A Study on Brushless DC Motor for High Torque Density

Transcription

1 Intenational Jounal of Mechanical and Mechatonics Enineein A Study on Bushless DC Moto fo Hih Toque Density Jun-Moo Seo, Jun-Hwan Kim, Se-Hyun Rhyu, Jun-Hyuk Choi, and In-Soun Jun, Senio Membe, IEEE Abstact Bushless DC moto with hih toque density and slim topoloy fo easy loadin fo obot system is poposed and manufactued. Electomanetic desin is executed by equivalent manetic cicuit model and numeical analysis. Manufactued moto is tested and veified chaacteistics compain with conventional BLDC moto. Keywods Bushless DC moto, Robot joint module, Toque density, Pole/slot atio I I. INTRODUCTION N sevice and humanoid obot systems, each pat composin oveall system is developin in a fom of module suitable fo easy constuction. Joint divin systems ae one of the most momentous pats which could detemine obot pefomance. Especially in multi-dof divin module, output chaacteistics of each actuato could affect divin eliability and efficiency of oveall system. Slim shaped motos o actuatos ae pofitable to make up joint module compain with conventional type, because space fo divin module and oveall system volume could be educed [1]. Slotless motos which ae applied in obot systems ae adequate fo small sized joint module due to the elative small diamete, howeve, the axial lenth is much lone than the slotted one. That means, inteated actuato module combined with deceleato and contolle in axial diection is not suitable fo joint module. Futhemoe, the induced toque is smalle and otational speed is hihe than the slotted type []. Slot type motos with multi-poles have hih inductance value and shot axial lenth compaed with slotless model, but they have weak point fo educin diamete of coe size due to the slot confiuation. Except some special applications which have enouh space in axial diection, slim shaped slot type moto is adequate fo joint module fo obot. Especially, if inteated actuatin modules connected with deceleatin ea tain and contolle in the fowad and backwad sides ae equied, shape of slot type motos is suitable fo joint module system [3]. In this study, to develop the moto with hih toque density and efficiency in iven small space, toque constant is detemined as one of the Jun-Moo Seo is with Intellient Mechatonics Reseach Cente, KETI (Koea Electonics Technoloy Institute), KOREA (phone: ; fax: ; sjm@keti.e.k) Jun-Hwan Kim is with Intellient Mechatonics Reseach Cente, KETI (Koea Electonics Technoloy Institute), KOREA ( kjh@keti.e.k) Se-Hyun Rhyu is with Intellient Mechatonics Reseach Cente, KETI (Koea Electonics Technoloy Institute), KOREA ( shhyu@keti.e.k) Jun-Hyuk Choi is with Intellient Mechatonics Reseach Cente, KETI (Koea Electonics Technoloy Institute), KOREA ( cjh@keti.e.k) In-Soun Jun is with Intellient Mechatonics Reseach Cente, KETI (Koea Electonics Technoloy Institute), KOREA ( isjun@keti.e.k) Stato coe(split) PM Roto coe Shaft Fi. 1 Basic stuctue of the poposed moto with phase A windin layout. The stato coe is split key factos to be impoved []. Toque constant is elated to the flux linkae o inductance and the inductance is affected by windin tun numbe and eluctance of manetic cicuit. In split coe stuctue, coil fill facto can be inceased, which can incease windin tun numbe o educe coppe loss with bie coil diamete. Pole and slot numbe ae also consideed in this study fo impovin toque constant and efficiency. II. DESIGN AND SIMULATIONS Geneally, as the pole numbe is inceased, the induced toque and ion loss ae inceased in constant output condition. The pole/slot atio affects windin facto and the facto is elated to toque constant. Theefoe, pole and slot numbe should be detemined considein manufactuin capabilities, windin facto, and ion loss. Distibuted windin has a meit to incease windin facto (maximum facto 1), howeve, end tun pat can be obstacle fo educin coppe loss and oveall axial lenth of moto. Split coe with concentated windin is applied in the poposed model, windin facto is equied to maximize as possible. Table I shows the windin facto accodin to the pole/slot combinations [4]. As can be seen in Table I, if the pole/slot atio is 1/1, 14/1, 16/1, /4,, the maximum windin facto of.966 can be obtained. Theefoe, in iven oute diamete of 45mm, pole/slot atio of 1/1 is detemined considein windin facto, manufactuin capabilities. In this stuctue, we choose paallel-cicuits pe phase which ae maximum paallel-cicuit without ciculatin cuents in ode to incease coil fill facto with espect to the coil diamete decease. 84

