A Robust Three-Phase Active

8/2/2019 A Robust Three-Phase Active

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IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 46, NO. 3, JUNE 1999 483

A Robust Three-Phase ActivePower-Factor-Correction andHarmonic Reduction Scheme

for High PowerBang Sup Lee, Member, IEEE, Jaehong Hahn, Student Member, IEEE, Prasad N. Enjeti, Senior Member, IEEE,

and Ira J. Pitel, Fellow, IEEE

Abstract This paper proposes a robust three-phase activepower-factor-correction (PFC) and harmonic reduction schemesuitable for higher power applications. The proposed system isa unique combination of a low-kilovoltampere 12-pulse rectifiersystem with a single-phase boost PFC scheme to shape the inputcurrent to near sinusoidal waveshape. The voltampere rating ofthe active PFC converter is 0.05 pu and is not exposed to linetransients under varying load conditions. The proposed system issuitable for utility interface of higher power rectifiers employed inpower supplies and adjustable-speed drive systems which demandclean input power characteristics in the range of 1500 kW. Theproposed system is rugged and, in the event the active controlwere to fail, the system reverts to 12-pulse operation with fifthand seventh harmonic cancellation. Analysis and design of thesystem is examined in detail, and simulation and experimentalresults on a 10-kVA prototype are shown.

Index TermsClean power, harmonic reduction, three-phaserectifier.

I. INTRODUCTION

IN MOST POWER electronics applications, diode rectifiersare commonly used in the front end of a power converter asan interface with the electric utility. The rectifiers are nonlinear

in nature and, consequently, generate harmonic currents into

the ac power source. The nonlinear operation of the diode

rectifiers causes highly distorted input current. The nonsinu-

soidal shape of the input current drawn by the rectifiers causes

a number of problems in the sensitive electronic equipment

and in the power distribution network. The distorted input

current flowing through the system produces distorted voltages

at the point of common coupling (PCC). Thus, the increased

harmonic currents result in increasing voltampere ratings of

the utility equipment, such as generators, transmission lines,

and transformers. In addition to the inefficient use of electric

energy, the discontinuous conduction of the bridge rectifier

Manuscript received November 18, 1997; revised November 15, 1998.Abstract published on the Internet March 1, 1999.

B. S. Lee is with Texas Instruments Incorporated, Dallas, TX 75243 USA(e-mail: [email protected]).

J. Hahn and P. N. Enjeti are with the Power Electronics Laboratory, De-partment of Electrical Engineering, Texas A&M University, College Station,TX 77843-3128 USA (e-mail: [email protected]).

I. J. Pitel is with Magna-Power Electronics, Boonton, NJ 07005 USA.Publisher Item Identifier S 0278-0046(99)04127-1.

results in a high total harmonic distortion (THD) in the input

lines and can lead to malfunctioning of the sensitive electronic

equipment. The recommended practice, IEEE-519, and IEC

1000-3 have evolved to maintain utility power quality at

acceptable levels [1][3].

In order to meet IEEE-519 and IEC 1000-3, a cost-effective

and economical solution to mitigate harmonics generated

by power electronic equipment is currently of high inter-

est. One approach is to use three single-phase power-factor-

corrected rectifiers in cascade [11][13]. The main advantage

of this configuration is that a well-known single-phase power-

factor=correction (PFC) technique can be used in three-phase

applications. However, this approach suffers from several

disadvantages, which include the following: 1) cascading

three single-phase PFC circuits requires the use of additional

diodes; 2) increased component count; 3) complicated input

synchronization logic; and 4) higher dc-link voltage due to

boost current shaping. At best, input THD of 10% can be

achieved [14].Another approach is to employ a single boost switch in

conjunction with a three-phase diode rectifier bridge [15]. This

system requires discontinuous operation, resulting in much

higher dc-bus voltage and high EMI. Both of the above two

methods are suitable for 10-kW output power and, hence,

not practical in higher power ranges.

In this paper, a robust three-phase clean-power rectifier

system is proposed [22]. The proposed system combines the

unique features of a low-kilovoltampere 12-pulse rectifier

scheme along with a single-phase boost PFC scheme to shape

the input current to a near sinusoidal waveshape ( 1% THD).

The proposed rectifier system is suitable for clean-power utility

interface of power electronic systems in 1500 kW ranges. Thesingle-phase boost PFC stage is rated at 0.05 pu and assists in

shaping the input current under varying load conditions. The

following sections describe the system in more detail.

