Torque Control of Brushless Direct Current Motor Drives using a Single Current Sensor with High Reliability

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1 Journl of Artfl Intellgene n Eletrl Engneerng, Vol. 5, No. 19, Novemer 216 Torque Control of Brushless Dret Current Motor Drves usng Sngle Current Sensor wth Hgh Rellty Astrt Mohsen Edpour 1, AhdFrznfr 2 1,2 Deprtment of Eletrl Engneerng. Ahr Brnh, Islm Azd Unversty, Ahr, Irn Eml: m.edpour@yhoo.om, hd_frznfr@yhoo.om Due to the smple struture, hgh torque densty, low mntenne, nd hgh effeny, rushless dret urrent (BLDC) motors re wdely used n utomton nd ndustrl ppltons. A ontrol strtegy sed on sngle urrent sensor s proposed for four-swth three-phse BLDC motor system to lower ost nd mprove rellty. The whole workng proess of the BLDC motor s dvded nto sx modes. Phse nvolves four modes, nludng modes 2, 3, 5, nd 6. Only one swth wll work n these modes. In modes 1 nd 4, two swthes wll work smultneously nd the urrent flows through phses nd. Compred to the most reent nd hghly performed torque ontrol strtegy, the proposed strtegy offers n mproved rellty thnks to the hevement of lned swthng frequenes of the nverter upper nd lower swthes. Furthermore, the torque rpple s dmpedsgnfntly durng setor-to-setor ommuttons usng hysteress urrent ontroller. The effetveness of the proposed system hs een vldted y smulton results usng MATLAB/Smulnk softwre n vrous operton ondtons. Keywords: Brushless Dret Current (BLDC) motor, Torque ontrol, Current sensor four-swth nverter, Hgh relle ontrol. 1- Introduton In reent yers, vrle speed drves equpped wth eletrl motors re extensvely ntegrted n vrous ppltons. Permnent mgnet rushless dret urrent (BLDC) motors offer mny dvntges nludng hgh effeny, low mntenne, greter longevty, redued weght nd more ompt onstrutons. The BLDC motors hve een wdely used n vrety of ppltons n ndustrl utomton nd onsumer pplnes euse of ther hgh power densty nd ese of ontrol [1], [2]. Nowdys, mny studes hve foused on how to redue the ost of the BLDC motor nd ts ontrol system wthout performne degrdton [3-5]. The ost reduton of vrle-speed drves suh s BLDC motor drves s omplshed y usng two pprohes. One s the topologl pproh nd the other s the ontrol pproh. From topology pont of vew, mnmum numer of swthes nd elmntng the mehnl sensors re requred for the nverter rut. In the ontrol pproh, lgorthms re desgned nd mplemented n onjunton wth redued omponent nverter to produe the desred speed-torque hrtersts [6]. 21

2 In reent yers, mny reserhes hve een onduted on ost-effetve drves nd ontrol tehnques for BLDC motors. In [7], new speed ontrol method usng the elerton feed-forwrd ompenston s proposed to mprove the speed response hrterst for four-swth three-phse BLDC motor. The dsturne torque estmton method s dopted to mprove the roustness of the method. An orgnl study on the generted torque rpples due to phse ommutton n the four-swth three-phse BLDC motor s presented n [8]. A urrent ontrol tehnque s developed to mnmze ommutton torque for the entre speed rnge. An dptve Nerofuzzy nferene system ontroller s proposed n [9]. Ths developed desgn does not requre n urte model of the motor nd hs frly smple struture. The four-spe-vetor sheme ws used n [1], the sx ommutton modes sed on urrent ontrol y two urrent sensors. Some work hs lso een done on sensorless BLDC motor drves [11], [12]. In ths pper, ost-effetve ontrol strtegy for four-swth three-phse BLDC motor drves usng only sngle urrent sensor s proposed. The proposed ontrol strtegy s sed on only one hysteress urrent ontroller for three phses. Moreover, further ttenuton of the torque rpple durng ommutton ntervls hs een gned thnks to the use of n pproprte torque ontroller. Seton 2 explns the BLDC motor operton prnple. In seton 3, nlyss of the proposed four-swth three-phse BLDC motor drve system sed on sngle urrent ontrol strtegy s explned. Fnlly, smulton results re gven seton BLDC Motor Oprton Pnpl The BLDC motor employs DC power supply swthed to the sttor phse wndngs of the motor y power deves, the swthng sequene eng determned from the rotor poston. The phse urrent of BLDC motor, n typlly retngulr shpe, s synhronzed wth the k EMF to produe onstnt torque t onstnt speed. Fg.1 shows the struture of sx-swth three-phse BLDC motor drve. These motors re drven y threephse nverter wth sx-steps ommutton. The ondutng ntervl for eh phse s 12 o eletrl degree. Therefore, only two phses ondut urrent t ny tme, levng the thrd phse flotng. The typl mthemtl model of the BLDC motor s desred s follows: v v v N N N R L R L R L d dt e e e (1) L ( L M ) S L (2) Where, v N represents the termnl phse voltge wth respet to the str pont, s the retngulr-shped phse urrent, e s the trpezodl-shped k EMF, nd R, L S nd L M re the resstne, self-ndutne nd mutul-ndutne, respetvely. T The eletromgnet torque s expressed s: e 1 ( e e e ) (3) r 22