2 Intenational Jounal of Mechanical and Mechatonics Enineein TABLE I COMBINATION OF NUMBER OF SLOTS AND POLES WITH BALANCED CONCENTRATED WINDING P S (a) moto stuctue and flux path (b) Simplified manetic cicuit Fi. Manetic cicuit model Basic stuctue of the poposed moto is shown in Fi. 1. The thee phase BLDC moto with 1 pole/1 slot has double layeed concentated windin and hihh eney pemanent manet (NdFeB mateial) in oto coe. The fundamental object of desin pocess is to detemine the back EMF of moto, so ai ap flux density calculation is equied in the fist step. In this study, manetic cicuit model is used to compute desin paametes and finite element analysis is applied to confim the esults and execute specific desin. Fi. shows the manetic cicuit of moto. In Fi. (b), the manetic flux Ф can be expessed as Φ Rm = Rm + KR Φ = 1 (1) Φ R 1 + K R whee R m and R ae manet and ai ap eluctance espectively m EMF@1pm[V] Fi. 3 Flux line of the desined moto Anle[deee] Fi. 4 Thee phase back EMF at 1,pm, Ф is flux souce, and K is eluctanc5e facto which inceases ai ap eluctance slihtly to compensate fo the missin steel eluctance[5]. The ai ap flux can be witten as Kl () Φ = KlΦ = Φ µ Am 1+ K l m A whee K l is the flux leakae facto. Considein the flux linkae wavefom which vaies fom a maximum positive value Ф to a maximum neative value Ф, back EMF ove half an electic cycle is iven by dλ dλ NΦ E = = ω e = pωm = Keω (3) m dt dθ e π a whee λ is flux linkae and p is pole pai numbe, N is the numbe of conductos pe phase, and a is the numbe of paallel paths. Usin the windin coefficient K w, the back EMF constant K e can be expessed as U V W 85

3 Intenational Jounal of Mechanical and Mechatonics Enineein Fi. 5 Ion loss distibution at ate condition TABLE II IRON LOSS DISTRIBUTION AT RATE CONDITION Loss Stato coe Roto coe Hysteesis loss[w] Eddy cuent loss[w] Ion loss[w] Total ion loss[w] 1.37 TABLE III MOTOR SPECIFICATIONS Item Value Moto type 3 phase 1p/1s Rate speed [pm] 6, Rate toque [mnm] 4 Rate powe [W] 15 Divin voltae [V] 48 Diamete of stato coe [mm] 43. Diamete of oto coe [mm]. Active lenth [mm] 5 Ai ap [mm].5 PM emanency [T] 1.3(Nd sinteed) Numbe of tuns/phase 7 pnφ Kw Ke = (4) π a The width of teeth body and stato yoke ae detemined by (5) and (6) [5]. π Ro B wtb = (5) N K B w sy s st t π Ro B = (6) N K B m st sy whee R o, K st, N s, N m, B t, and B sy ae oto adius, stackin facto, numbe of slot and pole, flux density of teeth and stato yoke, espectively. D finite element simulations ae used to confim electomanetic chaacteistics of the desined moto. Fi. 3 shows flux line of the simulated model and Fi. 4 shows the back EMF popety of desined moto at otational speed of 1,[pm]. Fom those esults, we could estimate EMF o toque constant and no-load speed. Thouh the detemined paametes includin applied voltae and coil esistance, evolution speed and input cuent chaacteistics with espect to loadin toque ae estimated. Fi. 5 and Table II show the ion loss analysis esults. As expected, eddy cuent loss which is popotional to the squae of fequency and flux density is dominant at ate condition of 6,[pm]. Oveall ion loss is 1.37[W] and coe loss can be calculated by coil esistance and Fi. 6 Manufactued moto Fi. 7 Measued back EMF induced in each phase coil at 1,pm input cuent. The desin paametes of the poposed moto ae shown in Table III, finally. III. MEASUREMENT AND VERIFICATION A. Manufactuin and test Fi. 6 shows manufactuin pocess of the desined moto. As mentioned befoe, the split coe is applied to the poposed moto fo inceasin coil fill facto. We build up independent windin to sepaated stato coes and combine the all coes usin fomin ji, and then connect windins each othe. In ode to simplify windin connection and educe windin space, additional PCB is used and assembled to windin pat. Paallel manetized Pemanent manet is attached to the suface of oto coe keepin constant ap. Thee-phase back EMF of the manufactued moto at 1,[pm] is appeaed in Fi. 7. and input cuent wavefom at ate condition is shown in Fi. 8. Fo the loadin toque test, the moto is connected to toque measuin system as in Fi. 9. Measuement equipment consists of DC powe supply, dynamomete fo output chaacteistics estimation, powe analyze fo input powe calculation, and laptop compute fo display and load contol. Sensoless BLDC amplifie is used to dive the poposed Fi.1 shows output chaacteistics of manufactued moto. As can be seen in this fiue, no load speed is about 7,[pm] and maximum efficiency is 89[%]. In ate condition of 15[W], 86