II. PROPOSED SYSTEM

Fig. 1(a) shows the circuit topology of the proposed rectifier

system. The proposed system (Fig. 1) combines the unique

features of an autotransformer-based 12-pulse rectifier system

and a low-cost single-phase boost-type active current-shaping

02780046/99$10.00 1999 IEEE


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484 IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. 46, NO. 3, JUNE 1999

(a)

(b)

(c)

(d)

Fig. 1. Proposed robust three-phase clean-power rectifier system. (a) Circuit diagram. (b) Winding configuration of ZSBT. (c) Winding configuration ofthe AIPT. (d) Implementation of the single-phase boost PFC circuit.

circuitry to achieve clean input power characteristics. An auto-

transformer is employed to generate 30 phase-shifted voltages

to rectifier bridges I and II [16]. Fig. 2 shows the vector

diagram and winding configuration of the autotransformer.

From the line voltage applied to node (Fig. 2), voltages

and are generated due to the interconnection of

transformer windings. To achieve 30 phase shift between

and is necessary. This arrangement results

in low kilovoltamperes, since the autotransformer does not

provide isolation. Rectifiers I and II are connected in parallel

(Fig. 1) via zero-sequence blocking transformers (ZSBTs)

[17] and an active interphase transformer (AIPT) [19]. The

purpose of the ZSBT is twofold: 1) to offer high impedance

to cross conduction paths between the diodes in rectifiers I

and II and 2) offer low impedance and promote independent

operation of rectifier bridges I and II in a parallel-connected


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LEE et al.: A ROBUST THREE-PHASE ACTIVE PFC AND HARMONIC REDUCTION SCHEME FOR HIGH POWER 485

nonisolated 12-pulse rectifier system. Further, ZSBTs are

symmetrically placed to result in near-equal impedance in the

two parallel conduction paths of rectifiers I and II. Power

electronic converter loads, such as power supplies (dc/dc

converters) and variable-frequency inverters (dc/ac converters)

can be connected from the center tap of the AIPT to the

negative rail [Fig. 1(a)]. Single-phase boost PFC circuitry is

connected across the auxiliary winding of the AIPT [Fig. 1(a)

and (d)]. The boost converter output is fed back to the dc

link. The boost converter is controlled by popular control

circuit, such as a Motorola MC34261, to draw a current

in phase with the voltage . The auxiliary winding current

in the AIPT is then shown to alter the shape of the

utility input current to a near-sinusoidal current shape.

With the auxiliary winding current set to zero (i.e., boost

converter disenabled), the utility input current exhibits 12-

pulse characteristics, i.e., fifth and seventh harmonic currents

are cancelled. The kilovoltamperes of the boost converter

connected across the AIPT is 0.05 pu of the output power,

which is low.

III. ANALYSIS

In this section, analysis of the proposed system is presented

in detail.

A. Autotransformer Voltage and Current Relationships

Fig. 2 shows the winding configuration and the associated

vector diagram of the autotransformer. From Fig. 2, the fol-

lowing equation can be written:

(1)

(2)

where is the line-to-neutral voltage of phase and

(3)

Also,

(4)

where is the rms of the line-to-line voltage.

From the autotransformer winding configuration and the

following MMF relationship, the input current can beexpressed as

(5)

(6)

A detailed analysis of the autotransformer can be found in [16].

B. Rectifier Output Voltage Analysis

As explained in the previous section, the ZSBTs exhibit

high impedance to zero-sequence currents and ensure indepen-

(a)

(b)

Fig. 2. Reduced kilovoltampere delta-type polyphase autotransformer. (a)Vector diagram. (b) Winding configuration.

dent operation of rectifier bridges I and II and 120 conduction

for each rectifier diode [17].

1) ZSBT: For the purpose of detailed voltage analysis,

an equivalent circuit of the proposed system in Fig. 1(a) is

developed and is shown in Fig. 3. The equivalent circuit

consists of two positive and negative groups of diodes along

with ZSBT and AIPT connections [Fig. 3(a) and (b)].

