An Efficient Bridgeless PFC Cuk Converter Based PMBLDCM Drive

Transcription

1 ISSN (Onlne) Vol. 2, Issue 2, February 214 An Effcent Brdgeless PFC Cuk Converter Based PMBLDCM Drve Jomy Joy 1, Amal M.R 2, Rakesh R 3, Kannan S.A 4, Anna Rana 5 M Tech Scholar, Power Electroncs, Toc H nsttute Of Scence And Technology, Ernakulam, Kerala, Inda 1 M Tech Scholar, Power Electroncs, Toc H nsttute Of Scence And Technology, Ernakulam, Kerala, Inda 2 M Tech Scholar, Power Electroncs, Toc H nsttute Of Scence And Technology, Ernakulam, Kerala, Inda 3 M Tech Scholar, Power Electroncs, Toc H nsttute Of Scence And Technology, Ernakulam, Kerala, Inda 4 Assstant Professor, Department of EEE, Toc H nsttute Of Scence And Technology, Ernakulam, Kerala, Inda 5 Abstract: A new brdgeless Cuk PFC converter drvng a permanent magnet brushless DC motor drve s proposed here. In the case of a conventonal BLDCM drve system there wll be a rectfer and a PFC converter connected to the drve through a voltage source nverter. In ths project t s replaced by a brdgeless PFC Cuk converter and the voltage source nverter connected to the PMBLDCMD. Ths mproves the effcency of the drve as well as mantans a unty power factor. Ths s because of the brdgeless topology ntroduced whch does not have an nput dode brdge rectfer. That s there wll be less number of semconductor swtches n the current flowng path. The brdgeless Cuk converter s desgned to work n dscontnuous conducton mode. The proposed PMBLDM drve s desgned wth necessary controls and modeled n MATLAB Smulnk and smulated results are presented. Also a comparson s made between proposed drve system and the conventonal Cuk rectfer fed PMBLDCM drve. Keywords: Cuk converter, Power factor correcton (PFC), Brdgeless Cuk converter, low conducton losses, total harmonc dstorton, permanent magnet brushless DC motor (PMBLDCM). I. INTRODUCTION The applcatons f PMBLDC motors are ncreasng n the day to day lfe because of ts features lke low mantenance, hgh effcency, and wde speed range. More over t s rugged due to the permanent magnets on the rotor. The commutaton n a PMBLDCM s done by a three phase voltage source nverter. The PMBLDCM can be used n varous applcatons lke ar condtonng system, electrc tracton etc. In all these applcatons the drve system has long lfe, low runnng cost and reduced electrcal and mechancal runnng stresses. But the condton s that the qualty of the power supply should meet specfc standards lke IEC A PMBLDCM has developed torque drectly proportonal to phase current and ts back EMF, whch s proportonal to the speed. That s, t has a constant current n ts stator wndngs wth varable voltage across ts termnals mantans constant torque n a PMBLDCM under varable speed operaton [1]. Speed control scheme used s a normal PWM control. However, the control of VSI s done by electronc commutaton based on the rotor poston sgnals of the PMBLDC motor. In conventonal cases a PMBLDCM drve s fed from a sngle-phase ac supply va a dode brdge rectfer (DBR) followed by a capactor at dc lnk. The capactor draws current n short pulses. Ths wll generate harmoncs and yeld poor PF, resultng n poor power qualty. Therefore varous PFC converter topologes are avalable n order to meet the requred IEC standard. Most of the PMBLDC drve from the supply va dode brdge rectfer and a capactor. But the capactor draws pulsated currents whch results n harmoncs due to an uncontrolled chargng of the dc lnk capactor. So PFC converters are mplemented n front of the dc lnk capactor n order to supply a constant DC current. Therefore, a PF correcton (PFC) converter among varous avalable converter topologes [3] s applcable for a PMBLDCMD. Among these topologes most of them use boost topology at them front end. But the swtchng