a 24-pulse ac–dc converter employing a pulse doubling ... links/mtech/power...doubling technique...

314 IETE JOURNAL OF RESEARCH | VOL 54 | ISSUE 4 | JUL-AUG 2008

A 24-Pulse AC–DC Converter Employing a Pulse Doubling Technique for Vector-Controlled Induction

Motor DrivesBhim Singh, Vipin Garg and Gurumoorthy Bhuvaneshwari

Department of Electrical Engineering, Indian Institute of Technology, Delhi, New Delhi - 110 016, India.

AbstrAct

This paper deals with various multipulse AC–DC converters for improving the power quality in vector-controlled induc-tion motor drives (VCIMDs) at the point of common coupling. These multipulse AC–DC converters are realized using a reduced rating autotransformer. Moreover, DC ripple reinjection is used to double the rectification pulses resulting in an effective harmonic mitigation. The proposed AC–DC converter is able to eliminate up to 21st harmonics in the supply current. The effect of load variation on VCIMD is also studied to demonstrate the effectiveness of the proposed AC–DC converter. A set of power quality indices on input AC mains and on the DC bus for a VCIMD fed from different AC–DC converters is also given to compare their performance.

Keywords: Autotransformer, Multipulse AC–DC converter, DC ripple reinjection, Pulse doubling, VCIMD.

1. INtroductIoN

The advances in power semiconductor devices have led to the increased use of solid-state converters in vari-ous applications such as air conditioning, refrigeration, pumps, etc. employing variable frequency induction mo-tor drives [1]. These variable frequency drives generally use the three-phase squirrel cage induction motor as the prime mover due to its advantages like rugged, reliable, maintenance free, etc. These induction motor drives are mostly operated in a vector control mode [2] due to its capability of giving a performance similar to that of a DC motor. These drives are fed by a six-pulse diode bridge rectifier, which results in injection of harmonics in the supply current, thus deteriorating the power quality at the point of common coupling (PCC), thereby affect-ing the nearby consumers. To have a control on these harmonics, an IEEE Standard 519 [3] has been reissued in 1992, giving the benchmark for limiting current and voltage distortion.

Harmonics can be reduced using different active or pas-sive waveshaping techniques. The active waveshaping techniques result in an increased loss, complex control and higher overall cost. The passive waveshaping tech-niques use passive filters consisting of tuned L–C circuits. However, they require careful application and may produce unwanted side effects, particularly in the pres-ence of power factor (PF) correction capacitors. The most rugged, reliable and cost effective solution to mitigate these harmonics is to use multipulse methods [4-12]. In

multipulse converters, the autotransformer-based con-figurations provide the reduction in magnetics rating as the transformer magnetic coupling transfers only a small portion of the total kVA of the induction motor drive. Various 12-pulse-based rectification schemes have been reported and used in practice for the purpose of line cur-rent harmonic reduction [7-12]. With the use of a higher number of multiple converters, the power quality indices show an improvement, but at the cost of large magnetics resulting in a higher cost of the drive. To achieve similar performance in terms of harmonic current reduction, DC ripple reinjection has been used [13-15].

This paper presents an autotransformer-based 24-pulse AC–DC converter with reduced rating magnetics. A pulse multiplication technique is used to improve various power quality indices to comply with the IEEE standard 519 [3]. The scheme needs two additional diodes along with a suitably tapped interphase reactor for increasing the number of pulses. This arrangement results in elimination up to the 21st harmonic in the input line current.

Moreover, the effect of load variation on the vector-con-trolled induction motor drive (VCIMD) is also studied. The proposed AC–DC converter is able to achieve near unity PF in a wide operating range of the drive. A set of tabulated results giving the comparison of different power quality parameters such as total harmonic distor-tion (THD) and crest factor (CF) of AC mains current, PF, displacement factor and distortion factor, and THD

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315IETE JOURNAL OF RESEARCH | VOL 54 | ISSUE 4 | JUL-AUG 2008

of supply voltage at PCC is presented for a VCIMD fed from an existing six-pulse AC–DC converter, as shown in Figure 1, referred to as Topology ‘A’, 12-pulse converter, Topology ‘B’ and proposed 24-pulse AC–DC converter, Topology ‘C’.

