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PWM Swtchng Strategy for the Elmnaton ofCommon Mode Voltage of a Two-level Inverter

Drve wth an Open-end Wndng Inducton Motor

ConguratonP Srinivaan, Venugopal Reddy,Stunt Mmbrs EEE V T Soaekhar

bstractAdjule peed dive e known o geneeommon mode volge whih ue moo hf volge ndeing uen. I w demoned h wo wo-levelinvee onneed o eihe ide of n open-end windinginduion moo i ple of hieving he funionlly of heelevel invee. The ommon mode volge geneed y heelevel invee n e elimined y wihing only he volge

pe veo ominion whih do no podue he ommonmode volge. A PWM wihing egy o elimine heommon mode volge uing n open-end winding induionmoo dive i peened in hi ppe, whih end o void heeleoi oupling of he o nd oo eduing he einguen nd lekge uen. The peen heme ue ingleDC-link wih ou 58% of he DC-volge omped oonvenionl wo-level VSI.

--Open-end winding, Induion moo, Commonmode Volge, Spe veo modulion, Being Cuen.

I NTRODUCTION

MUltilevel inverter for high voltage, high powerdrive have gained popularity in the recent pat

aer the introduction of televel neutral point clampedinverter by Nabae t a [1] with low power device rating athat of two level inverer With the ue of multilevel inverterthe harmonic content in the outut voltage can be reducedwhich enable operation at leer equency with leerwitching loe

Stemmler and Guggenbach [] intigated that three-levelnctionality can be realized with an open-end windinginduction motor driven by two-level inverer om either ideThi circuit conguration oer principal advantage uch a

P. Srinivasan and B. V engopal Reddy are Researhers wih Dearmen of Elecical Engineeing, Naional sie of Technology, Waranga, Pradesh, dia 506004emi:

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V. T. Somasekhar is wih Dearme of Elecrical Engineeing, Naionalsie of Technology, Warangal, Padesh, dia 506004 (email:v

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abence of neutral point uctuation and redundant witchingtate combination Exploiting thee advantage, the completeelimination of common mode voltage i procured

The high dV/dt due to the power device witching in PWMinverter i mainly reponible for common mode voltage It

create the o called ha voltage The teep riing andfalling pule of thi voltage can excite the capacitive coupling between the tator winding and the tator ame and the rotorThi paper preent a PWM witching trategy to dual twolevel inverer fed open-end winding induction motor toeliminate the motor coon-mode voltage and reulting bearing and leakage cuent without applying device to themotor, adding paive component, or limiting the modulationindex

II FFECT F WM NV ERTERS N NDUCTION OTOR

EARGS

Conventional inverer generate alteating comonmode voltage within the motor winding that caue anelectrtatic (capacitive) coupling between the rotor and thetator winding and frame, enabling voltage to build up onthe motor ha [3][5] The bearing are not in electricalcontact with the inner and outer race becaue the greae uedha a parial inulating eect Therefore, the chargeaccumulate on the rotor aembly until it exceed thedielectric capability of the bearing greae The reultingeect i a equently repeated ahover current that in timecan damage the bearing urface due to the ElectricDicharge Machining (EDM) eect, or electroplating of theace teel and bearing ball (pitting and uting) The

phenomenon of ha voltage producing circulating hacuent ha been recognized ince 190Since the introduction of the IGBT technology, there ha

been a documented increae in electrically induced bearingfailure; and hortening mechanical life of bearing In piteof the extended tudy of the prblem over the pat few year[6]-[9], there i no atifactory explanation for thi

phenomenon

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III D U NV ERTER ED PENND DING NDUCTION

OTOR ONFIGURTION IT OMMON DC-L

The chematic of a dual two-level inverer fed three-phaeopen-end winding induction motor fed om a ingle powerupply i hown in Fig 1 In thi cheme, each of the dualtwo-level inverter can prduce eight pace vector locationindependent of the other a hown in Fig 2 reulting in atotal of 6 pace vector combination pread over the 19pace location a hown in Fig [10] The number 1 - 8denote the tate aumed by and - 8' denote theame for INV The witching tate of the two inveer aretabulated in Table 1

]

Fig. . D inve fed oeed winding indction motor drive

4 ·++)f -) 4 .++)

1, , I 6(+-+) : :t }c :+�

Fig.2. Voltage vectors for inveer Lf and inveer2 (Right)