losses are hgh due to the presence o f the dode brdge. Ths affects the effcency of the whole drve system. Several topologes are proposed n order to maxmze the effcency of power supply. Brdgeless topologes are one such converter whch can reduce the swtchng losses by reducng the number of power semconductor swtches n the current conducton path [4] [5]. By usng ths brdgeless topology the nput dode brdge s avoded and therefore conducton losses are reduced whch yeld a better effcent system. Mostly used converter topology s brdgeless boost converter. But t s applcable only for boost operaton and moreover t has hgh start up nrush current and lack of galvanc solaton [4]. The proposed topology n [6] ntroduces a buck brdgeless converter but has the dsadvantages lke low output voltage, hgh output voltage rpple. The topology proposed n [7] a SEPIC converter has relatvely hgh output rpple due to the dscontnuous output current. So f these converters are used n a drve system Copyrght to IJIREEICE 138

2 ISSN (Onlne) Vol. 2, Issue 2, February 214 dsadvantages of those converters wll decrease the effcency of the whole drve system. The cuk topology based converter offer varous advantages ahead of the above topologes, such as such as easy mplementaton of transformer solaton, natural protecton aganst heavy nrush current occurrng at start-up or overload current, lower nput current rpple, and less electromagnetc nterference (EMI) assocated wth the dscontnuous conducton mode (DCM) topology. The DCM s preferred over other modes for havng some added advantages lke natural near-unty power factor, the power swtches are turned ON at zero current, and the output dodes are turned OFF at zero current[8] [9]. II. BRIDGELESS CUK CONVERTER The brdgeless Cuk converter proposed n [1] yelds the perfect result so that the drve system wll be effcent as well as power factor s mproved to unty. The proposed converter n Fg (1) acts as an AC-DC converter wthout an nput dode brdge; so named as a brdgeless topology. Fg 1: Brdgeless Cuk Converter [1] The brdgeless Cuk converter has the advantage over the conventonal cuk converter n the case of swtchng losses. Two DC DC Cuk converters are connected as n Fg 1 to form the brdgeless topology. One of the Cuk DC-DC converters wll operate for each half-lne perod (T/2) of the nput voltage. Accordng to Fg 1 there are one or two semconductor(s) n the current conducton path. Therefore the current conducton losses n the actve and passve swtches are further reduced and the crcut effcency s mproved compared to the conventonal Cuk converter. Common mode nose problem due to the pulsatng output voltage wth respect to the ground s a major drawback of almost all converters. So n order for balancng the crcut there by prevent the common mode nose problem, here output voltage s always connected to the nput ac lne through the slow-recovery dodes D p and D n. Thus, the proposed topology does not suffer from the hgh commonmode EMI nose emsson problem. As n the brdgeless converter shown n Fg (1) there are two power semconductor swtches, Q 1, Q 2 along wth two recovery dodes D p,. The swtches can be drven by the same control wth the condton that Q 1 wll be ON at postve cycle of the nput voltage and Q 2 vce versa. Ths can reduce the control crcutry complexty Assume that the converter s operatng at a steady state n addton to the followng assumptons: pure snusodal nput voltage, deal lossless components. The output flter capactor s large enough such that the voltage across t s constant. Durng the postve half cycle of the nput AC, the frst dc dc Cuk crcut, L 1 Q 1 C 1 L o1 D o1, wll be actve through the postve dode D p. Ths connects the nput ac source to the output. Durng the negatve half-lne cycle, the second