IEEETRANSACTIONS ONINDUSTRYAPPLICATIONS, VOL. IA-21, NO. 6,NOVEMBER/DECEMBER1985
Three-Phase Regenerative Converter with Controlled Flywheeling
SUBBANNA P. BHATAND GOPAL K. DUBEY, SENIOR MEMBER, IEEE Abstract-The low-speed performanceofa dc drive can beimproved
by operating the three-phase fully controlled bridge converter with controlled flywheeling. The analysisand performanceof the drive with controlled flywheeling is described. The modes of operation of the converter system areidentified, and a method of performance calcula- tion, taking these modes of operation into account, is presented.
Nomogramsandtheanalytical methodofcalculatingthem arepresented for thecalculation of optimumvalue offilterinductance. Theperform- anceof thedrive with controlled flywheelingiscomparedwith that with conventional control. Themodes ofoperationand certain aspects of drive performanceareverified experimentally.
I. INTRODUCTION
HREE-PHASE fully controlled converters are widely used in medium-power dc drives. The performance of suchadrive in the converter outputvoltagerange (0.5 > E,,,
> -0.5) can be improved by incorporating controlled flywheeling
[11,
[21. In this paper, various aspects of three- phase convertersystememploying controlled flywheelingand feedingaseparately exciteddc motor are studied. Thevarious modes of converteroperationare identified, andtheiroscillo- grams are presented. The drive is analyzed using digital simulation, and various performance characteristics are ob- tained fora2.2-kW motor. Nomogramsarepresented for the controlled flywheeling and the normal control techniques, from which a filter inductance can be calculated for any dc separately excited motor. The various parameters of the system performance with the controlled flywheeling are comparedwiththose withthe normalcontroltechnique for the same developed power. The modes ofoperation and certain aspects of thedriveperformance are verifiedexperimentally.II. MODESOF CONVERTER OPERATION
Fig. 1 shows the three-phase converter system and its equivalent circuit. Since the controlled flywheeling is possible onlyina restricted range ofthe outputvoltage(0.5 > E,,, >
-0.5), the system operation is broadly
classified
into four modes of system operation which arelisted inTable I.In the case of dc motor load, if the armature current is discontinuous, the waveform of converter output voltage dependsnotonlyonthefiring anglebut alsoonthemotorback
PaperIPCSD 85-01 and83-29, approved by theStatic Power Converter Committee of the IEEE Industry Applications Societyforpublication inthis TRANSACTIONS. Manuscriptreleased forpublicationJanuary 21, 1985.
S. P. Bhat is with the Department of Electrical Engineering, Karnataka RegionalEngineering College, P.O. Srinivasnagar-574 157, DakshinaKan- nada District,KarnatakaState, India.
G.K.DubeywaswiththeDepartment of ElectricalEngineering, Virginia Polytechnic Institute,Blacksburg, VA24061.Heisnowwith the Department ofElectrical Engineering, Indian InstituteofTechnology, Kanpur, 208016, India.
Ia
(a) (b)
Fig. 1. Three-phaseconverterfeedingdc motor. (a)Three-phaseconverter system.(b)Equivalentcircuit.
TABLEI
Modeof Rangeof Range of
System System Firing Angle, Flywheeling
Operation Condition a,P Angle, a,,
I motoring 0 < ap < 7r/3
II motoring 7r/3 < ap< 27r/3 an = 0 Hli regeneration ap = (2ir/3 - 5) 0 < ax, < 7r/3 IV regenerating - 7r/3 < a,n < 27r/3
TABLEII
Mode of Mode of Nature of Relationship Refer to Converter System System Armature Between a, Figure Operation Conditiona Operation Currentb ,B, and -y Number
1 M I D ap< ,p <-yp 2(a)
2 M I D .<cap < -yp 2(b)
3 M I D ,p <-yp < ap 2(c)
4 M I C - 2(d)
5 M II D ,(p,rr3< < ap 2(e)
6 M II D r/3 < ,p< ap 2(f)
7 M II C - 2(g)
8 R III D On < an<TYn 2(h)
9 R III C - 2(i)
10 R IV D (3n < On <'Yn 2(j)
11 R IV D n <Eyn <a,n 2(k)
12 R IV C - 2(1)
aM = motoring, R = regenerating.
bD = discontinuous, C = continuous.
