1

PWM Regenerative Rectifiers: State of the ArtJ. Rodrıguez,Senior Member, IEEE,J. Dixon, J. Espinoza,Member, IEEE,and P. Lezana.

Abstract— New regulations impose more stringent limits tocurrent harmonics injected by power converters, what is achievedwith Pulse Width Modulated (PWM) rectifiers. In additionseveral applications demand the capability of power regenerationto the power supply.This paper presents the state of the art in the field of regenerativerectifiers with reduced input harmonics and improved powerfactor.Topologies for single and three-phase power supply are consid-ered with their corresponding control strategies.Special attention is given to the application of voltage and currentsource PWM rectifiers in different processes with a power rangefrom a few kilowatts up to several megawatts.This paper shows that PWM regenerative rectifiers are a highlydeveloped and mature technology with a wide industrial accep-tance.

Index Terms— Power electronics, regeneration, rectifier, highpower factor.

I. I NTRODUCTION

T HE AC-DC conversion is used increasingly in a widediversity of applications: power supply for microelectron-

ics, household-electric appliances , electronic ballast, batterycharging, DC-motor drives, power conversion, etc... [1].As shown in Fig. 1 AC-DC converters can be classifiedbetween topologies working with low switching frequency(line commutated) and other circuits which operate with highswitching frequency.The simplest line-commutated converters use diodes to trans-form the electrical energy from AC to DC. The use ofthyristors allows for the control of energy flow. The maindisadvantage of these naturally commutated converters is thegeneration of harmonics and reactive power [1], [2].Harmonics have a negative effect in the operation of theelectrical system and therefore, an increasing attention is paidto their generation and control [3], [4]. In particular, severalstandards have introduced important and stringent limits toharmonics that can be injected to the power supply [5], [6],[7].One basic and typical method to reduce input current harmon-ics is the use of multipulse connections based on transformerswith multiple windings. An additional improvement is the useof passive power filters [3]. In the last decade active filtershave been introduced to reduce the harmonics injected to themains [8], [9], [10].Another conceptually different way of harmonics reductionis the so called Power Factor Correction (PFC). In theseconverters, power transistors are included in the power circuitof the rectifier to change actively the waveform of the inputcurrent, reducing the distortion [11]. These circuits reduceharmonics and consequently they improve the power factor,which is the origin of their generic name of PFC.Several PFC topologies like Boost and Vienna rectifiers [12],

[13], [14], [15], are not regenerative and are suited for appli-cations where power is not fed back to the power supply.However, there are several applications where energy flow canbe reversed during the operation. Examples are: locomotives,downhill conveyors, cranes, etc... In all these applications, theline side converter must be able to deliver energy back to thepower supply.This paper is dedicated to this specific type of rectifiers, shownwith dashed line in Fig. 1, which operate in four quadrantswith a high power factor. These rectifiers, also known as ActiveFront End (AFE), can be classified asVoltage Source Rectifiers(VSR) andCurrent Source Rectifiers(CSR).The following pages present the most important topologies andcontrol schemes for single and three phase operation. Specialattention is dedicated to the application of these converters.

4 Boost

4 Vienna

4 Others

Rectifiers

PFC

4 Voltage Source Rectifier

4 Current Source Rectifier4 Multipulse

4 Dual Converters4 Multipulse

4 Others

Non Regenerative Regenerative (AFE)SCRDiode

Line Commutated

Fig. 1. General classification of rectifiers.

II. PWM VOLTAGE SOURCERECTIFIERS

A. Single-Phase PWM Voltage Source Rectifiers.

1) Standard for Harmonics in Single-Phase Rectifiers:The relevance of the problems originated by harmonics inline-commutated single-phase rectifiers has motivated someagencies to introduce restrictions to these converters. TheIEC 61000-3-2 International Standard establishes limits to alllow-power single-phase equipment having an input currentwith a “special wave shape” and an active input powerP<600W. The class D equipment has an input current witha special wave shape contained within the envelope givenin Fig. 2-b). This class of equipment must satisfy certainharmonic limits. It is clear that a single-phase line-commutatedrectifier shown in Fig. 2-a) is not able to comply with thestandard IEC 61000-3-2 Class D as shown in Fig. 3. Fortraditional rectifiers the standard can be satisfied only byadding huge passive filters, which increases the size, weightand cost of the rectifier. This standard has been the motivationfor the development of active methods to improve the qualityof the input current and, consequently, the power factor.

2

a)

C

L

vs

is

Load

0,015 t [s]

is

[A]

-400

-300

-200

-100

0

100

200

300

400

vs[V]

Class D

Envelope vs

is

b)

0 0,005 0,01 0,02 0,025 0,03

-15

-10

-5

0

5

10

15

Fig. 2. Single-phase rectifier: a) circuit; b) waveforms of the input voltageand current.

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37

Amplitude [A]

Standard IEC 61000-3-2 Class D

Fig. 3. Harmonics in the input current of the rectifier of Fig. 2-a)

2) The Bridge connected PWM Rectifier:a) Power circuit and working principle:Fig. 4-a) shows

the power circuit of the fully controlled single-phase PWMrectifier in bridge connection [16], which uses four transistorswith antiparallel diodes to produce a controlled DC voltageVo. For an appropriated operation of this rectifier, the outputvoltage must be greater than the input voltage, at any time(Vo > Vs). This rectifier can work with two (bipolar PWM)or three (unipolar PWM) levels as shown in Fig. 4.The possible combinations are:

i Switch T1 andT4 are in ON state andT2 andT3 are inOFF state,vAFE = Vo. (Fig. 4-b))

ii Switch T1 andT4 are in OFF state andT2 andT3 are inON state,vAFE = −Vo. (Fig. 4-c))

iii Switch T1 andT3 are in ON state andT2 andT4 are inOFF state, orT1 andT3 are in OFF state andT2 andT4

are in ON state,vAFE= 0. (Fig. 4-d)).

The inductor voltage can be expressed as:

vL = Ldisdt

= vs(t)− kVo (1)

where k=1,-1 or 0.If k=1, then the inductor voltage will be negative, so the inputcurrentis will decrease its value.

P

a)

T1

T2

Vo LoadC

+

T3

N

vs

+ T4

is

vL

vAFE

b) c) d)

L

vs

+

is

Vo

C

P

N

vL

L

vs

+

is

vL

P

L

vs

+

is

Vo

C

N

vL

vAFE

vAFE

L

Fig. 4. Single-phase PWM rectifier in bridge connection. a) power circuit.Equivalent circuit with b)T1 andT4 ON; c) T2 andT3 ON ; d) T1 andT3

or T2 andT4 ON.

Voltage

Controller

Current

Controller

Vo ref +

-

Vo

+

-

isref

vs

T1,T

2

is

T3,T

4

Fig. 5. Control scheme of bridge PWM Rectifier.

