Figure No. 2 : I-V characteristics of a solar panel
The I-V characteristics of a typical solar cell are
as shown in the Figure .When the voltage and the current
characteristics are multiplied we get the P-V characteristics as
shown in Figure. The point indicated as MPP is the point at
which the panel power output is maximum.
Figure No. 3 : P-V characteristics curve of photovoltaic cell
Push Pull
A push–pull converter is a type of DC-to-DC converter, a
switching converter that uses a transformer to change the
voltage of a DC power supply. The distinguishing feature of a
push-pull converter is that the transformer primary is supplied
with current from the input line by pairs of transistors in a
symmetrical push-pull circuit. The transistors are alternately
switched on and off, periodically reversing the current in the
transformer. Therefore current is drawn from the line during
both halves of the switching cycle.
Figure No 4: Half Bridge Push Pull Convertor

VL= [(Vd-1) (Nm/No)-0.5]*2*D
L=0.5* VI *D
C= (80*10-6
* dI)/VO
MPPT and Algorithm
A typical solar panel converts only 30 to 40 percent
of the incident solar irradiation into electrical energy.
Maximum power point tracking technique is used to improve
the efficiency of the solar panel. According to Maximum
Power Transfer theorem, the power output of a circuit is
maximum when the Thevenin impedance of the circuit (source
impedance) matches with the load impedance. Hence our
problem of tracking the maximum power point reduces to an
impedance matching problem.
In the source side we are using a boost convertor connected to
a solar panel in order to enhance the output voltage so that it
can be used for different applications like motor load. By
changing the duty cycle of the boost converter appropriately
we can match the source impedance with that of the load
impedance.
Perturb & Observe(P&O) Algorithm
Inverter
The dc-ac converter, also known as the inverter,
converts dc power to ac power at desired output voltage and
frequency. The dc power input to the inverter is obtained from
an existing power supply network or from a rotating alternator
through a rectifier or a battery, fuel cell, photovoltaic array or
magneto hydrodynamic generator. The filter capacitor across
the input terminals of the inverter provides a constant dc link
voltage. The inverter therefore is an adjustable-frequency
voltage source. The configuration of ac to dc converter and dc
to ac inverter is called a dc-link converter.
The single-phase units can be joined to have three-phase or
multiphase topologies. Some industrial applications of
inverters are for adjustable-speed ac drives, induction heating,
standby aircraft power supplies, UPS (uninterruptible power
supplies) for computers, HVDC transmission lines, etc
Pulse Width Modulation Control
The fundamental magnitude of the output voltage
from an inverter can be controlled to be constant by exercising
control within the inverter itself that is no external control
circuitry is required. The most efficient method of doing this is
by Pulse Width Modulation (PWM) control used within the
inverter. In this scheme the inverter is fed by a fixed input
voltage and a controlled ac voltage is obtained by adjusting
the on and the off periods of the inverter components. The
advantages of the PWM control scheme are :
a) The output voltage control can be obtained without addition
of any external components.
b) PWM minimizes the lower order harmonics, while the
higher order harmonics can be eliminated using a
filter.
Figure No. 5: Sinusoidal PWM Generation
The disadvantage possessed by this scheme is that
the switching devices used in the inverter are expensive as
they must possess low turn on and turn off times, nevertheless

Filter
Comparing the parallel and series active filter as
shown in Figure, the parallel filter has better performance on
system efficiency, since the active filter only processes the
ripple energy and the PV array outputs the average power. The
parallel active filter cannot boost the solar array output voltage
to facilitate the inverter design.
Figure No. 6: Single Stage Inverter with Active Filter
For series active filter, it is better to use boost
converter as the first stage, which has continued current
without any switching ripples. The objective of the DC/DC
controller is to regulate the output voltage of the DC/DC
converter to be constant, and the objective of the inverter
controller is to regulate the output current of the inverter to be
pure sinusoid.
For instance, if the output voltage of the active filter is
100VDC and the voltage ripple is 3V, then the capacitance
needed is 4.4μF/Watts from equation (3.8), which is about 10
times smaller than the passive filter. The controller of the
inverter has two loops. The outer loop is the DC voltage
regulation loop; the other is the output current regulation
loop. Note that there is a low pass filter on the loop of the
inverter controller, which will filter out the 120/100Hz ripple
on the DC bus to get the average value of the DC bus. Then
the bandwidth of the outer loop is lower than 120/100Hz.
PCB Layout
Figure No. 7 : PCB Layout
Converter Parameters
Parameters Rating
Switching Frequency 40 KHz
Duty Ratio .45
O/p Capacitors 40 uH
Gate Pulse Voltage 12
Figure No. 8 : Controller Circuit
Simulation of Push Pull Converter
Simulation of Inverter on Matlab

Result
Different waveforms are observed given below:
1. Gate Pulses for Push Pull Converter
2. Output Voltage at different Inputs:
At 289 V:
At 401 V:
Conclusion
By using DC-DC converter topology here above
circuit is work up to 150 watt. The converter is designed for
100 watt and efficiency in open loop is 98%. Half Bridge
Push-Pull converters are basically used for low power
applications up to 200 watt. For high power applications
flyback and forward converter topologies are used.
It has been highlighted that there is a vast resource
available and PV technology is one of the most feasible
renewable energy’s for electricity generation within the urban
environment.
Future Scope
Future scope of this project is to provide controlled
close loop with PID controller and to design full bridge
sinusoidal inverter. The technology is reliable and relatively
simple to install and easy to maintain. Considering the
expertise that exists in the UK it is strange that PV does not
play a greater part in our lives. One of the main reasons is that
electric power generated from PV is too expensive to compete
in Scotland and the UK due to the low prices of fossil-fuel,
nuclear and even wind power.
Reference
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Generation, Marcel Dekker, New York,2000.
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4, pp. 78-94, July-August 2007.
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energy resources and microgrid”, Renewable & Sustainable
Energy Reviews, vol. 12, pp. 2472-2483, 2008.
[4]. LipingGuo, John Y. Hung and R. M. Nelms, “Evaluation
of DSP-Based PID and Fuzzy Controllers for DC–DC
Converters”, IEEE Transactions on Industrial Electronics,
Vol.56, No. 6, pp: 2237-2248, June 2009.
[5].Mehdi Neshat, Ali Adeli, Azramasoumi and Mehdi
sargolzae, “A Comparative Studyon ANFIS and Fuzzy
Expert System Models for Concrete Mix Design”,
International Journal of Computer Science Issues, Vol. 8,
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[6]. L.Umanand and S.R Bhat, Design of magnetic component
for Switch Mode Power Converter, Wiler Eastern Limited,
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[8]. Switching Power supply-Pressman 3rd
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Design a Highly Efficient Push-Pull converter for Photovoltaic Applications

Design a Highly Efficient Push-Pull converter for Photovoltaic Applications

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