CHAPTER ONE

1.1 INTRODUCTION
Today, electricity is the major concern of the world. Especially in developing
countries like ours, In Ethiopia the problem of electricity is serious. Frequent
power interruption, high cost of electrical bills, damage of electrical device
because of overloads are common. As researches indicate, Ethiopia has a huge
potential of renewable energy sources like solar and wind. But it is not being
benefited from those sources a lot. In our country, the usual way to eliminate
electrical power interruption is by using generator. This will enhance
environmental pollution by adding carbon di oxide emission to the ozone layer.
Solar, is the simplest to construct among other renewable energy sources. It
requires only a simple photovoltaic generation cell to provide electricity. PV
panels have no moving parts and can be as lightweight or bulky as the
application requires. It is more economical source of energy for sub-Saharan
countries like Ethiopia.

Some of power supply system's consisting of generator mainly operated with

manual system. The main problems associated with a manual switching system
are as follows: interrupted power supply, device damage due to frequent
commutations, possible causes of fire outbreak due to switching sparks and
frequent high maintenance cost due to changeover action and wear and tear of
mechanical parts. In this paper, we did the design analysis how to minimize
these problems by the design of an "AUTO-SWITCHING POWER SUPPLY SYSTEM
FROM DIFFERENT ENERGY SOURCES".

Therefore the major aim of this work is to exploit the ubiquitous microcontroller
facilities in bringing about automation of changeover process. One of the most
critical needs of an embedded system such as this is to decrease power
consumption and space and this is achieved in this work This system was
designed to proper solution to the shortcomings of the already existing manual
changeover by performing power swap from public power to generator
automatically and vice-versa with the addition of solar power source.
 1.2 STATEMENT OF PROBLEM

In our country the major source of power supply for above 80 percent of
currently used power utility is hydro power due to this interruption of electrical
power supply will sometimes occur. Due to this we are forced use electricity
even with shifts. On the other hand, we don't have a habit of using renewable
source such as solar power supply, wind power supply and so on while we have
plenty of them. So to minimize our cost of power consumption we have to use
renewable source

1.3 OBJECTIVE
1.3.1 General objective

The main objective of this project concern on the following: -

1. To save the cost of electrical bills by replacement of renewable energy

source.

2. Minimize power interruption using various options of electrical power

sources. The only case that power can be interrupted is when all power
sources are not available. This may occur rarely.

3. To develop a habit of using renewable energy sources.

1.3.2 Specific objective

 Design and construct a PIC based automatic transfer switch that
can switch Load from different power supply with simplicity.
 Introduction of a circuitry that can sense power outage using
voltage sensing element and at the same time Sense fluctuation and
power supplied to the load at any point in time.
 To design and develop a hardware and software of PIC
microcontroller based ATS

1.4 List of research questions

Before mention the questions arising in this project we would like to say
why we motivate to choose these project area, we are looking different
problems regarding with this sector, based on this problems we have put
different question which can be solved, and we are facing with it and
 make challenge us. The question which arising in this project will be as
follow:-
 Why do we have the habit of using renewable source easily?
 How can prevent power interruption?
1.5 Significance of the study

The purpose of this project is to design and construct a PIC based

automatic changeover switch that provides a solution to the erratic power
supply problem we are facing in Ethiopia today. The automatic transfer
switch is a unique switching system that can be used to effect the change
from one power supply to another as well as to ensuring
consistency in the supply to a particular network or load.

The uniqueness of this equipment lies in its ability to maintain constant

supply to the main circuit being supplied by compensatory for the time
lapse or delay that usually accompanies the manual switching from one
source to another

1.6 Delimitation and limitation of the study

1.7 Methods and materials used in the project
In this project we are using different mechanisms to achieve our goal,

1.8 Scope of the project

The main scope of this project is to ensure the continuous consumption of

power supply from mains, generator, and solar sources, optimally in a way to
save mains and generator fuel by using an appropriately programmed
microcontroller in the most effective way. Emergency power systems are the
types of systems that may include lighting, generators, fuel cells and other
apparatus, to provide backup power resources in crisis or when the regular
system fail. It mainly focuses on where the place which needs continuously
power consumption such as campus in critical area, hospital and so on. But
specifically our project will be applied on medium hospital.
 CHAPTER TWO

LITRATURE REVIEW
2.1 REVIEW OF EXISTING WORK
To ensure the continuity of power supply, many commercial/industrial facilities
depend on both utility service and on-site generation (generator set). And
because of the growing complexity of electrical systems it becomes imperative
to give attention to power supply reliability and stability. Over the years many
approaches have been implored in configuring a changeover system. This
system doesn’t consider other possible renewable energy sources that can
supply enough power to the existing work and this can add electrical bills and
environmental hazards by relaying up on only diesel generators for backups.
The existing system has other backdrawns since it doesn’t consider full power
generation of the generator power interruption happens as main utility goes off.
Today the invention of power electronic switches makes conversion of one form
of electrical power to the other so solar power can also be the best source of
electrical power.