In the positive group, the cathodes of the diodes

and are at a common potential . Therefore, the diodewith its anode at the highest potential will conduct the current

. The cathodes of the diodes and are at a

common potential [Fig. 3(a)]. Therefore, the diode with its

anode at the highest potential will conduct the current ,

and the rest of the diodes are reverse biased. Similarly, in the

negative group [Fig. 3(b)], the diodes with their cathodes at

the lowest potential will conduct, and the rest of the diodes are

reverse biased. Thus, the voltage across the ZSBT depends on

the conduction sequence of diodes. Further, the voltage across

the ZSBT , , is identical to , since they are

magnetically coupled with each other. From the equivalent


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(a)

(b)

Fig. 3. Equivalent circuit of the dc-side output. (a) Upper side diodes of

rectifiers I and II. (b) Lower side diodes of rectifiers I and II.

circuit [Fig. 3(b)], we have

(7)

for

for(8)

where , and is one period of .

Fig. 7(d) shows the instantaneous waveshapes of voltages

and due to the conduction of

positive and negative groups of diodes, as shown in Fig. 3.

Mathematically, can be expressed in Fourier series as

follows. The node voltage at and are given by

(9)

(10)

Fig. 4. Switching function Sa 1

for rectifier I.

From Figs. 1(a) and 3, we have

(11)

(12)

Equation (12) can be simplified as

(13)

Substituting (4) in (13), we have

(14)

It should be noted that contains only tripplen fre-

quency components, hence, if properly designed, the ZSBT

impedes the flow of tripplen harmonic currents. In other words,

the ZSBT ensures independent 6-pulse operation of the two

rectifier bridges I and II.

2) Voltage Analysis of AIPT and Output Voltage: TheFourier series representations of the voltages and

[Fig. 7(d)], i.e., the voltages between and nodes with

respect to the neutral, can be expressed as [18]

(15)

(16)

(17)

Now, from the equivalent circuit [Figs. 3(a) and 1(a)], the

voltage across the AIPT becomes

(18)


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(a) (b)

(c)

Fig. 5. Computation results by (32) and (33). (a) Shape of the injected current Ix

for sinusoidal-shaped input current Ia

. (b) Input line current Ia

afterI

x

is injected. (c) Input line current Ia

with Ix

= 0 .

Substituting (14) and (17) in (18), we have

(19)

Equation (19) can be simplified as

(20)

Fig. 7(e) shows the waveshape of the voltage across the

AIPT. From (15) and (16), the dc output voltage at node

with respect to neutral [Fig. 3(a)] is

(21)

Similarly, the output voltage at node [Fig. 3(b)] is as

follows:

(22)

Therefore, the average dc output load voltage of the

proposed system is

(23)

Substituting (4) in (23), we have

(24)

The output voltage is about 3.5% higher than a conventional

6-pulse system.

C. Input Current Analysis

In this section, the input current analysis is discussed. In

order to analyze the input utility line current , which can be

expressed in terms of the injected current and output current

, switching functions are introduced [19]. The switching

function for phase (Fig. 4) is given by

(25)

is identical to rectifier input current , as shown in

Fig. 7(c), except for magnitude. For phase and , the switch-

ing functions can also be written as

(26)

Similarly, the switching functions for rectifier II are as follows:

(27)

Therefore, the input currents through the diode rectifiers I and

II can be written in terms of the switching functions and the

rectifier output currents as follows:

and (28)


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(a) (b)

(c) (d)

(e) (f)

Fig. 6. Simulation results after Ix

is injected. (a) Input line current Ia

. (b) Frequency spectrum of Ia

. (c) Rectifier I input current Ia 1

. (d) Triangular-shapedinjected current I

x

. (e) Rectifier I output current Io 1

. (f) Rectifier II output current Io 2

.

The following equation can be written for the AIPT to describe

the relationship between currents and and the injected

current [Fig. 1(c)]:

(29)

where and are the number of turns on the AIPT

[Fig. 1(c)] . From (6) and (29), we have rectifier output

currents in terms of the injected current as follows:

(30)

(31)

Equation (5) can now be modified using (30), (31), and

switching functions (28) as

(32)

Equation (32) illustrates the relationship between injected

current , output current , and input current . For input

current to be sinusoidal, the injected current as a function


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(a) (b)

(c) (d)

(e)

Fig. 7. Simulation results with Ix

= 0 . (a) Input line current Ia

. (b) Frequency spectrum of Ia

. (c) Rectifier I input current Ia 1

. (d) Vp n

; V

q n

; V

0

p n

;

V

0

q n

; and the voltage across the ZSBT, VZ S B T

. (e) voltage across the AIPT, Vm

.