2.  CIRCUIT ConFIGURATIonS oF 12-PULSE AC–DC ConVERTERS

For harmonic elimination, the required minimum phase shift is given by [5] Phase shift = 60o/number of converters.

For achieving a 12-pulse rectification, the phase shift be-tween the two sets of voltages may be either 0o and 30oor ±150 with respect to the supply voltages. In this work, an autotransformer based on the 0o and 30o phase shift has been studied to reduce the size of the magnetics, as shown in Figure 2.

Figure 3 shows the schematic diagram of a 12-pulse autotransformer-based AC–DC converter with a phase shift of +0o and 30o, referred to as Topology ‘B’. Similarly, Figure 4 shows the schematic diagram of a 12-pulse autotransformer-based AC–DC converter with a phase shift of +0o and 30o along with the pulse multiplication circuit, referred to as Topology ‘C’.

3.  DESIGn oF THE PRoPoSED 24-PULSE AC–DC coNVerter

This section presents the design technique for achieving 12-pulse rectification in the proposed AC–DC converter.

3.1  Design of an Autotransformer for the 24-Pulse Converter

To achieve the 12-pulse rectification, the necessary re-quirement is the generation of two sets of line voltages of equal magnitude that are 30o out of phase with respect to each other. The number of turns required for the 0o and 30o phase shift is calculated as follows: Consider phase ‘a’ voltages in Figure 2 as

Va′ = Va + K1 Vca - K2Vbc (1)

Vb′ = Vb + K1 Vab - K2Vca (2)

Assume the following set of voltages:

Va = V∠0o, Vb=V∠-120o, Vc = V∠1200,Vab = 1.732V∠30o, Vbc = 1.732V∠90o, Vca = 1.732V∠-30o (3)

Similarly,

r

i as

PWM CurrentController

Estimator forisx * , i sy *,

LimiterSpeed Controller

ias *

Fieldweakening

isx * i sy*

ThreePhase

VCIMD

i bs

i cs

V dc

IGBT Based Inverter

imr*

+

-

Cd

T

i as

ibs

A

B

C

r

2*

2*

6 Pulse Diode BridgeRectifier

3 Phase ,415 V , 50 Hz

Field Orientation andReference Current

Generation

i bs* ics*

r-+

L dZ s

Zs

Z s

isa

isb

isc

T *

Figure 1: Six-pulse diode bridge rectifier fed vector controlled induction motor drive. (Topology A).

Singh B, et al.: A 24-Pulse AC–DC Converter



Va′ = V ∠+30o, Vb′ = V∠-90o, Vc′ = V ∠150o (4)

where, V is the rms value of the phase voltage.

Using the above equations, K1 and K2 can be calculated. These equations result in K1 = 0.0843 and K2 = 0.229 for the desired phase shift in the autotransformer.

The phase-shifted voltages for phase ‘a’ are

Va′ = Va + 0.0843 Vbc + 0.229 Vca (5)

VbVa’’

’Vc

Vc

Va

V b

Figure 2:  Proposed autotransformer winding  connection diagram.

3phase,VCIMD

IGBT Based Inverter

A

B

C

3 Phase, 415V, 50 Hz

+

VdcCd

-

+

+

-

a

b

c

a'

b’

c'

Autotransformer

Zs

Zs

Zs

Vb’

Va’

Vc’

Vc

Va

Vb

Ld

Figure 3: Proposed autotransformer based 12-pulse converter (with phase shift of  00 and 300) fed VCIMD. (Topology B).

