International Journal of Scientific Research and Engineering Studies (IJSRES)

Volume 3 Issue 1, January 2016

ISSN: 2349-8862

www.ijsres.com Page 25

Analysis Of 3-ϕ Multi-Pulse Ac To Dc Converter Through Zig Zag

Transformer

Jyotsana Singh

M-Tech Student, Satyam College of Engineering Bhopal

Hitesh Lade

Professor, Satyam College of Engineering Bhopal

Abstract: This paper deals with the reduction of

Total Harmonic Distortion (THD) by using Multi-pulse

AC to DC Conversion technique. The three-phase multi-

pulse AC to DC conversion system have a phase-shifting

transformer and a three-phase source. Every such type of

converter provides a 6-pulse AC to DC conversion system,

that’s why in order to produce more sets of 6-pulse

systems, a uniform phase-shift is required and hence with

proper phase-shifting angle, 12, 18, 24, 30, 36 and higher

pulse systems have been produced. The performance

improvement of multi-pulse converter is achieved for total

harmonics distortion (THD) in supply current, DC voltage

ripples and form factor. This paper presents the discussion

of multi-pulse improved power quality ac-dc converter

(IPQC) configuration, comparative factors and selection of

specific.

Keywords: Multipulse conversion technique, 18-pulse

converter, 24-pulse converter, THD, output waveforms.

I. INTRODUCTION

The revolution in power electronics has opened an era

for widespread use of power converters of different power

rating from few Watts to Mega-Watts. AC-DC converters

are most widely used power converters as the distributed

electric power is AC supply, while the applications based

on DC supply as well as variable frequency AC supply,

need conversion of AC supply into DC supply.

Large current harmonics and poor power factor in the

utility interface are common problems in AC-DC converters.

These AC-DC converters are used invariably at the front

end in numerous applications which mayor may not be

electrically isolated from the AC supply system depending

on the rating and nature of the load and also the prevalent

'Standards' requirements. The applications such as

electrochemical, electrometallurgical and electrical heating

processes, HYDC systems, adjustable speed drives, battery

charging, aerospace and naval equipments, uninterruptible

power supplies (UPS) etc., use AC-DC conversion at the

front end. These processing industries and adjustable speed

drives are main applications where large amount of power

is involved in AC-DC converters. These AC-DC converters

are generally diode based, thyristor based or self

commutating device based converters depending on

applications, size and cost.

To comply with the stringent harmonic requirements set

by various standards such as IEEE-519, 1992, three-phase

multipulse AC-DC converters are becoming popular in

number of applications. These multipulse converters consist

of mainly bridge and full-wave rectifiers (controlled or

uncontrolled) for AC-DC conversion. The main feature of

multi-pulse AC-DC converters is its ability to reduce current

harmonics distortion which is synonymous to power quality

improvement. In multipulse AC-DC converters the

number of pulses (voltage ripples at output of AC-DC

converters in one cycle of AC supply voltage or steps in

the current at input of AC mains) is increased by using

phase staggering (or phase shifting), multiphase (or phase

multiplication), DC ripple-reinjection (or pulse

multiplication) and hybrid of these techniques. The

application of multipulse techniques in AC-DC converters

also results in eliminating and reducing the need of tuned

passive filters, active filters and hybrid filters, which are

bulky and lossy, complex and expensive.

In this work, AC-DC converters are mainly classified

on the basis of transformer configuration, and type of

diode and thyristor arrangement used. This has led to

classification as isolated and non-isolated, controlled and

uncontrolled, full-wave and bridge type AC-DC converters.

The detailed investigation in these categories is carried out

based on the different pulse number configurations and

technique employed in them. The classification has led to

formation of some new AC-DC converter configurations

that are investigated for their power quality improvement

capability.

International Journal of Scientific Research and Engineering Studies (IJSRES)

Volume 3 Issue 1, January 2016

ISSN: 2349-8862

www.ijsres.com Page 26

II. OBJECTIVE OF PRESENT STUDY

The present work is for analyzing various multi pulse

AC-DC converting for solving harmonics trouble in a three-

phase converter system.For performance comparison the

major factors considered are the total harmonic distortion

(THD) ripple percentage, form factor.

