Microsoft Word - 4-1781_s_ok_.docx Engineering, Technology & Applied Science Research Vol. 8, No. 3, 2018, 2646-2650 2646 www.etasr.com Boztas et al.: Design and Analysis of Multi-Phase BLDC Motors for Electric Vehicles Design and Analysis of Multi-Phase BLDC Motors for Electric Vehicles Gullu Boztas Electrical and Electronics Engineering Dpt University of Firat Elazıg, Turkey gboztas@firat.edu.tr Merve Yildirim Electrical and Electronics Engineering Dpt University of Firat Elazıg, Turkey merveyildirim@firat.edu.tr Omur Aydogmus Mechatronics Engineering Dpt University of Firat Elazıg, Turkey oaydogmus@firat.edu.tr Abstract—This paper presents a design and analysis of multi- phase brushless direct current (BLDC) motor for electric vehicles (EV). In this work, hub-wheels having 110Nm, 900rpm rated values have been designed for the proposed EV. This EV can produce 440 Nm without using transmission, differential and other mechanical components which have very high losses due to the mechanical fraction. The motors to be used in the EV have been designed as 3-, 5- and 7-phase by Infolytica/Motor Solve Software to compare their performances at the same load conditions. The same rotor geometry has been utilized for the motors. However, slot numbers and dimensions of the stator have been determined by considering the motor phase number. Performance curves of phase-currents, output powers, torques, efficiencies and power factors have been presented for these motors at the same operating conditions. It can be possible to use lower power switches in motor drive system thanks to the phase current reduction since the phase currents decrease proportionally to motor phase number. This work shows that the multi-phase BLDC motors are a good alternative in order to obtain lower torque and lower power inverter structure than the 3-phase BLDC motors which are used as standard. Keywords-brushless direct current motor; multi-phase motor; electric motor design I. INTRODUCTION Interest on electric vehicles (EV) has increased recently because of their environmental advantages, high energy efficiency, and low noise [1]. Significant properties of brushless direct current (BLDC) motors for EVs are high power density and high efficiency. Besides, there are important advantages such as small size, high reliability, not having rotor copper losses and low maintenance cost due to not having brushes [2, 3]. Therefore, BLDC motors are commonly preferred in industry applications. In [4], a novel five-phase wheel hub motor which occurs from identical electromagnetic units with U-shaped electromagnets in the stator and permanent magnets in the rotor is designed. The electromagnetic torque of the motor is calculated and analyzed by finite element method (FEM). Torque ripple, average torque, torque per ampere and the ratio of torque to copper loss are examined for optimal design and speed regulation. Authors in [5] propose a novel hub motor using variable electromagnetic (EM) gearing to leverage torque and rotation speed based on driving conditions. The performance of the motor in terms of voltage/current ratings and energy conversion efficiency is compared with other conventional motors. It is seen that this motor is useful for vehicle propulsion applications. Authors in [6] explain the design of permanent magnet (PM) BLDC hub motor using FEM analysis. The no-load and load characteristics are analyzed, torque and cogging torque of PM BLDC hub motor are calculated by Magnet Software 7.4.1 for different temperatures. Flux distribution and flux density in the core are also obtained. It is shown that PM BLDC hub motor can be used for applications including less cogging torque than total torque. In [7], a design of three phase PM BLDC hub motor which has high efficiency and power density and no cogging torque is realized for electrically powered two wheelers. Some methods are used to reduce the cogging torque and increase the net torque. PM BLDC motor is also analyzed by using 2D FEM. The simulation results are tested by experimental results. It is seen that PM BLDC hub motor has high efficiency and it is convenient for different scooter load and speed conditions. In [8], field oriented control based on hall-effect sensors of PM brushless hub motor is defined for four-wheel drive EV. The aim of the study is to obtain high efficiency and low torque ripple by a feedforward controller. Results show that the feedforward field oriented control reduces the motor torque ripple. Ironless axial flux PM in-wheel hub motor is designed by using multi-domain FEM analysis [9]. 