EMF. In such cases, the actual waveshape depends upon the relative magnitudes of
a,p, ,p,
andyp
(or t,,3,,,
and-y,).
Depending upon the waveshape of output voltage, the con- verter operation is classified into various modes which are listed in Table II and Fig. 2. A total of 12 modes areidentified, amongwhich modes 1-4 and 10-12 are commonfor boththe controlled flywheeling and the normal control techniques. A briefdescription of all the modes is given asfollows.
Four modes of continuousarmature currentexist(modes4, 0093-9994/85/1100-1431$01.00 © 1985 IEEE
1431
----40iac
16Ti12 T3 T4 T5T
T55 T5 $; Tj T1 | T3 T3 |i T5
1T61T6 1T2T 2 1 4 T4
=.s s>
'. /7/ /_'/ 7=\ \/
OIp/2!,=k (a)27J
cXp 13P-.pJ
14 T6 T6 T2 T2 T4 TL
e, iac
t/ // 7/ 7\ /Z
Tr 27T
(c)
T4 16T6 2 121 14
el ia 9S>
/ I
O flp'ap 7T 27T
(e)
Ti 15 T3 Ti |T T3
T4
T12
T61141
T2 1161 14< Q/ /X / /_
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(g)
T5 Tj Ti 3 T3 T5
T6 16 T' Tj2 T,_ __I Tz
Eb
/\ A c// 7
A7 / /t,
i. ~ ~ ~ ~~~TT2nT
~ ~p ~ (
T5 T 1 I T5
T4 16 T2 T.4
a/'~~~~==,7\7'/\ 'u 7
0 (Xp 77 27
(d)
TF T2 T3 T4 15 T6
T5~~1~jf Ti Ti, 13 ~ 1
14 16 Tr, 12 1 4
e, _ ~~~~-76a / / _ -','
/, ,g /a /t,
\ / \ ,''>Eb- -/
/ / /r / 2
(1)
sTIT5 13 g 13 T1TJ
T6 T4112 T2T
fin Cen --
ei(
eI,
T1 IT51
T3T
T5IT3I
16
1141
T2 T6 T4 T1 T6e0 a R17r
7X\2./ I' ' '\,.'
N'CBz
,=AB_K._
AC>' _BC ,/XN84,"" CA7- (i)Eb 12
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(h)
Onn ;
V\B /\ 2CBjr7
n / C , , 7X
\ 'I \f \ /
'I 7 \ 7/ \ \/
Ebt
(h)
Fig.2. Modesofconverteroperation. (a)Mode 1.(b)Mode2.(c)Mode 3.
(d)Mode 4.(e)Mode 5.(f)Mode6.(g)Mode 7.(h)Mode8.(i)Mode 9.
(j)Mode 10.(k)Mode 11 (1)Mode 12.
F7r
BHAT ANDDUBEY: THREE-PHASE REGENERATIVE CONVERTER
T5 T6 T1 T2 T3 T4
16 '16 12 T2 14 T,
Oin (n
lXn/[
e, ci \ /'<<,>
/ AX / ~\/o@ \/ 5/ \X \/t
E(
(k)
12 14 5
T6 T2
I
T T60\- ,A\A - , ',A2Az7
e / /\(n /\
Eb /
(1) Fig. 2. (Continued).
7, 9, and 12), one for each of the four modes of system operation (Fig. 2(d), (g), (i), and (1)). In these modes, the conductionofincomingthyristorsandthecommutation of the already conducting thyristors occur
simultaneously by
virtue of line commutation.Inthecase ofmode 1
(Fig.
2(a)), when thethyristorT,
is triggeredatotp,
thearmature currentisnonzero,and therefore T5 gets line commutated byTi.
(Symbols are defined in the Nomenclatureattheendof thepaper.) Since the instantaneous supply voltage is lessthanthemotorbackEMF, thearmature.current further reduces until it becomes zero. Since all the thyristors are supplied with the extendedgate pulses,
T,
and T6regainconduction at-yp,
when thesupply voltage becomes larger thanthe motor backEMF.In the case of mode 2 (Fig. 2(b)), at the instant
a,p
the armature current has already become zero, and the supply voltage is smaller than the motor back EMF. Therefore, thyristors T1 and T6comeintoconductiononlyat-yp.