If k=-1, then the inductor voltage will be positive, so the inputcurrentis will increase its value.Finally, if k=0 the input current increase or decrease its valuedepending ofvs. This allows for a complete control of theinput current.

b) Control scheme: The classical control scheme isshown in Fig. 5. The control includes a voltage controller,typically a Proportional-Integrative (PI) controller, which con-trols the amount of power required to maintain the DC-linkvoltage constant. The voltage controller delivers the amplitudeof the input current. For this reason, the voltage controlleroutput is multiplied by a sinusoidal signal with the samephase and frequency thanvs, in order to obtain the inputcurrent reference,isref. The fast current controller controls theinput current, so the high input power factor is achieved. Thiscontroller can be a hysteresis or a linear controller with aPWM-modulator [17].Fig. 6 shows the behavior of the output voltage and the input

current of the PWM rectifier in response to a step change inthe load. It can be observed that the voltage is controlled byincreasing the current, which keeps its sinusoidal waveformeven during transient states.As seen in Fig. 6, a ripple at twice of power supply frequency(2ωs) is present in the DC-link voltage. If this ripple passesthrow the voltage controller it will produce a third harmoniccomponent inisref. This harmonic can be reduced with a low-pass filter at the voltage measurement reducing the controllerbandwidth.Fig. 7 shows the behavior of voltage and current delivered by

the source. The input current is highly sinusoidal and keeps

3

40

60

80

100

120

140

160

-10

-5

0

5

10

1.46 1.48 1.5 1.52 1.54 1.56 1.58 1.6 1.62 1.64

-15

15

is

[A]VO

[V]

is

VO

Fig. 6. DC-link voltage and input current with 50% load step.

t

vs ,is v

s

is

Fig. 7. Waveform of the input current during normal operation.

in phase with the voltage, reaching a very high power factorof PF≈0.99.Fig. 8 presents the waveforms of voltage and current when

the rectifier works in the regeneration mode. Even in this case,the input current is highly sinusoidal.

3) The Voltage Doubler PWM Rectifier:a) Power circuit and working principle:Fig. 9 shows

the power circuit of the voltage doubler PWM rectifier. Thistopology uses only two power switchesT1 andT2, which areswitched complementary to control the DC-link voltage andthe input current, but requires two filter capacitorsC1 andC2.The voltage on each capacitor (VC1, VC2) must be higher than

t

vs , is

vs i

s

Fig. 8. Waveform of the input current during regeneration.

a)

b) c)

is L

vL

vs

+

T1

T2

V0Load

C1

C2v

AFE

L

C2

vL

vs

+

is

vAFEV

C1

L

C1

vL

vs

+

is

vAFE

VC1

VC2

VC2

Fig. 9. Single-phase PWM rectifier in voltage doubler connection: a) powercircuit; b) equivalent circuit with T1 ON; c) equivalent circuit withT2 ON.

the peak value ofvs to ensure the control of the input current.The possible combinations are:

i. SwitchT1 is in ON state⇒ vAFE = VC1, so the inductorvoltage is:

vL = Ldisdt

= vs(t)− VC1 < 0 (2)

asvL is negative, the input current will decrease its value.ii. SwitchT2 is in ON state⇒ vAFE = −VC2, so the inductor

voltage is:

vL = Ldisdt

= vs(t) + VC2 > 0 (3)

asvL is positive, the input current will increase its value.

Therefore the waveform of the input current can be controlledby switching appropriately transistorsT1 andT2 in a similarway as in the bridge connected PWM rectifier.

b) Control scheme:The control scheme for this topologyis almost the same than the control for the bridge connection asseen in Fig. 10. The most important difference is the necessityof a controller for voltage balance between both capacitors. Asimple P controller is used to achieve this balance [18].

Voltage

Controller

Current

Controller

Vo ref +

-

Vo

+

-

isref

vs

T1,T

2

Balance

Controller

Vo ref

2

+

-V

C2

+

+

is

Fig. 10. Control scheme of the voltage doubler PWM Rectifier.

B. Three-Phase Voltage-Source Rectifiers

1) Power circuit and working principle:It is well knownthat Voltage Source Inverters (VSI), like the one shown inFig. 11, can work in four quadrants. In two of these quadrants,the VSI works as a rectifier, that means, as a Voltage Source

4

VO

+a

b

c

AC SIDE

DC SIDE

PWM CONTROL

n

va

vc v

b

Fig. 11. Voltage Source PWM Inverter (VSI).

Control Block+

_

e

+

VoC

vx

DCload

IOidc

Three -Phase

PWM

VSR

Lx

Vo ref

Fig. 12. Operation principle of the VSR.

Rectifier or VSR. However, a stand-alone VSR requires a spe-cial DC bus able to keep a voltageVo without the requirementof a voltage supply. This is accomplished with a dc capacitorC and a feedback control loop.The basic operation principle of VSR consists on keeping

the load DC-link voltage at a desired reference value, using afeedback control loop as shown in Fig. 12 [19]. This referencevalueVo ref, has to be high enough to keep the diodes of theconverter blocked. Once this condition is satisfied, the DC-linkvoltage is measured and compared with the referenceVo ref.The error signal generated from this comparison is used toswitch ON and OFF the valves of the VSR. In this way,power can come or return to the AC source according withthe DC-link voltage value.When the DC load currentIo is positive (rectifier operation),

the capacitorC is being discharged, and the error signalbecomes positive. Under this condition, the Control Blocktakes power from the supply by generating the appropriatePWM signals for the six power transistor of the VSR. Inthis way, current flows from the AC to the DC side, and thecapacitor voltage is recovered. Inversely, whenIo becomesnegative (inverter operation), the capacitorC is overcharged,and the error signal asks the control to discharge the capacitorreturning power to the AC mains.The modulator switches the valves ON and OFF, followinga pre-established template. Particularly, this template couldbe a sinusoidal waveform of voltage (voltage source, voltagecontrolled PWM rectifier) or current (voltage source, currentcontrolled PWM rectifier). For example, for a voltage con-trolled rectifier, the modulation could be as the one shownin Fig. 13, which has a fundamental calledvx mod (see Fig.35), proportional to the amplitude of the template. There aremany methods of modulation [22], being the most popular the

0 0.005 0.01 0.015 0.02 0.025 0.03

0 0.005 0.01 0.015 0.02 0.025 0.03

0 0.005 0.01 0.015 0.02 0.025 0.03

0 0.005 0.01 0.015 0.02 0.025 0.03

-1

-0.5

0

0.5

1

-300

-200

-100

0

100

200

300

-600

-400

-200

0

200

400

600

-400

-300

-200

-100

0

100

200

300

400

V PWM an v

a)

V PWM ab

b)

V PWM an va mod

c)

a mod

d)

vtri

va mod

time [s]

Fig. 13. PWM phase voltages. a) triangular carrier and sinusoidal reference,b) PWM phase modulation, c) PWM phase-to-phase voltage, and d) PWMphase-to-neutral voltage.

so called Sinusoidal Pulse Width Modulation (SPWM), whichuses a triangular carrier (vtri) to generate the PWM patron.To make the rectifier work properly, the PWM pattern must

generate a fundamentalvx mod with the same frequency of thepower sourcevx. Changing the amplitude of this fundamental,and its phase-shift with respect to the mains, the rectifier canbe controlled to operate in the four quadrants: leading powerfactor rectifier, lagging power factor rectifier, leading powerfactor inverter, and lagging power factor inverter. Changingthe pattern of modulation, modifies the magnitude ofvx mod,and displacing the PWM pattern changes the phase-shift.The PWM control not only can manage the active power,but reactive power also, allowing the VSR to correct powerfactor. Besides, the AC current waveforms can be maintainedalmost sinusoidal, reducing harmonic contamination to themains supply.The interaction betweenvx mod and vx can be seen througha phasor diagram. This interaction permits to understand thefour-quadrant capability of this kind of rectifier. In Fig. 14,the following operations are displayed: a) rectifier at unitypower factor, b) inverter at unity power factor, c) capacitor(zero power factor), and d) inductor (zero power factor).CurrentIx in Fig. 14 is therms value of the source current

ix. This current flows through the semiconductors in the wayshown in Fig. 15. During the positive half cycle, transistorTN , connected at the negative side of the DC-link is switchedON, and currentix begins to flow throughTN (iTn). Thecurrent returns to the mains and comes back to the valves,