2.2 AUTOMATIC TRANSFER SWITCH (ATS)

Transfer switches, also known as changeover switches, are electrical devices

designed to power an electric load from multiple sources. They are mainly used
with generator sets in applications where the loads need, if not a fully
continuous, at least a steady supply of electric power []. Transfer switches could
be manually or automatically operated. A manual transfer switch box separates
the utility supply from the standby generator. Whenever there is power failure,
changeover is done manually by humans and the same happens when the public
utility power is restored and this is usually accompanied with loud noise and
electrical sparks . An Automatic Transfer Switch (ATS) is used with standby
systems. It includes a control circuit that senses mains voltage. When mains
power is interrupted, the control circuit starts up the generator set, disconnects
the load from the utility and connects it to the generator set. It then continues to
monitor the mains status. When mains power is restored, it commutes the load
from the generator back to the utility within a threshold time .
When the generator is disconnected, it goes through a cool-down process and
then automatically shuts down . Fig. 2 shows a schematic diagram of a typical
transfer switch. Transfer switches could be installed between two generators, a
generator and a utility supply or between alternate utility providers

Figure 2.1 automatic transfer switch

2.3 TRANSFORMER

A transformer is a device that transfers electrical energy from one circuit to

another through inductively coupled conductors (the transformer’s coils). A
varying current in the first or primary winding creates a varying magnetic field
through the secondary winding. This varying magnetic field induces a varying
electromotive force (EMF) or voltage in the secondary winding. This effect is
called mutual induction.
If a load is connected to the secondary, an electric current will flow in the
secondary winding and electrical energy will be transferred from the primary
circuit through the transformer to the load .in an ideal transformer, the induced
voltage in the secondary winding (V s) is in proportion with to the primary
voltage (Vp), and is giving by the ratio of the number of turns in the secondary
(Ns) to the number of turns in the primary (Np) as follow
Vs/Vp=Ns/ Np .........................................................................2.1

2.4 DC TO DC BOOST CONVERTER

Boost converter steps up the input voltage magnitude to a required output
voltage magnitude without the use of a transformer. The main components of a
boost converter are an inductor, a diode and a high frequency switch. These in a
coordinated manner supply po wer to the load at a voltage greater than the input
voltage magnitude. The control strategy lies in the manipulation of the duty
cycle of the switch which causes the voltage change.

Figure 2.2 DC to DC boost converter

2.4.1 Modes of Operation

There are two modes of operation of a boost converter. Those are based on the
closing and opening of the switch. The first mode is when the switch is closed;
this is known as the charging mode of operation. The second mode is when the
switch is open; this is known as the discharging mode of operation .

A. Charging Mode
In this mode of operation; the switch is closed and the inductor is charged by
the source through the switch. The charging current is exponential in nature but
for simplicity is assumed to be linearly varying [11]. The diode restricts the
flow of current from the source to the load and the demand of the load is met by
the discharging of the capacitor.
B. Discharging Mode
In this mode of operation; the switch is open and the diode is forward biased.
The inductor now discharges and together with the source charges the capacitor
and meets the load demands. The load current variation is very small and in
many cases is assumed constant throughout the operation.

Figure 2.3 Modes of operation of boost converter

2.5 DC TO AC POWER INVERTER

Voltage Source Inverter: The type of inverter where the independently
controlled ac output is a voltage waveform. The output voltage waveform is
mostly remaining unaffected by the load. Due to this property, the VSI have
many industrial applications .
Single Phase Full wave Bridge Inverter: It consists of two arms with a two
semiconductor switches on both arms with antiparallel freewheeling diodes for
discharging the reverse current. In case of resistive-inductive load, the reverse
load current flow through these diodes. These diodes provide an alternate path
to inductive current which continue so flow during the Turn OFF condition

Figure 2.4 DC to AC inverter

2.6 PI CONTROL STRATEGY

A PI controller is a closed loop controller. The letters P and I stand for:

P - Proportional

I - Integral

Figure 2.5 Block diagram of PI controller

PI controller works in a closed-loop system using the schematic shown above.
The variable (e) represents the tracking error, the difference between the desired
input value (R) and the actual output (Y). This error signal (e) will be sent to the
PI controller, and the controller computes the integral of this error signal. The
signal (u) just past the controller is now equal to the proportional gain (Kp)
times the magnitude of the error plus the integral gain (Ki) times the integral of
the error.

