Capsotone Report

i
“Performance Analysis of Single Phase Diode Clamped Rectifier”
CAPSTONE PROJECT-II
Submitted in partial fulfillment of the
Requirement for the award of
Degree of
BACHELOR OF TECHNOLOGY
IN
(Electrical and Electronics Engineering)
By
1. Deepak Choudhary (10901653)
2. Sandeep Pradhan (10904577)
3. Varun Agarwal (10906336)
Under the Guidance of
Mukul Chankaya
Transforming Education, Transforming India
(School of Electrical and Electronics Engineering)
Lovely Professional University
Punjab
Month and Year of Submission (APRIL 2013)

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CERTIFICATE
This is to certify that the Capstone project titled “Performance Analysis of Single Phase Diode Clamped
Rectifier” that is being submitted by “ Deepak Choudhary(10901653), Sandeep Pradhan(10904577),
Varun Agarwal(10906336)” is in partial fulfillment of the requirements for the award of BACHELOR OF
TECHNOLOGY DEGREE, is a record of bonafide work done under my guidance. The contents of this
Capstone project , in full or in parts, have neither been taken from any other source nor have been
submitted to any other Institute or University for award of any degree or diploma and the same is
certified.
Mukul Chankaya
Project Supervisor
(Lovely Professional University)
(Organization stamp)
Objective of the Capstone project is satisfactory / unsatisfactory
E x a m i n e r I E x a m i n e r I I
IF THE CANDIDATE HAS DONE HIS CAPSTONE OUTSIDE THE UNIVERSITY A CERTIFICATE TO THAT
EFFECT MUST BE ATTACHED HERE ON THE ORGANIZATIONS LETTER HEAD DULY STAMPED and SIGNED

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ACKNOWLEDGEMENT
The Student is free to acknowledge all those he feels he should acknowledge on the basis of the
guidance and help provided during the implementation of the Project work. If the student has
conducted his project elsewhere (viz. outside Lovely Professional University) appropriate
acknowledgement should be given to all concerned.
It is customary to acknowledge the University Management / respective School Dean for giving the
candidate an opportunity to carry out his studies at the University.
Reg. No. 10901653
Reg. No. 10904577
Reg. No. 10906336

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CERTIFICATE
This is to certify that Deepak Choudhary, Sandeep Pradhan, Varun Agarwal bearing Registration
no. 10901653, 10904577, 10906336 has completed objective formulation of Capstone project titled,
“Performance Analysis of Single Phase Diode Clamped Rectifier” under my guidance and supervision.
To the best of my knowledge, the present work is the result of his original investigation and study. No
part of the capstone has ever been submitted for any other degree at any University.
The capstone project is fit for submission and the partial fulfillment of the conditions for the
award of Bachelor of Technology (Electrical and Electronics Engineering)
Signature and Name of the Research Supervisor: -Mukul Chankaya
Designation: - Assistant Professor
School: - School of Electrical and Electronics Engineering
Lovely Professional University
Phagwara, Punjab.
Date : 26-April-2013

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DECLARATION
We (Deepak Choudhary-10901653, Sandeep Pradhan-10904577, Varun Agarwal-10906336) ,
student of Bachelor of Technology under Department of Electrical and Electronics Engineering of Lovely
Professional University, Punjab, hereby declare that all the information furnished in this capstone
project report is based on my own intensive research and is genuine.
This capstone does not, to the best of my knowledge, contain part of my work which has been
submitted for the award of my degree either of this university or any other university without proper
citation.
Date: 26-April-2013 Signature and Name of the student
Registration No. ...........
Signature and Name of the student
Registration No. ..........
Signature and Name of the student
Registration No. ...........

vi
Abstract
A control scheme for a single-phase diode clamped rectifier is used to achieve unity power
factor, balanced neutral point voltage and constant de bus voltage. Four power switches are used
in the rectifier to generate a two-level unipolar PWM waveform on the rectifier terminal voltage.
To balance the neutral point voltage, a capacitor voltage compensator is engaged. The
helpfulness of the control algorithm was verified by the computer simulations.

vii
Table of Contents
List of Figures………………………………………………..ix
Chapter 1
1.1 Introduction………………………………………………………………………1
1.1.1 Harmonic Indices………………………………………………………....2
1.1.2 RMS variations agreements………………………………………………2
1.2 Harmonic agreements…………………………………………………………….3
1.3 Harmonic Sources………………………………………………………………...4
1.3.1 Transformers……………………………………………………………...6
1.3.2 Arcing devices……………………………………………………………6
1.3.3 Arc furnaces……………………………………………………………..7
1.3.4 Rotating machine devices………………………………………………..8
1.4 Basics of Converter……………………………………………………………....9
1.4.1 Single phase half wave rectifier…………………………………………9
1.4.2 Single wave full wave rectifier………………………………………….10
1.5 Classifications of converter……………………………………………………..12
1.5.1 Half bridge diode clamped rectifier……………………………………..12
1.5.2 Single phase capacitor clamped rectifier………………………………...12
1.5.3 A new class of single-phase multilevel inverter…………………………13
1.5.4 Single phase unidirectional AC/DC converter with high power factor….13
1.5.5 Paralleling of single phase AC/DC converter with High power factor
correction……………………………………………………………..….14
Chapter 2
2.1 Single phase diode clamped rectifier…………………………………………….15
2.1.1 System configuration……………………………………………………..15
2.1.2 Principle of operations…………………………………………………...15
2.2 PWM technique………………………………………………………………….19
Chapter 3
3.1 Simulation……………………………………………………………………..…21
3.1.1 Simulations and experimental results………………………………….…21
3.1.2 MATLAB circuit…………………………………………………………22
3.1.3 Current waveform………………………………………………………..22
3.1.4 THD using FFT…………………………………………………………..23