Mode 3 (Fig. 2(c)) is different fromtheearliermodes in the sense that atthe instantap,
the supply voltage is larger than the motor backEMF. Therefore, the thyristors comeinto conductionas soon asthey aretriggered.
Inthe case of modes 1 and 3,adecrease in the motor back EMFconvertsthese modesinto mode4, whereasin thecaseof mode2,adecrease inthemotorback EMF makes both
p,B
and'yp
approach the triggering instantap.
Depending upon the magnitudeofa1p,
the decrease in motorbackEMFwould bring about thecondition ofeither(p
=cxp
< y, or,,p
< ap = yp.Inthe former case, mode 2 convertsitselfto mode 1 and in the lattercase tomode 3. Another remotepossibility is thatboth
p,,
and yp would touchcap
simultaneously. Inthat case, mode2directly
changes over to mode 4. A flowchart of the interrelationshipofthe variousmodesisgiven in Fig. 3. When mode 1 touches mode 4, the minimum of armaturecurrent
occurs atX = -yp >
ap,
andwhen mode 3touches mode 4, at X =ap
>-yp.
This information, which isuseful
for the calculationofmaximumarmaturecurrentripple, is also noted in Fig. 3.Modes 5-7 (Fig. 2(e)-(g)) belong to the second group (systemoperationmode
II).
Inthecase of modes 5 and 6, the armaturecurrent isdiscontinuous. Inthe caseof mode 6, the outputvoltagebecomeszero at 7r/3 (due to the flywheeling of theload)andremainssountilp,,,
whereasin the case of mode 5, the output voltage never becomes zero(,Bp
<cr/3).
However,if the motorbackEMF isreduced, mode 5 becomes mode 6 and finally mode 7 (Fig. 3(b)). Note that mode 5 is
(a)
(c)
(b)
(n (d)
Fig. 3. Flowchart ofconverteroperation. (a)System mode I. (b) System mode H. (c) Systemmode Ill. (d) System mode IV. Arrow indicates increase inIa,
similartomode3, exceptthattheybelongtodifferent modes ofsystemoperation.
Modes 8 and 9(Fig. 2(h)and(i)and
Fig. 3(c)) belong
tothe third group (system operation mode III). In this case, the systemis underregeneration, and theflywheeling
of the load occursfor certain duration.Modes 10-12(Fig. 2(j)-(1)) belongtothe last group. There are two modes of discontinuous armature current (modes 10 and 11). In the case of mode 11, the armature current has becomezero atA,,butat y,,whenthesupply voltagebecomes more positive than the generated EMF, the same set of thyristors
(TI
and T6) regain conduction. Ata,,,
thyristor T2 line commutates T6. An increase in the generated EMF converts mode 11 to mode 12. In the case ofmode 10(a,,
<ey,),
if the generated EMF is increased, y, approachesa,,.
Depending upon the magnitude of
a,,,
mode 10 may either becomemode 11 ordirectly changeover tomode 12. If mode 10 directly changes over to mode 12, the armature current assumes a minimum value ata,,
On the other hand, when mode 11 changes overto mode 12, itoccursat X = ay, <a,,
A flowchartofthemodes belonging tothis group is given in Fig.
3(d).
