1 TProject Thesis format_BTech

8/7/2019 1 TProject Thesis format_BTech

http://slidepdf.com/reader/full/1-tproject-thesis-formatbtech 1/18

i

³ POWER FACTOR CORRECTION FOR 3-PHASE

DIODE RECTIFIERS´

MINI PROJECT REPORT

Submitted in partial fulfillment of the

requirement for the award of the Degree of

BACHELOR OF TECHNOLOGY

IN(B.TECH EEE)

By

SUMIT KUMAR(07BEE158)

RISHI KUMAR(07BEE133)

Under the Guidance of

Prof . SUBRAMANIUM .K.SELECT(VIT University).



ii

(SELECT)

VELLORE INSTITUTE OF TECHNOLOGY (University)

VELLORE. (TN) 632014

³ POWER FACTOR CORRECTION FOR 3-PHASEDIODE RECTIFIERS´

A PROJECT REPORT

Submitted in partial fulfillment of therequirement for the award of the

Degree of

BACHELOR OF TECHNOLOGY

IN

(B.TECH EEE)

BY

SUMIT KUMAR(07BEE158)

RISHI KUMAR(07BEE133)

Under the Guidannce of

Prof.SUBRAMANIUM.K.SELECT(VIT University)

CERTIFICATE

This is to certify that the Project work titled ³ power factor correction

technique for 3-phase diode rectifier ´

that is being submitted by ³ SUMIT KUMAR(07BEE158)and RISHI KUMAR(07BEE133) is in partial fulfillment of

the requirements for the award of BACHELOR OF TECHNOLOGYDEGREE, is a record of bona fide work done under my /our guidance.

The contents of this Project work, 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 thesame is certified



iii

External Guide Internal Project Supervisor

(Name of the Organization)

(Organization stamp

Approved by

DIRECTOR

(SELECT)

ABSTRACT

A novel active power factor correction method for power supplies

with three phase front end diode rectifiers is proposed and

analyzed.The implementation of this method requires the use of an

additional single switch boost chopper.The combined front endconverter draws sinusoidal ac currents from the ac power source

with nearly unity input power factor while operating at a fixed

switching frequency.This paper shows that when the active input power factor correction is also used to regulate the converter dc

bus voltage,the converter performance can improve substantially

in comparison with the 3-phase ac to dc converters.Theseimprovements include component count reduction,simplified input

synchronization logic requirements,and smaller reactive

componenets.Finally selected theoretical results are verified

experimentally.



iv

CONTENTS

1.INTRODUCTION

2. DESCRIPTION OF THE PROPOSED SYSTEM.

a)AC TO DC RECTIFIER.

b)INPUT FILTER/.

c)BOOST INDUCTOR.

d)3-PHASE DIODE RECTIFIER.

e)POWER FACTOR CORRECTION STAGE.

f)DC LINK FILTER CAPACITOR.

3.ANALYSIS GUIDELINES

a)INPUT CURRENT ANALYSIS.

b)SYSTEM ANALYSIS.

4.DESIGN ANALYSIS



v

a)DERIVATION OF RECTIFIER OUTPUT CURRENT.

b)OUTPUT FILTER DESIGN.

5.CONCLUSION.

INTRODUCTION

The conversion of ac line voltages from utilities has been dominated by

phase controlled or diode rectifiers.The non ideal character of the input

current drawn by these rectifiers creates a number of problems for the power

dissipation network and for other electrical systems in the vicinity of the

rectifier including:

1) Phase displacement of the current and voltage fundamentals

requires that the source and distribution equipment handle

reactive power increasing their volt ampere ratings.

2) High input current harmonics and low input power factor.

3) Lower input current harmonics and low input power factor.

4) Lower rectification efficiency because of large rms values

of the input current.



vi

5) Input ac mains voltage distribution because of the associated

high peak currents.

6) High reactive component size.

To combat these disadvantages system designers are increasingly

incorporating active input power factor correction methods [2] to [4].For

medium to high power applications the input rectifier is fed from a 3-phase

ac source.Application of the bang bang hysteresis control method to control

method to improve the input power factor of a three phase ac to dc converter

has been discussed fro [3] to [4].This topology yields unity power factor and

is clearly much superior than the original phase controlled ac to dc

topologies.However it suffers from certain disadvantages:1) It requires complicated synchronization logic.