A phase-shifted voltage (e.g., Va′) is obtained by tapping a portion (0.0843) of line voltage Vbc and connecting one end of approximately 0.229 of the line voltage (e.g., Vca) to this tap. The kVA rating of the transformer is calcu-lated as [5]

kVA = 0.5∑Vwinding Iwinding (6)

where Vwinding is the voltage across one winding and Iwinding is the current flowing at full load through the same winding. The kVA rating of the interphase transformer and the zero sequence blocking transformer (ZSBT) is also calculated using the above relationship.

4.   DC RIPPLE REInJECTIon In 12-PULSE AC–DC coNVerters

Figure 4 shows a reduced rating autotransformer-based 24-pulse AC–DC converter fed VCIMD. This configura-tion needs one ZSBT to ensure an independent opera-tion of the two diode rectifier bridges. It exhibits a high impedance to zero sequence currents, resulting in a 120o conduction for each diode and also results in equal current sharing in the output. An interphase reactor tapped suitably to achieve pulse doubling [15] has been connected at the output of the ZSBT. The rectifier output voltages vd1 and vd2, shown in Figure 4, are identical except for a phase shift of 30o (required for achieving 12-pulse operation), and these voltages contain ripples of six times the source frequency. The AC–DC converter output voltage vdc is given by




vdc = (vd1 + vd2)/2 (6)

Similarly, the voltage across the interphase reactor is given as

vm = vd1 – vd2 (7)

vm is an AC voltage ripple of six times the source fre-quency, as shown in Figure 5.

4.1  Design of the Interphase Reactor

Pulse multiplication has been obtained [13-14] for controlled converters with a tapped interphase reactor and two additional diodes. The details of pulse mul-tiplication arrangement for diode bridge rectifiers are presented in Figure 6. The voltage appearing across the interphase reactor vm is an AC voltage ripple of six times the source frequency. Thus, depending on the polarity of the impressed voltage across the interphase reactor, diodes D1 or D2 conduct. Figure 7 shows the waveforms of the diode currents showing the changeover of cur-rents through the diodes, which results in achieving the 24-pulse characteristics. The turns ratio of the interphase reactor is given by [16]

N1/No = 0.2457 (8)

4.2  Design of the ZSBT

The ZSBT helps in achieving an independent operation of the two rectifier bridges, thus eliminating the unwanted

conducting sequence of the rectifier diodes. The ZSBT offers a very high impedance for zero sequence current components. Figure 5 shows the voltage waveform across the ZSBT. It contains only triplen frequency com-ponents resulting in a smaller size, weight and volume of the transformer.

5. VcImd

Figure 1 shows the schematic diagram of an indirect VCIMD. In the rotor flux-oriented reference frame, the reference vector isx (flux component of the stator current) is obtained as

isx* = imr + τr (∆imr/∆T) (9)

where imr is the magnetizing current. The closed loop proportional-integral (PI) speed controller compares the reference speed (wref) with motor speed (wr) and generates the reference torque T*(after limiting it to a suitable value) as

T*(n) = T*

(n-1) + Kp {we(n) - we(n-1)} + KI we(n) (10)

where, T*(n) and T*

(n-1) are the outputs of the PI controller (after limiting it to a suitable value) and we(n) and we(n-1) refer to the speed error at the nth and (n-1)th instants. Kp and KI are the proportional and integral gain con-stants. The torque component of the stator current reference vector isy is obtained from the output of the PI controller as

Vd1 Vd2

IGBT Based Inverter

A

B

C3 Phase, 415V, 50 Hz

6 -Pulse Diode Bridge Rectifier

6 Pulse Diode Bridge Rectifier

+

-

a

b

c

a'

Autotransformer

Zs

Zs

Zs

IPT

3phase,VCIMD

+

VdcCd

-

Ld

ZSBT D1 D2

ZSBT

+

Vb’

Va’

Vc’

Vc

Va

Vb

b'

c'

Figure 4: The proposed 24-pulse ac-dc converter fed VCIMD (Topology C).




