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Multiphase Induction motor-a Novel Design Prof. Dr.Archana S. Nanoty, Principal, Dr. Jivraj Mehta Institute of Technology, Mogar, Anand, Gujarat Abstract— Variable-speed AC motor drives with more than three phases (multi-phase drives) have several advantages when compared to the standard three-phase realizations [1,2]: the current stress of the semiconductor devices decreases proportionally with the phase number, torque ripple is reduced, rotor harmonic currents are smaller, power per rms ampere ratio is higher for the same machine volume and harmonic content of the DC link current for VSI fed drives is reduced. Other advantages include an improvement in the noise characteristics [3] and a reduction in the stator copper loss, leading to improved efficiency [4]. Further advantages are related to the higher reliability at the system level, since a multi-phase drive can operate with an asymmetrical winding structure in the case of loss of one or more inverter legs/machine phases [5,6] generate a rotatory field. Consequently, if one phase is lost the drive continues operating although at different rating values. Because of this reason, during the last three decades there is a growing interest to research several issues related to the use of multi-phase drives as a potential alternative for the conventional three-phase systems. This is especially true for dual three phase induction motor drives and their applications [4]. This induction machine has two sets of three-phase windings which are spatially phase shifted by 30 electrical degrees, as shown in figure 1. Applications of multi-phase induction motor drives are mainly related to the high-power/high-current applications, such as for example in electric ship propulsion [7,8], in locomotive traction [9,10] and in electric/hybrid electric vehicles [11]. Keywords— six-phase induction machines, split phase Winding. Magnetic circuit, Dual Stator machines INTRODUCTION:- Conventional 3-phase drives have been extensively used in industry applications. However, if one of the phases is lost, the rotatory field also disappears and the machine stops. The multi-phase drives offer the improvement of the system reliability, which is of great interest in specialized applications such as electric/hybrid vehicles or aerospace applications. Independently of the number of phases the multi-phase machine has, it only needs two degrees of freedom to Figure 1:- Six phase Induction Motor Split-phase electrical machines consist of two similar stator windings sharing the same magnetic circuit. Such a construction made it possible to extend the power range of solid-state based drives by sharing the total power between two drives [2,4]. Usually a split-phase machine is built by splitting the phase belt of a conventional three-phase machine into two equal parts with spatial phase separation of 30 electrical degrees. By using this arrangement, for the same air gap flux, the inverter dc bus voltage can be reduced by approximately a half, compared to a three-phase system, since the number of turns per phase is reduced [4]. Such structure has a disadvantage of the need for two or more inverters to drive the machine. Another advantage of using this kind of winding arrangement is harmonic cancellation. The sixth harmonic torque pulsation, which is common in a six-step three-phase drive, can be eliminated by using split-phase arrangement, [5, 6]. As in split-phase machines, the dual-stator machines consist basically of two independent stator windings sharing the same magnetic frame. Differently, a dual stator machine does not necessarily have similar winding groups. For example, a 6 different voltage rating or a different number of phases could be used for each winding group. The six-phase machine uses the same magnetic frame with the baseline machine. We have the 4-pole machine with 36 stator slots. In order to keep the leakage distribution balanced, the phases are displaced among the two stator layers. The six-phases are constructed such that one three-phase group is displaced from the other one by 30 electrical degrees. Thus we have an asymmetrical six phase machine where; One of the three-phase groups has the same structure of the baseline machine with half of the circuits and winding distributed in 3 slots per pole per phase (qA = 3). The second group is distributed into 4 slots per pole per phase (qX = 4) but keeping the same number of conductors per pole per phase. The stator size used is the stator used for 7.5 HP motor as the torque is very high about 40 % more than that of the original 3 phase 3 HP motor .The details of the stator dimensions are as follows. STATOR DIMENSIONS:- Stator Bore or Inner Diameter =125 mm Stator Slots = 36 ROTOR DIMENSIONS:θm = 2. θe / p θm = 2 . 30° / 4 = 15° mechanical (I) (II) Slot pitch = 360° / 36 = 10° mechanical (III) Outer Diameter =125 mm Rotor Slots = 28 Conductor size:- 22 SWG Conductors per slot = 104 Hence, the 30 electrical degrees displacement corresponds to 15°/10° = 1.5 slots. No. of Turns per phase= 312 Insulation:- ClassF We cannot implement such a configuration and have to use an approximation. This is how it is done: Figure 4:- Winding Diagram of ‘Phase C’ Figure 2:- Winding Diagram of ‘Phase A’ Figure 5:- Winding Diagram of ‘Phase X’ Figure 3:- Winding Diagram of ‘Phase B’ Figure 6:- Winding Diagram of ‘Phase Y’ Figure 7:- Winding Diagram of ‘Phase C’ Conclusion:- The motor testing results are as given below:When terminals ABC are supplied with 3 phase Ac. Supply Voltage Current Speed In Amp in ABC In RPM 60 V 0.94,0.9,0.9 1475 105 V 1.27,1.27,1.24 1489 152 V 1.82,1.77,1.75 1491 202 V 2.33,2.30,2.37 1492 When terminals XYZ are supplied with 3 phase AC. Actual Photograph of 6 ph stator at the time of winding Actual photograph of the motor with two three phase sets abc and xyz Supply Voltage Current Speed In Amp in ABC In RPM 60 V 0.91,0.84,0.84 1467 108 V 1.36,1.34,1.38 1484 154 V 1.8,1.88,1.82 200 V 2.41,2.32,2.38 1492 1486 Now the motor is to be run when both the three phase sets are supplied simultaneously i.e. six phase operation. For that we need to supply the motor through inverter. The torque obtained very high upto 40 % more than the three phase motor of same rating. Motor finds its application in Ship Propulsion, Air craft, Hybrid electric Vehicle Etc. where Large torque at lower speed is required. Also overall efficiency of the motor increases. Future Scope:- The motor stability can be calculated. The same motor may be controlled using other methods than Vector control, e.g. DTC or SLMC. Acknowledgement:- This motor design is carried out at JSL, Mogar. This has become possible only because of encouragement of Dr.K.K.Thakkar, Director,JSL and the staff at JSL Mogar in design section. References [1] Maria Imecs, Andrzej M. Trzynadlowski, Fellow, IEEE, Ioan I. Incze, and Csaba Szabo “Vector control schemes for Tandem converter fed induction motor drives” IEEE transactions on power electronics, vol. 20, no. 2, march 2005. [2] Bimal Bose, “Modern Power Electronics and AC Drives”, Prentice Hall [3] R. H. Nelson and P. C. Krause, “Induction machine analysis for arbitrary displacement between multiple windings,” IEEE Transactions on Power Apparatus and Systems, vol. 93, pp. 841-848, May 1974. [4] T. A. Lipo, “Flux sensing and control of staticac drives by use of fluxcoils,” IEEE Transactions on Magnetics, vol. MAG-13, Sept 1997 [5] O. Ojo and I. E. Davidson, “PWM-VSI inverterassisted stand-alone dual stator winding induction generator,” IEEE Transactions on Industry Applications, vol. 36, pp. 1604-1611,Nov 2000.