A '+ indicate that the top witching device in a leg of agven inerter ed ON', wherea a -' indicate that the bottom witching device in a leg of the given inverer ied ON' The ymbol and denote the three phae pole voltage of wherea the ymbol

and denote the ame for 2 a in Fig 1

(41 )

'-()

Fig.3.Sace vector locations with the cominations of the dalinveer scheme

In Fig O repreent the DC-li voltage of individualinveer which i equal to 2 and OG repreent the DClink voltage of the equivalent tee-level inverer which iequal to V From Fig it may be een that there are 19pace vector location, which form verice of equilateralector Six hexagon namely OBHGSF, OCJIH,ODLKJB, OENLC, OFQPND and OSRQE may beidentied with their center at , B, C, D, E and F

repectively,within the outer hexagon GIPR

TABLE ISCING STATES OF TE IDIV UAL IV ERTERS

State of Switches State of Switchesvererl ted on Inverer2 ted on

1(+ ) S, S, S 1(+) S S, S

2(++) S S, S 2 (++ ) S, S, S

3( + ) S, S, S 3(+) S 2' , S 3 " S 4

4(++) S, S, S 4 ( ++) S S, S

5(+) S, S, S 5 (+) S 4 , S 5 " S 6

6(++ S, S, S 6 (++ ) S S S

7(+++) S S, S 7(+++) SI , S " S 5

8( - ) S, S, S 8 ( ) S, S, S

ny leg of the two inverer can independently attain levelo or del2. The voltage acro a particular phae winding can

be obtained by

V A=V AOV AO

BB B B

CCvC cT II

OLE D ASE OLTAGES F E EV EL NV ERTER

olevoltage of olevoltage of Motor hase voltageNVl(V ) INV 2(V ) V =V V

V 4 V 4 0

V 4 V 4 V

V 4 V 4 0

V V V

The phae winding can attain one of the level, -Vdel2o and +d2. The combined eect of the voltage in thetee winding can be repreented by a voltage pace vector a dened by

j7 j7 V A'+ �B,e V CC' e (4)

From eqn () the voltage pace vector location fordierent witching combination are hown in g . Thivoltage pace ector can be equivalently repreented a theum of the voltage pace vector generated by the twotwo-level inverer If and are the voltage pace

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vector generated by and repectively, thereultant voltage pace vector i

r = 5In thi drive, the two inverer are operated with a

common DC-link voltage and are operated witha DC-link voltage of Thu, the um of the DC-linkvoltage i equal to , which i the DC-link voltage ofan equivalent conventional two-level inverer drive Thidrive circuit conguration along with uitable witchingcombination i capable of mitigating the common modevoltage at the location , and H, along with tightwitching

IV ROPOSED WM CEME OR T LAON F

OMMON ODE OLTAGE

The reference pace vector for the pace vector modulationi denoted a s i reolved into two component and

The voltage and V denote the intantaneou phae

reference voltage required for realizing They are obtained by projecting the tip of s onto a, b and c-phae axe

repectively, and are given by the claical phaetranformation a given below

Vb* = -13 1 [�;]va ] [

2/3 0]Vc* -13 -1

(6)

In thi paper, a pace vector-baed cheme i propoed which i baed on the cheme prpoed inKim and Su From Kim and Su, the ymbol T and Tdenote the time duration for which the active vector along the

leading and trailing edge of the ector in which the tip of i ituated are witched for it realization The ymbol Tdenote the time duration for which the null vector i witchedalong with the active vector The ampling interval T for thipace vector modulation i equal to the um of the timeduration, Th T and T The ymbol Tg' T and T,repectively, denote a, b and c-phae witching time periodduring which the output phae of the inverer are connected tothe poitive rail of the DC-link

"

A

B0

C

o

Fig.4. Conventional to-level Voltage Sore veeThe baic witching algorit decribed in Kim and Su

for the claical two-level inverter feeding three-phaeinduction motor i extended to the dual-inverter ytem for

computing the witching time of the witching device of thedual-inverer Thi witching algoritm i baed on theimaginary witching time period T T and T which are

proporional to the tree intantaneou phae referencevoltage and , the contant of proporionality beingequal to (TV) The ymbol T, T and T,repectively, denote the maximum, median and minimumvalue among the tree imaginary witching time Recently, a

pace vector-baed

witching cheme for the tee-level,dual-inverer fed open-end winding induction motor wa propoed uing thi witching algoritm Thi witching i briey reviewed in the following paragraph

