Efficiency Optimized Brushless DC Motor Drive based on Input Current Harmonic Elimination

Transcription

1 Intrnational Journal of Powr Elctronics and Driv Systm (IJPEDS) Vol. 6, No. 4, Dcmbr 2015, pp. 869~875 ISSN: Efficincy Optimizd Brushlss DC Motor Driv basd on Input Currnt Harmonic Elimination Tridibsh Nag 1, Arijit Acharya 1, Dbashis Chattrj 2, Ashok K. Ganguli 2, Arunava Chattrj 2 1 Dpartmnt of Elctrical Enginring, Ntaji Subhash Enginring Collg 2 Dpartmnt of Elctrical Enginring, Jadavpur Univrsity Articl Info Articl history: Rcivd Fb 19, 2015 Rvisd Aug 5, 2015 Accptd Aug 28, 2015 Kyword: Brushlss DC motor Efficincy optimization Slctiv harmonic limination Snsorlss control Total harmonic distortion ABSTRACT This papr dscribs fficincy improvmnt of a position snsorlss brushlss dc motor with improvd puls width modulation schm for th invrtr compard to xisting ons. This is basd on Slctiv Harmonic Elimination. Th proposd mthod rducs Total Harmonic Distortion from th input currnt and armatur flux and thrby rducing th cor losss. Also th powr rquirmnt with th proposd switching tchniqu is much lssr than th xisting switching schm. Th ffctivnss of th proposd schm is dmonstratd through simulation and xprimntal rsults. Copyright 2015 Institut of Advancd Enginring and Scinc. All rights rsrvd. Corrsponding Author: Tridibsh Nag, Dpartmnt of Elctrical Enginring, Ntaji Subhash Enginring Collg, Tchno City, Garia, Kolkata , India. tridibshnag@gmail.com 1. INTRODUCTION Brushlss DC (BLDC) motors hav bn widly usd in various industris, automation and appliancs du to thir highr fficincy, improvd ruggdnss and powr dnsity. Brushlss DC (BLDC) motors with trapzoidal back lctromotiv forc (EMF) charactristics rquirs six discrt rotor position information for th invrtr as thy ar usd to triggr th switchs, hr mtal oxid smiconductor fild ffct transistor (MOSFET). Brushlss DC motors rquir lowr maintnanc du to th lack of mchanical commutator and thy hav high powr dnsity. For ths rasons thy ar idal for high torqu to wight ratio applications [1]. Th most important drawback of BLDC machin is high initial cost and rlativ highr complxity du to th convrtr part. Rducing losss through th injction of propr dirct axis currnt in th stator winding is also prsnt [2]. Th control algorithm dtrmins th optimal dirct axis currnt according to th oprating spd and loading conditions. Efficincy improvmnt through using both axial and radial flux also has bn studid [3]. Utilizing both radial and axial gaps can incras th ffctiv ara for torqu gnration and th fill-factor for th coil winding. By optimizing cor and prmannt magnt to minimiz th lctromagntic loss whil maintaining th sam lvl of torqu, th magntic saturation of th cor is also rducd. Th iron loss can b rducd by th flux-wakning control [4]-[6]. To rduc th air gap flux by th dmagntizing ffct du to th d-axis armatur raction, d-axis currnt is controlld. Optimal control mthod of armatur currnt vctor is proposd in ordr to minimiz th controllabl losss [7]. Switching tchniqus for BLDC motor torqu rippl rduction is proposd prviously using microcontrollr [8]. FPGA basd PWM is also prsntd in [9]. Also Fuzzy logic basd spd control is discussd in [10]. In th proposd control, th phas currnt wavform is switchd ffctivly to liminat som lowr ordr Journal hompag:

