新型24脉波整流器

Novel Topologies of 24-Pulse Rectifier with Conventional Transformers for Phaseshifting

A. N. Arvindan

Department of Electrical &.Electronics Engineering, SSN College of Engineering, Anna University (Chennai),

Chennai, India – 603 110

E-mail: lkana0@

Anirudh Guha

Department of Electrical &.Computer Engineering,

University of Texas,

Austin, TX 78712-0240, USA,

E-mail: anuguha87@

Abstract—Two 24-pulse rect

i f

i

er topolog

i

es based on phase

sh ft ng by convent onal magnet cs s proposed. Four 3-phase systems are obtai ned from a si ngle 3-phase source usi ng novel interconnection of conventional single- and 3-phase transformers. Phase shi fts of 15º and 30º are made usi ng phasor addi ti on of relevant li ne voltages wi th a combi nati on of si ngle-phase and

three-phase transformers respect

i vely. The four three-phase

systems are mutually di splaced from each other by 15º. Each three-phase system feeds a 6-pulse di ode recti fi er and the four d ode rect f ers are ser es cascaded to prov de a 24-pulse dc

output voltage. PSCAD based s

i mulat

i

on and exper

i

mental

results that confirm the design efficacy are presented.

Keywords-Total harmonic distortion, Multipulse converter, Multipulse rectifier, Power quality, Pulse number

I.I NTRODUCTION

The conventional ac-dc converters are developed using diodes and thyristors to provide controlled and uncontrolled unidirectional and bidirectional dc power, however, these converters have problems of poor power quality in terms of injected current harmonics, resultant voltage distortion and slowly varying rippled dc output at load end, low efficiency, and large size of ac and dc filters.To overcome these drawbacks and meet contemporary power quality standards [1]-[3] it has become imperative to address power quality issues like reducing harmonic currents, higher power factor, lower EMI/RFI at input ac mains and well-regulated dc output.

Increased awareness of power quality has led to the development of a new breed of ac-dc converters referred to as improved power quality ac-dc converters (IPQCs) [4],[5] that have been classified as switch-mode rectifiers, power-factor correctors, pulse width modulation rectifiers, multipulse rectifiers, etc. Multipulse rectifiers are unidirectional multipulse converters that are used for high power applications which involve high voltage and low current. This paper is about the design of magnetic for the realization of a 24-pulse rectifier involving the transformation of a single 3-phase system to four 3-phase systems using novel interconnections of conventional 3-phase and single-phase transformers. A 12-pulse rectifier is realized by cascading two 6-pulse rectifiers fed from two 3-phase systems displaced by 30º. The 24-pulse rectifier topology is obtained by cascading two 12-pulse rectifier systems which translates to cascading of four 6-pulse rectifiers fed from four 3-phase systems displaced by 15º.

II.M ULTIPULSE C ONVERTERS

The number of pulses in the dc output voltage within one time period of the ac source voltage is the pulse number. In high-power applications, ac–dc converters based on the concept of multipulse, namely, 12, 18, 24, 30, 36, 48 pulses are used to reduce the harmonics in ac supply currents. These are named as multipulse converters. They use either a diode bridge or thyristor bridge and a special arrangement of magnetics through transformers and tapped inductors.The variation of harmonics in the input current and the ripple frequency on the dc side for different pulse numbers are shown in Table I.

A. Bidirectional Multipulse Converters

These converters normally use thyristors and harmonics reduction is made effective with pulse multiplication [6], [7] using magnetics. The use of fully controlled thyristor bridge converters offers bidirectional power flow and adjustable output dc voltage. The use of a higher number of phases through an input multiple winding transformer and pulse multiplication using tapped reactor [8], and an injection transformer, reduces TH D to input ac currents and ripples in

the output dc voltage. The cost and weight of input transformers can be reduced by using autotransformers [9]-[11]

in low- and medium-voltage applications.

B.Unidirectional Multipulse Converters

Normally, diode bridges are used with a higher number of pulses for reducing harmonics in ac mains and reducing the value of ripple voltage in the dc output. These are developed in

12-, 18-, 24-, 30-, 36-, 48-pulse converters, through input multipulse auto/isolation transformers and ripple current

TABLE I

V ARIATION O F H ARMONICS A ND R IPPLE W ITH P ULSE N UMBER

Pulse

Number

AC Harmonics Ripple

Frequency

Ripple

Factor

1 1,2,3,… fs 1.21

2 1,3,5,…. 2fs 0.482

3 2,4,5,…. 3fs 0.182

6 5,7,11,…. 6fs 0.042

12 11,13,23,… 12fs 0.01

18 17,19,35,… 18fs 0.00643

24 23,25,47,… 24fs 0.0022

108 978-1-61284-379-7/11$26.00c 2011IEEE