The transfer function of the most basic form of PI controller,

Gc ( s )=K P+ K D s

The effects of increasing each of the controller parameter Kpand Ki can be

summarized as

Response Rise Time Overshoot Settling Time Steady State Error

Kp Decrease Increase Minor change Decrease

KI Decrease Increase Increase Eliminate

Table 2.1 Effect of Ki and Kp

2.7 Pulse-Width Modulated (PWM)

The Pulse Width Modulation (PWM) is a technique which is characterized by

the generation of constant amplitude pulse by modulating the pulse duration by
modulating the duty cycle. Analog PWM control requires the generation of both
reference and carrier signals that are feed into the comparator and based on
some logical output, the final output is generated. The reference signal is the
desired signal output maybe sinusoidal or square wave, while the carrier signal
is either a saw tooth or triangular wave at a frequency significantly greater than
the reference. There are various types of PWM techniques and so we get
different output and the choice of the inverter depends on cost, noise and
efficiency.
Most commonly used techniques are:-
 2.7.1 Single Pulse Width Modulation
In this modulation there is an only one output pulse per half cycle. The output is
changed by varying the width of the pulses. The gating signals are generated by
comparing a rectangular reference with a triangular reference. The frequency of
the two signals is nearly equal.

Figure 2.6 single pulses PWM

2.7.2 sinusoidal-PWM
In this modulation technique are multiple numbers of output pulse per half cycle
and pulses are of different width. The width of each pulse is varying in
proportion to the amplitude of a sine wave evaluated at the centre of the same
pulse. The gating signals are generated by comparing a sinusoidal reference
with a high frequency triangular signal.
Figure 2.7 sinusoidal PWM

will be explained. In order to output a sinusoidal waveform at a specific

frequency a sinusoidal control signal at the specific frequency is compared with
a triangular waveform
(See Figure 7a). The inverter then uses the frequency of the triangle wave as the
switching frequency. This is usually kept constant. The triangle waveform,
inverter, is at a switching frequency fs, this frequency controls the speed at
which the inverter switches are turned off and on. The control signal, voltage
control, is used to modulate the switch duty ratio and has a frequency f1.This is
the fundamental frequency of the inverter voltage output. Since the output of the
inverter is affected by the switching frequency it will contain harmonics at the
switching frequency. The duty cycle of the one of the inverter switches is called
the amplitude modulation ratio.

2.8 MICROCONTROLLER
A microcontroller is a computer control system on a single chip. It has many
electronic circuits built in to it, which can decode written instructions and
convert them to electrical signals. The microcontroller will then step through
these instructions and execute them one by one. As an example of this a
microcontroller we can use it to controller the lighting of a street by using the
exact procedures. Microcontrollers are now changing electronic designs. Instead
of hard wiring a number of logic gates together to perform some function we
now use instructions to wire the gates electronically. The list of these
instructions given to this microcontroller is called a program. There are different
types of microcontroller, this project focus only on the PIC16F877A
Microcontroller where it's pins as shown in the figure.

Figure 2.8 PIC16F877A

2.9 BATTERY
Battery condition and corresponding state of charge that we gathered from
reading of formerly used batteries for solar system is used to measure the
present state of charge of the battery. It's crucial to follow the ratings in our
design so that it may work well with batteries from any organization. The
following chart represents a clear idea about battery condition that are generally
used including charging and discharging both:

PERCENTAG VOLTAGE
E
BATTERY
20% 11.58
30% 11.75
40% 11.9
50% 12.06
60% 12.20
70% 12.32
80% 12.42
90% 12.5
100% 12.7

Table 2.2 Charge state of 12v battery

 CHAPTER THREE
METHODOLOGY

3.1 POWER SOURCES

In this project we are going to switch the following power sources accordingly.

Figure 3.1 Block diagram of power sources

From the block diagram it is shown that there are 3 sources of energies main
utility supply, solar energy and generator. Solar power system is one of
renewable energy system which uses PV modules to convert sunlight into
electricity. The electricity generated can be either stored or used directly by the
load with the use of appropriate power electronic converter circuit. From energy
of sun, solar panel is being heated. Due to heating of solar panel, DC power will
be generated. This power will be given to the DC-DC boost converter. Now
DC-DC boost converter will boost (step up) it to specified DC voltage which
will be appropriate to inverter. Inverter will convert this DC voltage into
required AC voltage. But this AC voltage will be pulsating and contains some
harmonics, to shape it to a form required by the load PI control strategy and
filter are being placed. After passing from filter, it will be pure AC power and
ready for load consumption.

Solar PV system is very reliable and clean source of electricity that can suit a
wide range of applications such as residence, industry, agriculture, livestock,
etc.