of the output current becomes

(33)

where is replaced by , which is the fundamental

component of . Therefore, (33) describes the exact shape

of for a given load current to result in a sinusoidal-

shaped input current . Fig. 5(a) shows the waveshape of

for to be sinusoidal. It is noted [Fig. 5(a)] that

exhibits discontinuities at specific intervals. This is due to

the denominator in (33) tending to a low value. Also, from

Fig. 5(a), it can be concluded that the waveshape ofresembles a triangular wave. Therefore, it is conjectured that,

by injecting a triangular waveshape current in the AIPT

auxiliary winding, a near-sinusoidal input current can be

obtained. Fig. 6 shows the validity of this assumption via

simulation. The waveshape of is a near-sinusoidal shape

with a triangular current in the AIPT winding. An important

result has been derived in this section, i.e., by injecting a

triangular wave shape of current in the AIP, a near-

sinusoidal input current % THD is obtained. Also,

from Figs. 6(d) and 7(e), it can be observed that the AIPT

auxiliary winding voltage [Fig. 7(e)] and the required


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TABLE IVOLTAMPERE RATINGS OF THE MAGNETICS

injected current [Fig. 6(d)] are both triangular in shape and

in phase. Therefore, low-cost single-phase boost PFC circuitry

along with its control IC can satisfy the criteria for and

to be identical in shape and in phase. The output power from

the boost PFC circuit is fed back to the dc link [Fig. 1(d)].

The load current is sensed and utilized in the control of

magnitude, such that input current is near sinusoidal,

even under varying output load conditions. Thus, the proposed

approach is a unique combination of a low-kilovoltampere 12-

pulse rectifier system along with a single-phase boost PFC

connected across the AIPT.

D. Component Ratings

In this section, the kilovoltampere ratings of each compo-

nent in the proposed system are calculated.

1) Voltampere Rating of the Autotransformer: From

Fig. 6(c), the autotransformer winding current rms value

can be shown to be

(34)

The currents and have the same rms

value as given in (34). From the MMF equations of the

winding configuration of the autotransformer [Fig. 2(b)], the

delta-connected winding current can be expressed as

(35)

Therefore, from Fig. 6(c) and (35), we have

(36)

The rms voltage of the winding voltage [Fig. 2(a)] is

(37)

The rms voltage of the delta-connected winding [Fig. 2(a)]

is

(38)

Thus, from (34) to (38), the equivalent voltampere rating of

the polyphase autotransformer is given by

VA (39)

where is the output power .


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(a) (b)

(c) (d)

(e)

Fig. 8. Experimental results with triangular injected current Ix

in AIPT. (a) Input line current Ia

(10 A/div). (b) Frequency spectrum of Ia

(500Hz/div). (c) Rectifier I input current I

a 1

(10 A/div). (d) Rectifier I output current Io 1

(10 A/div). (e) AIPT auxiliary winding ( Nx

) voltage Vx

andinjected current I

x

(2 A/div).

2) Voltampere Ratings of the Boost PFC, ZSBT, and AIPT:

In this section, the voltampere ratings of the ZSBT, AIPT, and

the boost current-shaping unit are calculated. From (14) and

(24), we have the rms voltage across the ZSBT as follows:

(40)

The rms currents through the ZSBT, as shown in Fig. 6(e)

and (f), are given by

(41)

Therefore, the voltampere rating of the ZSBT can be calculated

as follows:

VA (42)

From (20), the rms voltage of the AIPT, , is given by

(43)


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(a) (b)

(c) (d)

Fig. 9. Experimental results without the injected current Ix

. (a) Input line current Ia

(10 A/div). (b) Frequency spectrum of Ia

(100 Hz/div). (c) RectifierI input current I

a 1

(10 A/div). (d) Rectifier I output current Io 1

(10 A/div).

The voltage across the auxiliary winding in the AIPT, , is

given by

(44)

Fig. 6(d) shows the triangular current ; its rms is as follows:

(45)

Therefore, the voltampere rating of the boost PFC that pro-

duces is as follows:

VA (46)

By substituting (41), (43), (44) and (45) into (47), the voltam-

pere rating of the AIPT is

VA

(47)

Equation (46) shows that the voltampere rating of the boost

PFC is a small percentage of the output power. Also, the

voltampere ratings of the autotransformer, ZSBT, and AIPT

are a fraction of the output power. Therefore, the proposed

system shown in Fig. 1 results in high performance with

reduced kilovoltampere components and offers clean-power

utility interface.