Note that all the modes described may not occur in a practical
circuit,
since some of them would require the armaturecircuittimeconstant tobe very small. Oscillograms of nineoutof12 modes(exceptmodes 1,2,and11),which are observedfora2.2-kWmotor(TableIII)load, arerecordedin Fig. 4.1433
TABLEIII
DC MOTOR SPECIFICATIONS
Output power 2.2kW
Armaturevoltage 220 V
Shuntfieldexcitation 220 V
Currentrating 11.6A
Rated speed 1500r/min
Armature resistance 2.00
Armature inductance 32.5mH
(a (2 ms/div)
(a)
( t(2ms div) (c)
- >t (2ms/div)
(e)
>t(2 ms/div)
(g) (h)- t( 2ms/div)
(100Vfdiv)
(2A/dl,v)
W t(2ms/div)
(i)
Fig.4. Oscillogramsof modes ofconverteroperation. (a)Mode 3.(b)Mode 4. (c)Mode 5.(d)Mode 6.(e)Mode7.(f)Mode 8.(g)Mode 9.(h)Mode (10oV/div)|
(2A/div)
(100l d v)
i(
t15A/d'o)
(lOOVldiv)|
(2A/Ii tdIv)~
(100V/div)
(5AIdiv)t
(000V I)0
e oo0v/dlvz
i,
(2AIdiv)t
V/div)7
(2Al/dv)
b2ms/div)t
(b3
- tUns/div) (d)
3t(2msdiv)
(f) (10OVldiv)7
155A/div; t
(100V/div)
(2AIdwv)
BHATAND DUBEY: THREE-PHASE REGENERATIVE CONVERTER
III. CHOICE OFOPTIMUM VALUEOF FILTER INDUCTANCE The armature current ripple is an important factor in dc drives since itadverselyaffects the machine commutation and causes derating of the motor. If the armature current is discontinuous, themotorspeed regulationdeteriorates and the sparking at the commutator brushes becomes more pro- nounced. Therefore,usuallyafilterinductance isincorporated in the armaturecircuittolimit thecurrentripple. On the other hand, the filter inductancecannotbe madetoolargebecause of itscost,size,andweightconsiderations. The inevitable copper loss in the filter inductance, though small, is another factor whichcannotbeignored.Therefore, it would be very usefulto identify the optimum value of filter inductance required to eliminate discontinuous conduction in armature and to keep the current ripple within the specified permissible limits.
Dubey [3] has suggested a method ofchoosing an
optimum
value of filter inductance forchopper-fed
dc drives. This technique is extended here forthree-phase fully
controlled converter system. The equation governing the system per- formance canbe writtenas (Fig. 1)e=La
ddt Raia+Eb.(1)
Thevoltagesandthecurrents of the systemarenormalized against the following base values:
base voltage= base current=3Em-.
7rRa
Thus the normalizedsystemperformanceequationisgiven by en=tan diana +
ian
+Ebn-
dwt
tart
Start Read
r JIp1fnEbn
Read SoLve
I/,ao E q(2)
Obtain Obtain
X Y ian,lsn
Calculate CalcuLate
MCR IanCR r
Calculate Cacilulate CriticalEbn; Isn,13n,15n
Calculate CaLcuLate Critical Ion PF,DF
(a) (b)
Fig. 5. Flowchartfor systemanalysis.
angle, the armature current ripple becomes maximum and remains constant when the current is continuous.
MCR can be analytically calculated by obtaining current ripple for the continuous current modes ofconverter opera- tion. The expression for armature current is obtained by solving (2), from whichthe
expression
forcurrentslope
canbe derived. The instants atwhich the minimum and maximum of ianoccur(i.e., angles
XandY)
can bedeterminedby solving
theexpression forcurrent slope. TheMCR is thencalculated with thehelp of the followingexpression:(2)
To select an optimum value of filter inductance, the following curves must be obtained for a set of values of armature circuit time constant:
1) normalized maximum armature current ripple (MCR) versus the average output voltage;
2) normalized boundary curve separating the regions of continuous and discontinuous armature conduction on the speed-torque plane.
The analytical approach to obtaining these curves for a three-phase converter system with controlled flywheeling is briefly described. Acomputerflowchart is given in Fig. 5(a).
A. Calculation ofMCR
Foraparticularfiringangle, so far as the armature current is discontinuous, the current ripple depends upon the motor back EMF. When the armature current is continuous, any change in the motorback EMF causes change only in the dc component of armature current, and therefore, the ripple is independentofmotorback EMF. Thus, for a particular firing
MCR=Ian max -an
minI
2
(3)
Fourmodes of converteroperation exist (modes 4, 7, 9, and 12) in whichthe armature current iscontinuous. Theexpres- sion for armature current for the various continuous current modes aregiven later. The expressions for the slopes can be derived from these expressions. Since the converter output voltage and currentwaveformsrepeatafterevery
rl3
rad, the solution of (2) is provided only for the interval 0 < wt < r/3 in each case.Mode4: For the interval0 < wt <
alp, ian=COS
c[sin (ap 1+2-)
+
[sin (a1+ -14)-sin (ap+ -Ii
)]exp -
(wt
+ -ap)
cot*.