3.1.1 AC mains supply

The AC input supplies a 220V AC, 50Hz from the public supply.

3.1.2 Generator
3.1.2.1 Automatic Generator Start

Auto start generators are capable of remote start, meaning that these units
can be started by an external signal, such as one that might come from an
inverter when it detects a set battery voltage level. The control over the
generator’s operation that is, when to run and when to stop is external to
the generator, while the generator provides its own safety protection, such
as shutoff for low oil level, overheating, and other factors Among remote-
start generators, the simplest is the “two-wire start,” in which a closed
contact tells the generator to start and run. When the contacts open, the
generator stops. Automatic generator operation is at best a mixed
blessing. However, Poor Programming can lead to excessive runtime and
fuel consumption, yet not guarantee that batteries are adequately charged.
The most likely path to eventual failure is total dependence on a generator
in an unattended system.

3.1.2.2 GENERATOR SELECTION

3.1.3 Solar
 Solar Panels come in a variety of shapes and sizes.They are also made up of
different materials like for example while most panels are made from silicon
(the same material used in electronics),some solar panels are also made up of
thin film solar materials like Copper Indium Gallium Selenide or Cadmium
Tellerium. Solar Panels of standard 200-250 Watts are of 5-6 feet in lenght and
3.5 feet in width and can weigh as much as 25 kg.Solar Arrays are made up of a
number of Solar Panels which provide the required voltage and power of
electricity requirements.

Solar Panel is made up of Solar Cells which are the basic building blocks of a
Solar Panels.A Typical Solar Cell provides around 0.5 Volts and around 60-90
Solar Cells make up a typical solar panel which implies 30-45 Volts .This will
provide around 8-10 Amperes of Electricity for around  200-250 Watts of
Power. Solar Cells are also of different variety and efficiency.all information
about Solar Panel Efficiency and Solar Cells Efficiency can be read from panel's
specification.

Solar Panel of 200-250 Watt normally has dimensions 65 inches x 4o inches  x

1.80 inches and weight of around 20-25 kgs.Note Solar Panels made from Thin
Film have much bigger sizes because of lower efficiency,however their
thickness is lower and weight is also a bit lower than similar dimension
polysilicon solar panel.

3.1.3.1 Solar PV system sizing

1. Determining power consumption demands

The first step in designing a solar PV system is to find out the total power and
energy consumption of all loads that need to be supplied by the solar PV system
.our specified load is 1hp or 746watt.

2 Calculation of total Watt-hours per day for each appliance used.

Add the Watt-hours needed for all appliances together to get the total Watt-
hours per day which must be delivered to the appliances.

746w*10h=7460wh ..............................................................................3.1
3 Calculation of total Watt-hours per day needed from the PV modules.

Multiply the total appliances Watt-hours per day times 1.3 (the energy lost in
the system) to get the total Watt-hours per day which must be provided by the
panels.

Total appliance use = 746 *8Hr=5968wh/day

  =
Total PV panels = 5968Wh /dayx 1.3
energy needed 
  = 7758.4Wh/day.

4 Size the PV modules

Different size of PV modules will produce different amount of power. To
find out the sizing of PV module, the total peak watt produced needs. The
peak watt (Wp) produced depends on size of the PV module and climate of
site location. We have to consider “panel generation factor” which is
different in each site location.

For Ethiopia, the panel generation factor is about 5.3.

The system will be powered by 30Vdc, 200 Wp PV modules.

5 Calculation of the number of PV panels for the system

Divide the answer obtained in item 4 by the rated output Watt-peak of the PV
modules available to you. Increase any fractional part of result to the next
highest full number and that will be the number of PV modules required.

Result of the calculation is the minimum number of PV panels. If more PV

modules are installed, the system will perform better and battery life will be
improved. If fewer PV modules are used, the system may not work at all during
cloudy periods and battery life will be shorter.
 =7758.4 Wh/ 5.3
Total Wp of PV panel
capacity needed
  = 1463.8Wp
Number of PV panels = 1463.8Wp / 200Wp
needed
  = 7.3modules

          Actual requirement = 8 modules

3.1.3.2 SOLAR BATTERY SIZING

The battery type recommended for using in solar PV system is deep cycle
battery. Deep cycle battery is specifically designed for to be discharged to low
energy level and rapid recharged or cycle charged and discharged day after day
for years. The battery should be large enough to store sufficient energy to
operate the appliances at night and cloudy days. To find out the size of battery,
calculate as follows:

   Calculate total Watt-hours per day used by appliances.

