inverter & its application in power system

“RAJASTHAN TECHNICAL UNIVERSITY, KOTA”
A
Seminar Report
Submitted
in partial fulfillment
for the award of the degree of
Bachelor of Technology in Electrical Engineering
Inverter & Their
Application in Power System
Submitted to: Submitted by:
Dr. Seema Agarwal Deepak Singh Chauhan
Professor 16/270,16EUCEE027
Dept. of Electrical Engg. B.Tech. VIII Semester
=======================================================================================================
DEPARTMENT OF ELECTRICAL ENGINEERING
RAJASTHAN TECHNICAL UNIVERSITY
RAWATBHATA ROAD, AKELGARH, KOTA, RAJASTHAN, 324010

RAJASTHAN TECHNICAL UNIVERSITY
(Approved by AICTE, New Delhi | Affiliated to RTU Kota, Rajasthan)
(NBA Accredited EE Department )
Candidates Declaration
It is hereby declared that the work, which is being presented in the Seminar Report titled
“INVERTER AND THEIR APPLICATION IN POWER SYSTEM” in partial fulfillment of the
award of Bachelor of Technology in Electrical Engineering and submitted in the department of Electri-
cal Engineering of Rajasthan Technical University, Kota is an authentic record of the work under the
supervision and valuable guidance of Mr. S.R.Kapoor, Professor, Dept. of Electrical Engineering.
The matter presented in the report embodies the result of the studies carried out by the student
and has not been submitted for the award of any other degree in this or any other institute.
Name of the Candidate : DEEPAK SINGH CHAUHAN
College Roll No. : 16 /270
RTU Roll No. : 16EUCEE027
Dr. Seema Agarwal
Professor
Department of EE
Mr. S. R. KAPOOR
Head of the Department
Department of Electrical Engineering
Rajasthan Technical University, Kota

Acknowledgement
... What makes us who we are should be glorified, personified and sung unto the stars!!
― Muse, Enigmatic Evolution
I would like to express my special thanks and gratitude to my Seminar guide, Dr. Seema
Aggarwal, Professor, and Mr. Muhammad Zaid ,Department of Electrical Engineering for providing
me a golden opportunity to work and prepare a Seminar report on the topic ““INVERTER AND
THEIR APPLICATION IN POWER SYSTEM”” and for paving the path towards the completion
of this report by his esteemed guidance and enlightenment.
I would also like to extend my sincere regards to Mr. S. R. Kapoor, my mentor and Head of
the Department, Electrical Engineering and all the faculty members in the department for providing
us their kind encouragement and cooperation in strengthening our knowledge in this field and for
providing me an opportunity to work.
- Deepak Singh Chauhan

ABSTRACT
In this Seminar report first we will talk about power electronics converter and their types like
cycloconverter, diode rectifier, inverter, chopper, static switch .Then we study about Inverter and
their working principal where we differentiate among AC and DC. Then we will know about Tech-
nical background of inverter and type of inverter square wave inverter and sine wave inverter and
their output characteristic. Then we discuss classification of inverter based upon charging process,
output characteristics, source, load, PWM Technique. Then we will discuss standard inverter func-
tionalities.
Then we study additional function of inverter. As a result of the rapid rise of distributed generation
(DG) from Renewable energy sources, the grid becomes more vulnerable. Therefore, DG systems
are needed to be controlled with high flexibility and reliability to get rid of those vulnerabilities.
At the same time the power quality is also needed to be developed. To help this process the tradi-
tional solar inverters are also should be advanced with some additional smart functions as “Smart
Inverters”. The advantages, along with the disadvantages, are given in order to better understand-
ing of these functions

CONTENT
Candidates Declaration i
Acknowledgement ii
Abstract iii
CHAPTER No. NAME OF CHAPTER PAGE. No
A INTRODUCTION 1
1. INVETER 4
1.1 Difference between AC and DC electricity 4
1.2 What is Inverter 5
1.3 How does an inverter works 6
1.4 Input and output voltage 7
2. HISTORY 9
2.1 Early inverter 9
2.2 Controlled rectifier inverter 9
2.3 Rectifier and inverter pulse No 9
3. TYPES OF INVERTER 12
3.1 Types of Inverter 12
3.1.1 Square wave inverter 13
3.1.2 Pure sine wave inverter 15
3.1.3 Modified sine wave inverter 17
3.1.4 What are inverter like? 18
3.2 Battery 19

3.2.1 Series configuration 19
3.2.2 Parallel configuration 19
4. CLASSIFICATION OF INVERTER 21
4.1 According to the output characteristics
4.1,1 Square wave inverter
4.1.2 Sine wave inverter
4.1.3 Modified sine wave inverter
4.2 According to the source of inverter 22
4.2.1 Current source inverter
4.2.2 Voltage source inverter
4.3 According to the type of load 23
4.3.1 Single phase inverter 25
4.3.2 Three phase inverter 28
4.4 According to the different PWM technique 30
4.4.1 Simple Pulse Width Modulation (SPWM) 31
4.4.2 Multiple Pulse Width Modulation (MPWM) 32
4.4.3 Sinusoidal Pulse Width Modulation (SPWM) 33
4.4.4 Modified sinusoidal Pulse Width Modulation (MSPWM) 34
4.5 According to No. of output load 34
5. Additional Functional Of Inverter 35
5.1 Introduction 35
5.2 The issue with the current inverter 35
5,3 Development of smart inverter 38
5.4 IEEE1547 standard on smart inverter 39
5.5 Function of smart inverter 40
5.5.1 Function for power system stabilization
5.5.2 Communication based function to improve the user friendliness
6. ADVANCED INVERTER &THEIR FUNCTINALITIES
6.1 Standard inverter functionalities 46
6.1.1 Power transfer 50
6.1.2 Voltage Conversion & Grid synchronization 50

6.1.3 Disconnection and Anti-islanding protection 50
6.2 Advanced inverter 51
6.2.1 Reactive power Control 51
6.2.2 Voltage ride through 51
6.2.3 Frequency ride through 51
7. BENEFITS and DRAWBACK OF INVERTER TECH.53
8. SOME ADVANCEMENT &APP. OF INVERTER 55
8.1 DC power source usage 55
8.2 Uninterruptable power supplies 56
8.3 Electric motor speed control 57
8.4 Power grid, solar inverter, induction heating, HVDC 58
9. CONCLUSION 59
10. REFERENCE 60

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(A) Introduction
One of the most significant battles of the 19th century was fought not over land or resources
but to establish the type of electricity that powers our buildings.
At the very end of the 1800s, American electrical pioneer Thomas Edison (1847–1931)
went out of his way to demonstrate that direct current (DC) was a better way to supply
electrical power than alternating current (AC), a system backed by his Serbian-born arch-
rival Nikola Tesla (1856–1943). Edison tried all kinds of devious ways to convince people
that AC was too dangerous, from electrocuting an elephant to (rather cunningly) supporting
the use of AC in the electric chair for administering the death penalty. Even so, Tesla's
system won the day and the world has pretty much run on AC power ever since.
As the technology for the power semiconductor devices and integrated circuit develops, the
potential for applications of power electronics become wider. There are already many
power semiconductor devices that are commercially available, however, the development
in this direction is continuing.
The power semiconductor devices or power electronic converter fall generally into six
categories : -
1. AC to DC Converter (Controlled Rectifier)
2. DC to DC Converter (DC Chopper)
3. AC to AC Converter (AC voltage regulator)
4. DC to AC Converter (Inverter)
5. Static Switches
6. Diode Rectifier
The design of power electronics converter circuits requires design the power and control
circuits. The voltage and current harmonics that are generated by the power converters can
be reduced or minimized with a proper choice of the control strategy.
Power Electronics defined as Power Electronics defined as the application of solid the
application of solid - state (devices) electronics for the control and state (devices)
electronics for the control and conversion of electric power. Conversion of electric power.

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POWER ELECTRONICS APPLICATION
Power Electronics Application Power electronics have already found an important place in
modern technology and are now used in a great variety of highpower product, including
heat controls, light controls, electric motor control, power supplies, vehicle propulsion
system and high voltage direct current (HVDC) systems.
POWER ELECTRONIC SWITCHING DEVICES
1. Uncontrolled turn on and off (Power Diode)
2. Controlled turn on uncontrolled turn off (Thyristors)
3. Controlled turn on and off characteristic (Power Transistor, BJT, MOSFET, GTO, IGBT)
4. Continuous gate signal requirement (BJT, MOSFET, IGBT)
5. Pulse gate requirement (SCR, GTO)
6. Bipolar voltage-withstanding capability (SCR, GTO)
7. Unipolar voltage-withstanding capability (BJT, MOSFET, GTO, IGBT)
8. Bidirectional current capability (TRIAC)
9. Unidirectional current capability (SCR, GTO, BJT, MOSFET, IGBT)

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Static converters
Static converter is a power electronic converter that Static converter is a power electronic
converter that can conversion of electric power from one to another. can conversion of
electric power from one to another. The static power converters perform these function of
The static power converters perform these function of power conversion. power conversion.
The Power Electronic Converter can be classified into r can be classified into six types: six
types:
1. Diode Rectifier
2. AC to DC Converter (Controlled Rectifier)
3. DC to DC Converter (DC Chopper)
4. AC to AC Converter (AC voltage regulator))
5. DC to AC Converter (Inverter)
6. Static Switches
Diode Rectifiers :- A diode rectifier circuit converts AC voltage into a fixed DC voltage.
The input voltage to rectifier could be either single phase or three phase.
AC to DC Converters :- An AC to DC converter circuit can convert AC voltage into a
DC voltage. The DC output voltage can be controlled by varying the firing angle of the
thyristors. The AC input voltage could be a single phase or three phase.
AC to AC Converters: - This converters can convert from a fixed ac input voltage into
variable AC output voltage. The output voltage is controlled by varying firing angle of
TRIAC. These type converters are known as AC voltage regulator.
DC to DC Converters: - These converters can converter a fixed DC input voltage into
variable DC voltage or vice versa. The DC output voltage is controlled by varying of duty
cycle.
Static Switch :- Because the power devices can be operated as static switches or
contactors, the supply to these switches could be either AC or DC and the switches are
called as AC static switches or DC static switches