5

PWM Control Block+

_

e

+

V REF

VOC dc

load

v x LSix

Vx mod

a)

Ix V

Vx mod

jwd

Ix Vx

Vx mod

jwd

Ix Vx

Vx mod

jw

Vx mod

Vx

jw LSIx

vx ix

vx ix

vxix

vx ix

b)

e)

d)

c)

IOidc

IxLS

IxLS

IxLS

Ix

o

S

Fig. 14. Four-quadrant operation of the VSR. a) the PWM force commutatedrectifier, b) rectifier operation at unity power factor, c) inverter operation atunity power factor, d) capacitor operation at zero power factor, and e) inductoroperation at zero power factor.

closing a loop with another phase, and passing through adiode connected at the same negative terminal of the DC-link.The current can also go to the dc load (inversion) and returnthrough another transistor located at the positive terminalof the DC-link. When transistorTN is switched OFF, thecurrent path is interrupted, and the current begins to flowthrough diodeDP , connected at the positive terminal of theDC-link. This current, callediDp in Fig. 15, goes directly tothe DC-link, helping in the generation of currentidc, whichcharges capacitorC and permits the rectifier to produce dcpower. InductancesLs are very important in this process,because they generate an induced voltage which allows forthe conduction of diodeDP . Similar operation occurs duringthe negative half cycle, but withTP andDN . Under inverteroperation, the current paths are different because the currentsflowing through the transistors come mainly from the DCcapacitorC. Under rectifier operation, the circuit works likea Boost converter, and under inverter it works as a Buckconverter.

2) Control Scheme:a) Control of the DC-link voltage:The control of the

DC-link voltage requires a feedback control loop. As it wasalready explained in section II-B, the DC voltageVo iscompared with a referenceVo ref, and the error signal “e”obtained from this comparison is used to generate a templatewaveform. The template should be a sinusoidal waveform withthe same frequency of the mains supply. This template isused to produce the PWM pattern, and allows controlling the

LS

DC

load

IOTP

TN

DN

DP

iTn

iTp

iDn

++

-

VO C

iDp

idc

ix

ix

iTn

iDp

idc

t

vx

Fig. 15. Current waveforms through the mains, the valves, and the DC-link.

rectifier in two different ways: 1) as a voltage source currentcontrolled PWM rectifier, or 2) as a voltage source voltagecontrolled PWM rectifier. The first method controls the inputcurrent, and the second controls the magnitude and phase ofthe voltagevx mod. The current controlled method is simplerand more stable than the voltage-controlled method, and forthese reasons it will be explained first.

b) Voltage source current controlled PWM rectifier:This method of control is shown in the rectifier of Fig. 16.The control is achieved by measuring the instantaneous phasecurrents and forcing them to follow a sinusoidal currentreference template,Iref . The amplitude of the current referencetemplate,I, is evaluated using the following equation:

I = Gce = Gc(Vo ref − Vo) (4)

Where Gc is shown in Fig. 16, and represents a controllersuch as PI, P, Fuzzy or other. The sinusoidal waveform of thetemplate is obtained by multiplyingI with a sine function,with the same frequency of the mains, and with the desiredphase-shift angle, as shown in Fig. 16.However, one problem arises with the rectifier, because the

feedback control loop on the voltageVo can produce instability[20]. Then, it is necessary to analyze this problem duringthe design of the rectifier. According to stability criteria, andassuming a PI controller, the following relations are obtained:

Ix ≤ CVo

3KpLs(5)

Ix ≤ KpVx

2RKp + LsKi(6)

These two relations are useful for the design of the currentcontrolled VSR. They relate the values of DC-link capacitor,DC-link voltage, rms voltage supply, input resistance andinductance, and input power factor, with therms value of the

6

PWM generation

e

Vo

+LOAD

Synchr.GC

I

= Vsinwt

sin( wt+ j )

sin( wt+ j-120° )

sin( wt+ j-240° )

ia,b,c

Iref

+

_

ia

ic

X

X

X

A B C

LS R

ib

va

vc

vb

ia

ic

Vo ref

Fig. 16. Voltage source current controlled PWM rectifier

input current,Ix. With these relations the proportional andintegral gains,Kp andKi, can be calculated to ensure stabilityof the rectifier. These relations only establish limitations forrectifier operation, because negative currents always satisfy theinequalities.With these two stability limits satisfied, the rectifier will keepthe DC capacitor voltage at the value ofVo ref (PI controller),for all load conditions, by moving power from the AC to theDC side. Under inverter operation, the power will move in theopposite direction.Once the stability problems have been solved, and the si-nusoidal current template has been generated, a modulationmethod will be required to produce the PWM pattern forthe power valves. The PWM pattern will switch the powervalves to force the input currentsIx, to follow the desiredcurrent templateIref . There are many modulation methods inthe literature, but three methods for voltage source currentcontrolled rectifiers are the most widely used:PeriodicalSampling(PS),Hysteresis Band(HB), andTriangular Carrier(TC).

c) Voltage Source voltage controlled PWM rectifier:Fig. 17 shows a single-phase diagram from which the controlsystem for a voltage source voltage controlled rectifier isderived [21]. This diagram represents an equivalent circuitof the fundamentals, i.e, pure sinusoidal at the mains side,and pure DC at the DC-link side. The control is achievedby creating a sinusoidal voltage templatevx mod, which ismodified in amplitude and angle to interact with the mainsvoltage vx. In this way the input currents are controlledwithout measuring them. Voltagevx mod is generated using thedifferential equations that govern the rectifier.

From Fig. 17 the following differential equation can bederived:

vx(t) = Lsdixdt

+ Rix + vx mod(t) (7)

Assuming thatvx(t) = V sin(ωt + ϕ), then the solution forix(t), to get a voltagevx mod able to make the rectifier workat constant power factor should be of the form:

ix(t) = I(t) sin(ωt + ϕ) (8)

+LOADVo

idc

C

IO

LS R

ix(t)vx mod (t)v

x(t)

ac-dc

conversion

SOURCE RECTIFIER LOAD

Fig. 17. One-phase fundamental diagram of the voltage source rectifier.

PWM generation

e

VO

+

Vo ref

LOAD

Synchr .GC

I

= Vsinwt

cos (wt)

+

_

X -Xs

-R -sL sX

+

sin (wt)

Vsin (wt)

v mod a vmod b v mod c

idc IO

LS Ria

ic

ib

va

vc

vb

Fig. 18. Implementation of the voltage controlled rectifier for unity powerfactor operation.

Equations (7), (8), andvx(t) allow to get a function of timeable to modify vx mod in amplitude and phase, which willmake the rectifier work at fixed power factor. Combining theseequations withvx(t), yields:

vx mod =

[XsI sin ϕ +

(V −RI − Ls

dI

dt

)cos ϕ

]sin ωt

−[XsI cosϕ +

(RI + Ls

dI

dt− V

)sin ϕ

]cos ωt

(9)

This equation can also be written for unity power factoroperation. In such a casecos ϕ = 1, andsin ϕ = 0:

vx mod =

(V −RI − Ls

dI

dt

)sin ωt−XsI cos ωt (10)

The implementation of the voltage controlled rectifier for unitypower factor operation is shown in Fig. 18. It can be observedthat there is no need to sense the input currents. However,to ensure stability limits as good as the limits of the currentcontrolled rectifier of Fig. 16, blocks−R − sLs and −Xs

in Fig. 18, have to emulate and reproduce exactly the realvalues ofR, Xs andLs of the power circuit. However, theseparameters do not remain constant, and this fact affects thestability of this system, making it less stable than the systemshown in Fig. 16.

d) Space-Vector Control:Another point of view is tocontrol the three-phase VSR ind-q vector space. The input

7

va

vb

vc

vmod a

vmod b

vmod c

R Lsia

ib

ic

a)

Lsw is R is

is

vmod

vs

q

d

c)

vsvmodR Lsis

b)+

Fig. 19. Power circuit a) before transformation; b) after transformation. c)d-qspace vector quantities.