   Battery loss (Bl)= 0.85
   Depth of discharge(Dd) = 0.6
   the nominal battery voltage(Vn)=12v
   number of days of autonomy =0.25 day

Total appliances use = 746w*8h=5968wh .....................................................3.2

    Nominal battery voltage = 30V

    Days of autonomy = 0.5 day
Total appliance use∗days
    Battery capacity = Vn∗Dd∗Bl
.....................................3.3

5968 wh∗0.25
= 12 v∗0.6∗0.85
 =243.79AH

   

3.1.3.3 SOLAR CHARGE CONTROLLER SIZING

A charge controller limits the rate at which electric current is added to or

drawn from electric batteries. It prevents overcharging and prevent against
overvoltage, which can reduce battery performance or lifespan, and may
pose a safety risk. It may also prevent completely draining ("deep discharging")
a battery, or perform controlled discharges, depending on the battery
technology, to protect battery life. Charge controllers are sold to consumers
as separate devices, often in conjunction with solar or wind power generators,
for uses such as off-the-grid home battery storage systems.

Figure 3.2 Battery charge controller

We have to select solar charge controller to match the voltage of PV array and
batteries and then identify which type of solar charge controller is right for our
application. Solar charge controller should have enough capacity to handle the
current from PV array. For the charge controller, the sizing of controller
depends on the total PV input current which is delivered to the controller
According to standard practice, the sizing of solar charge controller is to take
the short circuit current (Isc) of the PV array, and multiply it by 1.3.
Solar charge controller rating = Total short circuit current of PV array x 1.3

 PV module specification

    Pm = 200 Wp
    Vm = 16.7 Vdc
    Im = 6.6 A
    Voc = 20.7 A
    Isc = 7.5 A

 Solar charge controller rating = (8 panels x 7.5 A) x 1.3 = 78 A

 So the solar charge controller should be rated 78 A at 12 V or
greater.                                                         .

3.1.3.4 DESIGN OF DC TO DC BOOST CONVERTER

Boost Converter is a DC-DC converter for which Output voltage is greater

than input voltage. When the MOSFET switch is ON, the current through the
inductor Increases and the inductor start to store energy. When the
MOSFET switch is closed, the energy stored in the inductor starts
dissipating. The current from the voltage source flows through the fly back
Diode D to the load. The Voltage across the load is greater than the input
voltage and is dependent on the rate of change of the inductor Current. Thus
the average voltage across the load is greater than the input voltage and is
determined with help of the duty cycle of the gate pulse to the MOSFET
switch.

Figure below shows the schematic diagram for the boost converter used in
this design to step up the PV output voltage to a higher level suitable for the
DC/AC inverter operation that connected to the utility.

Vs
V 0= .........................................................................3.4
1−D

T on
D= ............................................................................3.5
T
 T= T on +T off ...................................................................3.6

Transfer Function of Boost Converter

Basic circuit of the boost converter is shown in Figure above. Here, L is

the inductor and R is the resistor which is consider as a load. Is the
current flowing through the circuit. Switch is triggered by the pulse which is
generated by PWM technique. Switch remains on during Ton cycle and off
during Toff cycle so triggering is depends on the duty cycle. V0 is the D.C.
output voltage. is the output of the boost converter Where Vs is source
voltage Vo is the output voltage of the converter D is the duty cycle .

di
V¿ = L* dts ...................................................................3.7

Using Laplace transformation

V ¿(s) = L*s*is(s)............................................................3.8
From the figure V o can be given as
V O (s)= i s (s)*R.................................................................3.9

From equation 3.8 and 3.9

V O (s) R
V ¿ (s)
= L∗s
........................................................................3.10
Figure

3.3 closed loop bloc diagram of boost converter

Transfer Function of Closed Loop System

Now to achieve proper objective of converter, it is needed to measure and

maintain output voltage at required voltage

R K
V O= ( )*[V ¿ + ( K P + I )*e]...................................................................3.11
L∗s s

Taking V ref =0
R K 1 R
V O + [( ) * ( K p + i) * ( ) * V O] = V ¿ * (
L∗s s 1−D L∗s
) ......................................3.12
R
VO L∗s
=
( L∗sR )∗( K + s )∗( 1−D ))]
V¿ KI 1
[1+( P

.....................................................................3.13

BOOSTER PARAMETERS
Overall booster efficiency is taken 95%. From this input power of booster is
809.55w. Minimum input voltage to the booster is 120V. Maximum Input
voltage of the booster is 160V. Output voltage of Booster is 220V. Relation
between input voltage and output to control the output voltage of booster PI
controller is Used which is shown in figure. As shown in Reference voltage
is compared with actual output voltage and error in output voltage e is
calculated. Error e is passed through PI controller. The output of PI
controller is given by equation 9. The output of PI controller is compared
with triangular wave which will generate pulses which is given to the
MOSFET of the dc to dc boost converter. So close loop control makes the
output voltage of dc to dc boost converter constant.

pf = unity.
ƞinverter =97 %
ƞbooster = 95%
f sw = 3.2kHz
PbstrI = PinvtrO + Pinvtrloss + Pbstrloss.......................................3.14
= 746w + (0.03*746w) +[0.05*(746w+0.03*746w)]
= 809.55w.