viii
3.2 Simulation at different Sources of Harmonics………………………………….24
3.2.1 Single Phase Diode Clamped Rectifier with Asynchronous Motor…….24
3.2.2 Single Phase Diode Clamped Rectifier with Non-Linear ………………26
Chapter 4
4.1 Hardware Implementation…………………………………………………..29
4.1.1 MOSFET………………………………………………………….29
4.1.2 Pulse Amplification and Isolation Circuit…………………….......30
4.1.3 Snubber Circuit…………………………………………………....33
Conclusion and Future Scope…………………………………………………………...34
References……………………………………………………………………….35
Biodata

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List of Figures
Fig 1.1 Equivalent circuit diagram of transformer……………………………………..6
Fig 1.2 Arc Furnace………………………………………………………………….....7
Fig 1.3 half wave rectifier………………………………………………………………9
Fig 1.4 Full wave rectifier with center tap……………………………………………..10
Fig 1.5 Bridge rectifier………………………………………………………………....11
Fig 2.1 Single Phase diode clamped rectifier…………………………………………..15
Fig 2.2 Six Modes of Single Phase Diode clamped Rectifier………………………….17
Fig 2.3 PWM Model……………………………………………………………………19
Fig 2.4 Waveform of PWM……………………………………………………………20
Fig 3.1 Model of Single Phase Diode Clamped Rectifier with Inductor………………22
Fig 3.2 Waveform of Single Phase Diode Clamped Rectifier with Inductor………….22
Fig 3.3 FFT analysis of Single Phase Diode Clamped rectifier with Inductor…………23
Fig 3.4 Model of Single Phase Diode Clamped Rectifier with IM…………………….24
Fig 3.5 Waveform of Single Phase Diode Clamped Rectifier with IM………………..24
Fig 3.6 FFT analysis of Single Phase Diode Clamped rectifier with IM………………25
Fig 3.7 Model of Single Phase Diode Clamped Rectifier with Non-Linear……………26
Fig 3.8 Waveform of Single Phase Diode Clamped Rectifier with Non-Linear……….26
Fig 3.9 FFT Analysis of Single Phase Diode Clamped Rectifier with Non-Linear……27
Fig 4.1 Pulse Amplification and Isolation Circuit……………………………………..30
Fig 4.2 snubber Circuit...................................................................................................33

1
Chapter 1
1.1Introduction
It is simple circuit configuration. A large number of passive elements, fixed compensation
characteristics and series and parallel resonance are the disadvantages of passive filters. Active
single-phase rectifiers have been aimed to make sinusoidal line current. Conventional two-level
PWM schemes for power factor correction were developed for many years. A new single-phase
neutral point diode clamped rectifier is presented. Four power switches are engaged in the aimed
rectifier reside of eight power switches used in the diode clamped converter. In the aimed control
algorithm, sinusoidal pulse width modulation scheme are employed to perform dc-link voltage
regulation, neutral point voltage balance and line current tracking respectively. Based on the
adopted control scheme, four power switches are turned on or off to draw a nearly sinusoidal line
current in phase with mains voltage. The voltage stress of power switches is clamping to half of
dc-link voltage.

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1.1.1 Harmonics Indices
Power electronic devices improve electrical power quality and reliabilities but present a double-
edged coordination problem with harmonics. Not only do they produce harmonics, but they also
are typically more sensitive to the resulting distortion than more traditional electromechanical
load devices. End users expecting a better level of service may actually familiarity more
problems. This section discusses power quality indices for assessing the quality of power service
with respect to harmonic voltage/current distortion.
1.1.2 RMS Variations Agreements
Part of the purpose of an interconnection agreement would be to educate end users on the
realities of power delivery by wire and the costs associated with mitigating voltage sags and
interruptions. Another part would be the establishment of some formal means by which the
utility records and evaluates the fault performance of its power delivery system.
Some of the key issues that should be addressed are
1. The number of interruptions expected each year.
2. The number of voltage sags below a certain level each year. The level can be defined in terms
of a specific number such as 70 or 80 percent. Alternatively, it can be defined in terms of a curve
such as the CBEMA or ITI curve.
3. The means by which end users can mitigate RMS variations.
4. Responsibilities of utilities in analyzing the performance of the power delivery system,
following up with fault events, etc.
5. Maintenance efforts to reduce the number of faults for events within the control of the utility.