[1-exp (--
cot-Ebn.
(4)1435
Forthe interval
ap
< wt < 7r/3,ian-COS V[sin
(wt+- iA)[sin
(ap
+ )- sin ()]* exp
[-(wt-a,p)
cot4J
[l-exp
( ccot ')]-Ebn
(5)Sincethereare twoexpressionsfor
ian
in differentintervals, itisusefultoknow the interval in which Xand Yoccur. Since, for continuous armature current, the instants X and Y are independent of average armature current, the interval in which they occur depends upon which of the discontinuous current modes comes in contactwith the continuous current mode at the critical point (i.e., when the armature current is just continuous). Inthepresent case, from Fig. 3(a),,p
<s X. In anycase,cap
< Y. Therefore, it isenoughif theexpressionfor current slope in the intervalap
< wt < 7r/3 is obtained by differentiating (5).Mode 7: In this case, r/3 < ap < 27r/3. For the interval0
< wt <
(a,p
-(7rI3)),
ian
=Cos ; sin-sin
acp+ 3- ) exp[(
2 a) cotexp
(-wt
cot[l-exp
I(-j
cotKKI]
-
Eb.
(6)Forthe interval
(a,p
-(qrI3))
< wt < ir/3,an= cos [sin (wt+ - )- [sin
(P+j
3 )^ exp
{- (j-UP)
cot43
-sin
4]
exp(-
wt cot4)
[I exP (- cot j] -
Ebn
(7)In this case, both X and Y can be obtained
(Fig.
3(b))by differentiating (7)
valid for the interval(aup
-(7r/3))
< wt <r/3.
Mode 9: For the internal 0 < wt < a,ian--Cos + [sin (wt-4)
+[sin Q + sin (an
exp
-( cotnc ) }]
exp (-wt cot {)
[1-exp
(-- cot4')]]
-
Eb,t
For the interval
a,,
< cot < 7r/3,ian= -cos [sin (a, 4) exp {-(wt-a,) cot 4}
+sin 4 exp (-wt cot
0)j
I[1exP
-i cot ')]] E(9)
In this case, X =
a,,
and 0 < Y <an.
Therefore, the expressionforcurrent slope isobtainedby differentiating (8).Mode 12: For
the
interval 0 < wt < (a, -(-/3)),
ian
-cos jsin (wt±+-4')
- [sin
(an
-)sin (an -1]exp
{-(wt+
3 -an)cot
+[-exP (3fct <)]Ehn
.Forthe interval
(ae,
-(7r/3))
< wt < 7r/3,ian Cos ; sin (wt -)
- [sin (can---O)-sin (an 41]
* exp
{-(wt+±-an)
cot43
[-exp
- cot )]]-E
(10)
(1
1) FromFig. 3(d),X<a,,
Inany case, Y<a,,.
Theexpression for current slope is obtained by differentiating.Fig. 6(a)showstheplotof MCRagainstthe average output voltage. For the controlled flywheeling technique, the MCR assumes a peak value atE, = 0.4 and reducesto zero with the average output voltage, whereas for the normal control technique, thepeakMCRoccurs at zerooutputvoltage.These peakvaluesof MCR areplotted
against
armaturecircuit time constant in Fig. 6(b).B. Separation
of
Regionsof
Continuous and Discontinuous Armature ConductionIn ordertoseparatethe regionsof continuous and discontin- uous armature conduction in the speed-torque plane, it is requiredtoobtain the critical values ofmotorback EMF
(Ebn)
and averagearmature current(Ia,),
atwhich thecurrentisjust
continuous. Having obtained theangle
at whichian
becomes minimum, in the earlier section, the criticalEbn
can be obtained by forcingian(X)
= 0 in theappropriate equations.