III. MULTI PULSE METHODS

A large number of publications have appeared in the

field of multi-pulse converters, many giving new concepts and

verifying their claims by simulations and experimental work.

Paice [1] proposed maximizing the efficiency of a 12 pulse

AC-DC converter based on a hexagonal autotransformer

arrangement. Choi [2] in his paper has presented new

autotransformer arrangements with reduced KVA capacities

are presented for harmonic current reduction and to improve

AC power quality of high current DC power supplies.

Simulation results are given in the paper. Falcondes and

Babri [3] has proposed a new isolated high power factor 12

KW power supply based on 18-pulse transformer

arrangement. The topology used involves a simple control

strategy. Simulations and experimental results are given in

paper.

S.Kim Etal [4] has given an analysis and design of a

passive and novel interconnection of a star/delta transformer

approach to improve power factor and reduce harmonics

generated by a three phase diode rectifier. Chen Etal [5] has

proposed a new passive 28-step current shaper for three phase

rectification .with a phase shifting transformer on the ac

side, per phase input current is shaped into sinusoidal

waveform. Tolbert [6] his work provides the cascade inverter

for large automotive drives. Here back to back diode clamped

converter is used, simulation and experimental results are

given in paper. This chapter presented a review of available

literature on power quality improvement pertaining to AC/DC

converters. The next chapter presents a detailed study of

multi-pulse converters.

A. MULTI-PULSE METHODS

The term multi-pulse method is not defined precisely. In

principle, it could be imagined to be simply more than one

pulse. However, by proper usage in the power electronics

industry, it has come to mean converters operating in a

three phase system providing more than six pulse of DC

per cycle.

Multi-pulse methods involve multiple converters

connected so that the harmonics generated by one converter

are cancelled by harmonics produced by other converters. By

this means, certain harmonics related to number of converters

are eliminated from the power source. In multi- pulse

converters, it is assumed that the DC link uses a filter such

that any ripple caused by the DC load does not significantly

affect the DC current.

Multi-pulse systems result in two major accomplishments

namely,

Reduction of ac input line current harmonics.

Reduction of DC output voltage ripple.

Reduction of ac input line current harmonics is

important as regards the impact the converter has on the

power system.

Multi-pulse methods are characterized by the use of

multiple converters or multiple semiconductor devices with a

common load.

Phase shifting transformers are an essential ingredient

and provide the mechanism for cancellation of harmonic

current pairs, e.g. the 5th and 7th harmonics or the 11th and

13th so on. Thus for harmonic current reduction the multi-

pulse converters are fed from phase shifting transformers. The

phase shift has to be appropriate.

B. ZIG-ZAG PHASE SHIFTING TRANSFORMER

The Zigzag Phase-Shifting Transformer implements a

three-phase transformer with a primary winding connected in

a zigzag configuration and a configurable secondary

winding. The model uses three single-phase, three- winding

transformers. The primary winding connects the windings 1

and 2 of the single-phase transformers in a zigzag

configuration. The secondary winding uses the windings 3 of

the single phase transformers and they can be connected in

one of the following ways: Y with accessible neutral

Grounded Y Delta (D1), delta lagging Y by 30 degrees Delta

(D11), delta leading Y by 30 degrees. If the secondary

winding is connected in Y, the secondary phase voltages are

leading or lagging the primary voltages by the Phi phase

angle specified in the parameters of the block. If the

secondary winding is connected in delta (D11), an additional

phase shift of +30 degrees is added to the phase angle. If the

secondary winding is connected in delta (D1), a phase shift of

-30 degrees is added to the phase angle.

IV. MULTI PULSE CONVERTERS

A. SIX-PULSE CONVERTER

As the basic converter unit of HVDC transmission is used

for rectification, where electrical power flows from the AC

side to the DC side and inversion where the power flow is from

the DC side to the AC side. Thyristor valves operate as

switches which turn on and conduct current when fired on

receiving a gate pulse and are forward biased. The six pulse

Converter Bridge shown in Fig 1.

The characteristic AC side current harmonics generated

by 6-pulse converters are 6n±1, Characteristic DC side

voltage harmonics generated by a 6-pulse converter are of the

order 6n±1.