4 Intenational Jounal of Mechanical and Mechatonics Enineein density defined as the atio of toque and volume (weiht) can be compaed each othe. The detailed specifications of the TABLE IV DESIGN PARAMETERS OF AFPM AND RFPM MOTOR Desin paamete Pole/slot Conventional 1/9 Poposed 1/1 Rated input voltae [V] Oute diamete of coe [mm] Windin facto.956 Ai ap [mm] PM emanency [T].5 1.3(sinteed NdFeB) Active lenth [mm] Paallel cicuit pe phase Numbe of tuns pe phase Speed [pm] Fi. 8 Input cuent wave plot of manufactued moto Oscilloscope Test moto Contolle Dynamomete Powemete Fi. 9 Toque measuin system Eff. N Po I Toque [Nm] Po I Eff. [W] [A] [%] Fi. 1 Output chaacteistics of manufactued moto otational speed, toque, and efficiency ae 6,[pm], 4mNm, and 88[%], espectively. B. Pefomance compaison In ode to analyze elative toque density and efficiency of the poposed moto, we compaed with conventional moto havin diffeent pole/slot atio. The compaed moto has also split stato coe with concentated windins and simila ate output powe and cuent density. The main diffeence between two motos is axial lenth of stato and oto coe. That means, by measuin output toque at the same input condition, toque Conventional moto Poposed moto Fi 11 assembled two motos assembled poposed moto and compaative moto ae shown is Table IV.. To estimate the toque density of the motos, back EMF o static toque measuement could be used. In this study, static toque is measued by applyin diect cuent of 1[A] to two phases. In this condition, toque chaacteistics with espect to oto position ae measued and the esults ae shown in Fi. 1.. Peak to peak toque values of the conventional and poposed moto ae about 145[mNm] and 141[mNm]], espectively. It means toque constant and no load speed of two motos is almost the same.. Theefoe, toque density is hihe in poposed moto compaed to the conventional moto. Also the maximum efficiency of the poposed moto is about 5[%] hihe than the conventional moto. This esult is caused by hihe windin facto due to the pole/slot atio and lowe ion and coe loss due to the lowe pole numbe and hihe coil fill facto. Fi. 13 shows coin toque 87

5 Intenational Jounal of Mechanical and Mechatonics Enineein Toque [mnm] Toque [mnm] Anle[deee] Fi. 1 Static toque compaison Fi. 13 Coin toque compaison of two motos. As can be seen in Fi. 13, coin toque of the poposed moto is smalle than the conventional one with the same slot openin lenth. This eason why the coin toque is detemined fom the least common multiple of pole and slot numbe and the moe numbe of toque cycle, the less manitude of coin toque is obtained [6]. IV. CONCLUSION popoesed moto conventional moto Anle[deee] poposed moto conventional moto In this study, bushless DC moto with hih toque density is poposed and manufactued. Manetic desin is executed by equivalent manetic cicuit and D FE model, and optimal pole/slot atio and slot/teeth space fo hih toque and efficiency ae detemined. Thouh the output chaacteistics compaison, we confim the toque density and efficiency of the poposed one is supeio to conventional 1p/9s moto. Those slim shaped divin machines ae expected to apply divese aeas demandin hih toque and small space as well as obot joint module. obot joint module, Powe Electonics Confeence (IPEC), pp.1336, June. 1. [] N. Bianchi, S. Bolonani, and F.Luise, Analysis and desin of PM bushless moto fo hih-speed opeations, IEEE Tans. Eney Conves., vol., no. 3, pp , Sep.5. [3] M. Makovic, Y. Peiad, Simplified desin methodoloy fo a slotless bushless DC moto, IEEE Tans.Manetics, vol. 4, No. 1, Dec.6. [4] F. Manussen and C. Sadaanani, Windin factos and Joule losses of pemanent manet machines with concentated windins, Electic Machines and Dives Confeence,. IEMDC`3 IEEE Intenational., vol. 1, pp. 333, June. 3. [5] D. Hanselman, Bushless Pemanent Manet Moto Desin, second edition, The wites collective, 3 [6] C. Beton, J. Batolome, J.A. Benito, G.Tassinaio, I.Flotats, C.W.Lu, B.J. Chalmes, Influence of machine symmety on eduction of coin toque in pemanent-manet bushless motos, IEEE Tans. Manetics, vol. 36, no. 5, pp , Sep. REFERENCES [1] Jun-Moo Seo, Se-Hyun Rhyu, Joo-Han Kim, Jun-Hyuk Choi, In-Sun Jun, Desin of axial flux pemanent manet bushless DC moto fo 88