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1.2 Harmonics Agreements
Although harmonics problems are not as widespread as rms voltage variation problems,
harmonics from ASDs and other electronic loads can have a severe impact on other end-user
equipment. In some cases, the equipment will fail to operate properly, while in other cases, it
may suffer premature failure. Therefore, agreements regarding harmonics can be very important.
The chief tool for the enforcement of harmonic emissions at the utility- customer interface is
IEEE Standard 519-1992.10 This is a two- edged sword: One part of the standard places limits
on harmonic currents that can be injected by end-user loads onto the system, while another part
effectively establishes minimum requirements for the utility. Agreements on harmonics should
reflect this bilateral nature [12]
.
Some of the key issues that should be addressed are
1. Definition of the PCC.
2. Limitation of the harmonic current distortion level at the PCC to that set by IEEE Standard
519-1992 or to another value allowed by a specified exception.
3. Periodic maintenance schedules for filters and other mitigating equipment. Some equipment
will require constant monitoring by permanently installed devices.
4. Responsibilities of utilities, such as
a. Keeping the system out of harmonic resonance
b. Keeping records about new loads coming onto the system (this is getting tougher to do with
deregulation)
c. Performing engineering analyses when new loads come onto the system to prevent
exacerbation of existing problems
d. Educating end users about mitigation options
e. Periodic monitoring or constant monitoring by permanently installed devices to verify proper
operation of the system.
5. Definition of responsibilities for mitigation costs when limits are exceeded. Is the last end user
who created the excess load responsible or is the cost shared among a class of end users and the
utility?

4
1.3Sources of Harmonics
Electrical power system harmonic problems are mainly due to the substantial increase of non-linear loads
due to the technological advances, such as the use of power electronic circuits and devices, in ac/dc
transmission links or loads in the control of power systems using power electronics or microprocessor
controllers [12]
. Such equipment create load-generated harmonics throughout the system.
Prior to the appearance of power semiconductors, the main sources of waveform distortion were
electric arc furnaces, the accumulated effect of fluorescent lamps and to a lesser extent electrical
machines and transformers.
In general, harmonic sources are given below:
 Converters,
 Devices which includes semi-conductor elements,
 Generators,
 Motors,
 Transformers,
 Lightening equipment working by gas discharge principle,
 Photovoltaic systems,
 Computers,
 Electronic ballasts,
 Uninterruptable power supplies,
 Switching power supplies,
 Welding machines,
 Control circuits,
 Frequency converters,
 Static VAR compensators,

5
 Arc furnaces,
 HVDC transmission systems,
 Electrical Communication systems.

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1.3.1 Transformers
Bobbins that have iron core will cause harmonics in electrical power systems. Transformers
are the most commons between those [3]
. As being one of the most important elements in
power systems, transformers are the oldest nonlinear elements known. The magnetization
characteristic of a transformer’s core is non-linear and will produce harmonics as it is
saturated.
The equivalent circuit of a transformer is given. Here and shows the primary circuit
resistance and the leakage reactance, and shows the secondary resistance and leakage
reactance that is transformed (reduced) to the primary respectively. Rfe is the resistance
which symbolizes the iron losses and is the current related to this losses. In parallel to the
resistance, shows the magnetization reactance and are the related current passes through.
1.3.2 Arcing Devices
The voltage-current characteristics of electric arcs are highly non-linear. Following arc ignition
the voltage decreases due to the short-circuit current, the value of which is only limited by the
power system impedance.
Fig-1.1

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The main harmonic sources in this category are the electric arc furnace and discharge type
lighting with magnetic ballasts.
1.3.3 Arc Furnaces
Arc furnaces may range from small units of a few ton capacities, power rating 2–3 MVA, to
larger units having 400-ton capacity and power requirement of 100 MVA. The harmonics
produced by electric arc furnaces are not definitely predicted due to variation of the arc feed
material. The arc current is highly nonlinear, and reveals a continuous spectrum of harmonic
frequencies of both integer and non-integer order. The arc furnace load gives the worst
Fig-1.2

8
Distortion, and due to the physical phenomenon of the melting with a moving electrode and
molten material, the arc current wave may not be same from cycle to cycle.
There is a vast difference in the harmonics produced between the melt and refining stages.
As the pool of molten metal grows, the arc becomes more stable and the current becomes
steady with much less distortion. Figure below, shows erratic RMS arc current in a supply
phase during the scrap melting cycle, and table below, shows typical harmonic content of
two stages of the melting cycle in a typical arc furnace.
1.3.4 Rotating Machine Harmonics
Rotating machines produce harmonic due to the field distribution of salient poles, the magnetic
permeance is related with slots and the saturation of the main circuit [6]
.
As a result of small asymmetries on the machine stator or rotor slots or slight irregularities in the
winding patterns of a three phase winding of a rotating machine, harmonic currents can develop.
These harmonics induce an electromotive force (emf) on the stator windings at a frequency equal
to the ratio of speed/wavelength. The resultant distribution of magneto motive forces (mmfs) in
the machine produces harmonics that are a function of speed. Additional harmonic currents can
be created upon magnetic core saturation.
The harmonics produced by a synchronous generator will not be taken into consideration if the
generator’s power rating is smaller than 1000 kVA.