D�(U

!

i!:v -Fig.4. Space vector locations with the cominations of the dal-invee scheme

mentioned earlier, two two-level inverer connected toeither end of an open-end winding induction motor icapable of achieving the nctionality of a three level inverterFrom g 3, OG repreent the dc li voltage of the dualinverter

TABLECOMMON MODE OLAGE CONRBUONS FROM DFFEREN

COMBNAONS

-<4 <6 <12 0 <12 <6

8-4' 1-7'8-6'

5-7'8-2'

3-7'5-5' 1-4'2-5'

4-4'3 -5' 3-6'5-2'

4 -6' 8-5' 3 - ' 8-7' 5-4' 4-7'

6-4'8-' 5-1 ' 3-4' 5-6' 7 - 4'

2-4'8-1 ' 3-1 ' 3-2' 16' 7 -6'

4-2'8-8' 5-8' 1 -5' 1-2' 4-5'

6-2'6-7'

3 -8' 1-' 4 -3' ,4 -1 ', 7-2' 2-6'

1-8' 1-1' 6 -5',6 -3' , 2-7'

2-2' 4-8' 2- 3', 2 -1' , 7 -5'

6-8' 7-8'6-1' 7 - '

2-8'6-6'

5 -3' 7-1 '

<4

7 - 7'

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The common-mode voltage of the dual inverter drivedened with reference to the motor ame, which is earhed, isgiven by:

V� = G) (V A' + VB' + Vc, +VA" + VB" + Vc,) (7)

The points G, I, K, M, P, and R are the locationscorrespondng to nerter state combnatons 14',25',36',41',

52', 63', where the coon mode oltage becomes zero asshown below and the possibility of bearing cuents andleakage currents due to electrostatic coupling and its associated

problems are also avoided. The common mode voltage is given by [1]

Table- III presents the common mode voltagescoesponding to all of the space vector combinations of theopen-end winding induction motor drive shown in g. 1.

Considering a space vector combination 1', where 1(+--)

represents the state of inverter 1 and 4' (-++) represents thestate of inverer 2. Upon calculating common mode voltageom (7), it is evident that common mode voltage becomeszero for the space vector combination 1'; similarly, it is the

same for the other combinations such as 25', 36', 1',52'and 63'. In the work presented in this paper, theselocations are used exclusively to eliminate the common modevoltages.

It may be obsered that, this is same as the maximumvalue of peak ndamental phase voltage generated by theconventional two-level inverter (which has common modevoltages and its associated problems) with Sinusoidal Pulse Width Modulation. This maximum value of peakndamental phase voltage is 15% less than to the peakndamental amplitude that can be generated with the spacevector based pulse width modulation. This can becompensated with a additional boost in the dc-lik voltage.

Hence it can be veried that with a dc-lik voltage of 0.57(15% boost over) the proposed scheme with common modeelimination, can generate the same maximum ndamentalamplitude of the phase voltage equivalent to that generated

by a conventional two-level inverter which uses a dc-likvoltage of as in Fig. .

Vd4

Yd

Fig. .VSI with Serie connected witche

It is a nown fact that the oltage rating of a given powersemiconductor device limits the DC-link voltage in a twolevel inverer. If a higher DC-link voltage is employed, oneis constrained to connect the devices in series to increase the

voltage rating of the overall string of the devices as shown ing. 5. However, the static and dynamic balancing ofvoltages of individual devices in the string could becumbersome and could call for devices, which are exactlymatched for a successl operation in the series connection.

The advantage of the dual inverer driven open-endwinding induction motor drive with the proposed PWMstrategy is that it avoids the series connection of individual

switching devices to achieve the operability o a high DClink voltage. At the same time,it also achieves the avoidanceof coon-mode voltage and its undesirable eects whichwere described earlier. By resoring to the SE PWMtechnique described in [22], it is possible to operate the dualinverer drive with a single DC power supply as shown inFig.. However, the resulting drive system is still equivalentto a two level inverter drive.

