This document describes a technique for generating a pure sinusoidal pulse width modulation (PWM) signal for a three-phase voltage source inverter. It discusses using three sine waves displaced by 120 degrees as reference signals to generate PWM pulses for each phase of the inverter. The output waveforms are analyzed theoretically and experimentally. Simulations are carried out using software to demonstrate harmonic reduction with the PWM technique. An innovative prototype model is developed and its simulation results are verified experimentally. Microcontrollers are used to generate the PWM pulses. The technique aims to improve power quality by producing a pure sine wave output from the inverter.

1. Pure Sinusoidal PWM Signal Generation Technique
for Three Phase Voltage Source Inverter with
Simulation of PWM Inverter
Aftab Rafeeq and Atta-ur-Rehman Bilal Masood
Department of Electrical Engineering Department of Electrical Engineering
Superior University Superior University
Main Raiwind Road, Lahore, Punjab Province, Pakistan Main Raiwind Road, Lahore, Punjab Province, Pakistan
{aftab_rafeeq & rehman10138}@yahoo.com bilal.masood@superior.edu.pk
Abstract - Inverter is the most important device to the ever-
increasing reliance on electronic devices which utilize alternating
current power highlights the problems associated with the
unexpected loss of power from the Electric grid and in the
industry. The main purpose is to design pure sine wave inverter
otherwise it disturb the power quality like variation in voltage
magnitude, transient in voltages and currents, harmonic content
in the waveforms for AC power etc. The places where the
electrical infrastructure is not well-developed, brown-outs can
prove to be fatal which makes electronic instruments defective.
Therefore, there is a need for cost-effective and reliable pure-sine
wave inverters. The Pulse Width Modulation (PWM) technique is
one of the most popular new techniques, with this technique
harmonics are reduced of inverters. These are used by three sine
waves displaced with 120 phase difference as reference signals for
three phase inverter which is obtaining pure sine wave in direct
current-to-alternating current inverter [1]. The output
waveforms in the proposed Pulse-width modulation inverter are
investigated both theoretically and experimentally. The switching
scheme from direct current to alternating current results in
unwanted harmonic voltages in the range of the switching
frequency and higher, which can be easily filtered out.
Simulations and experimental work are carried out and results
presented to demonstrate the feasibility of the proposed
approach. Simulation is carried out by using PROTEUS
(software) and in the experimental work an innovative design
prototype model is proposed and developed to verify the
simulation results. In this project automatic voltage regulator
microcontroller (ATMEGA 328P) is used to generate the Pulse-
width modulation pulses. The simulation results are shown
harmonic reduction pure sine wave with PWM techniques. If we
do not have pure sine signal, our appliances give sound during
their working due to harmonics. If we have impure signal, our
load will heat up. Due to impure signal the life of load decreases.
Due to pure sine wave we can improve power quality and power
factor.
Index-PWM, AC, DC, UART, ADC
I. INTRODUCTION
In the last years, new energy sources have been proposed and
developed due to the dependency and constant increase of
costs of fossil fuels. On other hand, fossil fuels have a huge
negative impact on the environment. In this context, the new
energy sources are essentially renewable energies. It is
estimated that the electrical energy generation from renewable
energy sources will increase from 19%, in 2010, to 32%, in
2030, leading to a consequent reduction of CO2 emission. In
rural areas particularly in the developing world, where most of
the population up to 80% is located, more than 1 billion
people lack the essential energy services to satisfy the most
basic needs and to improve their social and economic status.
The growing energy demand around the world led us to utilize
these renewable energy resources. In recent years, the efforts
to spread the use of renewable energy resources instead of
pollutant fossil fuels and other forms have increased. To
utilize these renewable energy resources an inverter is
essential which converts DC power to AC power as most of
the renewable energy is found in DC form. In hybrid power
system and micro-grid system the use of inverter is significant.