2 870 ISSN: harmonics which will rduc th harmonics gnratd by th stator flux. This will also nsur that th BLDC to hav minimal cor losss. Figur 1 shows th quivalnt circuit of a BLDC motor. R a La a R b L b b R c L c c Figur 1. Equivalnt circuit of a BLDC motor 2. BLDC MOTOR MODEL Th thr phas voltag quations from th quivalnt circuit of Figur 1 for th BLDC motor can b writtn as, va Ra 0 0 ia La 0 0 ia a d v b 0 Rb 0 i b 0 Lb 0 i b b dt v c 0 0 R c i c 0 0 L c i c b (1) Whr, v = stator voltag, R = stator rsistanc, i = stator currnt, L= stator inductancs and = back mf. Th abov quantitis ar dfind for thr phass a-b-c. Th mchanical dynamic quation for th motor can b givn as, d Tm () t (t) B J TL ( t) (2) dt Whr, T m (t) = dvlopd lctromagntic torqu, ω (t) = rotor angular vlocity, B = viscous friction constant, J = rotor momnt of inrtia and T L = load torqu. Th back EMF (a phas) can b dscribd as, k () t a (3) Whr, k = pr-phas back EMF Th voltag quation in Laplac domain can b obtaind from (1) and (2) for phas a as, V () s R I () s L si () s k () s (4) an a a a a From (4), th phas currnt can b givn as, V () () a( ) an s K s I s R sl a a (5) Th lctromagntic torqu T m can b xprssd as, T m ( i a a i b b i c c) (6) IJPEDS Vol. 6, No. 4, Dcmbr 2015 :

3 IJPEDS ISSN: PROPOSED SHE PWM BASED LOSS MINIMIZATION For a Trapzoidal mf machin considrd, th back mf and phas currnt wavforms for phas a considring 120 o switching ar givn in Figur 2(a) for normal switching and Figur 2(b) for PWM switching rquird for spd control applications. From Figur 2(a) th harmonic currnts can b obtaind as, Figur 2. Phas currnt wavform for 120 o conduction mod (a) normal switching (b) PWM switching Th corrsponding xprssion for th currnt wavform for 120 o conduction mod can b givn as, 4I Ia [cossint cos3sin 3t cos5sin 5t cos 7sin 7 t...] (7) Putting α = 30 o in quation (7), th harmonic spctrum can b givn in Figur 3. Figur 3. Harmonic spctrum for 120 o conduction mod for normal phas currnt wavform Using th proposd switching with rmoval of 5 th and 7 th harmonics as shown in th proposd Slctiv Harmonic Elimination basd (SHE) PWM switching of Figur 2(b), th harmonic spctrum can b shown in Figur 4. Figur 4. Harmonic spctrum for 120 o conduction mod for SHE-PWM phas currnt wavform Efficincy Optimizd Brushlss DC Motor Driv basd on Input Currnt Harmonic... (Tridibsh Nag)

4 872 ISSN: Th phas currnt of BLDC motor for 120 contains harmonics as vidnt from Figur 2(a). It is rasonably apparnt that by liminating th currnt harmonics, th cor losss can b minimizd, thus highr fficincy in th givn spd rang can b obtaind. For rmoval of 5 th and 7 th harmonics from th wavform, thr switchings ar prformd pr quartr cycl of th currnt wavform. Of th thr switchings, two ar usd for limination of th 5 th and 7 th harmonics and on switching is usd for adjustmnt of th fundamntal. This procss of slctiv harmonic limination basd PWM is mployd using a PIC basd microcontrollr PIC18F452. Th block diagram of th xprimntal stup is shown in Figur 5. L 230V, 50Hz, 1-Φ AC C BLDC SHE-PWM pulss Microcontrollr 18F452 Figur 5. Block diagram of th xprimntal stup Hystrsis Loss: This loss is du to th rvarsal of magntisation of th armatur cor. Th cor undrgos on complt cycl of magntic rvarsal aftr passing undr on pair of pols. Hystrsis loss is givn by wll known Stinmntz quation xprssd as, W K B f Watts (8) h h 1.6 max Whr f = Fundamntal frquncy, Bmax is th maximum flux dnsity of th stator cor and K h = Hystrsis constant. Taking harmonic componnts into account for a thr phas balancd systm, (8) can b modifid as, W K B f K B f K B f n trm (9) max 5max 5 7max 7... th h h h h Eddy Currnt loss: Whn prmannt magnt rotor of th BLDC motor rotats, flux linkag changs in stator armatur cor. Thus according to th laws of lctromagntic induction an.m.f is inducd in th cor body which sts up larg currnt in th cor du to its small rsistanc. Th powr loss du to th flow of this currnt is known as ddy currnt loss. Th ddy currnt loss pr unit cor volum W is givn by rlation (10), W K B f Watts (10) 2 2 max Again, taking harmonic componnts in account (10) can b modifid as, W K B f K B f K B f n trm (11) th max 5max 5 7 max 7... As vidnt from quation (9) and (11), both th losss contain harmonic trms. Rmoval of th 5 th and 7 th ordr harmonics from th phas currnt will nsur rducd harmonic contnt in th inducd flux linkags. Rmoval of ths harmonics from th phas currnt will contribut to a inducd flux wavform with minimal cor losss. Consquntly, th input powr rquirmnt for th BLDC motor will diminish. IJPEDS Vol. 6, No. 4, Dcmbr 2015 :