3D FEM analysis is realized in different physical domains showing temperature distribution, cooling system heat flows and the motor is tested experimentally. Results show that the designed in-wheel hub motor has high torque and high efficiency. Different control methods for PM brushless hub motor of four-wheel drive EV are defined in [10]. BLDC and PMSM control are combined. Since the performance of the sinusoidal current control is very good and the torque ripple is much lower than that of the block commutation algorithm, this control is preferred at low speeds. On the other hand, the noise is high at middle and high speeds due to switching and harmonics. Therefore, sinusoidal control or field oriented control and block commutation algorithm are used for low, middle and high speeds respectively. Results show that low noise and successful performance are obtained Engineering, Technology & Applied Science Research Vol. 8, No. 3, 2018, 2646-2650 2647 www.etasr.com Boztas et al.: Design and Analysis of Multi-Phase BLDC Motors for Electric Vehicles for four-wheel drive EV by the proposed approach. Feedforward and feedback speed regulation control of hub motor for EV with in-wheel motor is explained in [11]. The linear feedforward control with the incremental PID feedback control is realized and these control methods can be switched easily considering the driving demand and the running condition. It is obtained from the results that this control method provides a good speed regulation and shows the drivability of the in-wheel EV. The control methods of an EV driven by two rear hub motors are defined to examine the ride quality of EV in [12]. Vehicle dynamics with 11 degrees-of- freedom are modeled by using MATLAB’s Simulink. Simulations with PID controller, fuzzy-PID controller and without controller are realized and compared with each other. According to the simulations, these control methods improve yaw rate and the stability of the EV based on the steering and contribute to EVs with hub motors. In [13], computer aided design (CAD) of a PM BLDC hub motor is realized. Designed PM BLDC hub motor with 30W, 48V, and 310rpm is used for a fan application. Flux density in the air gap and iron, stack length, slot space factor, length of the air gap and the number of the magnet poles are taken as design variables. Furthermore, the parametric analysis of BLDC hub motor is realized to develop the design in terms of the efficiency and size of the motor. By using FE analysis, designed algorithm is verified and the torque angle characteristics are obtained in the paper. In this paper, three different BLDC motors have been designed for the comparison of motor performances based on the phase number. The slot numbers, dimension and geometry of the stator are changed to achieve a good comparison on the effect of the phase number. However, the rotor geometry of the compared motors is the same. It has been shown that the rated currents of the stator winding inversely decrease with the number of the phases. Thus, it can be possible to use lower power switches in the motor drive systems. The output power, efficiency and power factor remain as constant values for the compared motors in this study. As a result, it can be observed that increasing of the motor phase number is an advantage in terms of the motor quality. In this work, the pole number and the slot numbers of the designed motors have been taken as 24 and 27 (3-ph), 55 (5-ph), 63 (7-ph), respectively. Furthermore, torque and rated speed values of the motors are approximately 110Nm and 900rpm, respectively. II. MODELING OF BLDC MOTOR In modeling of a 3-phase BLDC motor, armature winding and torque equations are used [14]. The equivalent circuit of BLDC motor having trapezoidal back EMF is shown in Figure 1. Back EMF and torque constant is a function of the rotor position. As seen in the Figure 1, the voltage equations within the armature windings based on the back EMF can be given by (1) [14].                                                                    nnnn e e e I I I L I I I R V V V : : : :. : :. : : 2 1 2 1 2 1 2 1    (1) R1 L1 e1 R2 L2 e2 Rn Ln en 1.PH 2.PH n.PH Fig. 1. BLDC equivalent circuit where n is the phase number, V1, V2,….., Vn are the supplied voltages to each phase R is armature winding resistance, I is phase current, L is inductance and e is back EMF. There is a (360/n) phase angle between back EMFs of each phase as follows [14] )(. ))1( 2 ( : : ) 2 ( )( )( : : )( )( 2 1 t n n k n k k te te te en en en n                                            (2) where ken is back EMF constant of one phase of the n-phase motor. Output torques of each phase are given by [14]: )1( 2 1 2 1 )( : : )( )( . ))1( 2 ( : : ) 2 ( )( )( : : )( )(                                                       tI tI tI n n k n k k tT tT tT nTn Tn Tn n      (3) where kTn is torque constant of a phase of the n-phase motor. Total output torque can be defined as ne TTTT  ...21 (4) where Te is total output torque. III. MULTI-PHASE MOTORS DESIGN In motor design, nominal speed and torque values should be firstly determined. According to these two parameters, motor mechanical restrictions like motor dimension should be taken into consideration. It is also important to obtain a geometry for reducing torque ripples. Generally, torque ripples can be reduced by increasing the BLDC pole number. In this paper, three different motors have been designed: 3-phase, 