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Chapter 1
Inverter
The only trouble is, though many of our appliances are designed to work with AC,
smallscale power generators often produce DC. That means if you want to run something
like an ACpowered gadget from a DC car battery in a mobile home, you need a device
that will convert DC to AC—an inverter, as it's called.
1.1 Difference between DC and AC electricity?
When science teachers explain the basic idea of electricity to us as a flow of electrons,
they're usually talking about direct current (DC). We learn that the electrons work a bit like
a line of ants, marching along with packets of electrical energy in the same way that ants
carry leaves. That's a good enough analogy for something like a basic flashlight, where we
have a circuit (an unbroken electrical loop) linking a battery, a lamp, and a switch and
electrical energy is systematically transported from the battery to the lamp until all the
battery's energy is depleted.
In bigger household appliances, electricity works a different way. The power supply
that comes from the outlet in your wall is based on alternating current (AC), where the
electricity switches direction around 50–60 times each second (in other words, at a
frequency of 50–60 Hz). It can be hard to understand how AC delivers energy when it's
constantly changing its mind about where it's going! If the electrons coming out of your
wall outlet get, let's say, a few millimeters down the cable then have to reverse direction
and go back again, how do they ever get to the lamp on your table to make it light up?
The answer is actually quite simple. Imagine the cables running between the lamp
and the wall packed full of electrons. When you flick on the switch, all the electrons filling
the cable vibrate back and forth in the lamp's filament—and that rapid shuffling about
converts electrical energy into heat and makes the lamp bulb glow. The electrons don't
necessarily have to run in circle to transport energy: in AC, they simply "run on the spot."

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Fig. 1.1 A typical Power Inverter
1.2 What is an inverter?
Basically, a power inverter, or inverter, is an electronic device or circuitry that changes
direct current (DC) to alternate current (AC).
Direct current (DC) is the unidirectional flow of electric charge. Direct current is
produced by sources such as batteries, power supplies, thermocouples, solar cells, or
dynamos. Direct current may flow in a conductor such as a wire, but can also flow through
semiconductors, insulators, or even through a vacuum as in electron or ion beams. The
electric current flows in a constant direction, distinguishing it from alternating current
(AC). A term formerly used for this type of current was galvanic current.
Alternating current (AC), is an electric current in which the flow of electric charge
periodically reverses direction, whereas in direct current (DC, also dc), the flow of electric
charge is only in one direction. The abbreviations AC and DC are often used to mean simply
alternating and direct, as when they modify current or voltage.
The input voltage, output voltage and frequency, and overall power handling depend
on the design of the specific device or circuitry. The inverter does not produce any power;
the power is provided by the DC source.
A power inverter can be entirely electronic or may be a combination of mechanical
effects (such as a rotary apparatus) and electronic circuitry. Static inverters do not use
moving parts in the conversion process.
An inverter does the opposite job and it's quite easy to understand the essence of how
it works. Suppose you have a battery in a flashlight and the switch is closed so DC flows
around the circuit, always in the same direction, like a race car around a track. Now what
if you take the battery out and turn it around. Assuming it fits the other way, it'll almost
certainly still power the flashlight and you won't notice any difference in the light you get—
but the electric current will actually be flowing the opposite way. Suppose you had
lightning-fast hands and were deft enough to keep reversing the battery 50–60 times a
second. You'd then be a kind of mechanical inverter, turning the battery's DC power into
AC at a frequency of 50–60 hertz.
Of course the kind of inverters you buy in electrical stores don't work quite this way, though
some are indeed mechanical: they use electromagnetic switches that flick on and off at high
speed to reverse the current direction. Inverters like this often produce what's known as a
squarewave output: the current is either flowing one way or the opposite way or it's instantly
swapping over between the two states:

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Diagram of simple square wave pattern.
These kind of sudden power reversals are quite brutal for some forms of electrical
equipment. In normal AC power, the current gradually swaps from one direction to the
other in a sine-wave pattern, like this:
Fig. 1.3 Diagram of Simple Sine Wave Pattern.
Electronic inverters can be used to produce this kind of smoothly varying AC output from
a DC input. They use electronic components called inductors and capacitors to make the
output current rise and fall more gradually than the abrupt, on/off-switching square wave
output you get with a basic inverter.
Inverters can also be used with transformers to change a certain DC input voltage into a
completely different AC output voltage (either higher or lower) but the output power must
always be less than the input power: it follows from the conservation of energy that an
inverter and transformer can't give out more power than they take in and some energy is
bound to be lost as heat as electricity flows through the various electrical and electronic
components. In practice, the efficiency of an inverter is often over 90 percent, though basic
physics tells us some energy—however little—is always being wasted somewhere!
1.3 How does an inverter work?
Imagine you're a DC battery and someone taps you on the shoulder and asks you to
produce AC instead. How would you do it? If all the current you produce flows out in one
direction, what about adding a simple switch to your output lead? Switching your current
on and off, very rapidly, would give pulses of direct current—which would do at least half
the job. To make proper AC, you'd need a switch that allowed you to reverse the current
completely and do it about 50‐60 times every second. Visualize yourself as a human battery
swapping your contacts back and forth over 3000 times a minute.

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In essence, an old-fashioned mechanical inverter boils down to a switching unit
connected to an electricity transformer. We know that a transformer is an electromagnetic
devices that change low-voltage AC to high-voltage AC, or vice-versa, using two coils of
wire (called the primary and secondary) wound around a common iron core. In a
mechanical inverter, either an electric motor or some other kind of automated switching
mechanism flips the incoming direct current back and forth in the primary, simply by
reversing the contacts, and that produces alternating current in the secondary—so it's not
so very different from the imaginary inverter that sketched out. The switching device works
a bit like the one in an electric doorbell. When the power is connected, it magnetizes the
switch, pulling it open and switching it off very briefly. A spring pulls the switch back into
position, turning it on again and repeating the process over and over again.
Fig. 1.4 Concept of Power Inverter
The basic concept of an electromechanical inverter is that DC feeds into the primary
winding (pink zigzag wires on the left side) of a toroidal transformer (brown donut),
through a spinning plate (red and blue) with criss-cross connections. As the plate rotates, it
repeatedly switches over the connections to the primary winding, so the transformer is
receiving AC as its input instead of DC. This is a step-up transformer with more windings
in the secondary (yellow zigzag, right-hand side) than the primary, so it boosts a small AC
input voltage into a larger AC output. The speed at which the disk rotates governs the
frequency of the AC output. Most inverters don't work anything like this; this simply
illustrates the concept. An inverter set up this way would produce a very rough square wave
output.
1.4 Input and Output Voltage
Input voltage:-
A typical power inverter device or circuit requires a relatively stable DC power
source capable of supplying enough current for the intended power demands of the system.
The input voltage depends on the design and purpose of the inverter. Examples include

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• 12 VDC, for smaller consumer and commercial inverters that typically run from a
rechargeable 12 V lead acid battery.
• 24 and 48 VDC, which are common standards for home energy systems.
• 200 to 400 VDC, when power is from photovoltaic solar panels.
• 300 to 450 VDC, when power is from electric vehicle battery packs in vehicle-to-grid
systems.
• Hundreds of thousands of volts, where the inverter is part of a high voltage power current
power transmission system.
Output voltage:-
The AC output voltage of a power inverter is often regulated to be the same as the grid
line voltage, typically 120 or 240 VAC, even when there are changes in the load that the
inverter is driving. This allows the inverter to power numerous devices designed for
standard line power. Some inverters also allow selectable or continuously variable output
voltages.
1.5 Output power:-
A power inverter will often have an overall power rating expressed in watts or
kilowatts. This describes the power that will be available to the device the inverter is
driving and, indirectly, the power that will be needed from the DC source. Smaller
popular consumer and commercial devices designed to mimic line power typically range
from 150 to 3000 watts.
Not all inverter applications are solely or primarily concerned with power delivery; in some
cases the frequency and or waveform properties are used by the follow-on circuit or device.

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Chapter 2
History
2.1 Early inverters
From the late nineteenth century through the middle of the twentieth century, DC-to
AC power conversion was accomplished using rotary converters or motor generator sets
(M-G sets). In the early twentieth century, vacuum tubes and gas filled tubes began to be
used as switches in inverter circuits. The most widely used type of tube was the thyratron.
The origins of electromechanical inverters explain the source of the term inverter.
Early AC-to-DC converters used an induction or synchronous AC motor direct-connected
to a generator (dynamo) so that the generator's commutator reversed its connections at
exactly the right moments to produce DC. A later development is the synchronous
converter, in which the motor and generator windings are combined into one armature, with
slip rings at one end and a commutator at the other and only one field frame. The result
with either is AC-in, DC-out. With an M-G set, the DC can be considered to be separately
generated from the AC; with a synchronous converter, in a certain sense it can be
considered to be "mechanically rectified AC". Given the right auxiliary and control
equipment, an M-G set or rotary converter can be "run backwards", converting DC to AC.
Hence an inverter is an inverted converter.
2.2 Controlled rectifier inverters
Since early transistors were not available with sufficient voltage and current ratings for
most inverter applications, it was the 1957 introduction of the thyristor or silicon-controlled
rectifier (SCR) that initiated the transition to solid state inverter circuits.
12 Pulse line
Commutated
Inverter