3 Journl of Artfl Intellgene n Eletrl Engneerng, Vol. 5, No. 19, Novemer 216 Where, s the mehnl speed of the r rotor nd Te s the eletromgnet torque. The equton of moton s: d r ( Te TL Br ) / J (4) dt Where, B s the dmpng onstnt, J s the moment of nert of the drve nd T L s the lod torque. S 1 S 3 S 5 Fg.2. Bk EMF pttern nd referene urrent generton 3- Anlyss of the Proposed Drve System S 4 S 6 S 2 Fg.1. The struture of BLDC motor drve The ommutton tmng s determned y the rotor poston, whh n e deteted y Hll sensors or estmted from motor prmeters f t s sensorless system. For the three phses BLDC motor, the phse to phse k EMFs nd phse urrent wveforms re shown n Fg. 2. In order to otn n urte result for dynm performne, however, t s neessry to tke nto ount lrge numer of the hrmons. An lterntve nd more relst method s to use the tul k-emf nd urrent wveforms n stte vrle form. Usng ths method, the struture of the rotor of the BLDC motor nd ts hgh resstvty llows the neglet of ndued urrents n the rotor. Ths smplfes the modelng euse there s no need to tke nto ount the rotor dmper wndngs effets nd the relted equtons n e elmnted [13] Four-swth three-phse BLDC motor drve desrpton Fg. 3 shows the onfgurton of fourswth nverter for three-phse BLDC motor. Aordng to Fg. 3, two ommon ptors re used nsted of pr of rdges, nd phse s out of ontrol euse t s onneted to the mdpont of the seres ptors. Compred wth the onventonl sx-swth three-phse nverter for the BLDC motor, the whole workng proess of the BLDC motor n ths pper s dvded nto sx modes, s shown n Tle 1. Tle.1. Workng Mode of the Four-Swth Three-Phse BLDC Motor Mode Hll vlues Workng phse , , , , , , - Current Restrnt Condutn g deves I, I S 1, S 4 I S 1 I S 3 I, I S 2, S 3 I S 2 I S 4 23

4 S1 S3 S 2 S 4 Fg.3. Four-swth three-phse nverter Phse nvolves four modes, nludng modes 2, 3, 5, nd 6. Only one swth should work n the four modes. These modes re dvded nto two su-opertng modes. In modes 1 nd 4, phses nd hve urrent flowng through them, nd should e equl to zero. To vod urrent wveform dstorton, pproprte swth sgnls should e used n dfferent workng modes respetvely, whh mply tht some new ontrol shemes should e developed. Here, mode 1 s tken s n exmple to demonstrte the whole workng proess tht s dentl n mode 4. Mode 1 s dvded nto four su-opertng modes,.e. modes 11, 12, 13, nd 14, s shown n Fg. 4. Swthes S1 nd S4 work n mode 11 wth u U nd u. Dodes D2 nd D3 work n mode 12 wth u nd u U. Swth S1 nd dode D3 work n mode 13 wth u U nd u U. Swth S4 nd dode D2 work n mode 14 wth u nd u. Aordng to Fg. 4, the four su-opertng modes hve dfferent rules for djustng the phse urrents. Fg.4.. Su-opertng modes of mode1 Mode 11 Fg.4.. Su-opertng modes of mode1 Mode 12 Fg.4.. Su-opertng modes of mode1 Mode 13 Fg.4.d. Su-opertng modes of mode1 Mode 14 24