-

+

-

+

id

iq

-

+

iq ref

id refVo ref

VoModulator

T1

T2

T3

T4

T5

T6

VoltageController

iq Controller

id Controller

vmod d

vmod q

Fig. 20. Space-Vector control scheme.

currentsia, ib andic can be represented by a unique complexvector

−→i s = id + j iq, defined by:

[idiq

]=

23

[cos θ sin θ

− sin θ cos θ

] [1 − 1

2 − 12

0√

32 −

√3

2

]

iaibic

(11)whereθ = ωst.This transformation can be applied to

vmod =

vmoda

vmodb

vmodc

fundamental component of the VSR PWM voltages definedin II-B.1, and tovs = [va vb vc]′, where can be demonstratedthat the voltage vector obtained is−→v s = vd, and that the anglebetween

−→i s and−→v s correspond to the shift between the input

current and the input voltage of each phase.The power circuit obtained with this transformation and thecontrol scheme are presented in Figs. 19 and 20.The DC-link voltageVo is controlled by a PI regulator, whichprovides the value ofid ref, while iq ref is fixed to zero in orderto obtain power factor 1. These references are compared withthe input currents which are in d-q coordinates according to(11). Two controllers, typically PI, give the valuesvmodd andvmodq to be generated by the VSR.The gate drive pulses for the transistorsT1 . . . T6, can beobtained in two ways: transformingvmodd and vmodq to α-βvector space according to:

[vmodα

vmodβ

]=

[cos θ − sin θ

sin θ cos θ

][vmodd

vmodq

](12)

and aSpace Vector Modulation(SVM) scheme, or applyingthe complete inverse transformation:

vmoda

vmodb

vmodc

=

1 0− 1

2

√3

212 −

√3

2

[cos θ − sin θ

sin θ cos θ

] [vmodd

vmodq

]

(13)and using aSPWMas shown in Fig. 13.

III. PWM CURRENT SOURCERECTIFIERS

Current source rectifiers (CSRs) are the dual of voltagesource rectifiers (VSRs). In fact, they can produce identicalnormalized electrical variables for which equivalent gatingpatterns have been found. This task is performed by themodulating techniques that must ensure that all the specialrequirements of the topology are met. A general power topol-ogy and the control strategy and modulating technique blocksare depicted in Fig. 21.

A. Power circuit and working principle

The main objective of these static power converters is toproduce a controllable DC current waveform from the ACpower supply (see Fig. 21). Due to the fact that the resultingAC line currentsir = [ira irb irc]′ feature highdi/dt and theunavoidable inductive nature of the AC mains, a capacitivefilter should be placed in between. Thus, nearly sinusoidalsupply currentsis = [isa isb isc]′ are generated that justifies theuse of such topologies in medium-voltage adjustable speeddrives (ASDs), where high-quality waveforms are required.Due to the fact that the CSR can be modelled as a controllableDC current source, the natural load is a current source inverter(CSI) as in ASDs [23]. Additionally, the positive nature ofthe DC currentidc and the bipolarity of the DC voltageVo

constrains the type of power valves to unidirectional switcheswith reverse voltage block capability as in GTOs and therecently introduced IGCT [24].In order to properly gate the power switches of a three-phaseCSR topology, two main constraints must always be met: (a)the AC side is mainly capacitive, thus, it must not be short-circuited; this implies that, at most one top switch (S1, S3, orS5) and one bottom switch (S4, S6, or S2) should be closedat any time; and (b) the DC bus is of the current-source typeand thus it cannot be opened; therefore, there must be at leastone top switch and one bottom switch closed at all times,Fig. 21. Both constraints can be summarized by stating that atany time, only one top switch and one bottom switch must beclosed [25]. The constraints are reduced to nine valid states inthree-phase CSRs, where states 7, 8, and 9 (Table I) producezero AC line currents,ir. In this case, the DC-link currentfreewheels through either the switchesS1 andS4, S3 andS6,or S5 andS2.There are several modulating techniques that deal with thespecial requirements of the gating patterns of CSRs and canbe implemented online. Among them are: (a) the carrier-based; (b) the selective harmonic elimination; (c) the selectiveharmonic equalization, and (d) the space-vector technique.

8

TABLE I

VALID SWITCH STATES FOR ATHREE-PHASECSR.

State State ira irb irc

S1, S2 ON; S3, S4, S5, S6 OFF 1 iDC 0 −iDC

S2, S3 ON; S4, S5, S6, S1 OFF 2 0 iDC −iDC

S3, S4 ON; S5, S6, S1, S2 OFF 3 −iDC iDC 0

S4, S5 ON; S6, S1, S2, S3 OFF 4 −iDC 0 iDC

S5, S6 ON; S1, S2, S3, S4 OFF 5 0 −iDC iDC

S6, S1 ON; S2, S3, S4, S5 OFF 6 iDC −iDC 0

S1, S4 ON; S2, S3, S5, S6 OFF 7 0 0 0

S3, S6 ON; S1, S2, S4, S5 OFF 8 0 0 0

S5, S2 ON; S6, S1, S3, S4 OFF 9 0 0 0

dc

filter

V o

+

-

i dc

L dc

C r

v r

L r

input

filter

current source

rectifier load

a

b

c

S 1 S 3 S 5

S 4 S 6 S 2

i r v s i s

ac

supply

modulating technique

control strategy

i c

S i dc , i sq

state variables

Fig. 21. Three-phase CSR topology, modulation, and control.

B. Control Scheme

1) Modulating Techniques:The modulating techniques usea set of AC normalized current referencesic = [ica icb icc]′

that should be sinusoidal in order to obtain nearly sinusoidalsupply AC currents (is), as shown in Fig. 21. To simplifythe analysis, a constant DC-link current source is considered(iDC = IDC).

a) Carrier-based Techniques.:It has been shown thatcarrier-based PWM techniques that were initially developedfor three-phase voltage source inverters (VSIs) can be extendedto three-phase CSRs. In fact, the circuit detailed in [25] obtainsthe gating pattern for a CSR from the gating pattern developedfor a VSI. As a result, the normalized line current is identicalto the normalized line voltage in a VSI for similar carrierand modulating signals. Examples of such modulating signalsare the standard sinusoidal, sinusoidal with zero sequenceinjection, trapezoidal, and deadband waveforms.Fig. 22 shows the relevant waveforms if a triangular carrieritri

and sinusoidal modulating signalsic are used in combinationwith the gating pattern generator introduced in [25]. It canbe observed that the line current waveform (Fig. 22-c) is

180 270 90 360

ω t

i ca i tri i cc i cb

180 270 90 360

ω t 0

S 1 on

180 270

90 360 ω t

0

i r a i ra 1

i dc

15 7 3 19 23 31 27 11 5 1 9 13 17 21 29 25

i ra

f f s

0.8·0.866· i dc

a)

b)

c)

d)