5 IJPEDS ISSN: With th rmoval of lowr ordr harmonics in phas currnt wavform, th torqu pulsation also gts rducd. 4. RESULTS AND DISCUSSION A simulation study for th proposd schm was carrid out using MATLAB/Simulink R2012b. To validat th simulation, an xprimntal study was also conductd using an xprimntal BLDC motor. Th complt spcification of th motor is providd in Tabl 1. Th rquird 48V DC for th BLDC motor is obtaind through a singl phas diod bridg rctifir modul. Th DC voltag is filtrd with a LC filtr bfor it is fd to th thr phas invrtr drivr. Th PIC microcontrollr is usd for gnrating SHE basd PWM for th BLDC drivr. Th switching angls for th PWM ar calculatd offlin and ar stord in th microcontrollr for onlin us. Tabl 1. BLDC spcifications Paramtrs Spcifications/Ratings Motor typ Surfac Prmannt Magnt typ Ratd Powr 350W Ratd Voltag 48V Ratd Spd 450 r/min No. of pols 12 Winding 3-phas star connctd Rsistanc 2.5 Ω Inductanc 11.2 mh Th simulatd wavform for th phas currnt for normal phas currnt is shown in Figur 6(a) and with proposd switching is shown in Figur 6(b). Figur 6. Simulatd wavform for phas currnt for spd rfrnc of 450 rpm for 120 o conduction mod for (a) normal switching (b) proposd SHE PWM switching Similar phas currnt wavform was obtaind with th xprimntal stup. Th xprimntal wavforms wr stord using a Tktronix mak digital storag oscilloscop. Th normal phas currnt is shown in Figur 7(a) and with proposd switching is shown in Figur 7(b). Th input powr vrsus motor spd at no-load is plottd to justify th lowr powr rquirmnt for th proposd SHE-PWM control. As obsrvd from th plot of Figur 8, with th proposd control, th powr rquirmnt dcrass than xisting switching control schm. A 20% rduction of powr rquirmnt can b obsrvd at ratd spd in th proposd switching schm which is of much rlvanc. Efficincy Optimizd Brushlss DC Motor Driv basd on Input Currnt Harmonic... (Tridibsh Nag)

6 874 ISSN: Figur 7. Exprimntal wavform for phas currnt for spd rfrnc of 450 rpm for 120 o conduction mod for (a) normal switching (b) proposd SHE PWM switching Figur 8. Plot for input powr vs motor spd 5. CONCLUSION A simpl fficincy optimization schm for BLDC driv systm is proposd. Th fficincy optimization is ralizd by liminating unwantd lowr ordr harmonics for th motor currnt and thrby rducing torqu pulsations. Slctiv Harmonic Elimination basd PWM is mployd for this purpos which rducs th convrtr switching losss. Th simulation and xprimntal rsults sum up th suitability of th proposd schm. REFERENCES [1] CW. Lu, "Torqu Controllr for Brushlss DC motors", IEEE Transactions on Industrial Elctronics, vol. 46, pp , [2] C. Cavallaro, t al., "Efficincy Enhancmnt of Prmannt-Magnt Synchronous Motor Drivs by Onlin Loss Minimization Approachs", IEEE Transactions on Industrial Elctronics, vol. 52, pp , [3] KJ. Kang, t al., "Dvlopmnt of a highly fficint brushlss dc motor utilizing both radial and axial air gaps", Journal of Applid Physics, vol. 111, [4] B. Snyrs, t al., "Fild Wakning in Burid Magnt ac Motor Drivs", IEEE Transactions on Industry Application, vol. IA-21, pp , [5] TM. Jahns, "Flux-Wakning Rgim Opration of an Intrior Prmannt-magnt Synchronous Motor Drivs", IEEE Transactions on Industry Application, vol. IA-23, pp , [6] BK. Bos, "A High-Prformanc Invrtr-fd Driv Systm of an Intrior Prmannt Magnt Synchronous Machin", IEEE Transactions on Industry Application, vol. IA-24, pp , [7] S. Morimoto, t al., "Loss Minimization Control of Prmannt Magnt Synchronous Motor Drivs", IEEE Transactions on Industrial Elctronics, vol. 41, pp , [8] SS. Bharatkar, t al., "Dual-mod Switching Tchniqu for Rduction of Commutation Torqu Rippl of Brushlss dc Motor", IET Elctric Powr Applications, vol. 5, pp , IJPEDS Vol. 6, No. 4, Dcmbr 2015 :