In industrial applications, such as single phase and Three
Phase Induction Motor & other rotating machines, variable
frequency &variable voltage supply is needed. To vary the
supply frequency and supply voltage, voltage source inverter
(VSI) is used. The voltage source inverters (VSIs), where the
independently controlled AC output is a voltage waveform,
behave as voltage sources required by many industrial
applications. While the single-phase VSIs cover low-range
power applications, three-phase VSIs cover medium to high-
power applications. Inverter is the most important device to
utilize the renewable energy sources efficiently. The
Sinusoidal Pulse Width Modulation (SPWM) technique is one
of the most popular PWM techniques for harmonic reduction
of inverters since there are used three sine waves displaced in
1200 phase difference as reference signals for three phase
inverter. In present, the SPWM switching signal is developed
with the help of distinct FPGAs, micro-controllers and micro-
processors. But for these types of accessories, it is necessary
the programming or coding. This paper shows the SPWM
technique for harmonic reduction & represents how to
generate SPWM switching signal using different simple
Operational-Amplifier (Op-Amp) circuits/analog circuits for
three phase pulse width modulated (PWM) voltage source
inverter (VSI). All the Op-Amp circuits are simulated and
their outputs are shown step by step. This analog circuit (Op-

2. Amp) controlled voltage source inverter is simulated for both
standalone load & high voltage sensitive loads/systems like
micro-grid system and large industrial machines respectively
without transformer & with transformer. Before and after the
harmonic reduction, the simulation results are shown, and
appropriate passive filter is used in it. Moreover, the paper
expresses two classic inverter based micro grid system
structures where one is with common DC bus & another one is
with common AC bus. Conventionally, there are two ways
Direct current (DC) or Alternating current (AC) in which
electrical power is transmitted. Direct current (DC) comes
from a source of constant voltage and is suited for small
devices and short level transmission. Alternating current (AC)
power consists of a sinusoidal voltage source in which a
continuously changing voltage (and current) can be used to
employ magnetic factors. Long distance electrical
transmission support AC power, since the voltage can be
promoted easily with the use of transformers and powerplants.
By enhancing the voltage, low current is needed to provide a
given amount of power to a load, decreasing the resistive loss
through conductors. However, AC power is not always
available and the need for mobility and simplicity has given
batteries an advantage in portable power. Since the energy
stored in a battery is in dc form so to use this stored power
from battery we need to convert this dc form of energy in to ac
form. For this conversion, here comes the concept of power
inverters [2]. The device which can convert electrical energy
of DC form into AC form is known as power inverter.
Inverters can come in many distinct varieties, differing in
price, efficiency, power and purpose. Generally inverters are
of two types: single and three phase inverters. According to
their output there are classified into three types: square wave,
modified-sine wave and pure sine wave. Square wave and
modified-sine wave inverters are less expensive to make but
high heat generation and high unused harmonic energy
delivered to a load. The output is not appropriate for delicate
electronic devices which rely on particular timing. Pure sine
wave inverters provide more accuracy, less heat generation
and less unused harmonic energy delivered to a load, but they
are more expensive and more complex in design. Pure sine
wave inversion is accomplished by taking a DC voltage source
and switching it across a load using an H-bridge. If this
voltage needs to be enhanced from the DC source, it can be
accomplished either after the AC stage by using a boost
transformer, or before the AC stage by using a DC-DC boost
converter. The inverted signal itself is collected of a pulse-
width-modulated (PWM) signal which encodes a sine wave.
The role cycle of the output is changed such that the power
transmitted is exactly that of a sine-wave. This output can be
used alternatively and can be filtered easily into a pure sine
wave. Here, the design of a true sine wave inverter, directing
on the inversion of a DC high-voltage source. It therefore
astimate the creation of a DC-DC enhance phase. DC-AC
inverters have been widely used in industrial applications such
as static frequency changes, uninterruptible power supplies
and AC motor drives. Nowadays , the inverters are also
playing important roles in renewable energy applications as
they are used to link a photovoltaic or wind system to a power
grid.
II. SINUSOIDAL PWM FOR THREE PHASE INVERTER
For three phase inverters there are three sinusoidal reference
waves (Vra, Vrb, Vrc) each shifted by 1200
. A carrier wave is
compared with reference signal corresponding to a phase to
generate the gating signals for that phase. Comparing the
carrier signal Vcr with reference phases Vra, Vrb and Vrc
produces g1, g3 and g5 respectively. The instantaneous line to
line output voltage is
Vab = Vs. (g1 g3)
The output voltage is generated by eliminating the condition
that two switching devices in the same arm cannot conduct at
the same time [3-6]. The normalized carrier frequency mf
should be odd multiples of three. Thus, all phase-voltage are
identical, but 1200
out of phase without even harmonics.
Moreover, harmonics at frequencies multiple of three are
identical in amplitude and phase in all phases. For instance, if
the ninth harmonic voltage is in phase a
Van9(t) = V9sin(9wt)
The corresponding ninth harmonic in phase b will be,
Vbn9(t) = V9 sin(9(wt – 1200))
= V9 sin(9wt 10800) = V9 sin(9wt)
Thus, the ac output line voltage does not contain the ninth
harmonic.
Vab = Van Vbn
Therefore, for odd multiples of three times the normalized
carrier frequency mf the harmonics in the AC output voltage
appear at normalized frequencies fh centered around mf and
its multiplies, specially at
n = jmf ± k
Where j = 1, 3, 5…….for k = 2, 4, 6….
And j = 2, 4,….for k = 1, 5, 7…..