dc dc Cuk converter crcut, L 2 Q 2 -C 2 L o2 D o2, s actve through negatve dode Dn, whch connects the nput ac source to the output. The operaton of the brdgeless rectfer s made n dscontnues node by sutable desgn of the actve and passve components lke nductors, capactors. By operatng the rectfer n DCM, several advantages can be acheved. These advantages nclude natural near-unty power factor, the power swtches are turned ON at zero current so less turn ON losses, and the output dodes (D o1 and D o2 ) are turned OFF at zero current so turn OFF losses are reduced. The brdgeless topology has an addtonal nductor as compared wth conventonal topology whch s a dsadvantage but the topology wll have good thermal performance. III. CONVERTER DESIGN The desgn of the converter s made as below wth certan mathematcal assumptons. The DCM operaton s obtaned wth the followng condton: 1 K e < K e crt = (1) 2(M+sn (ωt )) 2 where K e s a dmensonless conducton parameter and s gven by: K e = 2L e R L T s (2) The values of the parastc components are desgned such that they follow the DCM condton such that K e < K e crt _mn and those maxmum and mnmum values of K e- crt are as below: K e crt _mn = 1 2(M+1) 2 and K e crt _mn 1 2M 2 (3) Let nput voltage V ac= 1 V rms and V o =48V power P=15W the output current s gven by: P=VI; 15=48I; output current I=3.125A The output load resstance value s gven by: V o =IR; 48=3.125R; R=15.34 Ω. Let the swtchng frequency be 5 khz and output voltage should be less than 1%. L1 < 1%I L1 and v c1 < 5%V c1 (4) I L1 = D.V n F.L 1 (5) Copyrght to IJIREEICE 139

3 ISSN (Onlne) Vol. 2, Issue 2, February 214 I L2 = (1 D)V o F.L 2 (6) I L2 = (1 D)V o F.L 2 (7) V c1 = D.V d I d (8) V o.c.f From the equatons (6), (7), (8) the values of nductances and capactances are gven by: L 1 = L 2 =1mH L 1 =L 2 =22μH C 1 =C 2 =1μF C out =12μF waveform S d (t) to get the swtchng sgnal for the MOSFET of the brdgeless Cuk converter as If K d V DCerror > S d (t) then S = 1 else S = (1) where S denotes the swtchng of the MOSFET of the brdgeless Cuk converter and ts values 1 and represent on and off condtons, respectvely. B. PMBLDC motor drve The drve conssts of a voltage source nverter, an electronc commutator for controllng the voltage source nverter, and the PMBLC motor. IV. MODELLING OF THE PROPOSED DRIVE The brdgeless Cuk converter and PMBLDC motor are the man components of the proposed system as shown Fg 2. They are desgned and modeled to form the complete drve system 1) Electronc Commutator: The electronc commutator s used to generate the swtchng pulses for the voltage source nverter. The rotor postons are sensed by Hall Effect sensors and emf sgnals are generated. Ths s decoded to get the respectve swtchng sgnals as shown n Table 1. [2] TABLE I SWITCHING SIGNAL GENERATION BASED ON HALL EFFECT SENSOR SIGNALS [2] Hall sgnals Swtchng Sgnals Fg 2: Proposed Drve H a H b H c S 1 S 2` S 3 S 4 S 5 S A. Brdgeless PFC Converter The brdgeless a Cuk converter s desgned as n then above secton along wth a speed control and PWM control. 1) Speed Controller: V DCref s the reference voltage and V DC s the sensed voltage at the Dc lnk the error voltage s gven by: V DCerror = V DCref - V DC (9) Ths error sgnal s used to generate the pwm pulses by comparng t wth sawtooth waveform. 2) PWM controller: The voltage error sgnal s compared wth the sawtooth waveform and the pulses so generate wll feed the swtches. That s the voltage error s amplfed by gan K d and compared wth fxed frequency (f s ) sawtooth 1) Voltage source nverter: The nverter just performs the converson of DC-AC and the output of the VSI s fed to the phases of PMBLDC motor. The equvalent crcut of the VSI fed BLDC motor s shown as n Fg 3. The output of the VSI s as below: V ao = V dc /2 for S 1 =1 (11) V ao =-V dc /2 for S 2 =1 (12) V ao = V dc /2 for S 1 =1 and S 2 = (13) V an = V ao -V no (14) Where V ao, V bo, V co represents the voltages between the three phases(a, b, c) and the mdpont of the DC lnk voltage o as shown n the fgure. V an, V bn, V cn are the voltages Copyrght to IJIREEICE 14