The critical I,, can then be-calculated
by averaging
the armature currentfortheparticular
valueof critical back EMF.The expression for the critical values of
1,,,
for various continuous current modesaremode 4:
Ian(critical)---cos
Oep-Ebn(critical)
(12)BHAT AND DUBEY:THREE-PHASE REGENERATIVECONVERTER
025 Normal control C-Controtled flywheelnng
- Common for both NCand CF
-0 2 0 02
Eon (a)
Normal control Controlled flywheeling
Norrnol control -.- Controlled ftywheeling
Comn-on for both NC and CF
Fig. 7. Boundarycurvesseparatingregionsofcontinuousanddiscontinuous
5 armatureconduction.
13
(b)
Fig. 6. (a)Normalized maximumarmature current ripple. (b) Peak MCR
versesarmaturetimeconstant.
mode 7:
Ian(critical)
= 1+cos(aC + -Ebn(critical) (13)mode 9: Ian(critical)= -(1 COS an)
-Ebn(cntical)
(14)mode 12:
Ian(critica)
=cos -+an) Ebn(critical). (15) Fig. 7showsthenormalizedboundarycurvesseparating the regions ofcontinuous anddiscontinuous armature conduction for,the controlled flywheeling and the normal control tech-niques. The armature currentiscontinuousto the rightofthe boundary curve.
With the help of these boundary curves and the MCR characteristics, a filterinductancecanbechosen such that the
armature current remains continuousand thecurrentripple is keptbelowthespecified permissiblelimits forworst-caseload conditions.
From the knowledge of load on the motor shaft, a
normalizedcontourofminimumtorquefor thewholerangeof motor speed is obtained and superposed over the boundary
curves of Fig. 7. A filter inductance is so chosen that the boundary curve corresponding to the modified armature circuit time constant falls to the left of the minimum load contour. The value of filter inductance required to keep the MCR within the specified permissible limit is obtained from Fig. 6. The higher of the two values is finally chosen as the optimum filter inductance.
IV. SYSTEMANALYSIS
The system is
analyzed by simulating
it in adigital
computer. For any
particular firing angle,
thewaveforms of converteroutputvoltage,
armaturecurrent,andsourcecurrentare obtained from which the various parameters of
system performance,
such as motor speed-torquecharacteristics,
armature current
ripple,
systemefficiency, input
powerfactor,
distortionfactor,
sourcecurrentharmonics,andsourcecurrent(rms)
arecalculated. A computerflowchart for thepurposeisgiven
inFig. 5(b).
The formulas used for calculating the different parameters areianmax-ianmin
armature current
ripple
=CR= 2 3 7/3-3 enian
dwt overall power factor=PF=7r Isn
source current distortion factor=DF= n
Isn
(16)
(17)
(18)
The system
efficiency
isdefined separately for motoring and regeneration conditions:motoring efficiency
=71Mpower
developed by
the motor powerinput
to the systemEbnIan 3 xe3
_ e
in
dwtTr o
(19)
-1
0 03 Peak0 02 MCR
001_C
1437
IEEETRANSACTIONSON INDUSTRYAPPLICATIONS,VOL.IA-21,NO.6,NOVEMBER/DECEMBER1985
regeneration efficiency=riR
power delivered to the source power generated by the motor
3 2sri3
3 }
enian
dwt EI7ro
EbnIan (20)
V. SYSTEM PERFORMANCE AND EXPERIMENTAL VERIFICATION
The system performance is investigated on a 2.2-kW dc motor (Table III) load. Normalized speed-torque characteris- tics are obtained by plotting
Eb,
against Ian (Fig. 8). Since the range offiring angle for controlled flywheeling and normal control are different, the speed-torque characteristics are drawn for constant values ofEot,.
All the other system parameters, such as armature current ripple, system effi- ciency, power factor, source current distortion factor, source currentharmonics, and rms value of source current are plotted againstIa,,
for constant values ofEb,
(Figs. 8-12). The fact thatEb, isheld constant in plottingthese curves facilitates the comparison of the two control techniques for the same developed power.The speed-torque characteristics and system efficiency curves are experimentally verified, and these results are indicated by (o) in the corresponding diagrams. From the system performance curves, thefollowing points are noted.
1) The armature current ripple is substantially lower for controlledflywheelingtechnique at low motor speeds (Fig. 9), which improves the machine commutation and reduces the deratingofa motor.