5 Journl of Artfl Intellgene n Eletrl Engneerng, Vol. 5, No. 19, Novemer 216 In mode 11, nd rse qukly, nd vres proportonlly wth the k EMF of phse. In mode 12, nd drop qukly, nd hnges proportonlly wth the k EMF of phse. Compred wth modes 11 nd 12, flls muh quker n mode 13 nd rses muh quker n mode 14. In ft, when devtes sgnfntly from zero, modes 13 nd 14 work properly. When remns t zero, modes 11 nd 12 work. Beuse nd nnot e deteted, speed loop nd Hll sgnls re used here to dede the duty of PWM sgnls Control of drve system usng sngle urrent sensor The whole ontrol system s shown n Fg. 5. The ontrol system dopts the doule-loop struture. The nner urrent loop mntns the retngulr urrent wveforms, lmts the mxmum urrent, nd ensures the stlty of the system. The outer speed loop s desgned to mprove the stt nd dynm hrtersts of the system. The system performne s deded y the outer loop. If the dsturne used y the nner loop, t n e lmted y the outer loop. As shown n Fg. 5, the whole ontrol system s mde up of three ontrollers s follows: Controller 1: Bsed on the poston Hll sgnls, ontroller 1 works when the motor runs t modes 2, 3, 5, nd 6. The shemt of ontroller 1 s shown n Fg. 6. As the PID ontroller hs smple struture, hgh effeny, nd esy mplementton, the smple PID ontroller s used s speed ontroller n ths pper. The speed error n e represented s follows: e( t) ( t) (5) Where, s the referene speed vlue nd (t) s the mesured speed vlue t tme t. The output of the speed PID ontroller s the t threshold vlue of the urrent regultor I ( ). The smple hysteress ontroller s lso used s urrent regultor. The nput of the urrent regultor s: e ( t) I ( t) ( t) (6) 1 t u ( ) s the duty of PWM sgnls. Controller 2: In modes 1 nd 4, I th s lose to zero. When I th, equl to zero, nd onsequently, s regrded s. Controller 2 works t ths stge, nd phse nd swth synhronously sed on the speed loop, just s the trdtonl sx-swth method does, s shown n Fg. 7. The nput of ontroller 2 s: e( t) ( k) (7) Controller 3: When the motor runs t modes 1 nd 4, nd I, ontroller 3 works th nsted of ontroller 2, s shown n Fg. 8. When I nd, sed on the Hll th sgnls, the strtegy s t the stge of suopertng mode 13 or mode 43 (swth S3 work n mode 43) nd the mgntude of drops qukly. If, the ontrol flow wll qut from ontroller 3. When I nd, the strtegy s t the stge of su-opertng mode 14 or mode 44 (swth S2 work n mode 44), nd the mgntude of rses qukly. If, the ontrol flow wll qut from ontroller 3. th 25

6 Hll Sensor Sgnls Mode 2,3,5,6 Mode 1,4 I th - > Controller 1 Controller 2 PWM Genertor Four-swth Three-phse Inverter BLDC Motor < ω Controller 3 Lod Fg.5.Shemt of the whole ontrol system Aove ll, the purpose of ontroller 3 s to keep Adjustment to workng phse urrent should e done y ontroller 2, fter ontroller 3 quts. ω ω + - ω(t) + - ω(k) (t) PID Controller I (t) + - (t) BLDC Motor u 1(t) Hll sgnls Four-swth Inverter Fg.6. Shemt of ontroller 1 <I th (t) PID Controller BLDC Motor u 2 (t) Hll sgnls Four-swth Inverter Fg.7. Shemt of ontroller 2 >I th - >I th BLDC Motor Mode 13 Mode 43 Mode 14 Mode 44 Hll sgnls Four-swth Inverter Fg.8. Shemt of ontroller 3 PWM Genertor PWM Genertor Swth Sgnls 4- Smulton Results To evlute the performne of the proposed drve system, smulton models hve een estlshed usng MATLAB/Smulnk. The mn prmeters of BLDC motor re s follows: nverter rted DC-lnk voltge 3 VDC, 1.5 kw, 15 rpm, 2 poles, r. 4, Ls 13mH, totl rotor nd lod nert 3 J 41 kg.m2, torque onstnt.4 T V/(rd/se). The smplng ntervl s 5μse, nd mgntude of the urrent hysteress nd s.2a. A onventonl PWM sheme for the sxswth nverter s used for the four-swth nverter topology of the BLDC motor drve, nd ts phse urrent wveforms re shown n Fg. 9. From Fg. 9, t s noted tht nnot e hold t zero, nd t uses n ddtonl nd unexpeted urrent, resultng n urrent dstorton n phses nd, nd even n the rekdown of the system. s 26