UTION SULTS

The proposed PWM scheme for the dual inverer fed open

end winding induction motor drive is validated with simulationstudies using MATLAB/Simulink. Fig. 6 shows themodulating wave for the proposed common mode eliminationscheme. Fig. 7 shows the pole voltages for the two inverers.Fig. 8 shows the phase voltage at the motor terminals. FromFig. 9,it is evident that common mode voltage is eliminated tozer using the proposed PWM switching strategy.

�L-O.O05O.OlO.Ol5O.O2O.M=5O.

Fig. 6.Modlating wavefo

1-

o 5 5 5 3 35 5

IUo 5 5 5 3 35 5

l:to 5 5 5 3 35 5

i

Fig. 7.Pole V oltage of (top) and IV 2 (ottom)

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100

U

�

I �

I0

i

Jl

I

TIme

Fig. 8.Phase Voltage of the Two -Level ver

o.8

o 6

o•

o.2

· 2

· •· 6

. 8

10

Fig. 9.Common Mode V oltage

VII. ONCLUSION

A space vector based P to eliminatealteating common mode voltage for a dual-inverer fed openend winding induction motor drive is presented in this paper.

With the proposed scheme, the sha voltages do not occur inthe machine as no common mode voltage exists in the phasewindings and the dual inverer can be operated from a single

power supply. The proposed drive has a simple power circuitconsisting of two standard two-level inverters. The proposedscheme uses a single dc-link with half the voltage of thecommon mode elimination scheme based on the conventionalthree-level inverer. Even though tree-level congurationsetup is necessary, the proposed scheme is as that of a twolevel inverter, owning into the advantages such as half dc-linkvoltage is sucient, half the value of switch ratings, and themore predominant common mode voltage is being eliminated.

VII. EFERENCES

[ ] Nabae, L.Takahashi, and H.Agaki, A new neutral point clamped PWM verer," IEEE Trans.Ind.Applicat.,Vol.- 17, pp 518-523, sept. loct. 1981.

[2] H.Stemler, P.Guggenbach, "Congutions of high powe voltage source inverer drives," EPE.conf-1993, pp 7-12.

[3] S. Che,"Bearing cuent, EMI and so switching in induction motordrivesA systematic analysis, design and t," Ph.D.

Dissation, Univ. isconsin, Madison, 1995.[4] M. Erdman, R. . Kerkman, D. W. Schlegel, and G. L. Skibinski,

Eect of PM inverers on ac motor bearing cuents and sha voltages," IEEE Trans. In Applicat., vol. 32, no. 2, pp. 250259,1996.

[5] A. von Jouanne, P. Enjeti, and . Gray, Application Issues for PM adjustable speed ac motor drives," Industrial Applications Socie

Mag., pp. 1018, Sept.!Oct. 1996.[6] P. Link, Minimizing electric bearing curents in ASD systems,"

IEEE Indust App. Magazine July/August 1999 pp. 55-67.[7] von Jouanne, H. Zhang, Wallace, n Evaluation

Techniques for Bearing C ets, EMI and Over voltages in ASD Applications," IEEE Trans. on In Appl. vol. 34, No. 2,September/October 1997 pp.11 \3-1121.

[8] S. Chen, T. Lipo, "Beg cuents and Sha Voltages of an Induction Motor de Hard and So Switching vee Excitation," IEEE Trans. on In Appl, vol. 34, No. 2,Septemb/Octob 1998 pp.1 042- 1048.

[9] D.F. Busse, .M. Erdman, R.. Kerkm, D.W. Schlegel, G.L.Skibinski"The Eects of PM V oltage Source verers on the Mechanical Performance of Roll ing Bearings," EEE Trans. On InAppl. V o1.33, No.2, 1997, pp. 766-774.

[10] Somasekhar, V.T., Gopakum, K., Pittet, , and Ranganathn V.T.,PM inverer switching strategy for a dual two-level inveer fed open-end winding induction motor drive with a switched neutral," EE Proc., Electr. Power Appl., 2002, 149 ,(2), pp. 152160.

[ ] Kim, .S., and Su, S., A novel voltage modulation tecique of the space vector PWM" Con Proc. EC, 1995, pp. 742747.

[12] Somasekhar, V.T., Srinivas, S., and Gopakumar, , A space vector based PM switching scheme for the reduction of comon-mode voltages for a dual inv fed open-ed winding induction motor ive," Con Proc. IEEE-PESC, Recife, Brazil, 2005, pp. 8168212.

