Forming of Six-Phase Double Layer Induction Motor Windings

Forming of Six-Phase Double Layer InductionMotor WindingsBenas Kundrotas, Roma Rinkevičien÷Vilnius Gediminas Technical University (Lithuania)benas.kundrotas@dok.vgtu.lt, roma.rinkeviciene@vgtu.ltAbstract—The article deals with forming of two type sixphaseinduction windings: concentrated double layer short pitchcoil winding and concentrated double layer full pitch coilwinding. Two types of six-phase motor windings are discussed,magnetomotive forces are considered.I. INTRODUCTIONMultiphase (more than three phase) machine drives are thefocus of research recently due to their inherent advantagescompared to three-phase machine drives. Multiphasemachines drive has increased torque per ampere for the samevolume machine, reduced stator copper losses, and reducedrotor harmonic currents, high power handling capability bydividing the required power between multiple phases, reducedtorque pulsations and higher reliability. In particular, unlikein a three phase drive, the loss of stator phase does notprevent the machine from starting and running [1], [2].The applicability of multiphase motors is explored in shippropulsion, locomotive traction, electric vehicles, where themain advantage of multiphase drives consists of splitting thecontrolled current on more inverter legs, reducing the singleswitch current stress compared to the three-phase converters.Improved reliability is advantageous in nuclear power plantsfor its circulation pumps and for other similar applications inprocess industries [4] – [8].This paper presents forming of two types windings for sixphaseinduction motor, shows elaborated connection ofwinding sections and comparison of two types concentrateddouble layer windings: short pitch coil six-phase winding andfull pitch coil six-phase winding.II. SIX-PHASE WINDINGSDouble layer windings have many advantages over singlelayer windings: easier to manufacture and lower cost of coils,fractional-slot can be used, chorded-winding is possible,lower leakage reactance and therefore, better performance ofthe machine.Six-phase motor was elaborated by rewinding of threephase motor with number of slots S = 48 .Parameters of concentrated double layer short pitch coilsix-phase stator winding: total number of slots S = 48 ,number of poles 2P = 8 , number of phase m = 6 , pole pitch τ0= 6, slot angular pitch γ = 30 , number of slots per pole per0phase q = 1 , coil pitch y = 5 , phase spread σ = 30 , angle0between stator current phasors is 60 . Connection ofconcentrated double layer short pitch coil six-phase windingsection is presented in “Fig. 1”. Parameters of concentrateddouble layer full pitch coil six-phase stator winding: totalnumber of slots S = 48 , number of poles 2P = 8 , number of0phase m = 6 , pole pitch τ = 6, slot angular pitch γ = 30 ,number of slots per pole per phase q = 1 , coil pitch y = 6 ,0phase spread σ = 30 , angle between stator current phasors is060 . Connection of concentrated double layer full pitch coilsix-phase winding section is presented in “Fig. 2”.Fig. 1. Connection of concentrated double layer short pitch coil six-phasewinding section.1 phasestart1 7'612'13 19'1824'25 31'3036'37 43'4248'1 phaseend2 phasestart3 9'814'15 21'2026'27 33'3238'39 45'442'2 phaseend3 phasestart5 11'1016'17 23'2228'29 35'3440'41 47'464'3 phaseend4 phasestart7 13'1218'19 25'2430'31 37'3642'43 1'486'4 phaseend5 phasestart9 15'1420'21 27'2632'33 39'3844'45 3'28'5 phaseend6 phasestart11 17'1622'23 29'2834'35 41'4046'47 5'410'6 phaseendFig. 2. Connection of concentrated double layer full pitch coil six-phasewinding section.“Fig. 3” shows instantaneous current values in the slots ofconcentrated double layer short pitch coil six-phase windingat time instant t = 0 . Connection of concentrated double layershort pitch coil six-phase winding section and distribution ofmagnetomotive force is presented in “Fig. 4”.93

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20+ + + - - - - - - + + + + + + - - - - -+ + - - - - - - + + + + + + - - - - - -21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40- + + + + + + - - - - - - + + + + + + -+ + + + + + - - - - - - + + + + + + - -a)41 42 43 44 45 46 47 48- - - - - + + +- - - - + + + +b)Fig. 3. Instantaneous current values: a) at the time instant t = 0; b) in upper and lower levels of slots.Fig. 4. Connection of concentrated double layer short pitch coil six-phase winding section and distribution of magnetomotive force.“Fig. 5” shows instantaneous current values in the slots ofconcentrated double layer full pitch coil six-phase winding attime instant t = 0 . Connection of concentrated double layerfull pitch coil six-phase winding section and distribution ofmagnetomotive force is presented in “Fig. 6”.It is evident that in case of concentrated double layer shortpitch coil six-phase winding, instantaneous current values,during pole pitch margins, are the same in upper and lowerlevels of five slots and only once the values of instantaneouscurrent in upper and lower levels are different.94