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The commutation requirements of SCRs are a key consideration in SCR circuit designs.
SCRs do not turn off or commutate automatically when the gate control signal is shut off.
They only turn off when the forward current is reduced to below the minimum holding
current, which varies with each kind of SCR, through some external process. For SCRs
connected to an AC power source, commutation occurs naturally every time the polarity of
the source voltage reverses. SCRs connected to a DC power source usually require a means
of forced commutation that forces the current to zero when commutation is required. The
least complicated SCR circuits employ natural commutation rather than forced
commutation. With the addition of forced commutation circuits, SCRs have been used in
the types of inverter circuits described above.
In applications where inverters transfer power from a DC power source to an AC power
source, it is possible to use AC-to-DC controlled rectifier circuits operating in the inversion
mode. In the inversion mode, a controlled rectifier circuit operates as a line commutated
inverter. This type of
operation can be used in HVDC power transmission systems and in regenerative braking
operation of motor control systems.
Another type of SCR inverter circuit is the current source input (CSI) inverter. A CSI
inverter is the dual of a six-step voltage source inverter. With a current source inverter, the
DC power supply is configured as a current source rather than a voltage source. The inverter
SCRs are switched in a six-step sequence to direct the current to a three-phase AC load as
a stepped current waveform. CSI inverter commutation methods include load commutation
and parallel capacitor commutation. With both methods, the input current regulation assists
the commutation. With load commutation, the load is a synchronous motor operated at a
leading power factor.
As they have become available in higher voltage and current ratings, semiconductors such
as transistors or IGBTs that can be turned off by means of control signals have become the
preferred switching components for use in inverter circuits.
2.3 Rectifier and inverter pulse numbers:-
Rectifier circuits are often classified by the number of current pulses that flow to the
DC side of the rectifier per cycle of AC input voltage. A single phase half wave rectifier is
a onepulse circuit and a single phase full wave rectifier is a two-pulse circuit. A three-phase
half-wave rectifier is a three-pulse circuit and a three-phase full-wave rectifier is a six-pulse
circuit.
With three-phase rectifiers, two or more rectifiers are sometimes connected in series or
parallel to obtain higher voltage or current ratings. The rectifier inputs are supplied from
special transformers that provide phase shifted outputs. This has the effect of phase
multiplication. Six phases are obtained from two transformers, twelve phases from three
transformers and so on. The associated rectifier circuits are 12-pulse rectifiers, 18-pulse
rectifiers and so on...

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When controlled rectifier circuits are operated in the inversion mode, they would be
classified by pulse number also. Rectifier circuits that have a higher pulse number have
reduced harmonic content in the AC input current and reduced ripple in the DC output
voltage. In the inversion mode, circuits that have a higher pulse number have lower
harmonic content in the AC output voltage waveform.
Other notes
The large switching devices for power transmission applications installed until 1970
predominantly used mercury arc valves. Modern inverters are usually solid state (static
inverters). A modern design method features components arranged in an H bridge
configuration. This design is also quite popular with smaller-scale consumer devices.
Research
Using 3-D printing and novel semiconductors, researchers at the Department of
Energy's Oak Ridge National Laboratory have created a power inverter that could make
electric vehicles lighter, more powerful and more efficient.

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CHAPTER 3
TYPES OF INVERTERS
If one simply switch a DC current on and off, or flip it back and forth so its direction
keeps reversing, what he ends up with is very abrupt changes of current: all in one direction,
all in the other direction, and back again. Draw a chart of the current (or voltage) against
time and one will get a square wave. Although electricity varying in that fashion is,
technically, an alternating current, it's not at all like the alternating current supplied to our
homes, which varies in a much more smoothly undulating sine wave). Generally speaking,
hefty appliances in our homes that use raw power (things like electric heaters, incandescent
lamps, kettles, or fridges) don't much care what shape wave they receive: all they want is
energy and lots of it so square waves really don't bother them. Electronic devices, on the
other hand, are much more fussy and prefer the smoother input they get from a sine wave.
This explains why inverters come in two distinct flavors:
1) True/pure sine wave inverters (often shortened to PSW)
2) Modified/quasi sine wave inverters (shortened to MSW).
As their name suggests, true inverters use what are called toroidal (donut-shaped)
transformers and electronic circuits to transform direct current into a smoothly varying
alternating current very similar to the kind of genuine sine wave normally supplied to our
homes. They can be used to power any kind of AC appliance from a DC source, including
TVs, computers, video games, radios, and stereos. Modified sine wave inverters, on the
other hand, use relatively inexpensive electronics ( thyristors, diodes, and other simple
components) to produce a kind of "rounded-off" square wave (a much rougher
approximation to a sine wave) and while they're fine for delivering power to hefty electric
appliances, they can and do cause problems with delicate electronics (or anything with an
electronic or microprocessor controller). Also, if you think about it, their rounded-off
square waves are delivering more power to the appliance overall than a pure sine wave
(there's more area under a square than a curve), so there's some risk of overheating with
MSW inverters. On the positive side, they tend to be quite a bit cheaper than true inverters
and often work more efficiently (which is important if you want to run something off a
battery with a limited charge—because it will run for longer).
Although many inverters work as standalone units, with battery storage, that are
totally independent from the grid, others (known as utility-interactive inverters or grid-tied
inverters) are specifically designed to be connected to the grid all the time; typically they're
used to send electricity from something like a solar panel back to the grid at exactly the
right voltage and frequency. That's fine if main objective is to generate our own power. It's
not so helpful if we want to be independent of the grid sometimes or we want a backup
power source in case of an outage, because if our connection to the grid goes down, and
we're not making any electricity of our own (for example, it's night-time and our solar

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panels are inactive), the inverter goes down too, and we're completely without power—as
helpless as we would be whether we were generating our own power or not. For this reason,
some people use bimodal or birectional inverters, which can either work in standalone or
grid-tied mode (though not both at the same time). Since they have extra bits and pieces,
they tend to be more bulky and more expensive.
3.1 Types of inverters:-
Most of the Home appliance alternating electrical power is observed. However AC
power is not always available and the need for mobility and simplicity has given in batteries
Thus, for portable AC power, for this purpose inverter is needed. Inverters take a DC
voltage from an input terminal of a battery or a solar panel as input.
These inverters are classified by depending on their output as three types that is a square
wave, modified-sine wave and pure sine wave. Normally Off-the-shelf inverters are
generally either square wave or modified-sine wave and sine wave inverter. These 3 types
of inverters less expensive and it is modified though delivering the same average voltage
to a load, it is not appropriate for delicate electronic devices on the precise timing. Most of
the pure sine wave inverter offer having good accuracy it is very high load capacity, but
they are more complex in design and more expensive.
Pure sine wave inverters will power devices with more accuracy less power loss, and
less heat generation. Pure sine wave inversion process is accomplished by taking a DC
voltage source and switching it across a load using an H-bridge parameter. If this voltage
needs to be boosted from a DC source, It can be accomplished before the AC stage by using
a DC-DC boost converter or after the AC stage by using a boost transformer. The inverted
signal itself is composed of a pulse-width-modulated (PWM) signal the PWM signal is
encodes a sine wave. The duty cycle of the sine wave output signal is changed such that the
sine wave power is transmitted. This output power can be used alternatively.
There are two basic designs for producing household plug-in voltage from a lower-
voltage DC source, the first of which uses a switching boost converter to produce a higher-
voltage DC and then converts to AC. The second method converts DC to AC at battery
level and uses a line frequency transformer to create the output voltage.
3.1.1 Square wave inverter:-
This is one of the simplest waveforms an inverter design can produce and is best
suited to low-sensitivity applications such as lighting and heating. Square wave output can
produce "humming" when connected to audio equipment and is generally unsuitable for
sensitive electronics.

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Fig. 3.1 A Square Waveform
The conversion of DC to AC is most commonly done through the use of MOSFET inverter
circuits which can switch the voltage across the load, providing a digital approximation of
the desired AC signal. The simplest variant of this inversion is the production of a square
wave conversion of a sine wave. In the form of square wave, The load voltage must be
switched majorly from high voltage to low Voltage, without using for an intermediate
step (0V). In order to deliver the same power as the sine wave to be approximated, the
amplitude value of the square wave value and sine wave’s RMS value is same.
Fig. Square Wave Inverter Circuit Diagram
Therefore, the average voltages, and the power delivered will be the same for the two
waveforms. Square wave inverters are very rarely used in practice, as many devices which
utilize timing circuits that on something close to the sine wave from the power company
cannot operate with such a rough. In addition, a square wave has relatively large 3rd and
5th harmonic components which burn power and severely cut down on the efficiency of
devices using such inverters as a power source. In this bellow diagram op-amp is the main
part of the square wave signal diagram.
Applications of square wave inverter
Majorly square wave inverter applications voltage source inverter having many
applications in many low cost AC motor drives, That is like as an uninterrupted power

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supply and circuits utilizing electrical resonance between an inductor and capacitor.Some
examples of circuits utilizing like resonance phenomenon are induction heating units and
electronic ballasts for fluorescent lamps.
3.1.2 pure Sine wave inverter:-
A power inverter device which produces a multiple step sinusoidal AC waveform is
referred to as a sine wave inverter. To more clearly distinguish the inverters with outputs
of much less distortion than the "modified sine wave" (three step) inverter designs, the
manufacturers often use the phrase pure sine wave inverter. Almost all consumer grade
inverters that are sold as a "pure sine wave inverter" do not produce a smooth sine wave
output at all, just a less choppy output than the square wave (one step) and modified sine
wave (three step) inverters. In this sense, the phrases "Pure sine wave" or "sine wave
inverter" are misleading to the consumer. However, this is not critical for most electronics
as they deal with the output quite well.
Where power inverter devices substitute for standard line power, a sine wave output is
desirable because many electrical products are engineered to work best with a sine wave
AC power source. The standard electric utility power attempts to provide a power source
that is a good approximation of a sine wave.
Sine wave inverters with more than three steps in the wave output are more complex
and have significantly higher cost than a modified sine wave, with only three steps, or
square wave (one step) types of the same power handling. Switch-mode power supply
(SMPS) devices, such as personal computers or DVD players, function on quality modified
sine wave power. AC motors directly operated on non-sinusoidal power may produce extra
heat, may have different speed-torque characteristics, or may produce more audible noise
than when running on sinusoidal power.
Fig. 3.2 A Sine wave
Most of the power source for most applications is a 60Hz, 230v AC sine wave, Identical to
the 120V Vrms Source available. It is majorly available from some developed companies.
Most of the low power electronic household plug-in devices are designed to work with this
source (high power devices such as cooking ovens use a 240V source). These electronic
equipments will be Most likely to work properly and most efficiently on such a voltage and
current sources. The full sine wave source is produced Most easily for high power

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applications through rotating electrical machinery such as naval gas-turbine machineries,
homemade applications of diesel or gasoline backup generators or other types of generators
employed by power companies that employs a shaft torque to create an AC current.
These power sources provides a relatively clean, pure sine waves (lacking significant
harmonics and high frequency noise) thanks to their analog rotational things. Such as
rotating machinery can be an appropriate for low-power backup supply usage due to their
high cost, Huge size and required maintenance. There are mainly useful for pure sine wave
applications.
The Non sinusoidal waveform generated is also called as a relaxation oscillator. The op
amp relaxation oscillator is also called as a square wave generator. The frequency of the
oscillator is f=1/T. Here T is also known as a Time and f is a frequency of the oscillator. In
this op amp generator both Z1 and Z2. The unsymmetrical square wave can be had by
different square waves.
Advantages of the Pure Sine Wave Inverter
Office buildings considering a backup power inverter, a true sine wave model will allow
proper function of all electronic office equipment and fluorescent tube lighting. And some
of electronic equipments like a Toyostove, battery chargers, electric drills, digital clock
radios or other sensitive electronics should consider a true sine wave inverter to ensure
proper functioning of all household appliances.
Applications
It can applicable many power applications like electric tube light, kitchen appliances, power
tools, Tvs, radios, computers and many more electronics gadgets we are using.