Fig. 22. The three-phase CSR ideal waveforms for the SPWM: a) carrierand modulating signals; b) switchS1 state; c) AC current; d) AC currentspectrum.

identical to the obtained in three-phase VSIs, where a SPWMtechnique is used. This brings up the duality issue betweenboth topologies when similar modulation approaches are used.Therefore, for odd multiple of 3 values of the normalizedcarrier frequencymf , the harmonics in the AC current appearat normalized frequenciesfh centered aroundmf and itsmultiples, specifically, at

h = l ·mf ± k l = 1, 2, . . . (14)

where l = 1, 3, 5, . . . for k = 2, 4, 6, . . . and l = 2, 4, . . .for k = 1, 5, 7, . . . such thath is not a multiple of 3. Fornearly sinusoidal AC voltagesvr, the harmonics in the DC-linkvoltage ,Vo, are at normalized frequencies given by

h = l ·mf ± k ± 1 l = 1, 2, . . . (15)

where l = 0, 2, 4, . . . for k = 1, 5, 7, . . . and l = 1, 3, 5, . . .for k = 2, 4, 6, . . . such thath = lmf ± k is positive and nota multiple of 3. This analysis shows that for low switchingfrequencies very low unwanted harmonics will appear. This isa very undesired effect as in CSR there is a second order inputfilter and resonances could be obtained. This is why selectiveharmonic elimination is the preferred alternative as it allowsto specify the resulting spectra.

b) Selective Harmonic Elimination (SHE):This tech-nique deals directly with the gating patterns of the CSR. Itdefines the gating signals in order to eliminate some predefinedharmonics and control the fundamental amplitud of input

9

current ir. Under balanced conditions, the chopping anglesare calculated to eliminate only the harmonics at frequenciesh = 5, 7, 11, 13, . . . In [26] is proposed a direct method toobtain the angles to eliminate a given number of harmonics.However, just an even number of harmonics can be eliminated.On the other hand, [27] proposes to use single phase CSRsto form three-phase structures. This alternative alleviates theresulting non-linear equations to be solved; however, thenumber of power switches increases up to twice as comparedto the standard six-switches configuration. Also [28] proposesa method to eliminate an arbitrary number of harmonics, whilecontrolling the fundamental AC current component, by usingthe results obtained in VSIs [29]. Specifically, the generalexpressions to eliminateN − 1 (N − 1 = 2, 4, 6, . . . , even)harmonics are given by the following equations,

−N∑

k=1

(−1)k cos(nαk) =2 + mπ

4

−N∑

k=1

(−1)k cos(nαk) =12

for n = 5, 7, . . . 3N − 2

(16)

where α1, α2, . . . , αN should satisfyα1 < α2 < · · · <αN < π/2. Fig. 23-a shows the distribution ofα1, α2, andα3

to eliminate the 5th and 7th and Fig. 24 the values asa function of the desired fundamental AC current compo-nent. Similarly, the general expressions to eliminateN − 1(N − 1 = 3, 5, 7, . . ., odd) harmonics are,

−N∑

k=1

(−1)k cos(nαk) =2−mπ

4

−N∑

k=1

(−1)k cos(nαk) =12

for n = 5, 7, . . . 3N − 1

(17)

whereα1, α2, . . . , αN should satisfyα1 < α2 < · · · < αN <π/3.Fig. 23 shows that the line current does not contain the5th

and the7th harmonics as expected.The series/parallel connection of CSRs is used to improvethe quality of the waveforms by creating n-pulse converters[23],[30]. In fact, a delta-wye transformer naturally eliminatesthe 5th and 7th harmonics and, therefore, the first unwantedharmonics are the12th at the DC side and the11th and the13th at the AC side. The series/parallel connection increase thedegrees of freedom of the system, so modified SHE algorithmslike selective harmonic equalization presented in [31], can beused.

c) Space vector modulation (SVM):The objective isto generate PWM AC line currentsir that are on averageequal to the given referencesic. This is done digitally ineach sampling period by properly selecting the switch statesfrom the valid ones of the CSR (Table I) and the propercalculation of the period of times they are used. The selectionand time calculations are based upon the space-vector (SV)transformation [32]. The vector of line-modulating signalsiccan be represented by the complex vectorIc = [icα icβ ]′ by

S a 1

180 270 90 360

ω t 0

α 1 α 2 α 3

S 1

180 270 90 360

ω t 0

on

180 270

90 360 ω t

0

i ra

i ra 1 i dc

15 7 3 19 23 31 27 11 5 1 9 13 17 21 29 25

i ra

f f s

0.8· i dc

a)

b)

c)

d)

Fig. 23. Waveforms for the SHE technique in CSRs for5th and7th harmonicelimination: a) VSI gating pattern; b) CSR gating pattern; c) line currentira;d) spectrum of (c).

ra 1 / dc i

0 0.2 0.4 0.6 0.8 1.0 0˚

20˚

40˚

60˚

80˚

100˚

α 1

α 3

α 2

i

Fig. 24. Chopping angles for5th and 7th harmonic elimination andfundamental current control in three-phase CSRs.

10

θ

6

1 2

3

4 5

sector modulating vector I c

I 7,8,9

I 6

ω

state

α

β

I 3

I 2 = I i +1

I 1 = I i

I 4

I 5

1 ˆ c i

Fig. 25. The space-vector representation in CSIs.

means of,

icα =23

[ica − 0.5(icb + icc)] (18)

icβ =1√3(icb − icc) (19)

Similarly, the SV transformation is applied to the nine states ofthe CSR normalized with respect toiDC, which generates ninespace vectors (Ii, i = 1, 2, . . . , 9 in Fig. 25). As expected,I1to I6 are nonnull line current vectors andI7, I8, andI9 arenull line current vectors.If the modulating signal vectorIc is between the arbitrary

vectorsIi andIi+1, thenIi andIi+1 combined with one zeroSV (Iz = I7 or I8 or I9) should be used to generateIc. Toensure that the generated current in one sampling periodTs

(made up of the currents provided by the vectorsIi, Ii+1, andIz used during timesTi, Ti+1, andTz) is on average equal tothe vectorIc, the following expressions should hold,

Ti = Tsic sin(π

3− θ

)(20)

Ti+1 = Tsic sin(θ) (21)

Tz = Ts − Ti − Ti+1 (22)

where0 ≤ ic ≤ 1 is the length of the vectorIc. Although,the SVM technique selects the vectors to be used and theirrespective on-times, the sequence in which they are used, theselection of the zero space vector, and the normalized sampledfrequency remain undetermined. The sequence establishesthe symmetry of the resulting gating pulses and thus thedistribution of the current throughout the power switches.More importantly, the normalized sampling frequencyfsn

should be an integer multiple of 6 to minimize uncharacteristicharmonics by using evenly the active states of the converter,an important issue at low switching frequencies. Fig. 26 shows

180 270 90 360

ω t

i c α i c β

180 270 90 360

ω t 0

S 1 on

ω t

i ra i

15 7 3 19 23 31 27 11 5 1 9 13 17 21 29 25

i ra

f f s

0.8· i dc

180

270

90 360 0

ra 1 i dc

a)

b)

c)

d)

Fig. 26. Ideal waveforms for SV modulation: a) modulating signals; b)switch S1 state; c) AC current; d) AC current spectrum.

the relevant waveforms of a CSR SVM. It can be seen thatthe first set of relevant unwanted harmonics in the AC linecurrents are atfs.