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20+ + + - - - - - - + + + + + + - - - - -+ + + - - - - - - + + + + + + - - - - -21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40- + + + + + + - - - - - - + + + + + + -- + + + + + + - - - - - - + + + + + + -a)41 42 43 44 45 46 47 48- - - - - + + +- - - - - + + +b)Fig. 5. Instantaneous current values: a) at the time instant t = 0; b) in upper and lower levels of slots.1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48W1 U’1 V’1 W’1U1 V’2 V1 W’2 U2 V2 W2 U’2Fτ /2 τ /2xFig. 6. Connection of concentrated double layer full pitch coil six-phase winding section and distribution of magnetomotive force.In case of concentrated double layer full pitch coil sixphasewinding, instantaneous current values, during polepitch margins, are the same in all upper and lower levels ofslots. Research shows, that magnetomotive force amplitude ofsix-phase motor with concentrated double layer short pitch95

coil winding is smaller than six-phase motor withconcentrated double layer full pitch coil winding.Analysis of the considered first type of winding indicates,that during one pole pitch the relative magnetomotive forceF1(φ) has the shape, shown in “Fig. 7”. Analysis of thesecond type winding shows, that relative magnetomotiveforce F2(φ) in the one pole pitch displacement varies in theway, shown in “Fig. 8”.Fig. 7. Relative magnetomotive force F1(φ) ant its approximation by Fourierseries F1,Σ50(φ).the first harmonic of the first winding approximately is equalto 0.8 and that of the second winding is equal to 0.6. So fromthe view of first harmonic the motor with concentrated doublelayer short pitch coil winding will have higher efficiently thanmotor with concentrated double layer full pitch coil winding.Analysis shows, that even harmonics have the sameamplitude and they are equal to zero. Research indicates thatthe odd higher harmonics of concentrated double layer fullpitch coil winding having greater amplitude than concentrateddouble layer short pitch coil winding. While the higherharmonics increase torque oscillations and heat loss, it ispossible to state, that the first winding has greater efficiency.So research indicated that according to the harmonicspectrum, the concentrated double layer short pitch coilwinding has greater efficiency than concentrated double layerfull pitch coil winding.III. CONCLUSIONSThe advantages of multiphase motors against three phasemotors are discussed. The areas of application of themultiphase motors are considered.Two types of six-phase motor windings connections areanalysed: concentrated double layer short pitch coil windingand concentrated double layer full pitch coil winding.Concentrated double layer short pith coil six phase windinghas the first harmonic greater by 22 % than concentrateddouble layer full pith coil six phase winding.Research indicated that according to the harmonicspectrum, the short pith coil winding has greater efficiencythan full pith coil.REFERENCESFig. 8. Relative magnetomotive force F2(φ) ant its approximation by Fourierseries F2,Σ50(φ).Space harmonic spectrum of each winding magnetomotiveforce was obtained on the base of Fourier series. Analysis ofmagnetomotive forces gives information about higherharmonics that appear in the air gap. More detailedcalculation shows that concentrated double layer short pitchcoil six-phase winding has the first harmonic significantlygreater (22 %) than concentrated double layer full pitch coilsix-phase winding. Analysis shows, that relative amplitude of[1] E. Levi, “Multiphase electric machines for variable-speed applications,”IEEE Trans. Industrial Electronics, vol. 55(5), pp. 1893-1909, May2008.[2] R. Gregor, F. Barrero, M. J. Duran, M. R. Arahal, S. Toral, “Modelbased predictive current control of an asynchronous six-phase motordrive,” available from Internet: .[3] J. I. Leon, O. Lopez, L. G. Franquelo Fellow, J. Doval-Gandoy, S.Vazquez, J. Alvarez, F. D. Freijedo, “Multilevel multiphasefreedforward space-vector modulation technique,” IEEE Trans.Industrial Electronics, vol. 57(6), pp. 2066-2075, 2010.[4] E. Levi, “Multiphase electric machines for variable-speed applications,”IEEE Trans. Industrial Electronics, vol. 55(5), pp. 1893-1909, May2008.[5] O. Lopez, J. Alvarez, J. Doval-Gandoy, F. D. Freijedo, “Multilevelmultiphase space vector PWM algorithm,” IEEE Trans. IndustrialElectronics, vol. 55(5), pp. 1933-1942, May 2008.[6] R. Gregor, F. Barrero, S. Toral, M. J. Duran, “Realization of anasynchronous six-phase induction motor drive test-rig,” in Proc.International Conf. Renewable Energy and Power Quality, 2008.[7] R. S. Miranda, C. B. Jacobina, A. M. N. Lima, “Modeling and analysisof six-phase induction machine under fault condition,” IEEE Trans.Power Electronics, vol. 9(1), pp. 824-829, 2009.[8] I. Rata, P. Todos, I. Nuca, “A review of multiphase electric machines,”Electromechanical and Power Systems, vol. 6(1), pp. 154-159, 2007.96