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Various inverters may have different features making them better suited for different
specific applications. Very small inverters are available that connect to a car cigarette
lighter, with a single three-prong AC outlet as the output. Large inverters are generally
designed to be hardwired into a building electrical system. Some inverters offer 240 volts
output. The right inverter for any specific use can be found with the help of an experienced
inverter dealer.
It’s will be useful in all electronic applications,when using pure sine wave power. True
sine wave inverters will produce AC power as well as a better than utility power, Ensuring
that even the most sensitive equipment will run properly. While sine wave inverters are
more expensive than modifying sine wave models, The quality of their waveform can be
a definite advantage.
3.1.3 Modified sine wave inverter:-
A "modified sine wave" inverter has a non-square waveform that is a useful rough
approximation of a sine wave for power translation purposes.
Most inexpensive consumer power inverters produce a modified sine wave rather than
a pure sine wave.
The waveform in commercially available modified-sine-wave inverters is a square
wave with a pause before the polarity reversal, which only needs to cycle back and forth
through a three-position switch that outputs forward, off, and reverse output at the pre-
determined frequency. Switching states are developed for positive, negative and zero
voltages as per the patterns given in the switching Table . The peak voltage to RMS voltage
ratio does not maintain the same relationship as for a sine wave. The DC bus voltage may
be actively regulated, or the "on" and "off" times can be modified to maintain the same
RMS value output up to the DC bus voltage to compensate for DC bus voltage variations.
The ratio of on to off time can be adjusted to vary the RMS voltage while maintaining a
constant frequency with a technique called Pulse Width Modulation (PWM). The generated
gate pulses are given to each switch in accordance with the developed pattern to obtain the
desired output. Harmonic spectrum in the output depends on the width of the pulses and
the modulation frequency. When operating induction motors, voltage harmonics are usually
not of concern; however, harmonic distortion in the current waveform introduces additional
heating and can produce pulsating torques.
Numerous items of electric equipment will operate quite well on modified sine wave
power inverter devices, especially loads that are resistive in nature such as traditional
incandescent light bulbs.
However, the load may operate less efficiently owing to the harmonics associated with
a modified sine wave and produce a humming noise during operation. This also affects the
efficiency of the system as a whole, since the manufacturer's nominal conversion efficiency

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does not account for harmonics. Therefore, pure sine wave inverters may provide
significantly higher efficiency than modified sine wave inverters.
Most AC motors will run on MSW inverters with an efficiency reduction of about 20%
owing to the harmonic content. However, they may be quite noisy. A series LC filter tuned
to the fundamental frequency may help.
A common modified sine wave inverter topology found in consumer power inverters
is as follows:
An onboard microcontroller rapidly switches on and off power MOSFETs at high
frequency like ~50 kHz. The MOSFETs directly pull from a low voltage DC source (such
as a battery). This signal then goes through step-up transformers (generally many smaller
transformers are placed in parallel to reduce the overall size of the inverter) to produce a
higher voltage signal. The output of the step-up transformers then gets filtered by capacitors
to produce a high voltage DC supply. Finally, this DC supply is pulsed with additional
power MOSFETs by the microcontroller to produce the final modified sine wave signal.
3.1.4 Other waveforms:-
By definition there is no restriction on the type of AC waveform an inverter might
produce that would find use in a specific or special application.
3.1.5 Output frequency:-
The AC output frequency of a power inverter device is usually the same as standard
power line frequency, 50 or 60 Hertz.
If the output of the device or circuit is to be further conditioned (for example stepped
up) then the frequency may be much higher for good transformer efficiency.
3.1.6 What are inverters like?
Inverters can be very big and hefty—especially if they have built-in battery packs
so they can work in a standalone way. They also generate lots of heat, which is why they
have large heat sinks (metal fins) and often cooling fans as well. Typical ones are about as
big as a car battery or car battery charger; larger units look like a bit like a bank of car
batteries in a vertical stack. The smallest inverters are more portable boxes the size of a car
radio that we can plug into cigarette lighter socket to produce AC for charging laptop
computers or cellphones.
Just as appliances vary in the power they consume, so inverters vary in the power
they produce. Typically, to be on the safe side, you'll need an inverter rated about a quarter
higher than the maximum power of the appliance you want to drive. That allows for the

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fact that some appliances (such as fridges and freezers or fluorescent lamps) consume peak
power when they're first switched on. While inverters can deliver peak power for short
periods of time, it's important to note that they're not really designed to operate at peak
power for long periods.
3.2 Batteries
The runtime of an inverter is dependent on the battery power and the amount of power
being drawn from the inverter at a given time. As the amount of equipment using the
inverter increases, the runtime will decrease. In order to prolong the runtime of an inverter,
additional batteries can be added to the inverter.
When attempting to add more batteries to an inverter, there are two basic options for
installation: Series Configuration and Parallel Configuration.
Series configuration
If the goal is to increase the overall voltage of the inverter, one can daisy chain batteries in
a Series Configuration. In a Series Configuration, if a single battery dies, the other
batteries will not be able to power the load.
Parallel configuration
If the goal is to increase capacity and prolong the runtime of the inverter, batteries can be
connected in parallel. This increases the overall Amperehour(Ah) rating of the battery set.
If a single battery is discharged though, the other batteries will then discharge through it.
This can lead to rapid discharge of the entire pack, or even an over-current and possible
fire. To avoid this, large paralleled batteries may be connected via diodes or intelligent
monitoring with automatic switching to isolate an under-voltage battery from the others.

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Chapter 4
Classification of Inverter
Alternating Current (AC) power supply is used for almost all the residential, commercial
and industrial needs. But the biggest issue with AC is that it cannot be stored for future use.
So AC is converted into DC and then DC is stored in batteries and ultra-capacitors. And
now whenever AC is needed, DC is again converted into AC to run the AC based
appliances. So the device which converts DC into AC is called Inverter. The inverter is
used to convert DC to variable AC. This variation can be in the magnitude of voltage,
number of phases, frequency or phase difference.
Classification of Inverter
Inverter can be classified into many types based on output, source, type of load etc. Below
is the complete classification of the inverter circuits:
(I) According to the Output Characteristic
1) Square Wave Inverter
2) Sine Wave Inverter
3) Modified Sine Wave Inverter
(II) According to the Source of Inverter
1) Current Source Inverter
2) Voltage Source Inverter
(III) According to the Type of Load
1) Single Phase Inverter
1.1) Half Bridge Inverter
1.2) Full Bridge Inverter
2. Three Phase Inverter
2.1) 180-degree mode
2.2) 120-degree mode
(IV) According to different PWM Technique
1. Simple Pulse Width Modulation (SPWM)
2. Multiple Pulse Width Modulation (MPWM)
3. Sinusoidal Pulse Width Modulation (SPWM)
4. Modified sinusoidal Pulse Width Modulation (MSPWM)

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(V) According to Number of Output Level
1. Regular Two-Level Inverter
2. Multi-Level Inverter
(I) According to the Output Characteristic
According to the output characteristic of an inverter, there can be three different types
of inverters.
 Square Wave Inverter
 Sine Wave Inverter
 Modified Sine Wave Inverter
1) Square wave inverter
The output waveform of the voltage for this inverter is a square wave. This type of inverter
is least used among all other types of inverter because all appliances are designed for sine
wave supply. If we supply square wave to sine wave based appliance, it may get damaged
or losses are very high. The cost of this inverter is very low but the application is very rare.
It can be used in simple tools with a universal motor.
2) Sine wave
The output waveform of the voltage is a sine wave and it gives us a very similar output to
the utility supply. This is the major advantage of this inverter because all the appliances we
are using, are designed for the sine wave. So, this is the perfect output and gives guarantee
that equipment will work properly. This type of inverters is more expensive but widely
used in residential and commercial applications.
3) Modified sine wave
The construction of this type of inverter is complex than simple square wave inverter but
easier compared to the pure sine wave inverter. The output of this inverter is neither pure
sine wave nor the square wave. The output of such inverter is the some of two square waves.
The output waveform is not exactly sine wave but it resembles the shape of a sine wave

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.
(II) According to the Source of the Inverter
 Voltage Source Inverter
 Current Source Inverter
1) Current Source Inverter
In CSI, the input is a current source. This type of inverters is used in the medium voltage
industrial application, where high-quality current waveforms are compulsory. But CSIs are
not popular.
2) Voltage Source Inverter
In VSI, the input is a voltage source. This type of inverter is used in all applications because
it is more efficient and have higher reliability and faster dynamic response. VSI is capable
of running motors without de-rating.
(III) According to the Type of Load
 Single-phase Inverter
 Three-phase Inverter
1) single-phase inverter
Generally, residential and commercial load uses single phase power. The single-phase
inverter is used for this type of application. The single-phase inverter is further divided into
two parts;
 Single Phase Half-bridge Inverter
 Single Phase Full-bridge Inverter

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A) Single Phase Half bridge Inverter
This type of inverter consists of two thyristors and two diodes and connection is as shown
in below figure.
In this case, total DC voltage is Vs and divided into two equal parts Vs/2. Time for one
cycle is T sec.
For half cycle of 0 <t <T/2, thyristor T1 conducts. The load voltage is Vs/2 due to the upper
voltage source Vs/2.
For the second half cycle of T/2 <t <T, thyristor T1 is commutated and T2 conducts. During
this period, the load voltage is -Vs/2 due to the lower source Vs/2.
Vo = Vs/2

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By this operation, we can get alternating voltage waveform with 1/T Hz frequency and Vs/2
peak amplitude. The output waveform is a square wave. It will be passed through the filter
and remove unwanted harmonics which give us pure sine waveform. The frequency of the
waveform can be controled by the ON time (Ton) and OFF time (Toff) of the thyristor.
The magnitude of the output voltage is half of the supply voltage and source utilization
period is 50%. This is a disadvantage of half bridge inverter and solution of this is full
bridge inverter.
B) Single Phase Full-bridge Inverter
In this type of inverter, four thyristors and four diodes are used. The circuit diagram of
single-phase full bridge is as shown in below figure.
At a time two thyristors T1 and T2 conduct for first half cycle 0 < t < T/2. During this
period, the load voltage is Vs which is similar to the DC supply voltage.
For second half cycle T/2 < t < T, two thyristors T3 and T4 conducts. The load voltage
during this period is -Vs.