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1.4Basics of Converter
There are two type of single phase diode rectifier that converts single phase ac supply into dc
supply.
1.4.1 Single phase half wave rectifier.
1.4.2 Single phase full wave rectifier.
1.4.1 Single Phase Half Wave Rectifier
The simplest single-phase diode rectifier is the single-phase half-wave rectifier [8]
. A single-
phase half-wave rectifier with resistive load is shown in Fig. The circuit consists of only one
diode that is usually fed with a transformer secondary as shown. During the positive half-cycle of
the transformer secondary voltage, diode D conducts. During the negative half-cycle, diode D
stops conducting. Assuming that the transformer has zero internal impedance and provides
perfect sinusoidal voltage on its secondary winding, the voltage and current waveforms of
resistive load R and the voltage waveform of diode D are shown in Fig. By observing the voltage
waveform of,
Diode D in Fig it is clear that the peak inverse voltage (PIV) of diode D is equal to Vm during
the negative half-cycle of the transformer secondary voltage. Hence the Peak Repetitive Reverse
Voltage (VRRM) rating of diode D must be chosen to be higher than Vm to avoid reverse
breakdown. In the positive half-cycle of the transformer secondary voltage, diode D has a
forward current which is equal to the load current and, therefore, the Peak Repetitive Forward
Current (IFRM) rating of diode D must be chosen to be higher than the peak load current Vm=R,
in practice. In addition, the transformer has to carry a dc current that may result in a dc saturation
problem of the transformer core.
Fig-1.3

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1.4.2 Single Phase Full Wave Rectifier
There are two types of single-phase full-wave rectifier, namely, full-wave rectifiers with center-
tapped transformer and bridge rectifiers. A full-wave rectifier with a center-tapped transformer.
It is clear that each diode, together with the associated half of the transformer, acts as a half-
wave rectifier. The outputs of the two half-wave rectifiers are combined to produce full-wave
rectification in the load. As far as the transformer is concerned, the dc currents of the two half-
wave rectifiers are equal and opposite, such that there is no dc current for creating a transformer
core saturation problem. The voltage and current waveforms of the full wave rectifier by
observing diode voltage waveforms vD1 and v D2, it is clear that the peak inverse voltage (PIV)
of the diodes is equal to 2Vm during their blocking state. Hence the Peak Repetitive Reverse
Voltage (VRRM) rating of the diodes must be chosen to be higher than 2Vm to avoid reverse
breakdown. (Note that, compared with the half-wave rectifier shown in Fig., the full-wave
rectifier has twice the dc output voltage, as shown in Section 10.2.4.) During its conducting state,
each diode has a forward current that is equal to the load current and, therefore, the Peak
Repetitive Forward Current (IFRM) rating of these diodes must be chosen to be higher than the
peak load current Vm=R in practice.
Fig-1.4

11
Employing four diodes instead of two, a bridge rectifier as shown in Fig. 10.5 can provide full-
wave rectification without using a center-tapped transformer. During the positive half cycle of
the transformer secondary voltage, the current flows to the load through diodes D1 and D2.
During the negative half cycle, D3 and D4 conduct. The voltage and current waveforms of the
bridge rectifier are shown in Fig. 10.6. As with the full-wave rectifier with center-tapped
transformer, the Peak Repetitive Forward Current (IFRM) rating of the employed diodes must be
chosen to be higher than the peak load current Vm=R. However, the peak inverse voltage (PIV)
of the diodes is reduced from 2Vm to Vm during their blocking state.
Fig-1.5

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1.5 Classifications of Converters:
1.5.1 Half bridge diode clamped rectifier.
1.5.2 Single phase capacitor clamped rectifier
1.5.3 A new class of single-phase multilevel inverter.
1.5.4 Single phase unidirectional AC/DC converter with high power factor.
1.5.5 Paralleling of single phase AC/DC converter with power factor correction.
1.5.1 Half Bridge Diode Clamped Rectifier
A high power factor rectifier based on neutral point clamped scheme is aimed [1]
. The voltage
stress of each power semiconductor of the adopted rectifier is equal to the half dc bus voltage
instead of full dc link voltage in the conventional switching mode rectifier. The control signals of
the power switches are derived from the dc link voltage balance compensator, line current
controller, and dc link voltage regulator. The hysteresis current control scheme is employed to
draw a clean sinusoidal line current, high input power factor, regulated dc link voltage, and
balance capacitor voltages. Three voltage levels are generated on the ac terminal of the adopted
rectifier. To verify the aimed operation scheme, performance characteristics are given by the
experimental results.
1.5.2 Single Phase Capacitor Clamped Rectifier
A control scheme for a single-phase capacitor clamped rectifier is aimed. Flying capacitor
configuration has been employed as a power factor correction to achieve a high-input power
factor and low-current harmonics. The adopted rectifier allows higher voltage than the voltage
stress of the power switches to be achieved [4]
. The control scheme, based on a look-up table with
hysteresis current controller (HCC), can
(i) draw a nearly sinusoidal line current
(ii) achieve a unity power factor
(iii) reduce the current harmonics
(iv) Improve the unbalance problem between capacitor voltages. The applications of the
adopted converter can be also used in multilevel active power filters, uninterruptible