7 IJPEDS ISSN: [9] T. Sutikno, t al., "FPGA basd a PWM Tchniqu for Prmannt Magnt AC Motor Drivs", Intrnational Journal of Rconfigurabl and Embddd Systms, vol. 1, pp , [10] P. Agrawal, t al., "Comparativ Study of Fuzzy Logic Basd Spd Control of Multilvl Invrtr fd Brushlss DC Motor Driv", Intrnational Journal of Powr Elctronics and Driv Systm, vol. 4, BIOGRAPHIES OF AUTHORS Tridibsh Nag rcivd th Bachlor of Enginring dgr in Elctrical Enginring from Sikkim Manipal Univrsity of Mdical Scinc and Tchnology, Gangtok,Sikkim, India, in 2002 and Mastr of Elctrical Enginring Dgr with spcialization in Elctrical Machins from Jadavpur Univrsity, Kolkata, in 2004.Prsntly h is pursuing Ph.D dgr in th Dpartmnt of Elctrical Enginring, Jadavpur Univrsity, Kolkata, India and h is Assiatant Profssor in Elctrical Enginring Dpartmnt at Ntaji Subhash Enginring Collg Kolkata. His main rsarch intrst includs Control of Elctric Drivs & Powr Elctronics, Rnwabl Enrgy Gnration & Control. Arijit Acharya rcivd th Bachlor of Tchnology dgr in Elctrical Enginring from Wst Bngal Univrsity of Tchnology, Kolkata, in 2011 and Mastrs of Tchnology with spcialization in Powr Systm from Ntaji Subhash Enginring Collg, Kolkata in Prsntly h is working as Visiting Lcturr at Ntaji Subhash Enginring Collg, Kolkata. His main rsarch intrst includs Powr Elctronics, Elctric Drivs and Rnwabl Enrgy Rsourcs. Dbashis Chattrj rcivd th B.E.dgr in Elctrical Engg. from Jadavpur Univrsity, Kolkata, India, in 1990 and M. Tch. Dgr from IIT Kharagpur and Ph.D. dgr in Elctrical Engg. from Jadavpur Univrsity, Kolkata, in 1992 and 2005 rspctivly. From 1992 to 2002, h workd as a Sr. Excutiv Enginr in National Radio Elctronics Co. Ltd. in Drivs and Automation Systm, Dvlopmnt Excutiv in Crompton Gravs Limitd-Industrial Elctronics group and Asst. managr R&D in Philips India Ltd. in Lighting Elctronics Division. Currntly, h is Associat Profssor in Elctrical Engg. Dpartmnt at Jadavpur Univrsity, Kolkata. His main rsarch intrst includs Control of Elctric Drivs & Powr Elctronics, Rnwabl Enrgy Gnration & Control. Ashok K. Ganguli rcivd th B.E., MEE and Ph.D. dgr in Elctrical Engg from Jadavpur Univrsity, Kolkata, India, in 1968, 1979 and 1993 rspctivly. H has a larg numbr of intrnational and national publications and an industrial xprinc of svral yars. Currntly, h is Profssor in Elctrical Engg. Dpartmnt at Jadavpur Univrsity, Kolkata. His main rsarch intrst includs Machin Drivs & Powr Elctronics. Arunava Chattrj rcivd th B.Tch. and M.E. dgr in Elctrical Engg from Wst Bngal Univrsity of Tchnology and Jadavpur Univrsity, Kolkata, India, in 2008 and 2011 rspctivly. Prsntly, h is a CSIR Snior Rsarch Scholar in Elctrical Engg. dpartmnt at Jadavpur Univrsity working towards his Ph.D. His main rsarch intrst includs Elctrical Machin Drivs, Powr Elctronics & Rnwabl Enrgy Systms. Efficincy Optimizd Brushlss DC Motor Driv basd on Input Currnt Harmonic... (Tridibsh Nag)