[13] M. R. Baiju K. Mohapatra R. S. Knchan, Gopakum, A Dual Two-Level Inverer Scheme with Common Mode V oltage

Elimination for an Induction Motor Drive," EE Transactions On Powe Electronics, Vol. 19, NO. 3, May 2004.[14] Annette von Jouanne, Haoan Zhang, A Dual-Bridge veer

Approach to Eliminating Comon Mode Voltages and Bearing and Leakage Cuents," IEEE Trsactions on Power Electronics, V ol. 1 4, no. 1, January 1999.

[15] Dae-ook Kang Byog-Kuk Lee Jae-Hyn JeonTae-Jin im and Dong-Seok Hyn"A Symmetric Carrier Tecnique of CPWM forV oltage Balance Method of Flying-Capacitor Multilevel verer," IEEE Ts.on d. Electronics, Vo1.52, No.3, pp 879--888, June 2005.

[16] J. Roiguez, . S. Lai, and F. Z. Peng, Multilevel inveers: A survey of topologies, controls, and applications," EEE Trans. In Electron., vol. 49 , no. 4, pp. 724738, Aug. 2002.

[17] . H. Seo, C. H. Choi, and D. S. Hy, A new simplied space vector PWM method for three-level inveres," IEEE Trans. Power Electron., vol. 16, no. 4, pp. 545550, Jul. 2001.

[18] E.G.Shivakumar, Gopakum, S. Sinha, Ane Pittet, V.T. Rganathan, Space Vector Control of Dual vere Fed Ope-end inding duction Motor Drive," EPE Joual, Vo1.l 2, No.1 , pp.9 18 (2002).

[19] V.T. Somasekhar, K. Gopakum, M.R. Baiju, risna K. Mohapatra, L. Umnand "A multilevel invere system for an induction motorwith op-ed windings," IEEE Trns. on Industrial Electronics,V o1.52, No.3, pp. 824-836,(2005).

[20] M. R. Baiju , K. Gopakumar, Mohapaa, V. T. Somasekhar L. Umand, A high resolution multilevel voltage space phasor geeration for open-end winding induction motor drives," EPEJoual, V o3, No.4, pp. 29-37, (2003).

[21] V. T. Somasekhar, . Gopakumar M. R. Baiju, Krisna K. Mohapat and L . Umanand A Multilevel Inverer System for a n Induction Motor With Open-End indings," IEEE Trans.on Ind. Electronics, V ol. 52, No. 3,pp 824-836, Je 2005.

[22]V. T. Somasekhar, S. Srinivas, B. P. Reddy, C. N. Reddy, and

Sivakuar PWM sitcing strateg for the dnaic-balancing of zeo-sequece cuent for a dual-inverer fed open-end winding induction motor drive" Proc. ET Electr. Power App., vol. , no. 4, pp.591600, Jul. 2007

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DC & AC drives etc

Srinivasan Prada bane received his gradate

degree om Pondichey University in 2005 and the post gdate degree om Anna University 2008, his area of specialzation eing Powe Electronics and Drives. Presetly he is a DoctoralCandidate at National stitte of Technology, Warangal. His research interests are Mltilevelverers and AC Drives.

Mr BVenugpal Reddy received his gradatedegree in Electrical Engineering om NTUCollege of Engeeing ,Hydaad and the post gradate degree om NIT, Warangal in 200 nd 2005 respectively. He is crrently woring towds his Ph.D degree m National stitte of Technology, Warangal, dia. His research interests

are Mltilevel inverers, Mltilevel PWMSwitching Stategies, Mltilevel inversion realized trogh Openend winding dction motor drives,

Dr V T. Smasekhar received his gradate degreeom Regional Engineering College Warangal(presently the National Institte of Technology) in988 and the post gradate degree om the Indian Institte of Tecology, Bomay in 990, his area of specialization eing Powe Electrnics. Hewored as an R&D engineer at Ms Peetal Power Technologies, Bangalore and as a sior engineer at Ms Kirlosar Electric Co. Ltd., Mysore. He joined the faclty of electrical engineering at the National

stitte of Technology in 993, where he is cently seving. He received

his doctoral degree om the dian Institte of Science in 2003. His crrent interests are mltilevel inversion with opened indction motors, AC drives and PWM strategies.

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