VZSBT (V)

Vm(V)

Figure 5: Voltage waveforms Vm  (across  IPT)  and VZSBT (across ZSBT) at full load.

Id2

Id1

Id1 and Id2

figure 7: diodes d1 and d2 current waveforms.

N o

D 1 D 2

N 1

o

o

o

IPT

V m

Figure 6: Tapped interphase reactor alongwith diodes.

isy* = T*/(k isx

*) (11)

where k = (3/2)(P/2){M/(1+ σr)}

P, M and σr are the number of poles, mutual inductance and rotor leakage factor, respectively. These current com-ponents (isx and isy) are converted to a stationary reference frame using a rotor flux angle calculated as the sum of

the rotor angle and the value of slip angle as

w2* = isy*/(τr isx

*) (12)

Ψ(n) = Ψ(n-1) + (w2* + wr) ∆T (13)

Ψ(n) and Ψ(n-1) are the values of the rotor flux angles at the nth and (n-1)th instants, respectively, and ∆T is the sampling time taken as 100 µs.

These currents (isx*, isy

*) in the synchronously rotating frame are converted to a stationary frame three-phase current (ias

*, ibs*, ics

*) as given below

ias* = -isy

*sinΨ + isx*cosΨ (14)

ibs* = [-cosΨ + 3 sinΨ]isx

*(1/2) + [sinΨ + 3 cosΨ]isy*

(1/2) (15)

ics* = -(ias

* + ibs*) (16)

These three-phase reference currents (ias*, ibs

* and ics*) are

compared with the sensed motor currents (ias, ibs and ics). The current errors are amplified and fed to the pulse width modulation (PWM) current controller, which controls the duty ratio of different switches in the voltage source comverter (VSI), to develop necessary voltages to feed the cage induction motor.

6.   MATLAB-BASED SIMULATIon

The proposed AC–DC converter along with the VCIMD is simulated in a MATLAB environment along with Simulink and Power System Blockset toolboxes. Figure 8 shows the MATLAB model of the proposed AC–DC converter based on a pulse multiplication circuit con-nected on the DC side to improve the power quality. The simulated results have been presented to study the effect of load variation on the drive on various power quality indices and to show the reduction in the rating of magnetics in the proposed configuration.

7. results ANd dIscussIoN

The proposed AC–DC converter along with the VCIMD has been designed for retrofit applications where pres-ently a six-pulse diode bridge rectifier is being used. The input current of a six-pulse diode bridge rectifier fed VCIMD is shown in Figures 9–10. Figure 9 shows the supply current waveform along with its harmonic spectrum at full load, showing a THD of the AC mains current as 32.1%, which deteriorates to 66.66% at light load (20%), as shown in Figure 10. Moreover, the PF at full load is 0.936, which deteriorates to 0.812 as the load is reduced to 20%, as shown in Table 1. These results show that there is a need for improving the power quality at the AC mains to replace the existing six-pulse converter.




Table 1: Comparison of power quality parameters of a VCIMD fed from different ac-dc convertersSr. no. Topology THD Vs Is (A) THD of Is (%) DF DPF PF DC link voltage

(%) (V) Average FL LL (20%) FL LL (20%) FL LL (20%) FL LL (20%) FL LL (20%) FL LL (20%)

1 A 6.94 42.6 10.22 31.1 68.7 .955 .824 .983 .975 .939 .803 547 5562 B 4.04 40.7 8.54 9.51 15.66 .995 .988 .972 .979 .988 .986 565 5773 C 3.37 39.4 8.45 4.18 6.94 .999 .997 .997 .995 .996 .993 561 569

THD: Total hatmonic distortion, Vs: Supply voltage, Is: Supply current, DF: Distortion factor, DPF: Displacement factor, PF: Power factor, DC: Direct current, FL: Full load, LL: Light load

Figure 8: MATLAB block diagram of proposed ac-dc converter fed VCIMD (Topology ‘D’).