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Here we can get AC output voltage same as DC supply voltage and the source utilization
factor is 100%. The output voltage waveform is square waveform and the filters are used
to convert it into a sine wave.
If all thyristors conduct at the same time or in a pair of (T1 and T3) or (T2 and T4) then the
source will be short-circuited. The diodes are connected in the circuit as feedback diode
because it is used for the energy feedback to the DC source.
If we compare full bridge inverter with half bridge inverter, for the given DC supply voltage
load, output voltage is two times and output is power is four times in full bridge inverter.
2) Three Phase Bridge Inverter
In case of industrial load, three phase ac supply is used and for this, we have to use a three-
phase inverter. In this type of inverter, six thyristors and six diodes are used and they are
connected as shown in below figure.

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It can operate in two modes according to the degree of gate pulses.
 180-degree mode
 120-degree mode
A) 180-degree mode
In this mode of operation, conduction time for thyristor is 180 degree. At any time of period,
three thyristors (one thyristor from each phase) are in conduction mode. The shape of phase
voltage is three stepped waveforms and shape of line voltage is a quasi-square wave as
shown in the figure.
Vab = Va0 – Vb0
Vbc = Vb0 – Vc0
Phase A T1 T4 T1 T4
Phase B T6 T3 T6 T3 T6
Phase C T5 T2 T5 T2 T5
Degree 60 120 180 240 300 360 60 120 180 240 300 360
Thyristor
conducts
1 5
6
6 1 2 1 2 3 2 3 4 3 4 5 4 5 6
1 5
6
6 1
2
1 2 3 2 3 4 3 4 5
4 5
6

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Vca = Vc0 – Va0
In this operation, the time gap between the commutation of outgoing thyristor and
conduction of incoming thyristor is zero. So the simultaneous conduction of incoming and
outgoing thyristor is possible. It results in a short circuit of the source. To avoid this
difficulty, 120-degree mode of operation is used.
B) 120-degree mode

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In this operation, at a time only two thyristors conduct. One of the phases of the thyristor
is neither connected to the positive terminal nor connected to the negative terminal. The
conduction time for each thyristor is 120 degree. The shape of line voltage is three stepped
waveform and shape of the phase voltage is a quasi-square waveform.
Phase A T1 T4 T1 T4
Phase B T6 T3 T6 T3 T6
Phase C T2 T5 T2 T5
degree 60 120 180 240 300 360 60 120 180 240 300 360
Thyristor
conducts
1 6 2 1 3 2 3 4 4 5 6 5 1 6 2 1 3 2 3 4 4 5 5 6

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The waveform of line voltage, phase voltage and gate pulse of the thyristor is as shown in
the above figure.
In any power electronic switches, there are two types of losses; conduction loss and
switching loss. The conduction loss means ON state loss in the switch and the switching
loss means OFF state loss in switch. Generally, the conduction loss is greater than the
switching loss in most of the operation.

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If we consider 180-degree mode for one 60-degree operation, three switches are open and
three switches are closed. Means total loss is equal to three times of conduction loss plus
three times of switching loss.
Total loss in 180-degree = 3 (conductance loss) + 3 (switching loss)
If we consider 120-degree mode for one 60-degree operation, two switches are open and
rest of the four switches are closed. Means total loss is equal to two times of conductance
loss plus four times of switching loss.
Total loss in 120-degree = 2 (conductance loss) + 4 (switching loss)
(IV) Classification According to Control Technique
1. Single Pulse Width modulation (single PWM)
2. Multiple Pulse Width Modulation (MPWM)
3. Sinusoidal Pulse Width Modulation (SPWM)
4. Modified Sinusoidal Pulse Width Modulation (MSPWM)
The output of the inverter is square wave signal and this signal is not used for the load.
Pulse width modulation (PWM) technique is used to control AC output voltage. This
control is obtained by the controlling of ON and OFF period of switches. In PWM technique
two signals are used; one is reference signal and second is triangular carrier signal. The
gate pulse for switches is generated by comparing these two signals. There are different
types of PWM techniques.
1) Single Pulse Width modulation (single PWM)
For every half cycle, the only pulse is available in this control technique. The reference
signal is square wave signal and the carrier signal is triangular wave signal. The gate pulse
for the switches is generated by comparing the reference signal and carrier signal. The
frequency of output voltage is controlled by the frequency of the reference signal. The
amplitude of the reference signal is Ar and the amplitude of the carrier signal is Ac, then
the modulation index can be defined as Ar/Ac. The main drawback of this technique is high
harmonic content.

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2) Multiple Pulse Width Modulation (MPWM)
The drawback of single pulse width modulation technique is solved by multiple PWM. In
this technique, instead of one pulse, several pulses are used in each half cycle of the output
voltage. The gate is generated by comparing the reference signal and carrier signal. The
output frequency is controlled by controlling the frequency of the carrier signal. The
modulation index is used to control the output voltage.
The number of pulses per half cycle = fc/ (2*f0)
Where fc = frequency of carrier signal
f0 = frequency of output signal

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3) Sinusoidal Pulse Width Modulation (SPWM)
This control technique is widely used in industrial applications. In above both methods, the
reference signal is a square wave signal. But in this method, the reference signal is a sine
wave signal. The gate pulse for the switches is generated by comparing the sine wave
reference signal with the triangular carrier wave. The width of each pulse varies with
variation of amplitude of the sine wave. The frequency of output waveform is the same as
the frequency of the reference signal. The output voltage is a sine wave and the RMS
voltage can be controlled by modulation index. Waveforms are as shown in below figure.

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4) Modified Sinusoidal Pulse Width Modulation (MSPWM)
Due to the characteristic of sine wave, the pulse width of the wave cannot be changed with
variation in the modulation index in SPWM technique. That is the reason, MSPWN
technique is introduced. In this technique, the carrier signal is applied during the first and
last 60-degree interval of each half cycle. In this way, its harmonic characteristic is
improved. The main advantage of this technique is increased fundamental component,
reduced number of switching power devices and decreased switching loss. The waveform
is as shown in below figure.

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(V) According to the Number of Levels at the Output
 Regular Two-Level Inverter
 Multi-level Inverter
1) Regular two-level Inverter
These inverters have only voltage levels at the output which are positive peak voltage and
negative peak voltage. Sometimes, having a zero-voltage level is also known as a two-level
inverter.
2) Multilevel Inverters
These inverters can have multiple voltage levels at the output. The multi-level inverter is
divided into four parts.
- Flying capacitor Inverter
- Diode-clamped Inverter
- Hybrid Inverter
- Cascade H-type Inverter
Every inverter has its own design for operation, here we have explained these inverter
briefly to get an basic ideas about them.

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Chapter 5
Additional Function Of inverter
5.1 Introduction
As a result of the increase in power demand, the whole world is adapting the usage of
renewable energy. With this revolution, isolated areas, or large building schemes which
have Distributed Energy Resources (DER) are being converted to smart grids.
Due to the high saturation level of DER traditional inverters get stress with the system.
From several studies it has found that some issues contribute to these behaviors of inverters.
As a solution for these common problems the smart inverters come into play by solving
most of the problems of the traditional system. With the new technology the normal inverter
gets upgraded to smart inverters in order to withstand new challenges in the modern grid.
Since smart inverters work autonomously, they have a positive impact on the implemented
residential sector as well as the national power grid. The traditional grid requires constant
maintenance due to the stress, but smart inverters could help to address these localized
challenges and growth the flexibility of the system .
With the progress of the smart inverters in smart grids IEEE gave a standard ‘IEEE
1547 Standard” for smart inverters. The main purpose is to standardize the inter-links and
interoperability of DERs with the connected Electric Power Systems (EPS). Certain
standards and requirements for interlinks of DERs with the EPSs, and associated interfaces
were launched by this standard. Certain requirements for safety, interoperability,
functionality, security, testing and maintenance are specified in the standard .
When updated the traditional inverters to the smart inverters, it catches some
smartness with additional functions. Mainly there are two sides to consider for smartness
as improvement of the user friendliness and stabilize the power system.
The objective of this paper is to review the available technologies regarding functions
of smart inverters. The following sections in the paper describes the evolution of the current
smart inverter in detail along with smart inverter functions.
5.2. The issues with current inverters
The inverter plays a main role as a main component which is used to make the
interconnection between DERs and the power system. The inverters get stuck in some
abnormal conditions due to the complexity of the current power system. From those bunch
of issues few several issues are discussed as below.
1. Overheating
Most electronic components inside the inverters are sensitive to temperatures. High
temperatures will cause a considerable reduction of the power production, and if the