2) Closed and/or open Loop Operation:The main objectiveof the CSR is to generate a controllable DC-link current.However, the modulating techniques provide three modulatingsignals that add up to zero; therefore, there are two degreesof freedom. This rises the issue of being possible to controlindependently two electrical quantities. Several papers haveproposed different control strategies; for instance, synchronouscompensation [33], [34], power factor correction [35], [36],active filtering [37], [38], and more importantly, as part ofan ASD [23], [39]. All of which control the DC link current(which could also be the active AC current component) andthe second is the reactive AC current component. If the controlsystem is synchronized with the AC mains and the setting ofthe desired reactive AC current component is adjusted to agiven: (a) DC value, synchronous compensation is obtained,(b) AC waveform, active filtering is obtained, (c) DC valueequal to zero, unity displacement power factor is obtained.

IV. A PPLICATIONS OFREGENERATIVE PWM RECTIFIERS

A. Single-phase PWM Voltage Source Rectifiers

1) The PWM Rectifier in Bridge Connection :a) Single-phase UPS:The distortion of the input current

in the line commutated rectifiers with capacitive filtering isparticularly critical in uninterruptible power supplies (UPS)

11

+

R

S

Input 1 φ 100 V

THY1

TR1

THY2

THY SW Inverter Converter

Output 1 φ 100 V

Fig. 27. Single-phase UPS with PWM rectifier.

vs

is

Id

Line + transformer 4-quad-converter DC - Link Inverter Motor

3~VO

Fig. 28. Typical power circuit of an AC drive for locomotive.

fed from motor-generator sets. In effect, due to the highervalue of the generator impedance, the current distortion canoriginate an unacceptable distortion on the AC voltage, whichaffects the behavior of the whole system. For this reason, inthis application, it is very attractive to use rectifiers with lowdistortion in the input current.Fig. 27 shows the power circuit of a single-phase UPS, whichhas a PWM rectifier in bridge connection at the input side.This rectifier generates a sinusoidal input current and controlsthe charge of the battery [43], [44].

b) AC drive for locomotive:One of the most typicaland widely accepted areas of application of high power factorsingle-phase rectifiers is in locomotive drives [40]. In effect,an essential prerequisite for proper operation of voltage sourcethree-phase inverter drives in modern locomotives is the useof four quadrant line-side converters, which ensures motoringand braking of the drive, with reduced harmonics in the inputcurrent. Fig. 28 shows a simplified power circuit of a typicaldrive for a locomotive connected to a single-phase powersupply [41], which includes a high power factor rectifier atthe input.Fig. 29 shows the main circuit diagram of the 300 series

Shinkansen train [42]. In this application, AC power fromthe overhead catenary is transmitted through a transformer tosingle-phase PWM rectifiers, which provide the DC voltagefor the inverters. The rectifiers are capable of controllingthe input AC current in an approximate sine wave form andin phase with the voltage, achieving power factor close tounity on powering and on regenerative braking. Regenerativebraking produces energy savings and an important operationalflexibility.

2) The Voltage Doubler PWM Rectifier:a) Low-cost induction motor drive:The development of

low-cost compact motor drive systems is a very relevant topic,particularly in the low-power range. Fig. 30 shows a lowcost converter for low power induction motor drives. In this

PWM

CONVERTER SMOOTHING CAPACITOR

PWM INVERTER

OVERHEAD

CATENARY

TR

AN

SF

OR

ME

R

INDUCTION

MOTORS

GTO THYRISTOR

Fig. 29. Main circuit diagram of 300 series Shinkansen locomotives.

vs

+

+

-

+

-

C1

M0

C2

T1

T3

T5

T2

T4

T6

Fig. 30. Low-cost induction motor drive.

configuration a three-phase induction motor is fed throughthe converter from a single-phase power supply. TransistorsT1, T2 and capacitorsC1, C2 constitute the voltage-doublersingle-phase rectifier, which controls the DC-link voltage andgenerates sinusoidal input current, working with close-to-unitypower factor [44]. On the other hand, transistorsT3, T4, T5 andT6 and capacitorsC1 and C2 constitute the power circuit ofan asymmetric inverter that supplies the motor. An importantcharacteristic of the power circuit shown in Fig. 30 is thecapability to regenerate power to the single-phase mains.

b) UPS: Another common application for doubler-voltage rectifier is in low cost UPS system as described in[45]. The number of power switches can be decreased fromeight to four, as shown in Fig. 31.

B. Three-phase PWM Voltage Source Rectifiers

One of the most important applications of VSR is inmachine drives. Fig. 32 shows a typical frequency converterwith a force-commutated rectifier-inverter link. The rectifierside controls the input current and the DC-link, and the inverter

12

Vo

Rectifier Inverter

vs

is

Output100 V

Input100 V

T1

T2

Q1

Q2

Fig. 31. UPS with doubler-voltage rectifier.

CONTROLCONTROL

+

_

e

Vo

+

Vo ref

Fig. 32. Frequency converter with force commutated rectifier.

side controls the machine. The machine can be a synchronous,brushless DC, or induction machine. The reversal of speedand reversal of power are possible with this topology. At therectifier side, the power factor can be controlled, and even withan inductive load such as an induction machine, the sourcecan “see” the load as capacitive or resistive. The inverterwill become a rectifier during regenerative braking, which ispossible making slip negative in an induction machine, ormaking torque angle negative in synchronous and brushlessDC machines.

A variation of the drive of Fig. 32 is found in electrictraction applications. Battery powered vehicles use the inverteras rectifier during regenerative braking, and sometimes theinverter is also used as battery charger. In this case, the rectifiercan be fed by a single-phase or by a three-phase system.Fig. 33 shows a battery powered electric bus system. Thissystem uses the power inverter of the traction motor as rectifierfor two purposes: regenerative braking, and battery charger fedby a three-phase power source.Another application of VSR is in power generation. Power

generation at 50 or 60 Hz normally requires constant speedsynchronous machines. Besides, induction machines are notcurrently used in power plants because of magnetization

TRACTION

MOTOR

POWER

SOURCE

bc

a

CONTROL

BATTERY

PACK

+

_

POWER CONVERTER

(INVERTER RECTIFIER)

POWER

TRANSFORMER

SOFT START

FILTRES AND

SENSORS

DRIVING CHARGING

ELECTRONIC SWITCH

SELECTOR

Fig. 33. Electric bus system with regenerative braking and battery charger.

SLIP CONTROLWIND GENERATOR

MAINS

VO CONTROL

VO

Vo ref e

Fig. 34. Variable-speed constant-frequency wind generator.

problems. Using frequency-link force-commutated converters,variable-speed constant-frequency generation becomes pos-sible, even with induction generators. The power plant ofFig. 34 shows a wind generator implemented with an inductionmachine, and a rectifier-inverter frequency link connected tothe utility. The DC-link voltage is kept constant with theconverter located at the mains side. The converter connected atthe machine side controls the slip of the generator and adjustsit according with the speed of wind or power requirements.The utility is not affected by the power factor of the generator,because the two converters keep thecosϕ of the machineindependent of the mains supply. The last one can evenbe adjusted to operate at leading power factor. The sameconfiguration also works with synchronous machines.All the VSR above described, can also be implemented with

three-level converters [46], being the most popular the topol-ogy called diode clamped converter, which is shown in Fig. 35.The control strategy is essentially the same already described.This back to back three-phase topology is today the standardsolution for high power laminators, which typically demandfour quadrants operation [47]. In addition, this solution hasbeen recently introduced in high power downhill conveyorbelts which operate almost permanently in the regenerationmode [48].