Figure 9: AC mains current waveform of VCIMD fed by 6-pulse diode rectifier along with its harmonic spectrum at  full load (Topology ‘;A’).

1.34 1.35 1.36 1.37 1.38 1.39

-50

0

50

I s(A

)

Time (s)

0 200 400 600 800 1000 12000

50

100

Mag

(%of

50Hz

com

pon

ent)

Frequency (Hz)

THD = 31.13%

Figure 10: AC mains  current waveform of VCIMD  fed by 6-pulse diode rectifier along with its harmonic spectrum at light load (20%). (Topology ‘;A’).

0.92 0.93 0.94 0.95 0.96 0.97 0.98

-20

-10

0

10

20

I s(A

)

Time (s)

0 200 400 600 800 1000 12000

50

100

Mag

(%of

50Hz

compon

ent)

Frequency (Hz)

THD = 68.7%

7.1  Performance of a 12-Pulse Rectification-Based AC–DC Converter

To improve the power quality indices, a 12-pulse AC–DC converter fed VCIMD has been modelled and simulated. Figure 11 shows the waveform of the supply current along with its harmonic spectrum at full load. At full load, the THD of the AC mains current is 9.51% and the PF obtained is 0.988. At light load, the THD of the AC mains current is 15.66%, as shown in Figure 12 and the PF is 0.9864. It shows that the power quality parameters are not within the IEEE standard 519 limits [3].

7.2  Performance of the Proposed 24-Pulse Rectification-Based AC–DC Converter

To improve the power quality, pulse doubling has been used in the above configuration, referred to as Topology ‘C’. Figure 13 shows the dynamic performance of the proposed AC–DC converter (Topology ‘C’) at start and at load perturbation on VCIMD. It consists of supply voltage vs, supply current is, rotor speed ‘wr’ (in electrical rad/s), three-phase motor currents isabc, motor developed torque ‘Te’ (in N-m) and DC link voltage vdc (V).




Figure 11: AC mains  current waveform alongwith  its har-monic spectrum at full load  for Topology ‘B’.

Figure 12: AC mains  current waveform alongwith  its har-monic spectrum at light load (20%)  for Topology ‘B’.

Figure 13: Dynamic response of proposed harmonic mitigator (Topology ‘C’) fed VCIMD with load perturbation.

Figure 14: AC mains  current waveform alongwith  its har-monic spectrum  at full load for  Topology ‘C’.

1.38 1.39 1.4 1.41 1.42 1.43 1.44

-50

0

50I s

(A)

Time (s)

0 100 200 300 400 500 600 700 800 900 10000

20

40

60

80

100

Mag

(%of

50Hz

com

ponen

t)

Frequency (Hz)

THD = 9.51%

2.32 2.33 2.34 2.35 2.36 2.37 2.38-20

-10

0

10

20

I s(A

)

Time (s)

0 100 200 300 400 500 600 700 800 900 10000

20

40

60

80

100

Mag(%

of50Hzcom

pone

nt)

Frequency (Hz)

THD = 15.66%

0.1 0.2 0.3 0.4 0.5 0.6 0.7-500

0500

Vs(V

)

0.1 0.2 0.3 0.4 0.5 0.6 0.7-100

0100

I s(A)

0.1 0.2 0.3 0.4 0.5 0.6 0.70

200400

Spe

ed(R

/s)

0.1 0.2 0.3 0.4 0.5 0.6 0.7-100

0100

I abc(A

)

0.1 0.2 0.3 0.4 0.5 0.6 0.70

500

T(N

-m)

0.1 0.2 0.3 0.4 0.5 0.6 0.70

5001000

Time (Sec)

V dc(V

)

0.56 0.57 0.58 0.59 0.6 0.61 0.62-50

0

50

I s(

)ATime (s)

0 200 400 600 800 1000 1200 1400 1600 1800 20000

50

100

Mag

(%of

50Hz

compo

nent)

Frequency (Hz)