From equation 3.4

vmin=120v
vmax=160v
vout=220v
 V¿
D = 1- V 0 ..................................................................................3.15

D min = 0.2727
D max = 0.4545
From equation 3.5
T on = D*T ................................................................................. 3.16
T >T >In steady state conditions
∆I
V¿ = L* T on .............................................................................3.17

∆I = ripple current = 20% of input current

V inmin∗T onmax 120V ∗142.03 us
L= ∆ I max = 1.35 A =12.62mH

T onmax ∗I o
C= ∆Vo
..............................................................................3.18

∆V o = voltage ripple = 1% of output voltage

142.03us∗3.5 A
2.2 V
= 225.96uF
figure

3.1.3.5 DESIGN OF DC TO AC INVERTER

LC Filter Design
A low pass LC filter is required at the output terminal of Full Bridge
VSI to reduce harmonics generated by the pulsating modulation waveform.
While designing L-C filter, the cut-off frequency is chosen such that most of
the low order harmonics is eliminated. To operate as an ideal voltage
source, that means no additional voltage distortion even though under
the load variation or a nonlinear load, the output impedance of the inverter
must be kept zero. Therefore, the capacitance value should be maximized
and the inductance value should be minimized at the selected cut-off
frequency of the low-pass filter. Each value of L and C component is
determined to minimize the reactive power in these components because the
reactive power of L and C will decide the cost of LC filter and it is selected
to minimize the cost, then it is common that the filter components are
determined at the set of a small capacitance and a large inductance and
consequently the output impedance of the inverter is so high. With these
design values, the voltage waveform of the inverter output can be sinusoidal
under the linear load or steady state condition because the output impedance
is zero. But in case of a step change of the load or a nonlinear load, the
output voltage waveform will be distorted caused by the slow system
response as the output response is non-zero.

Using the closed relation between the filter capacitor value and the
system time constant, the capacitor value can be calculated. The effect
of the load current to the voltage distortion can be calculated from the
closed form. It is also possible to analyse how much the voltage
waveform isdistorted in the system in case of a nonlinear load.

Va ( s )−s Lf Ia ( s ) −R f Ia ( s ) Vc ( s )=0 ...................................................3.19

Va ( s )−Vc ( s )=Ia ( s ) ( s L f + Rf )...........................................................3.20

Va ( s ) Ia ( s ) ( s Lf + R f )
=1+ ............................................................3.21
Vc ( s ) Vc ( s )

Va ( s ) Ia ( s ) ( s Lf + R f ) s C f
=1+ .................................................................3.22
Vc ( s ) Ic ( s )

As ia=ic+io
 Vc( s)
Ia ( s )=Ic ( s ) + ................................................................................3.23
ZL

Ia (s) 1
=1+ ....................................................................................3.24
Ic (s ) sCfZL

Va(s)
Vc(s)
=1+ 1+
1
(
s Cf ZL )
( s L f Rf ) s C f ..............................3.25
2
Va(s) S Lf C f + S Lf + Rf C f S Z L + Rf Z L
Vc(s) = ZL
.......................................3.26
Vc(s) ZL
= 2
Va(s) s Lf C f +¿ S L +RCs Z +R +Z ¿
.................................................3.27
f L f L
PI controller is a feedback controller which detects the error value
which is the difference of the output signal and the desired or
reference signal. PI controller works to minimize this error by controlling
the system inputs. PI controller has two elements namely Proportional (P)
and Integral (I). Proportional part reduces the error while Integral part
reduces the offset. P depends on present error and I depend on past errors.
So, step response of a system can be improved by using PI controller.

After installing a PI Controller block the new response of the system will be
U ( s)
=PI *G( s ) ........................................................................................3.28
E( s)

KI
P I=¿K ¿+ .................................................................................................3.29
P
S

U (s )
E(s) (
P+
S
I
)
= K K *G( s ) ............................................................................3.30

Now PI element gains, Kp(proportional gain) and Ki(integral gain) should be

tuned to obtain a better system response. The effect of each parameters value
on increasing is given below.

Inverter is designed for output power of 746w. Power factor is taken

approximately unity because we are only having resistive loads. Overall
efficiency of inverter is taken 97%. From this output power of booster is
taken 768.38w.