2) Owing to the variations in power circuit control parameters

among the three individual converters,a complete triplen

harmonic elimination cannot be achieved.

3) The switching frequency is load dependent.

4) The number of components required for three phase ac to dc

converter is three times the single phase ac to dc converter.

5) The advantage of using a three phase inverter and

transformer ,better utilization of copper and core

utilization,cannot be achieved.

This paper addresses the analysis and design of a three phase ac to dc

converter which draws high quality input current wave forms from the ac

source and exhibits none of the above mentioned disadvantages.However ithas disadvantages of increasing the current stresses of the switching devices

and high frequency ripple content of the pre filtered ac input currents.



vii

DESCRIPTION OF THE PROPOSED SYSTEM

The proposed system consists of the two main power factor correction

stages.The first stage consists of a three phase ac to dc rectifier consisting of

an input filter ,a boost inductor,a three phase diode rectifier,an active power

factor correction stage,and a dc link filter capacitor .The second stage can be

modeled into any type of load requiring a regulated or unregulated dc bus

such as general purpose single phase or three phase inverters or dc to dc

converters with high frequency isolation.The active waveshapping of the

input current waveform can be obtained from the three boost chopper components Lia,Qb,and Db as shown in fig 1.The boost switch Qb is turned

on at constant frequency.The duty cycle of Qb,is varied for load variation

only and it is such that the input current is is always discontinuous.During

the on period of the boost switch all three input ac phases become shoted

through inductors Lia,Lib,Lic,the six rectifier diodes and the boost

switch.Consequently the three input currents Iia,Iib,Iic begin simultaneously

to increase at a rate propotional to the instantaneous values of their

respective phase voltages.Moreover the specific peak current values during

each on interval (fig 3(c)) are propotional to the average values of their input phase voltages during the same on interval.Since each of these voltage

average values varies sinusoidally the input current



viii

Peaks also vary sinusoidally(fig 3c).Moreover since the current pulses

always begin at zero,it means that their average values also vary

sinusoidally.Consequently all three input ac currents consists of the

fundamental(60 hz) components centered around the switching

frequency(fb) of the boost switch.Since this frequency can be of the order of



ix

several tens of khz,filter out the unwanted input current harmonics becomes

a relatively easy task.From fig3 it is also seen that input power control can

be achieved through pulse width modulation of the boost switch on interval

at constant frequency(fb).

Finally ,under the operating conditions described here the

displacement input power factor before filtering is unity.Consequently,the

overall power factor before filtering becomes equal to the harmonic input

power factor and

it is given by

power factor=((Iia/1.414)/(sqrt(Iia,n/sqrt(2))2)

where

Iia,n is the Fourier component of the nth harmonic component of the

current Iia.

It is noted that the current harmonics can be suppressed by a relatively

small input capacitor and inductor because of high frequency.Therefore the

overall input power factor after filtering is very close to unity.



x

INPUT CURRENT ANALYSIS

Regarding fig1 during the period when the boost switch is turned on,the

equivalent single ±phase circuit becomes as shown in fig 4a.The input

current rises at a rate determined by the input source voltage and the

inductor.The current through the inductor during this period is given by

E=Vm sin(wt)=Lia d(Iia)/dt.

Solving the above equations for Iia and substituting the initial

condition,Iia(wt)=0,when t=0 yields

Iia(wt)=Van(peak)/wLia[cos(wt1)-cos(wt2)]

During the period when the boost switch is turned off the current through the

inductor decreases at a rate determined by the input voltage(Van),output dc

voltage(VD),and the inductor (Lia).The single phase equivalent circuit under

this condition is shown in fig 4(b) from the boost converter theory therectifier input phase voltage when the boost switch is off is given by

Ven(wt)=1/(1-D)*Van(wt)



xi

where D is the duty cycle of the boost switch.The current through the

inductor during the period when the boost switch is off is given by

Van sin(wt)=Lia d(Iia)/dt+Ven

Solving the above equation we get

Iia(wt)=Van(peak)/wLia*[cos(t1)-cos(t2)]-Ven/Lia(t-t1)



xii

SYSTEM ANALYSIS

In this section the proposed converter is analyzed under steady state

conditions.The expressions derieved are subsequently used to obtain the

information necessary for proper converter design.The converter is analyzed

under the following assumptions:

1) All power switching devices are ideal and the forward drop

and reverse leakage currents of the diodes are negligible.