13
Power supplies and high-power motor drives. The experimental results are shown to
confirm the validity of the aimed concept.
1.5.3 A New Class Of Single Phase Multilevel Inverter
Multilevel power converters make it possible to use mature but voltage-limited power
semiconductors in high voltage, high power industry and utility applications. Different from high
frequency approach, the concept of direct output synthesizing provides efficient power
conversion with the advantages of better harmonic cancellation and compact ac filtering.
Conventional multilevel inverters, including diode-clamped, flying capacitor, and cascaded H-
bridge, are well defined but become clumsy for higher levels. This paper proposes a new single-
phase full-bridge multilevel topology, which requires less split-rail dc sources and significantly
reduced semiconductor switch devices. An n-capacitor switching problem is aimed and analyzed,
which leads to the new class of generalized multilevel structure featured with asymmetrical dc
sources and maximized output levels. Cascading basic five-level cells provides another structure
to build higher-level inverters with separate dc sources. The aimed multilevel inverters can be
potential for solar photovoltaic and energy storage applications.
1.5.4 Single Phase Unidirectional AC/DC Converter with high power factor
A novel single-phase unidirectional power flow rectifier is proposed to achieve power factor
correction and DC bus voltage regulation. Four active switches, two power diodes and two DC
side capacitors are used in the proposed circuit topology to generate a three-level PWM voltage
waveform on the ac terminal of the proposed rectifier. Compared with neutral-point-clamped and
capacitor-clamped topologies, no clamping diode or flying capacitor is used in the proposed
rectifier. The reference line current is derived from the DC tank voltage controller and a sine
wave generator in phase with mains voltage. The carrier-based current controller is used in the
inner loop to track the line current command. A neutral-point voltage compensator is adopted in
the control scheme such that the capacitor voltages on the DC side are balanced [10]
. The
effectiveness of the proposed control algorithm is verified by the computer simulations and
experimental results.

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1.5.5 Paralleling Of Single Phase AC/DC With Power Factor Correction
A high quality power system requires a power supply which offers low-harmonics, a high power
factor, high performance, reliability, manufacturability, and modularity. To meet these demands,
a parallel ACIDC converter is often used. In addition, each converter uses a smaller size of
magnetic components, lower power and faster semiconductor-switch. An ACDC converter can
be categorized into two types, non-isolated, and isolated between input and output with a high
frequency transformer.
The paralleling of isolated ACIDC converters has been published. However, these converters
operate in discontinuous inductor current modes (DICM) for easy control as well as low cost.
Hence, low-order harmonics will occur and dominate the low power factor. Another limitation of
the circuit is that the voltage stress of the main switch is two times that of the input voltage. A
high voltage switch is inevitably required. From this problem, we propose a method to improve
the low-order harmonics by employing the two-switch forward converter, operating in
continuous inductor current mode (CICM) with fixed-switching frequency. With sliding mode
control, the output current sharing of each converter is equaled. Finally, simulated and
experimental results verify the improved performance and reliability.

15
Chapter 2
2.1Single Phase Diode Clamped Rectifier
2.1.1 System Configurations
 1 boost inductor
 2 dc bus capacitor C1 and C2
 2 power diodes D3 and D4
 2 neutral point diode clamped diodes D1 and D4
 4 parallel switches T1-T4 with anti-parallel diodes.
2.1.2 Operations:
Consists of six modes:
For positive line current – mode 1, mode 2, mode 3
For negative line current – mode 4, mode 5, mode 6
For positive line current- a) Mode1
b) Mode 2
c) Mode 3
Fig-2.1

16
For negative line current d) Mode 4
e) Mode 5
f) Mode 6

17
OPERATION:
Modes 1, 2 and 3 are employed in the proposed control algorithm to generate rectifier terminal
voltage vxy = vdc, vdc/2 and 0 respectively (assumed vl = v2= vdc/2). On the other hand, modes
4, 5 and 6 are adopted to achieve vxy = 0, - vdc/2 and - vdc respectively in the negative line
current.
Before analysis of the operation modes, some assumptions are made:
- power switches are ideal,
- supply voltage is a constant value during one switching period.
Fig(a) shows the equivalent circuit of first operation mode. In this mode, no power switches is
turned on and positive line Current charges both capacitor voltages V1 and V2 to achieve
Voltage Vxy = Vdc. The line current is decreasing in this mode because Vs < Vdc. The dc side
currents Ip = Is, Io=0 and In=-In.
The Equivalent circuit of second mode is shown in fig(b). Power Switch T3 and diodes D2 and
D4 are turned on to obtain voltage Vxy = V2. The positive line current charges the capacitor C2.
The Dc load line discharges the capacitor C1. The boost inductor voltage equals Vs – V2. The dc
side currents Ip=0, Io=Is, and In= -Is.
The equivalent circuit of operation mode 3 is given in fig(c). Power switches T2 and T4 and
diode D4 are turned on to achieve voltage Vxy=0. The line current is linearly increasing because
Vl =Vs. In this mode two capacitor voltages are decreasing and supplying power to dc load. The
rectified line Voltage is short-circuited through the boost inductor in mode 4 Shown in fig(d).
Power switches T1 and T2 and diode D3 are turned on to obtain voltage Vxy=0. The inductor
current is linearly decreasing because Vl =Vs<0. The dc load current discharges the capacitors
Fig-2.2

18
C1 and C2. The dc side currents Ip=In= Io=0. The equivalent circuit of mode 5 is shown in
fig(e). Power switch T2 and diodes D1 and D3 are turned on to obtain Voltage Vxy = -V1. The
negative line current charges the capacitor Cl. The boost inductor voltage equals Vs+V1. The
capacitor Voltage V2 is discharged by the dc load. The dc side currents - supply voltage is a
constant value during one switching period, Ip=-Is, Io=Is and In=0. Fig(f) shows the equivalent
circuit of operation mode 6. In this mode, all power switches are turned off and negative line
current charges both dc bus capacitors to achieve voltage Vxy=-Vdc. The line current is
increasing in this mode because Vx+Vdc>0. The dc side currents Ip=-Is, Io=0 and In=Is.
According to above analysis of six operation modes, the dc side current Ip does not equal zero in
the modes 1, 5 and 6, Io does not equal zero in modes 2 and 5, and current In is not equal
to zero in modes 1,2 and 6.