Such that n is not a multiple of three. For nearly sinusoidal AC
load current, the harmonics in the DC link current are at
frequencies given by:
where j = 0,2,4….for k = 1,5,7…and j = 1,3,5…for k =
2,4,6…,such that is positive and not a
multiple of three. Because the maximum amplitude of the
fundamental phase voltage in the linear region (M ≤ 1) is
, the maximum amplitude of the fundamental ac output line
voltage is . Therefore, one can write the
peak amplitude as:

3. For 0 <M< 1
To further increase the amplitude of the load voltage, the
amplitude of the modulating signal can be made higher than
the amplitude of the carrier signal, which leads to over
modulation. The benefit of choosing the PWM over analog
control is increased noise immunity which the PWM is
sometimes used for communication. Diverting from an analog
signal to PWM can increase the length of a communications
channel dramatically. At the receiving end, a suitable RC
(resistor-capacitor) or LC (inductor-capacitor) network can
remove the modulating high frequency square wave and return
the signal to analog form. So, the filter requirement can be
decreased and the overall inverter size can be reduced. The
disadvantages of PWM are like more complex circuit for the
switching, higher switching loss due more to frequent
switching, difficult to implement and more Electro Magnetic
Interference (EMI) loss.
III. 180° CONDUCTION
In 180° conduction each transistor conducts 180⁰. Generally,
there are six modes of operating the switches, where in a cycle
the phase shift of each mode is 60º. In order to generate a
desired voltage waveform, the transistor conduction moves
from one state to another. The gating signals as shown in
Figure 1 are shifted from each other by 60º to obtain 3-phase
balanced (fundamental) voltages [8-11]. These all switching
states are shown in Table 1. The load can be connected in wye
or delta connection. The line current is determined when the
phase current are known. For a wye connected load, the line to
neutral voltages must be determined to find the phase current.
Fig. 1 Waveforms gating signal 180⁰ PWM
Table 1 Switch states
State State
no
Switch
state
Vab Vbc Vca
S1,s2,s6 on
S4,s5,s3 off
1 100 Vdc 0 -Vs
S2,s3,s1 on
S5,s6,s4 off
2 110 0 Vdc -Vdc
S3,s4,s2 on
S6,s1,s5 off
3 010 -Vdc Vdc 0
S4,s5,s3 on
S1,s2,s6 off
4 011 -Vdc 0 Vdc
S5,s6,s4 on
S2,s3 ,s1 off
5 001 0 -Vdc Vdc
S6,s1,s5 on
S3,s4,s2 off
6 101 Vdc -Vdc 0
S1,s3,s5 on
S4,s6,s2
7 111 0 0 0
S4,s6,s2 on
S1,s3,s5 off
8 000 0 0 0
IV. PROPOSED MODEL
For DC-AC, we required Automatic Voltage Regulator
(AVR), Microcontrollers, Logic circuit, Gate drivers,
Amplifiers and filters. We build a block diagram, as shown in
figure 2, Here we show out the diagram of single phase for
simplicity. In three phases we simply combine three single
phase circuits. AVR and Controllers control the circuit
Voltages and give a proper signal to Logic gates. Logic Gates
starts their switching and gives a high or (require) signal to
Gate Driver, with the help of Amplifiers. Gate Driver select
the mode And the send an AC signal to the Power Circuit. We
Get our Out Put from Power Circuit
Fig. 2 Block Diagram of pure sine wave inverter
A. Microcontrollers
In our Circuit we use 2 Microcontrollers AT89C51 and
ATMEGA-328P. Selection of Microcontroller contains

4. following features: Internal EEPROM, Serial synchronous
communication, Serial UART, Timers, Out-compares, Input
captures, PWM, ADC, Modem device, Digital signal
processing (DSP), Ports with wireless interface and related
processing instructions capable CPU, USB/PCI interface
devices. A microcontroller already contains all components
which allow it to operate standalone and it has been designed
in particular for monitoring and/or control tasks. The
processor includes memory; various interface controllers,
timers, an interrupt controller, general purpose I/O pins which
allow it to directly interface to the other equipment. Controller
AT89C51 get the input from DC source and start their
operation as we required from this [12-16]. Internally pin
configuration of micro controller AT89C51 is shown in Figure
3. Microcontroller ATMEGA328P circuit contains AVR
series. It is programmed to generate six 180° conduction gate
signals at digital PWM pins of 3, 5, 6, 9, 10 and 11. A PWM
signal is generated at a pin. Digital input output pins are 14 in
which 6 provide PWM output. AT89C51 was also used for
generating the three phase shift in the circuit. These circuits
are implemented on PROTEUS.
Fig. 3 Schematic Diagram of AT89C51
B. Logic Circuit
Logic circuit consist of an IC 74HC08. The main importance
of logic circuit is it protects the push-pull transistors and to
generate the square PWM in the circuit before the gate driver
signal, as shown in Figure 5. When the upper gate is ON, the
lower gate stays off and vice versa. First pair of AND gate
generates the Square PWM while the second AND gate
generates the negative and inverted square PWM. The output
of the logic circuit is supplied to Gate driver module [17].