We will get DC power from solar panels through boost converter and this
converter inverts DC to AC. This design and modulation is based on
MATLAB software. In circuit, for switching purpose IGBT is used. There
are many other devices also but IGBT has more advantages than others
which are shown by comparison with others. The main thing is that this
conversion and switching of IGBT is done using different types of PWM
methods. Here we are using SPWM method for conversion of AC power.
This method is very efficient than other methods and also it reduces
harmonics to very much extent in output. Project objective are, to design an
inverter model by using Power inverters are devices which can convert
electrical energy of DC form into that of AC. They come in all shapes and
sizes, from low power functions such as powering a car radio to that of
backing up a building in case of power outage. Inverters can come in many
different varieties, differing in price, power, efficiency and purpose. The
purpose of a DC/AC power inverter is typically to take DC power and
transform it into a 220 volt AC power source operating at 50 Hz, emulating
the power available at an ordinary household electrical outlet.
 SIMULATION RESULTS OF DC TO AC INVERTER

Inverter input is a 100V dc and the output is 220V AC. This inverter
can be used for household appliances.
 3.2 DESIGN OF SWITCHING SYSTEM
3.2.1 DESIGN OF CIRCUIT POWER SUPPLY

Fig 5v regulated supply

If the unregulated input of the 7805 is greater than 9v while the required output
is 5v the voltage regulator IC, starts getting hot and will be damaged. Hence we
will need an input into the 7805 to be approximately 9V for 5v output. Since,the
diode drops 0.7V and we have 4 rectifying diodes forming the full wave bridge,
the voltage drop will then be: -

0.7 ×4 = 2.8V
For a peak voltage of 9+2.8=11.8V peak.

For the r.m.s voltage=11.8v x √ 2 = 16.68v

Hence a transformer of a preferred value of 15V was employed. i.e 220V/15V

transformer
Assuming a ripple voltage of 15%

∆ V =15/100 x16.8v = 2.5v.

∆ t = 1/2f = 1/100 = 0.01sec

C1 = 0.01sec / 2.5 = 4000mF

A preferred value of 4000μF was however employed. To reduce the ripple left,
a compensating capacitor C2 was used and a 4065μF was employed.

Fig 12v regulated supply

3.2.2 PER DAY AMPERAGE OF BACK UP BATTERY AND

CIRCUIT DESIGN

To calculate the value of resistor, we have considered the output of

microcontroller is 5v and the voltage drop across base to emitter of transistor
is 0.7v

Given parameter h fe=100, Rcoil=400 Ω,

V LED I LED
Red 1.7V 10mA
Green 2.0V 25mA
Yellow 2.0V 25mA

From KVL
V μc−V 5−0.7 V 12 v
R1= be
= , Since I c= cc = =0.03A
Ib Ib R coil 400 Ω

Ic 0.03 A
I b= = 100 = 0.0003A
hfe
 5−0.7 5−0.7
R1 = = = = 1433Ω ≈ 1500Ω
Ib 0.0003 A

Therefore, the value of resistors R1, R2, R3 are equal.

V µc−V 5−1.7
R4 = led red
= 10 mA = 330Ω ≈ 300Ω
I led red

R4 = R5= 300Ω

V μC−V 5−2
R6 = led green
= 25 mA = 120Ω ≈100Ω
I led green

R6 = R7 = 100Ω

To calculate the total current, we assume 2 % no load current

 LCD current
V 5V
I LCD = = = 5mA
R 1K

I T = 3* I c + 3* I b + 2∗I led red + I led green + I led yellow + I LCD

'

¿ 3* 0.03A + 3* 0.0003A+ 2* 10mA + 25mA + 25mA + 5mA

¿0.1659A
I T = current at no load + I 'T
2
¿ *0.1659 + 0.1659
100
I T =¿0.169218A

Since, Battery capacity per day = I T * T = 0.169A * 24Hr

= 4.0612 AH

3.3.3 DESIGN OF VOLTAGE SENSING CIRCUIT

Three AC voltage sensing circuits continuously monitor the state of the

utility supply, generator, solar inverter and communicate it to the TS
microcontroller. The voltage sensor, as shown in the circuit diagram in Fig.,
is made up of a 220/24 V step down transformer, two resistors, a diode and a
capacitor. To ensure that 5V TTL requirement of the microcontroller is
not violated, a voltage divider circuit, consisting of R1 and R2 is used
to output about 5 V to the controller. This is achieved by setting the
ratio of R1 to R2 to be 10 is to 5. The values of R1 and R2 are
deliberately selected in the kilo ohm range in order to limit the sink current
to the microcontroller. The diode and capacitor C1 are used to give a
unidirectional DC to the respective input pin of the microcontroller.