4 ISSN (Onlne) Vol. 2, Issue 2, February 214 between the three phases and the neutral pont n. V dc s the DC lnk voltage. The 1and of swtches S 1 / S 2 represents the on and off of the respectve IGBTs. Smlarly all other phases are beng swtched. respectvely, and K t s the torque constant. From (2) we can easly generate the speed. The EMFs e a, e b, e c are trapezodal and gven by the dynamc equaton: E k = k K e ω m f k (θ r ) (21) where K e s the back emf constant. Electrcal rotor speed and poston are related by the equaton dθ r dt = P 2 ω m (22) Fg 3: Equvalent crcut of VSI fed PMBLDCMD 1) PMBLDC motor: The PMBLDC motor can be modelled by some set of dfferental equatons. Where dfferent equatons are used to generate speed, stator currents and back EMFs. The PMBLDCM has three stator wndngs and a permanent magnet at the rotor. So the crcut equatons of the phase wndngs are gven by: V a R Vb V c R R a b c L M o P a b c e e e L M a b c L M (15) Where V a, V b, V c are the phase voltages, a, b, c are the phase currents, e a, e b, e c are the back EMFs. The dynamc equatons of the phase voltage wth the condton M= can be wrtten as: V a = R a + L d dt a + e a (16) V b = R b + L d dt b + e b (17) V c = R c + L d dt c + e c (18) Where R s the resstance per phase, L s the nductance. From the above stator phase currents can be generated. The electromagnetc torque s gven by: T e = K t k f k (θ r ) k (19) T e T l = J dω m + Bω dt m (2) Where k= a, b, c. k s the phase current of k th phase, ω m s the rotor speed, f k ( ϴ r) s the back emf constant, T l s load torque, J, B are the rotor nerta and dampng constant V. PERFORMANCE EVALUATION OF THE PROPOSED DRIVE The proposed PMBLDCM drve system s evaluated and tested n a MATLAB Smulnk envronment. The results are then compared wth the conventonal system. That s the Brdgeless Cuk rectfer fed PMBLDCM drve s compared wth the conventonal Cuk PFC converter fed PMBLDCM drve. They are compared n terms of effcency, power factor etc. The smulaton of the proposed system s gven n Fg (4). The conventonal smulaton scheme s n Fg (6). TABLE II SIMULATION DETAILS OF THE BRIDGELESS CUK CONVERTER Input voltage 18 Swtchng Frequency Input nductors L 1 and L 2 Output nductors L o1 and L o2 Energy transfer capactors C 1 and C 2 Flter capactors C o Actve Swtches Q 1 and Q 2 Output dodes D o, D o1 and D o2 Input dodes D p and D n Flter L & C TABLE III MOTOR SPECIFICATIONS Armature nductance[l].85h Armature resstance[r] 1 khz 1mH 22μH 1μF 12 μf R dson =29mΏ V f =.9V V f =.7V L=1e -4 & C=39e ohm Rotor nerta[j].8e-3kg-m 2 Dampng constant[b] Back EMF Constant[Ke] Torque Constant[Kt] 1e-3 N.m.s/rad.175 V.sec 1.4 N.m/A Copyrght to IJIREEICE 141

5 ISSN (Onlne) Vol. 2, Issue 2, February 214 Fg 5 (c) Fg 4: Smulaton dagram of the proposed drve The proposed PMBLDCM drve system s speed, stator current, electromagnetc torque and back EMFs waveforms are as below: Fg 5 (d). The Fg 5(c) shows the quas trapezodal waveform. The quas waveforms whch synchronze wth the trapezodal back EMF generate a constant torque as n Fg 5(d). Fg 5(a) Fg 5(a) shows the stator phase currents of one phase. Each phase currents wll be 12 degree shfted. The rotor steady state speed s as n Fg 5(b) where at startng speed varous and by the controller acton t s set a steady state speed Fg 6: Smulaton dagram of the Conventonal Drve The proposed drve system s then compared wth the conventonal Cuk PFC converter based PMBLDCM drve n terms of THD to establsh that the proposed drve s effcent over the conventonal system. Fg 5 (b) The THD analyss s taken for speed, back EMF, stator current and electromagnetc torque of both proposed and conventonal system. Along wth ths the prmary am power factor correcton s also checked for both of the systems and tabulated as n Table IV. Copyrght to IJIREEICE 142