2) Because of reduction in the armature current ripple, the system efficiency improves with controlled flywheeling tech- nique at low motor speeds (Fig. 10).
3) Controlled flywheeling causes significant improvement in the overall system power factor (Fig. 11).
4) The drawback of controlledflywheeling techniqueis that itincreasesthe harmonic content in the source current which is reflected in the reduction of source current distortion factor (Fig. 11).
5) The experimental results of motor speed-torque charac- teristics (Fig. 8) and system efficiency (Fig. 10) corroborate reasonably well with thetheoreticalresults inthe first quadrant but show a deviation in the fourth quadrant. This deviation is attributed mainly to the demagnetizing effect of armature reaction and partly to the device and brush contact resistances.
These effects oppose each other in the first quadrant, which accounts forthe close relationship between the predicted and experimental results, whereas inthe fourth quadrant they aid each other and hence the notable deviation between the experimental and analytical results.
VI. CONCLUSION
The modes ofoperation of the three-phase fully controlled converteremploying controlledflywheeling are identified, and their oscillogramsarepresented. The system is analyzed using adigital simulationtechnique, andacomplete study of system
FucIiiy nnlr;.
- Controliod $IyV.1CQ'fl - Commocn fDr FC -I Cr
10^
-'OF<1
r EII oE63-0 Q
0 - 2E,-06
0 2 -_o, _
00.. 038 012
-023~~~ ~0 2 _
o
-0 6--
Ol 0
Fig.8. NormalizdscE-re Fig.8. Normnalizedspeed-torquecharacteristics.
CR innnl-
nFr)
-NorrmaL contrcl
- - Co'r,o,)lci fl/y\.hccl.rg _ Co~--rc,n 1-) boTh NC nn,
- E - E,>n=E6
~-
-E ,n- -. r~0
00 0 r. 008 012
(a)
L'^')lcrr
C, a0081-
0 0L
Et,, -0I
{
fEt,,E>=-~~~~~~~03
- B0- ,Ebn -0°Et,,=Et,r-O-0 63004 00 012
(b)
Fig.9. Normalizedarmature currentripple.(a)Motoring.(b) Regenerating.
1438
I
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BHAT AND DUBEY: THREE-PHASE REGENERATIVE CONVERTER
= = E hn0 t\0
N" C, E~~~r -c':0
N'--~~~~~~~~~~~~~~~~~~
;~~~~~~~. ---A.%.
t"lb, -3 I Normal controL
- - ControlLed flywvheelng Commnon ior both NC/CF
0 001. 008 012
( la (a)
DF
0-°
0 2
~) 2~
Eb,r08 Ets=O6
/*= =E~~~~~~t,=C)3
-EbmF 030EEb =0l
C:rrarT n -r r1rCt _. -.r, c"d tty:.*h< org9 ____C rnrnrc nrt~nt~r tC tre C F
L 0.
0.0 004 0)08
P.Ian (a)
0.12-1 I 0
0
61
-- - =
Ebn=-0-8
%,"l\1\ . 0 -t Eb0En,=-
%o
'-:1 DF
'06
-0 2
o \\
°ibn -01
00 0-04
Ican
008 012
Fig. 10. Systemefficiency. (a) Motoring. (b)(b) Regenerating.
-Normat controL
-- Controlled flywteel ;io
Cormon for both NC and CF 1 0-
E,,=0 8
_Eb,=06
--E 3n0 3
-E 1
PFPF~~~~~~~~~~0_-]an
004 008 012
Ebnr,0
-0 2 'M ~~- ~ ~ ~ ~~ -~- E =-0 3
0 0
/'E,=- 0O f
=Ebl=-~ 30-1
Ebl=-086
*.--
1. nE, -0 1
0-2
00 0;08
Ioan (b)
D12
Fig. 12. Source currentdistortion factor. (a)Motoring. (b)Regenerating.
ture conduction in the speed-torque plane. With the help of these nomograms, an optimum value offilter inductancecan
bechosen forany motor.