3.3.4 Design of Change-Over/Electrical Relay Isolation Stage

In our project specially hardware implementation uses electrical relay, it has
the major role in ATS and we have considering the following

 Physical size and pin arrangement: A relay is chose based on the

existing PCB to ensure that its dimensions and pin arrangement are
suitable for the designed project.
 Coil Voltage: The relay coil voltage rating and resistance were taken
into consideration.
 Coil Resistance: The circuit must be able to supply the current
required by the relay coil.
supply voltage
From Ohm’s law, Relay coil current = coil resistance

12 v
Relay coil current = 400 Ώ = 30mA
 3.3.5 Selection of the Size of Automatic Transfer

Switch to a designer load

With the input voltage supply from either power sources (V) = 220-240Va.c
supply

Generator power rating (P) = 1KVA

Assuming Power factor (Cos Ѳ) = Unity

Rated generator set current (I) in Ampere

power∈KVA 1∗1000
operating voltage
= 220 v
= 4.55A ≈ 5A

Therefore the contactor selected for the ATS is a 5A rated contactor.

CHAPTER FOUR

SIMULATION RESULTS
SIMULATION RESULTS OF DC TO DC BOOSTER
CHAPTER FIVE

CONCLUSION AND RECOMENDATION

REFERENCE
APPENDEX

MIKROC CODE

//OUTPUTS int solarV;

#define MainSolarCont RC3_bit void SourceInd();

#define GenCont RC4_bit void Display();

#define PFS RD5_bit // Lcd pinout settings

#define PFM RD6_bit sbit LCD_RS at RB5_bit;

#define PFG RD7_bit sbit LCD_EN at RB6_bit;

#define GENSTRT RD4_bit sbit LCD_D7 at RC2_bit;

#define SolarBatCont RC5_bit sbit LCD_D6 at RC1_bit;

sbit LCD_D5 at RC0_bit;

int Vmin=400; sbit LCD_D4 at RB7_bit;

int Vmax=980;

char x; // Pin direction

char var; sbit LCD_RS_Direction at TRISB5_bit;

int mainV; sbit LCD_EN_Direction at TRISB6_bit;

int genV; sbit LCD_D7_Direction at TRISC2_bit;

sbit LCD_D6_Direction at TRISC1_bit; {

sbit LCD_D5_Direction at TRISC0_bit; PFM=0;

sbit LCD_D4_Direction at TRISB7_bit; PFS=0;

PFG=1;

void SourceInd() }

if(var==1||VAR==3) }

{ void interrupt()

PFM=0; {

PFS=1; if (INTCON.INTF)

PFG=0; {

if(var==2) INTCON.INTF = 0;

{ }

PFM=1; }

PFS=0;

PFG=0; void Display()

} {

if(var==4&&x==1)

{ void main()

PFM=0; {

PFG=0; TRISA = 3;

PFS=~PFS; TRISD = 0;

delay_ms(250); TRISC = 0;

} portd=0;

if(var==4&&x==2) PORTC=0;
 ADCON1=128; }

if((mainV >= Vmin && mainV <=

Vmax)&&!(solarV >= Vmin && solarV
INTCON.GIE = 1;
<= Vmax))
INTCON.INTE = 1;
OPTION_REG.INTEDG = 0; {

Lcd_Init(); MainSolarCont=1;

Lcd_Cmd(_LCD_CLEAR); // SolarBatCont=0;
Clear display
GenCont=0;
Lcd_Cmd(_LCD_CURSOR_OFF);
// Cursor off var=2;

Lcd_Out(1,1,"Initializing...."); }

Delay_ms(1500); if(!(mainV >= Vmin && mainV <=

Vmax)&&(solarV >= Vmin && solarV
Lcd_Cmd(_LCD_CLEAR); <= Vmax))

while (1) {

{ MainSolarCont=0;

mainV = ADC_READ(0); SolarBatCont=0;

solarV = ADC_READ(1); GenCont=0;

genV = ADC_READ(5); var=3;

SourceInd(); if(!(mainV >= Vmin && mainV <=

Vmax)&&!(solarV >= Vmin && solarV
if((mainV >= Vmin && mainV <=
<= Vmax))
Vmax)&&(solarV >= Vmin && solarV
<= Vmax)) {

{ var=4;

MainSolarCont=0; }

MainSolarCont=0; if((var==4)&&!(genV >= Vmin &&

genV <= Vmax))
SolarBatCont=0;

var=1;
{
 MainSolarCont=0; {

SolarBatCont=1; MainSolarCont=0;

GenCont=0; SolarBatCont=0;

GENSTRT=1; GenCont=1;

x=1; GENSTRT=0;

} x=2;

if((var==4)&&(genV >= Vmin && } }}

genV <= Vmax))