5-phase and 7-phase. Designed motors structure is shown in Figure 2, in which while stator forms the interior of the motor, rotor is the outer of the motor. Stator and rotor structures and flux lines and flux densities of BLDC motors designed for different phases are shown in Figures 3 and 4, respectively. Flux lines and flux density of the three motors are illustrated in Figure 4. Ma cal sur and dif sta cur Th of the res illu sig low nu Engineerin www.etasr aximum flux lculated as 1.9 The designe rface mounted d outer rotor d fference is the ator slot area i rrent value c herefore, more the slot of 3-p e designed mo spectively. Mechanical a ustrated in Tab gnificantly red wer phase cur mber. In this ng, Technology r.com density obtai 94 T. Fig. 2. BLDC (a) ed motors ha d with radial m diameters have number of slo is needed for l changes inve e coil area is o phase BLDC m otors are 27, 5 and electrical ble I. As show duce inversely rrent will be o s way, both y & Applied Sci ined from sta C hub-motor struc Fig. 4. F ave the same magnets per p e been taken a ots and the slo lower phase n ersely with th obtained by re motor. The num 55, and 63 for parameters of wn in Table I, s y with the ph obtained by in cost and siz ience Research Boztas ator core has Rotor Core Stator Core Coil Magnet Air Gap Shaft cture (b) Flux lines and flu rotor structu pole and their as equal. 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PWM an sis of 5-phase Figures 6 and n low speeds i At 100 rpm s than 71% wh ximately 82% wards rated s nce analysis is igure 8. Des tained like the ower factor of gh speed regio are shown in rtional to the otor currents a ectively. y & Applied Sci reased to 10.3 nder full load c GNED MOTOR PAR 3-phase 5-p 96 164 1 27 300 3 80 274 2 115 1 curves of the desi nalysis for 3-phase motor is reali d 7, the perfo is worse than speed, the eff hile the efficie . However, th speeds are sig s realized for ired performa e other motors f the motors a ons. Stator ph n Figure 9. C number of t are 164A (3-ph ience Research Boztas 3 kW. Power conditions. RAMETERS phase 7-phase 96 96 102 70 55 63 300 300 80 80 274 274 170 189 igned motors e motor ized in Figure ormance of 5- that of the 3- ficiency of 5- ency of the 3- he performanc gnificantly si 7-phase moto ance from 7- . The output p are given in Ta hase currents Current value the phase. Th h), 102A (5-ph h V et al.: Design factor e 7. As -phase -phase -phase -phase ces of imilar. or and -phase power, able-II of the es are e rms h) and thre pha As How pha the the Vol. 8, No. 3, 20 and Analysis of Fig. Fig. Fig. 9. TABLE II. Phase Number P (k 3 1 5 1 7 1 The output t ee motors in F ase motors are the number wever, as see ase motor can phase numbe stator currents 018, 2646-2650 of Multi-Phase B 7. PWM ana 8. PWM ana Stator phase cur COMPARISON Low Speed Reg (150 rpm) Pout kW) Eff. (%) 1.8 82 1.8 71 1.8 70 torque curve Figure 10. The approximatel of phases in n in Figure 1 n be regarded er by more tha s. BLDC Motors f alysis for 5-phase alysis for 7-phase rrents of the desig NS FOR LOW/HIGH gion High PF Pout (kW) 0.15 10.3 0.15 10.1 0.15 10.1 is separately e torque rippl ly 10%, 5% an ncreases, torqu 0, the result o as sufficient. an 5 is useful 2649 for Electric Veh motor motor gned motors SPEED REGIONS h Speed Region (900 rpm) Eff. (%) PF 95 0.58 92 0.51 92 0.51 examined fo es of 3-, 5- an nd 6% respecti ue ripple red obtained by th Hence, incre l only for redu hicles or the nd 7- ively. duces. he 5- asing ucing foc Th Fir mo Th dim of by ana by cur and sam ob inc low sho ord ph and des EV bee Th out inc sig mo ph per [1] [2] [3] [4] Engineerin www.etasr In this study cus on compa hese motors u rstly, a 3-pha otor. This mot hen, 5-phase mensions of th the slots and considering alyses of the 3 Infolytica/M rves of phase d power facto me operating served that a creases, the p wer power sw ows that multi der to use low ase BLDC mo d power value signed motors V, total output en obtained as he other impo tput torque c creases, the gnificantly red otor are lower ase number rformance and X. Fu, “A nov International C Application, C M. Yildirim, M motor types International P Exposition, An S. M. Jang, H. brushless DC m Magnetics, Vo C. Sun, L. Bai shaped electro IEEE 9th Co Hangzhou, Chi ng, Technology r.com (a) Fig. 10. V. CO y three motors aring the effec used as wheel ase BLDC hu tor has inner and 7-phase he base motor dimensions of the motor p 3-, 5-, and 7-p Motor Solve S e-currents, outp ors have been conditions. as the numbe phase currents witches in mo i-phase BLDC wer power inv otors that are es have been c s. By consider t torque and o s 440 Nm and ortant characte curve. As th torque ripp duces. Howeve than that of o should be d usability whe REFE vel design for flyw Conference on Int Changsha, China, V M. Polat, H. Kuru and drives use Power Electronic ntalya, Turkey, pp W. Cho, S. K. Ch motor for centrifu ol. 43, No. 6, pp. 2 , X. Du, Y. 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