International Journal of Scientific Research and Engineering Studies (IJSRES)

Volume 3 Issue 1, January 2016

ISSN: 2349-8862

www.ijsres.com Page 27

Figure 1: Controlled six pulse converter bridges

B. TWELVE PULSE CONVERTER

When two six pulse converter bridge is connected in

series with two 3 phase system having phase difference of 30

electrical degree from each other. The phase difference

effected to cancel out the 6-pulse harmonics on the AC and

DC side. With the use of 12 pulse converter 5th

and 7th

harmonic are eliminated but still 11th

and 13th

harmonic are

present. Figure 2 shows a 12 pulse controlled converter.

Figure 2: Controlled twelve pulse converter bridge

C. TWENTY-FOUR PULSE CONVERTER

The 24-pulse converter and the corresponding

connections are shown in fig. 3. This connection contains four

six pulse converters having phase difference of 15 degrees

from each other, thus it provide twenty four pulse

rectification with much lower harmonics on AC and DC

side. Its AC output voltage would have 24n±1 order

harmonics i.e., 23rd, 25th, 47th, 49th harmonics.

Figure 3: Controlled 24 pulse converter

V. SIMULATION RESULTS OBTAINED FOR MULTI-

PULSE CONVERTERS

The simulation setups for respective multilevel converters

were initiated for estimation of DC output voltage, current and

its impact on source current is determined by monitoring the

form factor and ripple factor of the test circuits.

A. OUTPUT OF SOURCE CURRENT, LOAD CURRENT,

D.C. OUTPUT CURRENT

In the subsequent results displayed source current (SC),

Load current or output current (LC) and D.C output voltage

(OV) respectively. For all the converter bridge these output

is shown in figure 4 to 6 for 6, 12 and 24 pulse respectively.

International Journal of Scientific Research and Engineering Studies (IJSRES)

Volume 3 Issue 1, January 2016

ISSN: 2349-8862

www.ijsres.com Page 28

Figure 4: (a) Output for SC, LC, OV for 6 pulse, (b) Output for

SC, LC, OV for 12 pulse, (c) Output for SC, LC, OV for 24

pulse

VI. CONCLUSIONS

The various multi-pulse configurations, mainly non-

isolated were simulated using the software

SIMULIN/MATLAB and the results have been presented.

The effect of load variation on different multi-pulse

converters reveals that with RL, load because of inductance

there is smoothing effect on current, therefore current THD

decreases; whereas on RC load, the effect of capacitor is to

reduce voltage ripple and gives a smooth DC output. The

effect is similar for different multi-pulse converters.

The main objective of the present work is to investigate

the performance of multi- pulse converters. These converters

are studied in terms of harmonic spectrum of ac mains

current, output voltage THD. It is concluded that in general

with increase in number of pulses in multi-pulse case the

performance parameters of these converters are remarkably

improved.

REFERENCES

[1] D. A. Paice. “Auto connected hexagon transformer for a

12-pulse converter” Patent number: 5148357. 1992.

[2] Choi dewan, enjeti, pitel “autotransformer configurations

to enhance utility power quality of high power AC/DC

rectifier systems.”1996 IEEE.

[3] Babri Ivoand Jones, “a new three –phase low THD supply

with High–frequency isolation and 60v/200A regulated

DC supply” 2001.IEEE

[4] S. Kim, Enjeti,”A new approach to improve Power

Factor and reduce Harmonics in a Three-Phase Diode

Rectifier Type Utility Interface” IEEE trans.on Industry

appl,Vol.30,No.6,NOV/DEC 1994.

[5] Chen and Hong, “A new passive 28-step current shaper

for three- phase rectification.” IEEE transactions on

industrial electronics, vol.47, No.6, December 2000

[6] N. R. Zargari etal,”A multilevel thyristor Rectifier with

improved power factor” IEEE trans.on industry

applications, vol.33.No.5, SEPT/OCT. 1997.

[7] D. A. Paice, Power Electronic Converter Harmonics

“Multipulse Methods for Clean Power. New York’ IEEE

Press, 1996.

[8] N. Mohan, TUdeland and W. Robbins, “Power

Electronics Converters, Applications and Design, Second

Edition” New York: John Wiley & sons, 1995