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maximum operating temperature is reached it can even stop the production. Therefore a
method must be there to ensure the suitableness of the proposed thermal management
system in the designing stage of the inverter.
To get the maximum efficiency, a regular checking of cooling during the operational
period is highly advisable and it is better to make sure that the cooling or the ventilation
system is operating correctly. Additionally, a number of steps can be taken such as
installing and cleaning dust filters as well as removing soles that obstruct airflow, in order
to avoid extremely high temperatures.
For the optimal cost design of an inverter, increasing the switching frequency can
reduce the inductance and capacitance values. As a result of increasing the switching losses,
the cost of cooling will increase.
2. Isolation fault
Inverter will report an “isolation alarm” when a short-circuit occurs between various
parts of the inverter circuit. The main causes of these defects are the combination of
moisture, damage to the sleeve on the cabling, installation failure, and poor connectivity to
the DC cables in the panel. This is most common in areas with high humidity or near the
sea. In the event of an isolation fault, the inverter will stop working completely or the
inverter is not performing at its maximum capacity. In both cases, production is lost.
As a solution for this problem, preventive maintenance program can be scheduled.
Sensors are used to quantify the irradiance, temperature and wind situations and to measure
the fulfilment of the entire system at large PV stations .
3. Inverter does not restart after a grid fault
An inverter must be able to restart after a grid fault of an unbalance (if there are no
other faults). If the inverter does not reboot, a service group will have to come to the
location in order to reboot the system. This can lead to unnecessary product, loss of money
and time.
Use of a good monitoring system for 24/7 is much important for detecting the faults
as quickly as possible. All PV modules linked to the inverter will be unable to send power
until the fault or the error has been discovered. Therefore it is more important to have an
organized system. This is especially the case in areas where grid connectivity is not always
stable. Grid-connected inverters typically have software for parameter setting and system
monitoring which has the facilities to record the system operation and on-line visualization
in a remote manner. Also some of them can contain monitoring external signals such as
irradiance and temperature. Different products have different capabilities in these areas and
fields . Figure 1 shows a sample diagram for the remote monitoring system.

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Figure 1. Remote monitoring system.
4. The finding of MPPT
Almost all the current inverters operate on the concept of the Maximum Power Point
Tracking (MPPT) operation. This function has been developed with the intention of
maximizing the achievements of inverters. Due to the scale of today's large PV systems,
several rows of PV modules are linked together in series, called “strings”. However, not all
strings produce the same quantity of power as a consequence of many factors such as
shading, different placing, errors in panel, etc. The strings provide dissimilar voltages, and
in this respect the difference between the strings continuously changes. The MPPT
algorithm is designed in such a way that the inverter is always connected to the most
optimum supply voltage in spite of these variances in PV strings. The control period of
MPPT has an important impression on the efficiency of power generation and the steadiness
of the PV system. This always maximizes the production of electricity. Therefore it is
important to recognize the working order of the MPPT module in order to maximize the
efficiency. A sample diagram and a graph to describe the MPPT tracking system is shown
in Figure 2.

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Figure 5.2. MPPT tracking.
A number of algorithms has been established to track the maximum power point
efficiently. Most of the current MPPT algorithms suffer from slow tracking, which in turn
reduces the utility efficiency. It is difficult to estimate the efficiency of a PV inverter only
by considering the translation efficiency. Therefore to evaluate the overall efficiency of PV
inverter, the MPPT efficiency of PV inverter should be tested . The Table 1 below, shows
the summary of the above issues.
Table 1. Summary of the issues.
The issue Author’s comment
Faulty
installation
Expert worker must install the device using the installation manual and
must check with particular tests
Overheating There must be a proper cooling or ventilation system in the Inverter.
Preventive maintaining program must be there
Isolation Fault It is essential to confirm that the high quality DC cables are being used and
correctly installed. Maintenance must be carried out with the appropriate
safety standards.
Not restarting
after a grid
fault
It is better to make of high quality monitoring system for 24/7 to detect the
faults and errors as quickly as possible.
Finding of
optimum
MPPT
It is better to find a way to maximize the efficiency of finding the MPPT
and to catch the most optimum supply voltage from PV strings.
5.3. Development of the smart inverter
When considering the above issues, it indicates that the normal PV inverters do not
have the flexibility to manage large volumes of renewable energy and manage system
reliability. Most conventional inverters automatically are disconnected from the network at
specific voltages or frequencies. IEEE 1547 standard gives the requirements for full
disconnection of the inverter in some voltage variations. If there is a drop or spike in voltage
that reaches this margin, the inverter will cut off from the system. This looks like an error
to the defense equipment installed on the feeder and the result is a systemic power outage.
The smart inverters are flexible for these conditions which can prevent these problems.
When the conventional inverters get shut off, the smart inverters can continue to allow
power to flow. Smart inverters are remotely programmable components that allow to
control the ramp rates, inputs and outputs of the converter, accurately. Moreover, they
won’t just cut out like traditional inverters since their thresholds are adjustable.
Smart inverters let two-way communication with utility control centers. In addition,
advanced capabilities such as voltage and frequency sensors allow smart inverters to detect

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grid abnormalities and send the feedback to utility operators. The Figure 3 below, shows a
general block diagram of smart PV inverter system.
Figure 5.3 General block diagram of smart PV inverter.
5.4. IEEE 1547 standard on smart inverters
IEEE Standard 1547 was cited in the U.S. Federal Energy Policy Act of 2005, under
Section 1254
Interconnection Services, stating “Interconnection services shall be offered based upon the
standards developed by the Institute of Electrical and Electronics Engineers Standard 1547
for Interconnecting Distributed Resources with Electric Power Systems, as they may be
amended from time to time.” As shown in the Figure 4, there is a series of standards IEEE
1547 which addressed the standards for Grid integration of DERs .
From the series of standard, IEEE Standard 1547 (2003) was the first about DER
interconnection. Likewise the standard delivers requirements are applicable to the
performance, procedure, testing, safety considerations, and maintenance of the
interconnection. The IEEE 1547 necessities are universally needed for interconnection of
DER, including synchronous and induction machines, and power inverters and converters.
Under the IEEE 1547.8 it addresses the advanced controls and communications for
inverters supporting the grid and best practices focusing on the multiple inverters and
micro-grids, and provides information for the behavior of DER and interactions with grid
equipment (both operational and safety associated, including unintentional islanding) and
interconnection system reaction to abnormal circumstances .

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Figure 5.4. IEEE 1547 series of standards [16].
5.5 Functions of smart inverters
Considering the smart inverter functions and requirements to full fill common problems
of the inverters, it can be defined in two sections as, functions for power system
stabilization and communication based functions to improve the user friendliness. Figure 5
shows the sub functions of both categories.
Figure 5.5 Two main categories.
5.5,1. Functions for power system stabilization
The smart inverters came into play with some additional smartness by adding some
functions to supply a smooth service. In order to reach higher power system stability,

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efficiency [18] and reliability, and to improve the control [19] algorithms it is valuable to
arm the inverters with “smart” features. According to several researches [20] they had
identified seven high-priority inverter functions which are listed in Figure 6 that can stable
the power system. The seven functions are:
Figure 5.6. Seven functions.
1. Connect/Disconnect from grid
This function provides two options for an inverter to cease operation and disconnect
from the grid. The first is to set the power output to zero. This is also known as, a virtual
disconnect. The second is the physical operation of a switch to isolate the inverter from the
grid. This can be referred to as a physical disconnect.
Figure 5.7. Connect/ Disconnect mechanism.

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This function is not related to intentional islanding nor separating a customer from the grid.
It refers to the management of a switch, or virtual switch that separates at the DER from
the grid while leaving customers linking to the grid. In reference to the example diagram
in Figure 7, this function relates to the operation of the “Local DER Switch,” not the “Grid
Switch.” The Table 2 below, further explains this relationship .
This is a main function of an inverter which includes two kinds of powers as active
and reactive power. PV panel can be categorized as a DC power source. There is no reactive
power connected with PV itself. Therefore, the only intention of the inverter input side will
be to extract the maximum active power from the PV, and such control will be known as
MPPT . The inverter output side is dealing with the AC powers. That means active and
reactive power components are there since active reactive power (apparent power) is only
dealing with the AC side.
Grid frequency increases as a result of excessive generation and or insufficient load.
Therefore, its active power output is changed relative to grid frequency. The desired
response of the inverter is to reduce active power output when the frequency is high.
Likewise, it is desired for the inverter to increase active power output as frequency
decreases.
PV inverters typically have a maximum commanded power limit and are only able to
provide an over-voltage response if the inverter is already at full active power output.
Inverter should have the capability to provide voltage support to the grid via adjustment of
the inverter’s active power output, which changes in grid voltage .
Other than the pure active power, the system has a reactive power component also.
When considering the inverter circuits, the inverters will remain purposeless during night
hours when the renewable sources are not available. This decreases the efficient use of
these inverters. One way to rise the productive operation of these inverters is to generate
reactive power in each time when the renewable sources are not existing by operating them
as VAR compensators. As the number of grid-tied inverters rises, their usage part as VAR
compensators will support to reduce the necessity of additional capacity banks as well as
in the grid voltage regulation.
There are several special designed active filter inverters in the market . But they are
not appropriate for grid-tie uses. It will be very supportive to allow current grid-tied
inverters to operate in reactive power generation mode when there is no active power input
from PVs, which typically powers the control circuit, pays for the inverter internal fatalities,
and keeps a regulated DC bus voltage. In the absence of activated power, the difficulty is
to charge the DC bus and to keep it regulated within the certain limitations while injecting
the preferred level of reactive power into the power grid . For the inverter to operate in
reactive power mode, it must compensate for its internal power losses and maintain its DC
bus voltage within the appropriate range . When the renewable source does not exist the
inverter has to absorb little active power from the grid to pay for the inverter’s internal
losses, adjust the DC bus voltage to keep it within limits, as well as to keep the grid
connection and operate the inverters in VAR mode. Other than the active power generation