20
2.2.1 Waveforms
In this method of modulation, several pulses per half cycle is used as in the case of multiple-
pulse modulation. In MPM, the pulse width is equal for all the pulses. But in SPWM, the pulse
width is a sinusoidal function of the angular position of the pulses in a cycle.
For implementing SPWM, a high frequency triangular carrier wave Vc is compared with a
sinusoidal reference wave Vr of the desired frequency [15]
. The intersection of Vc and Vr waves
determines the switching instants and commutation of the modulated pulses. Hence Vc is the
peak value of triangular carrier wave and Vr that of the reference, or modulating, signal.
The carrier and reference wave are mixed in a comparator. When sinusoidal wave has magnitude
higher than the triangular wave, the comparator output is high otherwise it is low. The
comparator output is processed in a trigger pulse generator in such a manner that the output
voltages wave of the inverter has a pulse width in agreements with the comparator output pulse
width.
Fig-2.4

21
Chapter 3
3.1Simulations
3.1.1 Simulation and Experimental Results
The proposed control scheme of neutral point diode clamped rectifier is verified by the computer
simulations and experimental tests in a laboratory prototype. In the simulation, the line voltage is
220V/50Hz. The boost inductor is 3mH. The capacitance of the dc side capacitors is 2200pF.
The dc bus is controlled to equal 200V. Fig 5 shows the simulated waveforms for the two-level
unipolar PWM scheme. The line current is a sine wave in phase with the mains voltage. The ac
side voltage of the rectifier has two voltage levels on each half cycle. Fig. 6 shows the simulated
waveforms of the adopted rectifier for three-level PWM scheme. There are five different voltage
levels on each cycle. Three voltage levels 0, Vdc/2 and Vdc are generated in the positive half
cycle. Three voltage levels 0, -Vdc/2, -Vdc are generated in the negative half cycle. The line
current is a sine wave with nearly unity power factor and low total harmonic distortion (THD).
Fig. 7 shows the voltage variation between dc side capacitor voltages. The voltage ripple is about
10V. In the laboratory tests, a prototype circuit with a 1kW power rating was implemented. Fig 8
shows the measured waveforms of the mains voltage, line current and ac side voltage of the
adopted rectifier for two-level unipolar modulation. The experimental results of adopted rectifier
for three-level modulation are shown in Fig 9. A three-level voltage waveform on the ac side of
the rectifier in each half cycle is generated.

22
3.1.2 MATLAB Circuit
3.1.3 Waveforms
Current
Fig-3.1
Fig-3.2

23
3.1.4 THD Calculation using FFT
Fig-3.3

24
3.2Simulation at different Sources of Harmonics
3.2.1 Single Phase Diode Clamped Rectifier with an Asynchronous Motor
3.2.1.1 Model
Fig-3.4
Fig-3.5

25
3.2.1.2 FFT Analysis
Fig-3.6

26
3.2.2 Single Phase Diode Clamped Rectifier with Non-Linear Source
3.2.2.1 Model
Fig-3.7
Fig-3.8

27
3.2.2.2 FFT Analysis
Fig-3.9

28
Analysis
The proposed control scheme of the neutral-point diode clamped rectifier is verified by the
computer simulations Fig. 3.1shows the model. The MUR 860 fast-recovery diode is adopted for
the main power diodes. The MOSFETs (IRFP450) are used for the power switches.
The line voltage of the proposed rectifier is 220 V RMS. The boost inductance is 3mH. The
capacitance of the two capacitors is 2,200 pF.
After analyzing the circuit we have come to the conclusion that the circuit can overall improve
the power quality of the system by decreasing the voltage imbalance. We are using single phase
diode clamped rectifier to improve the system performance and to reduce the harmonics. Earlier
we were using inductor as a source of harmonics and reduce it. We got 1.54% THD. Hence it
indicates that we can reduce losses. Now we have used two different sources of harmonics such
as Non-linear like diode, single phase spilt phase induction motor. After that when we have
simulated in software. We got THD in case of non-linear is 4.43% and Single phase split phase
induction motor is .74%. from the above THDs we can say that any non-linear component or
device connect with the source or any harmonics coming from the transmission system reduces
easily using that single phase diode clamped rectifier with PWM technique. Now PWM is the
major technique to reduce harmonics from the system.

29
Chapter 4
4.1Hardware Implementation
Components Required for Hardware
1. MOSFET IRFP 460
2. Transistor 2N2222
3. Zener diode 12v
4. Resistors
a) 10K-2
b) 470K-1
c) 1.5K
5. Diode (IN5408-MIC)
6. Capacitors- 1microfarad and 2200 microfarad
7. Opto-coupler (MCT2E)
8. Transformer (220/12)
9. Gunn Diode
10. Connector
4.1.1 MOSFET
A power MOSFET is a specific type of metal oxide semiconductor field-effect transistor
(MOSFET) designed to handle significant power levels. Compared to the other power
semiconductor devices, for example IGBT, Thyristor, its main advantages are high commutation
speed and good efficiency at low voltages. It shares with the IGBT an isolated gate that makes it
easy to drive.
The power MOSFET is the most widely used low-voltage (that is, less than 200 V) switch. It can
be found in most power supplies, DC to DC converters, and low voltage motor controllers.