3) Design Example and Hardware Implementation: In this

section, a design example of the proposed system is detailed.

Assuming that output power is 30 kW and three-phase

line-to-line voltage is 240 V, the output voltage of the

proposed rectifier system can be calculated from (24) as

V (48)

The output current is given by

A (49)

The kilovoltampere ratings of the components for the above

specifications can be calculated from the procedure outlined

and are listed in Table I.


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a) Hardware implementation: Fig. 1(d) shows the boost

PFC implementation for realizing the active current source

to be in phase with , a condition set forth in (33) for clean

input power. The load current is sensed and fed back to the

boost PFC circuit. Motorola boost PFC MC34261 has been

employed in the test setup.

IV. SIMULATION

The proposed system shown in Fig. 1 has been simulated on

the PSIM simulation program, and the results

are presented in Figs. 6 and 7. A triangular injection current

into the auxiliary winding of the AIPT is shown in Fig. 6(d).

Simplifying the injected current to a triangular waveshape

yields a near-sinusoidal input current , as shown in Fig. 6(a),

and the frequency spectrum of the input current [Fig. 6(b)]

demonstrates near-sinusoidal operation in the utility input line

currents. Fig. 6(c) shows the respective rectifier input current

. Simulation results are shown in Fig. 7, when the boost

PFC circuit fails to inject the active current in the auxiliary

winding of the AIPT. Fig. 7(a) demonstrates a 12-pulse op-

eration with the fifth and seven harmonic cancellations in theutility input line currents when . The dc output voltage

to the load is not interrupted. Therefore, the proposed system is

very rugged and, in the event the active control were to fail, the

system reverts to 12-pulse operation. These results demonstrate

the superior characteristics of the proposed system.

V. EXPERIMENTAL RESULTS

The 208-V 10-kVA system shown in Fig. 1 has been con-

structed in the laboratory and is connected to supply

a bank of dc-link capacitors. A resistive load bank is then

used to load the dc link and to simulate switch-mode power

supplies (SMPS) and adjustable-speed drive loads. The results

are presented in this section.Fig. 8(a)(e) shows the system operation in active mode

at which the triangular current is injected into the AIPT

to draw near-sinusoidal input line current . Fig. 8(c) and

(d) shows diode input current and output current for

rectifier I. For rectifier II, input and output currents

are identical to and , except for a 30 phase shift. It

is clear that the two rectifier output currents are modulated by

the action of injected current [Fig. 8(e)]. Fig. 8(a) shows the

resulting input line current . The utility input current THD

is measured to be 3%.

Fig. 9(a)(d) shows the proposed system in fault mode, at

which the injected current is not injected, resulting in 12-

pulse operation in the input line current. Fig. 9(a) shows theinput line current with , and Fig. 9(b) illustrates the

frequency spectrum of .

VI. CONCLUSION

In this paper, a robust three-phase active PFC and har-

monic reduction scheme has been proposed. The proposed

system consists of fewer components with lower kilovoltam-

pere magnetics. It has been shown that by injecting a low-

kilovoltampere active current source into the

AIPT, near-sinusoidal input currents with 1% THD can be

obtained. Further, the active pulsewidth modulation (PWM)

inverter unit is not directly exposed to line transients. In the

event the active PWM control were to fail, the proposed

system reverts to 12-pulse operation with fifth and seventh

harmonics cancellation in the input utility line current. The

resultant system exhibits clean-power characteristics suitable

for utility interface of high-power ac motor drives and switch-

mode power supplies. A detailed analysis of the proposed

scheme, along with design equations, have been presented.

Experimental results from a 208-V 10-kVA rectifier system

have demonstrated the superiority of the proposed system.

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[17] S. Choi, B. S. Lee, and P. Enjeti, New 24-pulse diode rectifier systemsfor utility interface of high-power AC motor drives, IEEE Trans. Ind.

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fiers, U.S. Patent pending.


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Bang Sup Lee (S95M98) was born in Daejeon,Korea. He received the B.S. degree from ChungnamNational University, Daejeon, Korea, in 1987, theM.S. degree from Seoul National University, Seoul,Korea, in 1989, and the Ph.D. degree from TexasA&M University, College Station, in 1998, all inelectrical engineering.