7 Journl of Artfl Intellgene n Eletrl Engneerng, Vol. 5, No. 19, Novemer 216 The sme prolem s nherted y the fourswth mode, nd t uses the produed voltge vetors to e lmted nd symmetr, whh were well known s symmetr voltge vetors. Ths prolem hs een solved y proposed ontrol strtegy n ths pper. Fg. 9. Phse urrent wveforms of the fourswth three-phse BLDC motor when t s ontrolled y the onventonl PWM strtegy. Speed, phse urrents nd eletromgnet torque wveforms of the proposed drve system re depted n Fg. 1, when the fourswth three-phse BLDC motor s ontrolled y the sngle urrent sensor strtegy. The qus-squre wveforms of phse urrents usng proposed method verfy the good ontrol plty of BLDC motor n omprson to onventonl methods. As shown n Fg. 1, the urrent nd torque rpples n onduton regon re elmnted effetvely. The torque spkes n ommutton regon re lso very low. 5- Conlusons Improve the drve system rellty nd optmzng softwre desgn re the key ponts to mplement the proposed strtegy n ndustrl pplton for further reserh. Ths pper ntrodued new ost-effetve BLDC motor drve. Cost svng s heved y redung the numer of nverter swthes nd urrent sensors. The sngle urrent sensor ontrol strtegy s used y the outer ontrol loop to develop the performne of speed ontrol tht leds to the sme hrtersts of sx-swth onverter for the proposed fourswth nverter. In spte of onventonl method, the proposed ontrol strtegy s le to ontrol the motor n se of nverter swthes fult (up to two swthes fult) usng one urrent sensor nd pproprte speed ontrol loop. Fnlly, the proposed strtegy hs een verfed suessfully y smulton results. Referenes [1] A. Dr, F. De Bele, P. D'hese nd J. A. Melkeeek, "Improved Dynm Behvor n BLDC Drves Usng Model Predtve Speed nd Current Control," n IEEE Trnstons on Industrl Eletrons, vol. 63, no. 2, pp , Fe [2] A. H. Nssr, A. Vhed, nd H. Moghell, Anlyss nd ontrol of ommutton torque rpple n four-swth three-phse rushless DC motor drve, n Pro. IEEE Ind. Tehnol. Conf., 26, pp [3] A. H. Nsr, H. Moghel, nd A. Vhed, Adptve neuron-fuzzy ontrol wth fuzzy supervsory lernng lgorthm for speed regulton of 4-swth nverter rushless DC mhnes, n Pro. IEEE Power Eletron. Moton Control Conf., 26, pp [4] A. H. Nsr, A. Vhed, nd H. Moghel, A novel poston sensorless ontrol of fourswth, rushless DC motor drve wthout phse shfter, IEEE Trns. Power Eletron., vol. 23, no. 6, pp , Nov. 28. [5] A. Ru nd P. Young, "Hrdwre/Softwre Implementton of Fuzzy-Neurl-Network Self- Lernng Control Methods for Brushless DC Motor Drves," n IEEE Trnstons on 27

8 Industry Appltons, vol. 52, no. 1, pp , Jn.-Fe [6] B. K. Lee, T.H. Km, M. Ehsn; On the feslty of four-swth three-phse BLDC motor drves for low ost ommerl ppltons: topology nd ontrol, n IEEE Trns. Power Eletron., vol. 18, no. 1, pp , Jn 23. [7] C. S. Joe, S. R. Prnjoth nd V. J. S. Kumr, "Dgtl Control Strtegy for Four Qudrnt Operton of Three Phse BLDC Motor Wth Lod Vrtons," n IEEE Trnstons on Industrl Informts, vol. 9, no. 2, pp , My 213. [8] D.-H. Jung nd I.-J. H, Low-ost sensorless ontrol of rushless DC motors usng frequeny-ndependent phse shfter, IEEE Trns. Power Eletron., vol. 15, no. 4, pp , Jul. 2. [9] J.-H. Lee, T.-S. Km, nd D.-S. Hyun, A study for mproved of speed response hrterst n four-swth three-phse BLDC motor, n Pro. IEEE Ind. Eletron. So. Conf., 24, vol. 2, pp [1] J.-H. Lee, S.-C. Ahn, nd D.-S. Hyun, A BLDCM drve wth trpezodl k EMF usng four-swth three phse nverter, n Conf. Re. IEEE IAS Annu. Meetng, 2, vol. 3, pp [11] J. Sho, D. Noln, M. Tesser, nd D. Swnson, A novel mroontroller-sed sensorless rushless d (BLDC) motor drve for utomotve fuel pumps, IEEE Trns. Ind. Appl., vol. 39, no. 6, pp , Nov./De. 23. [12] M. Edpour, M R. AlzdehPhlvn, Performne Anlyss nd the Cost Effetve Poston Sensorless Control of Axl Flux PM Brushless DC Motor, Journl of Asn Eletr Vehles, vol. 11, no. 2, pp Deemer 213. [13] P.Plly nd R.Krshnn, Modelng, Smulton nd Anlyss of Permnent Mgnet Motor Drves, Prt II: The Brushless DC Motor Drve, IEEE Trnstons on Industrl Appltons, vol.25, no.2, pp , Apr

9 15 Speed (rpm) 1 5 Eletromgnet Torque (N.m) t (s) () t (s) () Phse A Phse B Phse C Phse Currents (A) t (s) () Fg. 1. Smulton wveforms when the motor s ontrolled y the sngle urrent sensor strtegy; () Speed urve, () Eletromgnet torque urve, () Phse urrent wveforms 29