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.

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