6 ISSN (Onlne) Vol. 2, Issue 2, February 214 Type TABLE IV PERFORMANCE DETAILS Conventonal Drve THD--Speed THD--Back EMF THD--Stator Current THD--Torque Power Factor (%) Proposed Drve The Table IV clearly yelds the result that the proposed brdgeless Cuk converter drve has less THD as compared wth the conventonal drve. The less THD shows that t the proposed drve has more accurate output than the conventonal drve. That s the proposed drve system s effcent over the conventonal system. More over the nput power factor of the same s almost unty. VI. CONCLUSION A new effcent permanent magnet brushless DC motor drve has been smulated and expermentally valdated, so can be used wth any load to yeld a good effcent workng system. Intally varous topologes of power factor correcton crcuts are evaluated and the result are confned such that the best sutable one s selected. It s analyzed that a cuk converter has the best result but the problem wth all the topologes s the conducton losses. So a brdgeless Cuk PFC converter s used. Ths converter s analyzed wth the PMBLDC motor drve and the drve has unty nput power factor and less conducton losses. So all together t s an effcent drve. The proposed PMBLDCMD s promsng varable speed drve for ar condtonng system, electrc tracton etc. All the problems of poor power factor, heavy nrush current, etc of can be mtgated by the proposed brdgeless Cuk PFC based PMBLDCMD. [5] W. We, L. Hongpeng, J. Shgong, and X. Danguo, A novel brdgelessbuck-boost PFC converter, n Proc. IEEE Power Electron. Spec. Conf., 28, pp [6] Yungtaek Jang, Mlan M Jovanovc Brdgeless Hgh power factor Buck converter, IEEE Trans. Power Electron., vol. 26, no. 2, pp , Feb. 211 [7] M. Mahdav and H. Farzanehfard, Brdgeless SEPIC PFC rectfer wthreduced components and conducton losses, IEEE Trans. Ind. Electron., vol. 58, no. 9, pp , Sep [8] Sebastan, J., Cobos, J.A., Lopera, J.M., and Uceda, J.: The determnaton of boundares between contnuous and dscontnuous conducton mode n PWM DC-to-DC converters used as power factor preregulators, IEEE Trans. Power Electron., 1995, 1, (5) [9] CnndA. Sabzal, E. H. Ismal, M. Al-Saffar, and A. Fardoun, New brdgelessdcm sepc and Cuk PFC rectfers wth low conducton and swtchnglosses, IEEE Trans. Ind. Appl., vol. 47, no. 2, pp , Mar./Apr [1] E. H. Ismal, Abbas.A.Fardoun, Ahmad.J.sabazal, Mustafa.A.Al- Saffar New effcent Brdgeless Cuk rectfers For PFC applcatons, IEEE Trans. power. Electron., vol. 27, no. 7, July BIOGRAPHY Jomy Joy was born n Kerala, Inda n 199. He obtaned hs bachelor degree from Anna Unversty, Chenna. He s currently pursung hs Masters degree n Power electroncs from Cochn Unversty of scence and technology, Kerala. Hs area of nterest ncludes power electroncs, electrcal drves and electrcal machnes. REFERENCES [1] J. F. Geras and M. Wng, Permanent Magnet Motor Technology,desgn and Applcaton. New York: Marcel Dekker, 22 [2] N. Mohan, M. Undeland, and W. P. Robbns, Power Electroncs: Converters, Applcatons and Desgn. Hoboken, NJ: Wley, 1995 [3] Hua We, Comparson of basc converter topologes for power factr correcton Unversty of central Florda, Orlando, [4] W. Cho, J.Kwon, E. Km, J. Lee, and B.Kwon, Brdgeless boost rectfer wth lowconducton losses and reduced dode reverserecovery problems IEEE Trans. Ind. Electron., vol. 54, no. 2, pp , Apr. 27 Copyrght to IJIREEICE 143