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this extends the use of PV inverters and help to improve the grid stability and voltage
regulation .
1.2 Var management
Under Var management, there are few Var control methods [30,31]. They are [20]
A. Unity Power Factor, Q = 0
The inverter is designed to function with a unity power factor, with partial or without
re-injection of reactive power to the grid.
B. Fixed Power Factor, Q(P)
The inverter function with a moderately leading power factor. It provides a regulation
to reduce the voltage deviations attributable to active power output variations.
C. Variable Power Factor, Q(P,R/X)
This method lets the inverter to flow the reactive power back into the grid by operating
with a variable power factor.
D. Volt/Var Control
This technique would allow the inverter to reply with a customized var reply, intended
by the local utility, by monitoring its own terminal voltage [32,33].
Each of these volt/var functions can be considered as a “Mode”. The following modes
have been recognized as a preliminary set for large collections of inverters. With a single
transmission instruction from the utility the inverters can be switched between these modes.
1) PV1 – Normal Energy preservation Mode
This mode is used as the normal state of operation for an inverter. (Inverters have one
volt/var characteristic during on-peak hours and a different one during off-peak hours.)
2) PV2 – Maximum Var Sustenance Mode
Provide support for reactive power needs. This directs the distributed inverters to
generate as many capacitive vars as possible.
3) PV3 – The Static Var Mode
Proposed to be used in cases where var generation does not differ with local voltage.
4) PV4 – The Passive Var Mode
This one is same as the PV3, with the exception that the percent var settings are
assumed to be zero. The PV inverter volt/var control function can provide suitable voltage
support for voltage deviations in primary and secondary sides due to variations in PV output
. Voltage deviations caused by usual load variations also can be reduced as well .
1.3 Storage management

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Many number of control methods have been identified for this function. Main part of
this function is charging and discharging management. Energy storage has been suggested
as the solution to the power imbalance issue of power generation and load demand in view
of the emergence of power grids with irregular renewable energy sources. Unlike
conventional control of grid connected power inverters for injecting power in to the grid,
the storage management control scheme puts the stability of the power grid as a high
priority while maintaining its normal bi-directional power flow functions. The function
mainly consists of the arrangement in battery’s monitoring, management of charging and
discharging, and output power control.
With the automatic charging and discharging approach meshed in the active power
control loop, many bidirectional [35] Energy sources with limited energy storage capacities
can be used with this function. With the help of this function distributed devices it can play
an important role to provide active and reactive power compensation for enlightening the
stability of the power grid .
1.4 Event/History logging
This function indicated a high priority on the need for a common method for event
logging and reporting. For a system, it is important to monitor the behaviors or inverters
and to record abnormal conditions and events.
All event log entries will contain the following 5 fields :
a) Date and time stamp:
The accuracy of this function is determined by the frequency of time synchronization
and the essential accuracy in keeping time of the PV system.
b) Data Reference:
The reference to the data point that activated the event log entry. For example, if the
event is a voltage associated event, the Data reference will be to that data object. Same as
if the event is a PV Mode event, the data reference will be the particular PV data object. c)
Value:
Value field refers for activating the event, including commands, record the changes of
monitored values, quality code changes, etc.
d) Event Code:
This field is to exclusively identify event type.
e) Optional Text Field:
This contains the text of supportive information to the system. This text field can be
used to offer additional specifics about the event.
The Event Code standard contains many codes for logging, with only a small fraction
relevant to PV and Storage systems.
1.5 Status reporting/reading

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This function allows the operating mode, status, and set points to be available to verify
operation . With increasing the penetration of DERs, it will increase the number of devices
that are owned and controlled by consumers and third parties. Therefore the system can be
disclosed to some cyber security issues and have to conform that the system is still authentic
and safe with a high DER penetration. The control architectures with the communication
network implementation directly determine extent of cyber-attacks coming through the
network. The smart inverter architecture must be enhanced to monitor the local system
status in order to identify the attacks and hazards at the physical device layer. Therefore the
cyber hazards can be sensed at an early stage. Also they can estimate the local voltage and
current to sense system variances. In this function, the directories of power quality,
unbalanced voltages/currents, and other occasions, will be intended to detect the cyber-
attacks .
1.6 Time adjustment
The ability to set the time in the DER device was considered as a main requirement,
in order to support the scheduling of functions, and the time-stamping and logging of
events.
Researches indicated that time-adjustment is generally supported by the specific
communication protocols. Therefore as a recommended method for time-adjustment for
distributed smart inverters is to apply the native time adjustment mechanism of the specific
communication protocol being applied. As examples, the “DNP3” and the “ZigBee Smart
Energy Profile 1.0” protocols have defined time-setting mechanisms that can be used for
synchronizing smart inverter devices . The Table 4 below, shows the technical possibilities
and the practical issues of above functions.
Table 4. Technical possibilities and practical issues 1.
Smart Inverter
Functions
Technical possibilities and practical issues
Connect/
Disconnect from Grid
Should have the ability to disconnect physically and virtually in
overload or malfunctioning situations
Power Output
Adjustment
Should have the ability to change the mode according to the
active power and reactive power components in day and night.
VAR Management Should have ability to change among the volt/VAR characteristic
“Modes” according to the situation and respond with a custom
VAR response
Storage Management
(Charging/Discharging)
A battery management system should be used for
charging/discharging management, and output power control.
Event/History Logging There must be a set of uniform event codes and a common way
to log and report the events.

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Status Reporting
/Reading
The device must be improved to monitor the status of the local
system in order to detect the cyber threats at an early stage.
Time Adjustment A specific communication protocol must be there as the time-
adjustment mechanism for synchronizing smart inverter devices
2. Communication based functions to improve the user friendliness
When comparing with the components in a grid system, one of the most important
objectives is the control of power inverters. These inverters implement interfaces between
the DGs and the grid bus. In smart inverter development an explanation of “smartness”
states to minimizing the requirement of communication. At the same time, being equipped
with communication protocols also indicates “smartness” since the necessity of
communication cannot be neglected. As well as these advantages, there is a main
disadvantage regarding security that can effect the communication and monitoring
improvements. Mainly, the privacy issues can spring up with these developments. A “smart
inverter” should provide some features as shown in the Figure 8 below.
Figure 5.8. Communication based functions.
2.1. Plug and play
Plug-and-play (PnP) is the ability for a smart inverter to add for a power system and operate
automatically without separate technical configuration. The PnP operation ensures in
system benefits of scalability, interoperability, resilience, and reliability. PnP can be
implemented at the power converters with flexible hardware structures and the smart
inverters for power grids in the purpose of distributing frequency/voltage regulation.
Plug and play means that a distributed power supply can access to the grid directly
without control and defend units. Management technology will be needed when distributed
power with the function of “plug and play” accesses to the grid. It consists of the control
strategy of the system change, energy management, quality of power maintenance etc.
Related technology of the inverter is difficult to implement in the short term because of the
level of development and the limits of the current standards. The power output of the

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inverters can always be set aside in the rating working point. Therefore, each component
can be controlled by itself according to the operational situation of the system by
implementing the technology of “Plug and Play” Control .
2.2. Self-awareness
Self-awareness becomes a significant function for decentralized systems to realize
advanced levels of autonomous behavior . For smart inverters, self-awareness aims to
improve the operative reliability and predicting the lifetime, thus enabling fail-safe or
maintenance actions and effectively avoiding terrible accident in systems using power
electronics. Additionally, it is expected that future smart inverters own certain degree of
intelligence, as knowledge of its role or status within its environment and the likely effect
of possible future actions .
2.3. Adaptability
The adaptability is another critical characteristic of a smart inverter. A smart inverter,
to be able to adapt itself to the variations of the system in the operating conditions. This
means the capability to evaluate the parameters, mostly the impedance of the grid, and
synchronization in terms of frequency. Unintended islanding is one of the most remarkable
functioning problems of grid system. This happens mainly due to grid failure, and the
inverters are required to be included with islanding recognition algorithms in order to self-
adapt, depending on the situation. Fault Tolerance and Islanding Detection are also
categorized in this category .
2.4. Autonomy
Outline of this function is the system being smart enough to decide its own operation
mode. Autonomous behavior is an elementary property for a distributed system.
Furthermore, smart inverter with autonomous operation can be necessary in case of limited
or no communication, or if desired for reliability . One common situation is autonomous
load power sharing using droop methods when multiple inverters operate in parallel. For
autonomous operation, smart inverters shall achieve skills such as dynamic grid feeding,
dynamic grid creating, black start, seamless power transfer, and the power quality
enhancement. Other autonomous functions in are required by the power utility for
distributed generations.
2.5. Cooperativeness
The meaning of this function is the ability of an inverter requires to be able to function
in cooperatively and together with other inverters in a grid. All the inverters are essential
to take some responsibility to regulate and rectify the unbalances and conflicts standing in
the system. Their process should be in alignment with other neighboring components, when

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they are in operation. Therefore further disturbances will be introduced to the system.
Furthermore, there are other aspects which lie in this category such as ramp rate control for
renewable energy sources, reactive power and harmonic current sharing and soft start
capability . The Table 6 below, summarizes the technical possibilities and practical issues
of above functions. The Table 7 below, shows the comparing between traditional inverters
and smart inverters considering the smart functions.
Table 6. Technical possibility and practical issues 2.
Smart Inverter
Functions
Technical possibility and practical issues
Plug and Play A safety and high speed communication protocol is needed
Self–Awareness Detection algorithm must be used to get certain degree of intelligence
Adaptability Feedback control method must be used. Required extra hardware and
other devices to the moderation process
Autonomy When there is limited or no communication, autonomy operation is
necessary for system reliability.
Cooperativeness Requirement of Communication is more than the other functions
since it has to communicate in between inverters
Table 7. Comparing of functions.
Smart Functions Traditional
inverters
Smart
inverters
Plug and play NO YES
Autonomy NO YES
Adaptability NO YES
Self-awareness NO YES
Cooperativeness NO YES
Physical and Virtual Connect/ Disconnect NO YES
Reactive power output at night NO YES
Dynamic Power factor NO YES
Dynamic battery charging management NO YES
Pre identification of attacks and hazards NO YES
Time scheduling NO YES