THD = 4.18%

The supply current waveform at full load along with its harmonic spectrum is shown in Figure 14 (Topology ‘C’), which shows that the THD of the AC mains cur-rent is 4.18% and the PF obtained is 0.996. At light load condition, the THD of the AC mains current is 6.94%, as shown in Figure 15 and the PF is 0.996. Table 2 shows the effect of load variation on the VCIMD to study various power quality indices. It shows that the proposed AC–DC converter is able to perform satisfactorily under load variation on VCIMD with almost unity PF in the wide operating range of the drive and the THD of the supply current is always less than 8%. This is within the IEEE standard 519 [3] limits for short circuit ratio (SCR) >20.

The variation of the THD of the AC mains current and PF with load on VCIMD fed from a six-pulse, 12-pulse and the proposed 24-pulse AC–DC converter is shown in Figures 16 and 17, respectively, showing a remarkable improvement in these power quality indices for the 24-pulse AC–DC converter.

Figure 15: AC mains  current waveform alongwith  its har-monic spectrum  at light load (20%) for  Topology ‘C’.

0.26 0.27 0.28 0.29 0.3 0.31 0.32-10

-5

0

5

10

I s(A)

Time (s)

0 500 1000 1500 20000

50

100

Mag

(%of50

Hzcomponent)

Frequency (Hz)

THD = 6.94%

The proposed 24-pulse converter needs an autotrans-former of 8.39 kVA, an interphase reactor of 0.432 kVA and a ZSBT of 2.08 kVA, totalling to a magnetics of




10.91 kVA, which is only 35.6% of the drive rating. The comparison of magnetics rating in different converters is shown in Table 3. Moreover, normally, the winding loss and core loss in the magnetics are approximately of the order of 3–5% of the magnetics rating. Because the magnetics rating is only 35.6% of the drive rating, therefore these losses are to be only of the order of 1.5–1.8% of the drive rating. Therefore, these losses generally lie in the range of 2–2.5% of the drive rating. It is also worth mentioning that the proposed converter configuration results in reduction in the AC mains current in the range of 7–17%, depending on the load on the drive. Therefore, it can be concluded that the overall energy consumption required for a particular process is expected to reduce in the proposed converter configuration.

Figure 16: Variation of THD with load on VCIMD in 6-pulse (Topology ‘A’), 12-pulse (Topology ‘B’) and proposed 24-pulse ac-dc converter (Topology ‘C’) fed VCIMD.

Figure 17: Variation of power factor with load on VCIMD in 6-pulse (Topology ‘A’), 12-pulse (Topology ‘B’) and proposed 24-pulse ac-dc converter (Topology ‘C’) fed VCIMD.

0.7

0.8

0.9

1

0 20 40 60 80 100 120Load (%)

PF

6-Pulse 12-Pulse 24-Pulse

Table 2: Comparison of power quality indices of proposed 24-pulse harmonic mitigator fed VCIMD under varying loads Load (%) THD (%) CF of Is DF DPF PF RF Vdc (V) Is Vt

20 6.94 1.56 1.45 0.997 0.995 0.993 1.43 56940 6.02 1.87 1.44 0.998 0.997 0.996 1.64 56760 5.12 2.43 1.42 0.999 0.997 0.996 1.85 56580 4.64 2.92 1.41 0.999 0.997 0.996 2.18 563100 4.18 3.37 1.41 0.999 0.997 0.996 2.68 561

VCIMD: Vector controlled induction motor drive, CF: Crest factor, RF: Ripple factor, THD: Total hatmonic distortion, DF: Distortion factor, PF: Power factor

8. coNclusIoNs

Reduced rating autotransformer-based 12- and 24-pulse AC–DC converters have been designed, modelled and compared with a six-pulse AC–DC converter feeding VCIMD. DC ripple reinjection technique for pulse dou-bling has been used for harmonic reduction in VCIMD. The pulse doubling technique needs only two additional diodes along with a suitably tapped inductor. The pro-posed AC–DC converter has resulted in a reduction in the rating of the magnetics, leading to the saving in the overall cost of the drive. The proposed AC–DC converter is able to achieve close to unity PF along with a good DC link voltage regulation in the wide operating range of the drive. The proposed AC–DC converter has demonstrated its capability in improving various power quality indices at the AC mains in terms of THD of the supply current, THD of the supply voltage, PF and CF. It can easily replace the existing six-pulse converters without much alteration in the existing system layout and equipments.