Fig. 4 Schematic diagram of logic circuit.
C. Gate Driver
The basic purpose of gate driver module is to optically isolate
the Microcontroller circuit from the Gates. The requirment of
the isolation is due to back emf of motor capacity and
hazardous peak voltage clamors that can disturb the control
logic inward the micro-controller. For this function a TLP 250,
a high speed opto coupler is used [18]. In our project, Gate
Driver get the input from Logic Circuit, start their work an
give an output to power circuit, as shown in Figure.
Fig. 5 Schematic Diagram of Gate driver circuit
D. Filter Circuit
This circuit is used to filter the unwanted level, harmonics and
distortion in the circuit. It contains diodes, heat sinkers, zener
diodes, capacitors and inductors. After achieving the wave-
form, then is will delivered to the filter circuit. Where it is
filtered and final three phase pure sine wave is achieved.

5. V.SIMULATION RESULTS
The Schematic diagram contains six IGBTs gates with built in
freewheeling diodes which is supplied by six pulses and DC
voltage source. Need of separate power supplies is due to a
fact that at any instance of operation Van, Vbn, and Vcn can
have any value (different from each other) so, if they have
particular supply they would little to give the same voltage
level of all 3 levels [19]. That is why individual Vpulse is
needed for 3 phase inverter. These simulation results are
carried out in PROTEUS. Simulation in PROTEUS is done
220V DC inverter. It shows various figures of both resistive or
linear load and Non resistive load such as motor load. Non
resistive load are basically inductive loads. The AVR and
Atmel are used to generate PWM signal and Square wave
signal with phase shift. The both signal are then synchronized
by the logic circuit to generate positive and negative cycles.
The two cycles are produced which then further transferred to
the amplifier circuit. The amplifier circuit will amplify the
signals. Gate drive circuit is granting PWM signal to the
IGBT’s. Signal given to the power circuit is then increases and
being inverted to give AC signal. Filters are used at the output
of the power circuit to give pure AC signal. The whole single
phase proposed model simulation result is shown in Figure 6.
Fig. 6 Schematic diagram of pure sine wave of Inverter
For three phase wave we use a Schematic Diagram as shown
in figure 7. In this circuit three single phase circuits are used
for required output.
Fig. 7 Schematic diagram of pure three phase sine wave
Inverter
We can see our output wave diagram of three phase inverter in
figure 8. All three phases are shown in different colours.
Fig. 8 Graph of pure sine wave inverter

6. VI. CONCLUSION
The goals for this project were to produce a pure sine wave
DC-AC inverter that would output at 50 Hz, 440 volts RMS,
would be cheap to manufacture, and fairly efficient through
this method. At 12 volts powering, the H-Bridge output is a
clean 50 Hz sine wave that can easily be controlled in size by
the size of the sine reference in the control circuit. It is in this
capability that the option of a closed loop control circuit could
be implemented. In looking at the components selected and
the simulations created before the actual construction of the
inverter, all plan was built in mind for the purpose of
effictiveness and keeping power losses to a minimum as
possible. One of the main elements in the power savings is the
use of a three level PWM signal rather of a two level, this
allows a much less average power output to produce the sine
wave required and assisting in the efficiency of the device.
This project is a stepping stone to a cheaper and efficient pure
sine wave inverter, by using the data collected, schematics and
recommendations of the product can be boost up. Simple
inclusion such as circuit protection and a closed loop control
scheme could greatly improve the performance of this project.
In its present condition, the project does work in the manner,
the team wished and has met every goal set at the
commencement of this venture. From all the simulation results
it is seen that the designed Op-Amp/Analog circuit controlled
PWM inverter works accurately. It fulfills all the requirements
for a voltage source inverter. The THD is less than 5% after
filtering. The inverter outputs can be varied by varying the
resistance of potentiometer. The inverter responses better for
standalone inductive loads like induction motor. If the power
is not enough to supply to the grid then it will supply the
power to the local standalone loads. If the carrier frequency is
increased much enough then the filtering system will be much
better and the loss will be less. But better response can be
achieved by using the feedback system, means the closed loop
control system. The future work can be done on the feedback
loop system.
VII. ACKNOWLEGDMENT
Alhamdulillah, the highest thank to ALLAH because with His
Willingness I possible to complete the research paper. I would
like to thank my supervisor Mr. Bilal Masood for his advice
and support throughout this paper. At the same time I would
like to express my gratitude to Dr. Farooq Aslam for sharing
his valuables ideas as well as his knowledge. I also wish
acknowledgement to the people who gives support direct or
indirectly to the paper, project and during the thesis writing.
Once again, thank you very much.
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