30
4.1.2 Pulse Amplification and Isolation Circuit
4.1.2.1 Optocoupler
An opt-isolator, also called an Optocoupler, photo coupler, or optical isolator, is a component
that transfers electrical signals between two isolated circuits by using light. Opto-isolators
prevent high voltages from affecting the system receiving the signal. Commercially available
opto-isolators withstand input-to-output voltages up to 10 kV and voltage transients with speeds
up to 10 kV/μs. A common type of opto-isolator consists of an LED and a phototransistor in the
same package. Opto-isolators are usually used for transmission of digital (on/off) signals, but
some techniques allow use with analog (proportional) signals.
An opto-isolator contains a source (emitter) of light, almost always a near infrared light-emitting
diode (LED), that converts electrical input signal into light, a closed optical channel (also called
dialectical channel), and a photo sensor, which detects incoming light and either generates
electric energy directly, or modulates electric current flowing from an external power supply.
The sensor can be a photo resistor, a photodiode, a phototransistor, a silicon-controlled rectifier
(SCR) or a triac. Because LEDs can sense light in addition to emitting it, construction of
symmetrical, bidirectional opto-isolators is possible. An optocoupled solid state relay contains a
Fig-4.1

31
Photodiode opto-isolator which drives a power switch, usually a complementary pair of
MOSFETs. A slotted optical switch contains a source of light and a sensor, but its optical
channel is open, allowing modulation of light by external objects obstructing the path of light or
reflecting light into the sensor.
4.1.2.2 Transistor
A transistor is a semiconductor device used to amplify and switch electronic signals and
electrical power. It is composed of semiconductor material with at least three terminals for
connection to an external circuit. A voltage or current applied to one pair of the transistor's
terminals changes the current through another pair of terminals. Because the controlled (output)
power can be higher than the controlling (input) power, a transistor can amplify a signal. Today,
some transistors are packaged individually, but many more are found embedded in integrated
circuits.
The essential usefulness of a transistor comes from its ability to use a small signal applied
between one pair of its terminals to control a much larger signal at another pair of terminals. This
property is called gain. A transistor can control its output in proportion to the input signal; that is,
it can act as an amplifier. Alternatively, the transistor can be used to turn current on or off in a
circuit as an electrically controlled switch, where the amount of current is determined by other
circuit elements.
There are two types of transistors, which have slight differences in how they are used in a circuit.
A bipolar transistor has terminals labeled base, collector, and emitter. A small current at the base
terminal (that is, flowing between the base and the emitter) can control or switch a much larger
current between the collector and emitter terminals. For a field-effect transistor, the terminals are
labeled gate, source, and drain, and a voltage at the gate can control a current between source and
drain.
The image to the right represents a typical bipolar transistor in a circuit. Charge will flow
between emitter and collector terminals depending on the current in the base. Since internally the

32
Base and emitter connections behave like a semiconductor diode, a voltage drop develops
between base and emitter while the base current exists. The amount of this voltage depends on
the material the transistor is made from, and is referred to as VBE.
4.1.2.3 Zener Diode
A Zener diode is a diode which allows current to flow in the forward direction in the same
manner as an ideal diode, but will also permit it to flow in the reverse direction when the voltage
is above a certain value known as the breakdown voltage, "zener knee voltage" or "zener
voltage" or "avalanche point".
The device was named after Clarence Zener, who discovered this electrical property. Many
diodes described as "Zener" diodes rely instead on avalanche breakdown as the mechanism. Both
types are used. Common applications include providing a reference voltage for voltage
regulators, or to protect other semiconductor devices from momentary voltage pulses.

33
4.1.3 Snubber Circuit
A Snubber is a device used to suppress ("snub") voltage transients in electrical systems.
Snubber are frequently used in electrical systems with an inductive load where the sudden
interruption of current flow leads to a sharp rise in voltage across the current switching device, in
accordance with Faraday's law. This transient can be a source of electromagnetic interference
(EMI) in other circuits. Additionally, if the voltage generated across the device is beyond what
the device is intended to tolerate, it may damage or destroy it. The snubber provides a short-term
alternative current path around the current switching device so that the inductive element may be
discharged more safely and quietly. Inductive elements are often unintentional, but arise from the
current loops implied by physical circuitry. While current switching is everywhere, snubbers will
generally only be required where a major current path is switched, such as in power supplies.
Snubbers are also often used to prevent arcing across the contacts of relays and switches and the
electrical interference and welding/sticking of the contacts that can occur.
Fig-4.2