C. Three-phase PWM Current Source Rectifiers

In commercial ASDs as the one shown in Fig. 36, the CSRhas the role of keeping the DC-link current equal to a referencewhile keeping unity displacement power factor. Normally, anexternal control loop, based on the speed of the drive, setsit [23], [39]. The commercial units for medium voltage andMW applications use a high performance front end rectifierbased on two series connected CSRs, as shown in Fig. 37.The use of a delta/way transformer naturally eliminates the5th, 7th, 17th, 19th, ..., 6(2q + 1)± 1 current harmonics at theAC mains. This allows the overall topology to comply withthe harmonic standards in electrical facilities, an importantissue in medium voltage applications. To control the DC-linkcurrent, the gating pattern is modulated preferable by means ofthe SHE technique. Thus, the pattern could eliminate the11th,13th, . . . and control the fundamental current component whichin turns controls the DC-link current. Additional advantagesof this ASD is the natural regeneration capability as theCSRs can reverse the DC-link voltage allowing the sustainedpower flow from the load into the AC mains. Finally, dueto the capacitive filter at the motor side, the motor voltagesand consequently the currents become nearly sinusoidal. Thisreduces the pulsating torques and the currents trough the

13

Vo IM

Fig. 35. Three-level Voltage Source Rectifier feeding a three-level Voltage Source Inverter.

ac

Mains

DC

Link

PWM

CSI

Output

FilterLoad

Vo

+

-

IM

Ci

imvlil

idc

Ldc

Cr

vrisvs

Lr

PWM

CSR

Input

Filter

ir

Fig. 36. ASD based on a current source DC-link.

ac

Mains

DC

Link

PWM

CSI

Output

FilterLoad

Vo

+

-

IM

Ci

imvlil

idc

Ldc

isvs

PWM

CSRs

Input

Transformer

CSR 1

CSR 2

Fig. 37. High power CSI with two series connected SCR.

neutral. These are two important considerations in mediumvoltage electrical machines.

V. CONCLUSIONS

This paper has reviewed the most important topologiesand control schemes used to obtain AC-DC conversion withbidirectional power flow and very high power factor.Voltage source PWM regenerative rectifiers have shown atremendous development from single-phase low power sup-plies up to high power multilevel units.Current source PWM regenerative rectifiers are conceptually

possible and with few applications in DC motor drives. Themain field of application of this topology is the line sideconverter of medium voltage current source inverters.Especially relevant is to mention that single-phase PWM re-generative rectifiers are today the standard solution in modernAC locomotives.The control methods developed for this application allow foran effective control of input and output voltage and currents,minimizing the size of energy storage elements.This technology has approximately three decades of sustainedtheoretical and technological development and it can be con-

14

cluded that these high performance rectifiers comply withmodern standards and have been widely accepted in industry.

REFERENCES

[1] N. Mohan, T. Undeland, W. Robbins,“Power Electronics: ConvertersApplications and Design,”Wiley Text Books, Third Edition, 2002,ISBN: 0471226939.

[2] A. Trzynadlowski“Introduction to Modern Power Electronics,”Wiley-Interscience, First Edition, 1998, ISBN: 0471153036.

[3] J. Arrillaga, N. Watson “Power System Harmonics,” John Wiley & Sons.Inc, Second Edition, 2003, ISBN: 0470851295.

[4] D. Paice“Power Electronic Converter Harmonics - Multipulse Meth-ods for Clean Power,” IEEE Press, Second Edition, 1996, ISBN:078031137X.

[5] “IEEE 519 Recommended practices and requirements for harmonicscontrol in electrical power systems,”Technichal Report, IEEE IndustrialApplications Society/Power Engineering Society, 1993.

[6] Limits for Harmonics Current Emissions (Equipment InputCurrent<16A per Phase), IEC 1000-3-2 International Standard,1995.

[7] Limits for Harmonic Current Emissions (Equipment Input Current up toand Including 16 A per Phase), IEC 61000-3-2 International Standard,2000.

[8] H. Akagi, Y. Tsukamoto, A. Nabae “Analysis and Design of an ActivePower Filter Quad-Series Voltage Source PWM Converters,”IEEETransactions on Industrial Electronics, Vol. 26, No 1, pp. 93-98, Feb.1990.

[9] F. Z. Peng, H. Akagi, A. Nabae “A New Approach to HarmonicCompensation in Power System - A Combines System of Shunt Passiveand Series Active Filters,”IEEE Transactions on Industrial Electronics,Vol. 26, No 6, pp. 983-990, Dec. 1990.

[10] H. Akagi, H. Fujita “New Power Line Conditioner for Harmonic Com-pensation in Power Systems,”IEEE Transactions on Power Delivery,Vol. 10, No 3, pp. 1570-1575, Jul. 1995.

[11] B. Singh, B. N. Singh, A. Chandra, K. Al-Hadad, A. Pandey, D.Kothari “A Review of Single-Phase Improved Power Quality AC-DCConverters,”IEEE Transactions on Industrial Electronics, Vol. 50, No5, pp. 962-981, Oct. 2003.

[12] O. Garcıa, J. Cobos, R. Prieto, P. Alou J. Uceda “Single Phase PowerFactor Correction: A Survey,”IEEE Transactions on Power Electronics,Vol. 18, No 3, pp. 749-755, May 2003.

[13] A. R. Prasad, P. Ziogas, S. Manias “An Active Power Factor CorrectionTechnique for Three-Phase Diode Rectifiers,”IEEE Transactions onPower Electronics, Vol. 6, No 1, pp. 83-92, Jan. 1991.

[14] J. Kolar, F. Zach “A Novel Three-Phase Utility Interface MinimizingLine Current Harmonics of High-Power Telecomunications RectifierModules,” Record of the 16th IEEE International TelecommunicationsEnergy Conference, Vancouver, Canada, pp. 367-374, Oct. 30-Nov. 31994.

[15] J. Kolar, U. Drofenik, F. Zach “Space Vector Based Analysis of theVariation and Control of the Neutral Point Potential of HysteresisCurrent Controlled Three-Phase/Switch/Level PWM Rectifier System,”Proceedings of the International Conference on Power Electronics andDrive Systems, Singapore, Vol. 1, pp.22-33, Feb.21-24 1995.

[16] O. Stihi, B. Ooi “A Single-Phase Controlled-Current PWM Rectifier,”IEEE Transactions on Power Electronics, Vol. 3, N 4, pp. 453-459, Oct.1988.

[17] J. Rodrıguez, L. Moran, J. Pontt, J. Hernandez, L. Silva, C. Silva, P.Lezana “High-Voltage Multilevel Converter With Regeneration Capa-bility,” IEEE Transactions on Industrial Electronics, Vol. 49, No 4, pp.839-846, Aug. 2002.

[18] Y. Lo, T. Song, H, Chiu “Analysis and Elimination of Voltage ImbalanceBetween the Split Capacitors in Half-Bridge Boost Rectifier,”Letters toEditor, IEEE Transaction on Industrial Electronics, Vol. 49, No 5, Oct.2002.

[19] J. W. Dixon, “Three-Phase Controlled Rectifiers,”Handbook of PowerElectronics, Chapter 12, M. H. Rashid, Editor in Chief, Academic Press,pp-599-627, 2001.

[20] B. T. Ooi, J. W. Dixon, A. B. Kulkarni, and M. Nishimoto, “Anintegrated AC Drive System Using a Controlled-Current PWM Rec-tifier/Inverter Link,” IEEE Transactions on Power Electronics, Vol. 3, N1, pp. 64-71, Jan. 1988.