As compared to normal control, controlled flywheeling offers a reduced zone of discontinuous conduction, lower armature current ripple, and
higher
system efficiency andpower factor. These beneficial effects are obtained without
any increase in the number or rating of the power circuit
componentand, therefore, withoutanysignificantincrease in thecost of the drive. Larger harmonic content in the source
currentand complexity offiringcircuit arethe drawbacks of controlled flywheeling.
VII. NOMENCLATURE
Ebn:606
Ebn=-08 -0-61_
-1 0L
Fig. 11. Overallpowerfactor.
performance is made. The theoretical results are compared with that of the normal control technique for the same
developed shaft power.
An analytical approach is presented to obtain normalized nomogramsfor maximum armaturecurrentrippleand bound- arycurvesseparatingthe continuous anddiscontinuousarma-
e,
Eo
EbEm
en, Eon, Ebn
i'a Ia ian, Ian MCR
x
y ap, a.
lyp
2Yn
Instantaneous and average output voltage of converter, V.
Motorback EMF, V.
Peaksupply voltage, V.
Normalized values ofe,
E,
andEb.Instantaneousandaveragearmaturecurrent, A.
Normalized values of ia andIa
Maximum normalized armature current ripple for a particularfiring angle.
Angleat which
i4,
is minimum, rad.Angleat which i4 is
maximum,
rad.Converterfiringand flywheeling angles, rad.
Extinction angles, rad.
= sin-]
(Eb/E,,)
- (w/3), rad.=r + sin-'
(Eb/E,,),
rad.1.0
1,M0 6
0-2
0
¶
1439
F
L.c I
I-or
VI = tan
I(wLe/R,), rad.
w Supply frequency, rad/s.
REFERENCES
[1] W. Farrer andD. F.Andrew, "Fullycontrolledregenerativebridges withhalf controlledcharacteristics,"Proc. Inst.Elec. Eng., vol. 125, pp. 109-112, Feb. 1978.
[2] W. Drury, W. Farrer, and B. L. Jones, "Performance of thyristor bridge converters employing flywheeling," Proc. Inst. Elec. Eng., PartB,vol. 127, pp. 268-276, July 1980.
[31 G. K. Dubey, "Calculation offilter inductance forchopper fed dc separatelyexcitedmotor,"Proc.IEEE, vol.66,pp. 1671-1673,Dec.
1978.
Subbanna P. Bhat received the B.E. degree in electronics and telecommunications and the M.
Tech. degree in industrial electronics from the UniversityofMysore, India, and the Ph.D. degree from the Indian Institute ofTechnology, Kanpur, in 1974, 1977, and 1984, respectively.
He joined the faculty of the Department of Electrical Engineering, Karnataka Regional Engi- neering College, Surathkal, India, affiliated with theMangalore University.
GopalK.Dubey (SM'83)received theB.E. (Hon- ors) degree from Jabalpur University, India in
I1963,
and the M. Techdegree inelectrical drives and control andthe Ph.D.degreein electrical drives from Indian Institute ofTechnology, Bombay, in 1965 and 1972, respectively.He was a teacher trainee from 1963 to 1966, Lecturer from 1966 and1972,and Assistant Profes- sor from 1973 to 1977 in the Department of Electrical Engineering,Indian Institute of Technol- ogy,Bombay.He hasbeen Professor in theDepart- ment of Electrical Engineering, Indian Institute ofTechnology, Kanpur, India, since 1978. He was a VisitingResearch Fellow and Commonwealth Scholar in thePostgraduateSchool of Electrical and ElectronicEngineering, UniversityofBradford, England,from October 1974 toDecember 1975. He was aVisiting Professor in theUniversity ofBritish Columbia, Vancouver, BC, Canada from August 1983 to August 1984, and in the Virginia
Polytechnic Institute and State University, Blacksburg, VA, fromSeptember 1984 to June 1985. His fields of interest are electrical drives, power electronics, control systems, and engineering education. He is a coauthor (withS. R. Doradla, A.Joshi,and R. M.K. Sinha) ofThyristorizedPower Controllers(Wiley Eastern) and authored over 100 research papers.
Dr.DubeyisaFellowofthe Institution ofEngineers,India(1978). Hewas awardedPandit Madan MohanMalviyaMemorial Gold Medal for 1975-1976 and theInstitution Prizefor 1977-1978bytheInstitution ofEngineers.