34
Conclusion and Future Scope
The total harmonic distortion of line current is 1.54w%.After analyzing the circuit we
have come to the conclusion that the circuit can overall improve the power quality of the
system by decreasing the voltage imbalance. A novel single-phase neutral-point diode-
clamped rectifier has been proposed to achieve high power factor, low current distortion,
low peak factor, and stable capacitor voltages. The proposed rectifier can be controlled to
operate in two- or three-level PWM. Based on the model analysis, the switching signals
of the power switches can be derived from the measured line current error and the mains
voltage. Experimental results show a good line current waveform with almost unity
power factor and low current harmonics to meet the requirements of IEC 1000-3-2 class
A. The transient response due to load change is about one cycle and voltage drop is about
5 V. According to measured results the proposed rectifier has the properties of high
power factor, low current distortion and fast dynamic response, based on the proposed
control algorithm.
These benefits include power factor correction, poor power factor penalty utility bill
reductions, voltage support, release of system capacity, and reduced system losses. A
high power factor signals maximum use of electrical power, while a low power factor
leads to purchasing more power to obtain the same load kW, which you pay for in
various ways on your utility bill. Dual Converter is an Electronic Device or Circuit made
by the combination of two bridges. One of them works as Rectifier (Converts A.C. to
D.C.) and other bridge works as Inverter (converts D.C. into A.C.). Thus an electronic
circuit or device in which two processes take place at same time, is known as Dual
Converter. The difference between single phase and three phase dual converter is just that
in Three phase we uses three phase rectifier at first stage, while in single phase dual
converter we make use of single phase rectifier circuit at first bridge. Dual converters are
mostly used at industries where we requires reversible D.C. Generally Dual Converters
are used for Speed Control of D.C. Motors etc.

35
References
1. Antchev M.H., M.P.Petkova, Control Method for Shunt Active Power Filter, Eurocon
2005, SCG, 22-24 November 2005, pp.18-20.
2. Antchev M.H., M.P.Petkova, A.T.Kostov, Hysteresis Current Control of Single-Phase
Shunt Active Power Filter, IASTED Int. Conf. PES2007, USA, 3-5, January
2007.
3. Boys. 1. T.; Green, A. W.: Current-Forced Single-phase Reversible Rectifier. IEE
Pr0c.B-136 (1989) no.5,
4. Dawande, M. S.; Kanetkar, V. R.; Dubey, G. IC: Three-phase Switch Mode Rectifier
with Hysteresis Current Control. IEEE Trans. on Power Electron. PE-I 1 (1996) no. 3,
pp. 20
5. Hwhgraf, C., Lesseter, R., Divan, D., and Lipo, T. A.: Comparison of multilevel
invertem for static VAR compensation. IEEE Industrial Applications Society Annual
Meeting, 1994,
6. La;, J. S., and Peng, F. Z.: Multilevel conve&& -a new breed of power converters.
IEEE Transactions on Industrial Applications, 32, 1996, pp. 14-16
7. Manias, S.: Novel Full Bridge Semi-controlled Switch Mode Rectifier.IEE Proc. 8-
138 (1991) no. 5,
8. Martinez, R.; Enjeti, P. N.: A High-Performance Single-phase Rectifier with Input
Power Factor Correction. IEEE Trans. on Power Electron. PE-I 1 (1996) no. 2, pp.
17-19
9. Muhammad H. Rashid, Power Electronics, Academic press, 2nd
Edition.
10. Ooi, B. T.: A Three-phase Controlled-Current PWM Converter with Leading Power
Factor. LEEE Trans. on Ind. Appl. IA-23 (1987) no. I, pp. he, pp-21-24
11. PSIM User’s Guide, Powersim Inc., June,2003
12. Peng, F. Z., Lai, J. S., Mckeever, J. W. and Vancoevering, J.: A multilevel voltage-
source inverter with separate dc sources for static var generation. IEEE Transactions
on Industrial Applications, 30, 1996.
13. R.C. Dugan, Electrical Power System Quality, Tata McGraw Hill Publisher, third
edition.
14. Salmon, J. C.: Circuit Topologies for Single-phase Voltage-Doubler Boost rectifiers.
IEEE Trans. on Power Electron. PE-8 (1993) no.2.
15. Sinha, G. and Lipo, T. A.: A four-level rectifier-inverter system for drive
applications. IEEE Industry Applications Magazine, 1998, pp.28-30
16. Shmilovitz D., D.Czarkowski, Z.Zabar, A Novel Rectifier/Inverter with Adjustable
Power Factor, PESC 1999, vol.1.
17. Uninterruptible power systems (UPS) – part 3: Method for specifying the
performance and test requirements, International standard IEC 62040 – 3, 1999.
18. Yip S.C., D.Y.Qiu, H.S-H.Chung, S.Y.Hui, A Novel Voltage Sensorless Control
Technique for a Bidirectional AC/DC Converter, IEEE Trans. On Power Electronics,
vol.18, No.6, November 2003.

36
Bio Data
Name: Varun Agarwal
Father’s Name: Shailendra Kumar Agarwal
Mother’s Name: Priyanka Agarwal
Date of Birth: 10-Sep-1991
Address: Shailly Super Store
Jhanda Chowk Badrinath marg
Kotdwara- 246149
Uttarakhand
12th
Percentage: 73.2%
10th
percentage: 64.5%
CGPA: 8.71
Technical Skills
Software: MATLAB.
Languages: C, C++
Hobbies: Badminton, Basketball
Name: Sandeep Pradhan
Father’s Name: Sananda Pradhan
Mother’s Name: Santi Lata Pradhan
Date of Birth: 14-oct-1991
Address: 1431-A, Maruti Vihar, Chakkarpur, Gurgaon.
12th
Percentage: 60%
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CGPA: 5.64
Technical Skills: MATLAB, Microprocessor-Portis, Kiel.
Languages: C, C++
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Father’s Name: Sarwan Kumar Choudhary
Mother’s Name: Babita Choudhary
Date of Birth: 19-Dec-1991
Address: R/O VPO Patlikuhal tehsil Manali distt. Kullu H.P 175129.
10th
Percentage: 54.58%
12th
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CGPA: 3.48

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