[21] J. W. Dixon and B. T. Ooi, “Indirect Current Control of a Unity PowerFactor Sinusoidal Current Boost Type Three-Phase Rectifier,”IEEETransactions on Industrial Electronics, Vol. 35, N 4, pp.508-515, Nov.1988.

[22] M. A. Boost and P. Ziogas, “State-of-the-Art PWM Techniques, aCritical Evaluation,”IEEE Transactions on Industry Applications, Vol.24, N 2, pp. 271-280, Mar. 1988.

[23] J. Rodrıguez, L. Moran, J. Pontt, R. Osorio and, S. Kouro, “Modelingand Analysis of Common-Mode Voltages Generated in Medium VoltagePWM-CSI Drives,” IEEE Transactions on Power Electronics, vol. 18,No 3, pp. 873-879, May. 2003.

[24] A. Weber, T. Dalibor, P. Kern, B. Oedegard, J. Waldmeyer, and E.Carroll, “Reverse Blocking IGCTs for Current Source Inverters,”ABBSemiconductors AGin PCIM 2000.

[25] J. Espinoza and G. Joos. “Current Source Converter On-Line PatternGenerator Switching Frequency Minimization,”IEEE Transactions In-dustrial Electronics, vol. 44, No 2, pp. 198-206, Apr. 1997.

[26] H. Karshenas, H. Kojori, and S. Dewan, “Generalized techniques ofselective harmonic elimination and current control in current sourceinverters/converters,”IEEE Transactions on Power Electronics, vol. 10,No 5, pp. 566-573, Sept. 1995.

[27] D. Sharon, and F.W. Fuchs, “Switched Link PWM Current SourceConverters with Harmonic Elimination at the Mains,”IEEE Transactionson Power Electronics, vol. 15, No 2, pp. 231-241, Mar. 2000.

[28] J. Espinoza, G. Joos, J. Guzman, L. Moran, and R. Burgos, “Selectiveharmonic elimination and current/voltage control in current/voltagesource topologies: A unified approach,”IEEE Transactions IndustrialElectronics, vol. 48, No 1, pp. 71-81, Feb. 2001.

[29] P. Enjeti, P. Ziogas, and J. Lindsay, “Programmed PWM technique toeliminate harmonics: A critical evaluation,”IEEE Transactions Indus-trial Applications, vol. 26, No 2, pp. 302-316, Mar. 1990.

[30] K. Imaie, O. Tsukamoto, and Y. Nagai, “Control Strategies for MultipleParallel Current-Source Converters of SMES System,”IEEE Transac-tions on Power Electronics, vol. 15, No 2, pp. 377-385, March 2000.

[31] J. Guzman, J. Espinoza, and M. Perez, “Improved performance of multi-pulse current and voltage source converters by means of a modified SHEmodulation technique,”in Conference RecordsIECON’02.

[32] M. Salo and H. Tuusa, “A Vector Controlled Current-Source PWMRectifier with a Novel Current Damping Method,”IEEE Transactionson Power Electronics, vol. 15, No 3, pp. 464-470, May. 2000.

[33] B. Han, S. Moon, J. Park, and G. Karady, “Static Synchronous Compen-sator Using Thyristor PWM Current Source Inverter,”IEEE Transactionson Power Delivery, vol. 15, No 4, pp. 1285-1290, October 2000.

[34] D. Shen and P.W. Lehn, “Modeling, Analysis, and Control of a Cur-rent Source Inverter-Based STATCOM,” IEEE Transactions on PowerDelivery, vol. 17, No 1, pp. 248-253, Jan. 2002.

[35] Y. Xiao, B. Wu, S. Rizzo, and R. Sotudeh,, “A Novel Power FactorControl Scheme for High-Power GTO Current-Source Converter,”IEEETransactions on Industry Applications, vol. 34, No 6, pp. 1278-1283,Dic. 1998.

[36] J. Espinoza and G. Joos, “State variable decoupling and power flowcontrol in PWM current source rectifiers,”IEEE Transactions IndustrialElectronics, vol. 45, No 1, pp. 78-87, Feb. 1998.

[37] M. Salo and H. Tuusa, “A Novel Open-Loop Control Method for aCurrent-Source Active Power Filter,”IEEE Transactions on IndustrialElectronics, vol. 50, No 2, pp. 313-321, Apr. 2003.

[38] R.E. Shatshat, M. Kazerani, and M. Salama, “Multi Converter Approachto Active Power Filtering Using Current Source Converters,”IEEETransactions on Power Delivery, vol. 16, No 1, pp. 38-45, Jan. 2001.

[39] N. Zargari; S. Rizzo; Y. Xiao, H. Iwamoto; K. Satoh, J. Donlon, “A newcurrent-source converter using a symmetric gate-commutated thyristor(SGCT),” IEEE Transactions on Industry Applications, vol. 37, No 3,pp. 896 - 903, May-June 2001.

[40] K. Hirachi, H. Yamamoto, T. Matsui, S. Watanabe, M. Nakaoka, “Cost-Effective Practical Developments of High-Performance 1kVA UPS withNew System Configurations and their Specific Control Implementa-tions,” European Conference on Power Electronics EPE 95, Spain 1995,pp. 2035-2040.

[41] K. Huckelheim, Ch. Mangold, “Novel 4-Quadrant Converter ControlMethod,”European Conference on Power Electronics EPE 89, Germany1989, pp. 573-576.

[42] T. Ohmae, K. Nakamura, “Hitachi’s Role in the Area of Power Elec-tronics for Transportation,”Proceedings of the IECON’93. Hawai, pp.714-718, Nov. 1993.

[43] P. Enjeti, A. Rahman “A New Single-Phase to Three-Phase Converterwith Active Input Current Shaping for Low Cost AC Motor Drives,”IEEE Transactions on Industry Applications, Vol. 29, No 4., pp. 806-813, Aug 1993.

[44] C. Jacobina, M. Beltrao, E. Cabral, A. Nogueira, “Induction Motor DriveSystem for Low-Power Applications,”IEEE Transactions on IndustryApplications, Vol. 35, No 1. pp. 52-60, Jan/Feb 1999.

15

[45] T. Uematsu, T. Ikeda, N. Hirao, S, Totsuka, T. Ninomiya, H. Kawamoto“A Study of the High Performance Single Phase UPS,”Record of the29th Annual IEEE Power Electronics Specialists Conference, PESC’98,Fukuoka, Japan, pp. 1872-1878.

[46] A. Draou, M. Benghanem and A. Tahri, “Multilevel Converters andVAR Compensation,” Chapter 25,Handbook of Power Electronics, M.H. Rashid, Editor in Chief, Academic Press, pp-599-627, 2001.

[47] M. Koyama, Y. Shimomura, H. Yamaguchi, M. Mukunoki, H. Okayamaand S. Mizoguchi, “Large capacity High Efficiency Three-Level GCTInverter System for Steel Rolling Mill Drivers,”Proceedings of the9th

European Conference on Power Electronics, EPE 2001, Austria, CD-ROM.

[48] J. Rodrıguez, J. Pontt, N. Becker, A. Weinstein, “Regenerative Driversin the Megawatt Range for High-Performance Downhill Conveyors,”IEEE Transactions on Industry Applications, Vol. 38, No 1, pp. 203-210, Jan/Feb 2002.

PLACEPHOTOHERE

Jose Rodrıguez

PLACEPHOTOHERE

Juan Dixon

PLACEPHOTOHERE

Jose Espinoza

PLACEPHOTOHERE

Pablo Lezana