From 1989 to 1994, he was a Design Engineerwith the Research and Development Center, Dae-woo Heavy Industries, Incheon, Korea. Since 1998,

he has been with Texas Instruments Incorporated,Dallas, TX, where he is currently a Systems Engineer. His work has includedthe design of active power-factor-correction and high-efficiency dc/dc con-verters, development of PWM inverters, and analysis of distributed powerelectronic systems. His research interests include power-factor-correctioncircuits, power quality issues, distributed power systems, new convertertopologies for power supplies, and motor drives.

Dr. Lee was the recipient of the IEEE Industry Applications Society ThirdPrize Paper Award in 1996.

Jaehong Hahn (S98) was born in Jindo, Korea.He received the B.S. degree from Seoul NationalUniversity, Seoul, Korea, in 1989. He is currentlyworking towards the Ph.D. degree in power elec-tronics at Texas A&M University, College Station.

From 1989 to 1994, he was a Design Engineerwith the Research and Development Center, Dae-woo Heavy Industries, Incheon, Korea. His interestsare in power electronics applications to power qual-ity and clean-power converters.

Prasad N. Enjeti (S86M88SM95) received theB.E. degree from Osmania University, Hyderabad,India, in 1980, the M.Tech. degree from IndianInstitute of Technology, Kanpur, India, in 1982,and the Ph.D. degree from Concordia University,Montreal, P.Q., Canada, in 1988, all in electricalengineering.

In 1988, he joined the Department of ElectricalEngineering, Texas A&M University, College Sta-tion, as an Assistant Professor. In 1994, he becamean Associate Professor and, in 1998, he became a

Professor. His primary research interests are advanced converters for powersupplies and motor drives, power quality issues and active power filterdevelopment, utility interface issues and clean-power converter designs, andelectronic ballasts for fluorescent, HID lamps. He holds one U.S. patent andhas licensed two new technologies to industry. He is the lead developer of thePower Quality Laboratory at Texas A&M University and is actively involvedin many projects with industry, while engaged in teaching, research, andconsulting in the areas of power electronics, power quality, and clean-powerutility interface issues.

Prof. Enjeti currently serves on the Executive Board of the IEEE IndustryApplications Society (IAS) as a Member of the Electronics CommunicationsCommittee. He was the recipient of the IAS Technical Committee Prize PaperAward in 1993, 1996, and 1998, the Second Prize Paper Award from the IEEE

TRANSACTIONS ON INDUSTRY APPLICATIONS for papers published from mid-year1994 to mid-year 1995, and the IEEE Industry Applications Magazine PrizeArticle Award for 1996. He is a Registered Professional Engineer in the Stateof Texas.

Ira J. Pitel (M73SM82F99) received the B.S.degree from RutgersThe State University of NewJersey, New Brunswick, the M.S. degree from Buck-nell University, Lewisburg, PA, and the Ph.D. de-gree from Carnegie-Mellon University, Pittsburgh,PA, in 1972, 1975, and 1978, respectively.

From 1973 to 1976, he was with GTE Sylvania,researching high-frequency ballasting techniques forgaseous discharge lighting. He joined Bell Labora-tories in 1978 and Exxon Enterprises in 1979. At

Exxon, he was involved in high-power converterstructures for ac motor drives, power processing for advanced battery systems,and controlled lighting. He was eventually transferred to one of Exxonssubsidiaries, Cornell-Dubilier Electronics, where he was Manager of Researchand Development. In 1981, he founded Magna-Power Electronics, Boonton,NJ, a company specializing in custom and standard power conditioningproducts. As President of the company, he is responsible for contract R&Dand manufacturing of its line of 10750-kW dc power supplies. In 1986, hejoined Texas A&M University as an Adjunct Associate Professor. His researchinterests are high-power ac-to-dc converters, static inverters, spacecraft powersupplies, and specialty lighting controls. He holds 21 patents in the field ofpower electronics.

Dr. Pitel is a co-recipient of the 1995 Society Prize Paper Award of theIEEE Industry Applications Society (IAS). He served as Committee Chairmanof the IAS Industrial Power Converter Committee in 19881989, DepartmentChairman of the IAS Industrial Power Conversion Systems Departmentin 19941995, and IAS Vice-President and President in 1998 and 1999,

respectively. He is a member of Eta Kappa Nu and Tau Beta Pi.

Documents

A Robust Three-Phase Active