APPeNdIX

Motor and controller specifications:Three-phase squirrel cage induction motor: 30 hp (22 kW), three-phase, four-pole, Y-connected, 415 V, 50 Hz, Rs = 0.2511 ohms, Rr = 0.2489 ohms, Xls = 0.4389 ohms,

Table 3: Comparison of rating of magnetics in different converter fed VCIMD Topology Transformer Interphase ZSBT Rating of rating (kVA) reactor rating rating magnetics (kVA) (kVA) % of drive rating

A 0.0 0.0 0.0 0.0B 10.1 2.0 0.0 39.5C 8.39 0.432 2.1 35.6

VCIMD: Vector controlled induction motor drive, ZSBT: Zero sequence blocking transformer




Xlr = 0.4389 ohms, Xm = 13.08ohms, J= 0.305 kg-m2.Controller parameters:PI controller: Kp = 15.0, Ki = 0.038.DC link parameters: Ld = 1.0mH, Cd = 3200 µF.Magnetics ratings:24-pulse-based converter: Autotransformer rating 8.39 kVA, interphase transformer 0.432 kVA, ZSBT 2.08 kVA.

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AUTHORS bhim singh was born in Rahamapur, U. P., India in 1956. He received his Bachelor of Electrical (Electrical) degree from the University of Roorkee, India in 1977 and his Master of Technology and Ph. D. degrees from IIT, Delhi, in 1979 and 1983, respectively. In 1983, he joined IIT as a Lecturer and in 1988 became a Reader in the Department of Electrical

Engineering, University of Roorkee. In December 1990, he joined as an Assistant Professor, than became an Associate Professor in 1994 and a Professor in 1997 at the Department of Electrical Engineering, IIT Delhi. field of interest includes power electronics and control of electrical machines. Dr. Singh is a Fellow of the Indian National Academy of Engineering, Institution of Engineers (India) and Institution of Electronics and Telecommunication Engineers. He is also a Life Member of Indian Society for Technical Education, System Society of India and National Institution of Quality and Reliability and Senior Member IEEE (Institute of Electrical and Electronics Engineers).

e-mail: [email protected]

Vipin garg received his Bachelor of Technology (Electrical) and Master of Technology degrees from NIT, Kurukshetra, India in 1994 and 1996 respectively and his Ph.D. degree from the Department of Electrical Engineering, IIT Delhi in 2006. In 1995, he joined as a Lecturer in the Department of Electrical Engineering, NIT, Kurukshetra. In January 1998, he joined IRSEE

Paper No. 8-B; Copyright © 2008 by the IETE

(Indian Railways His Service of Electrical Engineers) as an Assistant Electrical Engineer and became Deputy Chief Electrical Engineer in 2006. His field of interests includes power electronics, power conditioning and electric traction. He is a member of IEEE (Institute of Electrical and Electronics Engineers).


G Bhuvneshwari received his Master of Technology and Ph. D. degrees from IIT, Madras in 1988 and 1992, respectively. In 1997, she joined as an Assistant Professor and became an Associate Professor in 2006 at the Department of Electrical Engineering, IIT Delhi. Her field of interests includes power electronics, electrical machines and drives, active filters, and power conditioning. She is a fellow of the Institution of

Electronics and Telecommunication Engineers and is a Senior Member of IEEE (Institute of Electrical and Electronics Engineers).



a 24-pulse ac–dc converter employing a pulse doubling ... links/mtech/power...doubling technique...

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