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Chapter 6
Standard inverter functionalities
Introduction
Solar photovoltaic (PV) systems becoming more popular in modern electric power system
(EPS). Increasing of solar PV improving our electricity grid and creating a solution for
energy dependency, reliability for industrial, commercial, and residential applications.
However, the penetration of DSG such as rooftop, ground mounted, utility-scale solar
increases, there are some power and voltage quality issues occur in the EPS. Regions like
California, Germany with increased solar PV are already facing technical challenges with
grid operations due to the generation at load with high penetration of PV . The main reasons
for that issue is traditional power distribution networks are not designed to handle
bidirectional power flow. In order to mitigate such problems and increase clean energy
generation, the smart integration of DSG is important. Electric power conversion
technologies such as rectifiers (AC/DC), inverters (DC/AC), converters (DC/DC, AC/AC)
are the main building blocks of the distributed generation technologies .
Typical inverters are used to convert DC to AC, but during the conversion process there
are some losses, distortions created which will affect the quality of the transferred power.
Also, fast power fluctuations likely to occur with increasing renewable generation. To
avoid such problems some external elements are needed such as shunt capacitors, load tap
changers. In advanced inverters those external elements are integrated into same
equipment. Integrating multiple devices into same equipment saves capital investments and
system space . Besides these, several control strategies and topologies are developed to
improve power quality and efficiency of the system .
6.1 Standard inverter functionalities
In power distribution applications standard inverters produce a sinusoidal waveform with
appropriate frequency. They can be coupled with stand-alone, grid connected, or energy
storage devices to convert desired AC current. According to the IEEE standard 1547 and
Underwriter’s Laboratory (UL) 1741, DSG inverters are manufactured and tested to
provide reliable and safe functionalities more than the fundamental conversion of DC
power to AC power. Optimal power conversion, desired voltage level, and synchronization
with grid are important to supply quality power to the consuming devices. Safety for the
working professionals is augmented through ability to disconnect from the point of
common coupling (PCC) and the implementation of unintentional islanding protection

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1) Power transfer
Optimization of transferred power is achieved through MPPT technique with using special
algorithm, which computes the ideal equivalent resistance from measurements of system
parameters such as current, voltage, and the respective rates of change. Efficiency of an
inverter is evaluated with respect to the peak operation and overall performance under the
range of testing conditions. Many commercially available inverter models reaching 97%
peak efficiency or higher.
2) Voltage conversion and Grid synchronization
Generated power from distributed solar is delivered at different voltage levels depending
on the distribution size. The maximum voltage for distributed solar output is 4kV, which is
the lowest primary distribution voltage in the United States. Transformers or advanced
power electronics-based switching circuitry is used to step-up the voltage into consistent
levels.
One of the main functions of the inverters is to supply a waveform whose frequency is
identical to the grid frequency. For three phase interconnection applications phase
synchronization for each of the three phases is also required for grid synchronization.
Voltage loss is caused by phase differences, whereas frequency alignment changes result
power losses. Frequency and phase of the coupled network is controlled by special control
strategies of internal power electronics of the device. To mitigate flicker, harmonic
distortion, and other issues pulse width modulation (PWM) techniques and filtering are
used.
3) Disconnection and anti-islanding protection
Grid connected inverters are required to disconnect form the grid at the PCC during the
fault conditions. The fault indicating values for the frequency and voltage levels based on
the magnitude and duration of the signal is provided in standard IEEE 1547.
Unintentional islanding occurs when distributed solar generation continues to energize the
load after disconnection from grid. Islanding can be intentional and unintentional.
Intentional islanding is planned in advance carefully engineered for reliability and
powerquality
purposes; whereas, unintentional islanding is established by accident. Unintentional island
formation carries a range of potential consequences such as lacking capacity to satisfy load,
or failure to operate within specified voltage and current limits. These conditions may be
dangerous for workforce and public safety. According to the standard IEEE 1547 which
requires that disconnection must occur within two seconds of island formation.

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6.2 Advanced Inverters
As we mentioned above, the standard inverters supply grid-synchronized power to the grid
or the load with additional safety features like anti-islanding and detection of fault. The
advanced research on power conversion technologies made it possible that inverters are
now capable of doing beyond their standard functions. Advanced inverters has
functionalities such as supply and absorb reactive power by controlling and modulating
voltage and frequency, and voltage and frequency ride through capabilities which provide
extra safety and reliability of the system. Traditionally, capacitor banks were used to control
reactive power consumption of the grid, but the problem is that the capacitors do not have
fast switching ability to follow variability of reactive power. Advanced inverters solving
this issue with flexible supply or absorb reactive power. Ride-through functionality of the
advanced inverter depends on monitoring the frequency or voltage over or under nominal
levels, actuation of special algorithm to implement a response to low or high voltage for
resolving temporary condition. Voltage and frequency ride-through functionalities provide
dynamic support to the grid.
A. Advanced features
Advanced features of the inverters can be achieved by integrating power quality
conditioning elements and modification of software to by implementing new control
strategies.
1) Reactive Power Control
It is known that main part of the distribution consists of inductive load. Inductive loads
make phase difference between voltage and current waveforms, which cause losses in the
system. Loads with leading current waveform are useful because it resolves line losses and
improves voltage drop profile over the distribution network. Reactive power control in
inverter is also known as “VAR control” which helps to solve phase differences between
voltage and current waveforms. By resolving phase differences, the rising voltage levels,
power quality and efficiency of the power distribution can be significantly improved.
Advanced inverters are capable of contributing active power and reactive power at the same
time. Using the VAR control the power factor can be corrected to match the mix of resistive
and inductive loads on the circuit. Manipulation of the power output is achieved through
modes, which provide specific responses to the grid voltage levels. By considering the
modulated ramp rates, hysteresis, and randomization of the execution time window
different modes are applied to ensure stability.
2) Voltage ride through
One of the important aspects of an advanced inverter is to be able to ride through a
temporary fault in the distribution line. In a shortage event, part of the circuit experiences
an overcurrent for some duration. It can cause voltage dip, dissipation of excess power and
overheat, which might damage customer or utility equipment. Standard inverters are
required to identify fault, but sometimes faults can be temporarily. When the fault duration

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is negligible, which occur very short amount of time the system should stay online without
disconnecting from the network. Voltage ride-through ability of inverter will solve this
problem by monitoring and responding to voltage fluctuations. Increase and decrease of the
voltage levels can be achieved by injecting reactive power into the line.
3) Frequency ride through
Frequency ride through capability is the same phenomena with voltage ride through
capability. In this situation, when fault occurs in the distribution network the frequency
deviates from its nominal value. When the fault is temporary, the inverter must stay online
for certain time period for certain frequency values. Frequency ride-through capability of
advanced inverters resolves this and helps the system stay online without tripping for
negligible faults. Higher or lower frequency in the system can result over or under-supply
of active power to a circuit.

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Chapter 7
Benefits and Drawback of Inverter Technology
Benefits of Inverter Technology:
1. The efficiency of an AC is enhanced since the start/stop cycles are eliminated in a DC
Inverter AC. The AC does not operate at full power, but still maintains the desired
temperature. This is another reason why these ACs can still save energy even if there are
regular power outages.
2. Inverter ACs are cheaper to operate in almost all types of conditions.
3. Quicker cooling or heating (based on feature availability) can be achieved since an inverter
AC can pull the required current on its own to increase initial cooling or
4. heating. The inverter AC can calculate the current draw by using the indoor and outdoor
temperature difference.
5. DC Inverter ACs don’t put extra load on its power supply. Therefore you don’t see
fluctuations in electricity caused by them.
6. The life of components (used in the AC and other electrical household components) is
increased due to the same reason i.e. gentle power draw.
7. DC Inverter ACs are much quieter compared to conventional ones. The outdoor unit usually
makes far less sound as the unit is operating at a reduced rate. It eliminates the jerky start-
up sound as well.
8. These types of ACs often use an environment friendly refrigerant gas (R410A) which do
not cause harmful effects like the CFCs on the Ozone layer.
9. Inverter ACs offer a more stable operation and you usually won’t notice any changes when
it is operating. Cooling or Heating is maintained much more accurately as the AC doesn’t
turn off and the other aspects also add to its stable and gentle operation.
10. Most inverter ACs come with dual-mode air conditioning, which more or less makes up for
the higher price compared to cooling-only ACs. A dual-mode AC, which cools or heats
depending on the weather, will get you more savings throughout the year, making up for
its higher cost much faster.
11. It is possible to use DC Inverter ACs with UPS, Batteries or Solar Panels.
12. Most DC Inverter ACs keep working even at low voltages without any issues.
Drawbacks of Inverter Technology:
1. DC Inverter ACs cost more. Even without the dual-mode function, they still come with
high price tags. Square wave output waveform and not stable enough. (Square Sine wave
inverter)
2. Lack of power, cannot run the appliances with same power labeled; it’s easy to damage
the machine if customers are not familiar with the operation, the user needs to strictly follow
the manufacturers’ instructions. (Modified Sine wave Inverters)
3. Higher prices, the domestic customers know less about it. (Sine wave Inverters)

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4. line is relatively complex; high technically demanding for maintenance; more expensive.(
Pure sine wave inverter)
5. The built-in circuit becomes far more complex due to multiple conversions from AC
(Alternating Current) to DC (Direct Current) and back to AC (Alternating Current). 3-DC,
4-D or All DC inverter ACs have even more conversions taking place as there are more
components working on DC.
6. Repair costs increase as components are more sophisticated and as a result, more expensive.
They require more effort to build or repair.
7. Specialist technicians are hard to find for inverter ACs. Most local technicians have little
to no experience with these new ACs. Users might even have to get their AC fixed from its
manufacturer’s service centre, translating to more expense, if they can’t find a skilled
technician.
8. Conversion energy losses occur on every single one of the conversion steps. The losses can
go as high as 4-6%, depending on the conditions and quality of the equipment.
Manufacturers are aware of this and count it in the final power savings.
9. These ACs often come with R410A refrigerant gas while most technicians still only have
an R-22 (CFC-based) refrigerant gas. Users will have to ask their technicians to refill the
AC with R410A when required.
10. Only a few of the local brands offer 3-DC/4-D/All-DC Inverter ACs. So users might have
to wait for a while before their brand of choice starts selling a more energy saving type of
DC inverter AC.

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