2) Filter components are ideal.



xiii

3) The local voltage is ripple free.

Moreover the rated input rms voltage ,Van(rms),and rated output

power ,Pd,are assumed to be

Van(rms)=1.0 pu V

Pd=1.0 pu

Further assuming the ac source angular frequency is 1 pu from the value of

the peak current Iia(peak) for Lia=.1 pu is given by

Iia(peak)=Van(peak)/Lia*Tb/2.

INPUT FILTER DESIGN

In most of the specifications for power supplies the total harmonic distortion

(THD) content of the input line current is less than 5%.Also if the amplitude

of the dominant harmonic component of Ii1 is reduced to 3% of the

amplitude of the respective fundamental then THD of less than 5%can beensured.Therefore for the PWM method shown in Fig 3 the order of the

dominant harmonic component of the inductor current is fb-1.The harmonic

equivalent circuit is shown in fig 7.Regarding fig 7 the inductor harmonic

component current can be given by:

Ii,n=(Xcia*Iia,n)/(n*nXli1-Xci1)

where

n is the order of harmonic.

Xcia is the filter capacitor reactance at fundamental frequency.

Xli1 is the filter inductor reactance at fundamental frequency.



xiv

The above equation can be further simplified as

Xli1/Xci1=1/(n*n)[(Iia,n)/(Ii1,n)+1]

Xli1/Xci1=1/(fb-1)2[(Iia,fb-1)/(Ii1,fb-1)+1]

The evaluation of the above equation reveals that the size of the filter

component is a function of the boost switching frequency(fb).The size of the

filter components become smaller and smaller for higher switching

frequency.

Consequently all the harmonics of the input current become

smaller and smaller and the input power factor becomes unity.



xv

DESIGN EXAMPLE

To illustrate the significance and facilitate the understanding of theoretical

results obtained in preceding sections the following design examples aregiven:

Ac source rms voltage (Van(rms))=50V=1p.u.

Supply frequency=60 Hz

Rated output power=1 KW=1 p.u.

Input ac source angular frequency=377 rad/sec

Boost switch switching frequency(fb)=24 khz

From these values:

1 pu current=1000/150=6.66 A;

1 pu impedence=50/6.66=7.50 ohms;

1 pu angular frequency=377 rad/sec;

1 pu inductance=7.50/377=0.023 H;

1 pu capacitance=1/377*7.5=353.66 micro farad;

Lia=1.414850/1.414*6.66*(1/2400)=65.37 micro henry;

Cd=.7*100*.5/1.414*.01*400*1.414*1.732=2.53 pu=893.63 micro farad;



xvi

CONCLUSION

In this paper a novel active power factor correction method for three phase

diode rectifiers is proposed and analyzed. With the proposed method the

rectifier draws sinusoidal ac current from the source with unity power factor.Moreover , the proposed method eliminates the complicated

synchronization logic requirement,reduces the number of components, and

reduces the filter reactive components size.Finally ,the theoretical results are

verified experimentally.However the proposed method has the disadvantage

of increasing the switching stresses of the switching devices in comparison

with the conventional 3 phase ac to dc converter.



xvii

REFERENCES

[1] S.Manias,A.R. PRASAD and P.D. ZIOGAS,´Three phase inductor fedSMR converter with high frequency isolation and high power density and

improved power factor,´ in Proc.IEEE,vol 134 ,pt.B,no. 4,July 1987,pp.183-

191.

[2] M.J.Kocher and R.L.Steigward ,Án ac to dc converter with high quality

input waveforms,ÍEEE Trans.Ind Appl,vol.1a.19.no4 ,pp.586-

599,july/aug.1983.

[3] W.p. Marple,´Low distortion three phase power regulation,ÍBM

technology enclosure bulletin,´vol 22,no .3,pp.970-971.Aug 1979.

[4] D.Gauger el al,Á three phase off line switching power supply with unity

power factor and low TIF,ín Conf Rec.1986 IEEE INTELEC,pp.115-121.



xviii

1 TProject Thesis format_BTech

Documents

Transcript of 1 TProject Thesis format_BTech