Resonant Rectifier for Piezoelectric Sources

Transcription

1 Reonan Recifier for iezoelecric Source Sam Ben-Yaakov and Naan Krihely ower Elecronic aboraory, eparmen of Elecrical and Compuer Engineering Ben-Gurion Univeriy of he Negev,.0.Box 653, Beer-Sheva 84105, ISRAE Tel: ; Fax: ; ; Webie: hp:// Abrac A new recificaion cheme i propoed for increaing he available oupu power of elecrical generaor ha have a high oupu capaciance. The new recifier could be ueful in increaing he oupu power of piezoelecric generaor (ZG) ha conver mechanical vibraion o elecrical power. The improvemen i achieved by a onan circui ha elf commuae he volage acro he oupu erminal of he ZG and eliminaing hereby he huning of he oupu curren by he oupu capacior. SOURCE iin iou OA Keyword- onan recifier, piezoelecric generaor, dummy, diode bridge, commuaion. I. INTROUCTION iezoelecric (Z) elemen can be ued o generae elecrical energy from mechanical energy. Such elecrical generaor could be ueful in low power applicaion where mechanical moion i available. I ha been hown [1], for example, ha placing a Z ino a hoe ole can generae ufficien elecrical power for por enor and a local microproceor. Oher demonraed applicaion include a manual driven generaor for porable radio receiver []. iezoelecric elemen (randucer) belong o he general family of generaor ha are characerized by inernal capaciive impedance. The vibraing Z can be modeled a a inuoidal curren ource in parallel wih i elecrode capaciance (Fig. 1). The relaive low impedance of he inernal capacior will hu ome of he oupu curren and hereby lower he available oupu power. Coniderable effor ha been made o reduce or even eliminae hi drawback. The claical and inuiive oluion i o hun he capacior wih an exernal inducor whoe value i uned o he frequency of he exciaion. Conequenly, he impedance of he C onan nework will be high and all he available power will diipae ino he load [3]. Thi echnique ypically requi a large inducance value (over 1H) and i herefore an impracical oluion. Anoher propoed oluion wa o ynheize a negaive impedance [4] for reducing he equivalen capaciance. In [5] he auhor ugge he ue of virual grounded and floaing inducor o achieve he required inducor value. However, hee ype of implemenaion are generally poor repenaion of ideal inducor, hey are large in ize, difficul o une, eniive o componen variaion and require an exernal power ource. Conidering he fac ha, for a given exciaion frequency, he inducance value are Figure 1. Elecrical equivalen circui of capaciive curren ource driving a load. inverely proporional o he equivalen piezoelecric capaciance, he required inducance can be reduced by imply increaing he capaciance [6]. Thi ul i achieved by placing an addiional exernal capacior in parallel wih he piezoelecric randucer. Indeed, he inducance value i reduced ignificanly, bu o doe he damping raio. The high qualiy facor Q of hi arrangemen generae high reacive curren and make he generaor very eniive o he exciaion frequency. The reacive curren will caue coniderable power lo and a ligh change in frequency of he ource will caue a large power lo due o he huning effec of he C nework. In mo applicaion, he AC ignal produced by he Z generaor (ZG) need o be recified [7-9]. However, conidering he low power level involved, he recificaion cheme hould be a efficien a poible in order o improve he elecrical power harveing. A baic recificaion cheme (Fig. ) for an AC ource uch a he Z generaor will include a bridge recifier or a volage doubler. Boh uffer from he energy lo due o he oupu capacior of he ZG. Conequenly, for each recificaion cheme here i an opimal load iance for which he oupu power will be maximal [9-11]. The objecive of hi udy wa o develop a new recificaion cheme ha will improve he energy harveing from a ZG by eliminaing he huning effec of he oupu capacior. II. IOE BRIGE RECTIFIER Since he convenional diode bridge recifier (Fig. ) wa ued a a reference for comparing he improvemen of he new /05/$ IEEE. 49

2 iin B C I R V where I p and ω are he ampliude of he curren and angular frequency of he curren ource, pecively. The load power i, (R I 4ωCoV ) = π π R (4) ωcor 1+ π Figure. General opology of a capaciive curren ource loaded by a convenional diode bridge recifier circui. deign, we fir derive he expion for he maximum oupu power for hi cae. uring he ime inerval 1 ~ (Fig. 3) he capacior i clamped o he negaive volage (-(pk) ) and allow a curren pah from he ource o he load via B and B3 (Fig. ). The clamping volage i equal o um of he upu volage V and diode forward volage V : V = V + V (1) in(pk) uring he ime inerval ~ 3 (Fig. 3), he capacior i charged by he curren ource, and he capacior volage revere i polariy from -(pk) o (pk). A ha ime period no curren i available o he load. The C curren ha reache he load, i he average of (Fig. 3), I T = iou ()d iin ()d T = T () 0 where T i he period of. Following [7] we obain, 1 I 4ωCoV I = π π (3) ωcor 1+ π 3 (pk) Figure 3. Typical waveform of diode bridge recifier circui. The opimal load ha maximize he oupu power (aking ino accoun he diode volage drop) i he load ha maximize he power hrough he oupu load-diode combinaion, ou = + = I R + V I (5) iffereniaing Eq. (5) wih pec o R and equaing i o zero, we obain: R (op) π 1 = (6) V ωco (1 + ) V Noe ha in he abence of capaciance he power will be proporional o load iance, (R ) Co = 0 I = π R and he power ha could be exraced from he ource will, heoreically, approach infiniy (if R i made very high). In realiy, he high oupu volage generaed when R i large, will damp he Z onaor and hence limi he oupu power. III. NEW RECTIFIER CIRCUIT The propoed recificaion opology (Fig. 4) include an inducor ( ), wo wiche (SW 1, SW ), wo diode ( 1, ), a circuiry ha evaluae he derivaive of he capacior volage (d/d), and a comparaor (COM). A capacior loaded diode bridge recifie he AC acro he ZG oupu capacior ( ). The expeced waveform of he propoed recifier over a complee cycle are pened in Fig. 5. Auming ha a ime 1 (Fig. 5), he capacior i precharged o (-V -V ), he ource curren flow during ( 1 ~ ) o he load via B, B3. A ime inance, he ource curren change direcion, aring o charge during ime ~ 3 unil, ha i he derivaive of he capacior volage, reache he hhold level of he comparaor cauing i oupu (V c ) o wich o he low ae a ime 3. Thi urn on wich SW which iniiae a elf-commuaion inerval 3 ~ 4 via SW (7) 50

3 i I V V c iin B C R SW 1 SW i V c d d COM Figure 4. The propoed onan recifier circui. Auming a high qualiy facor Q, he onan ime inerval 3 ~ 4 can be eimaed by: π = 4 3 = π Co (8) ω Figure 5. Key waveform of he onan recifier circui. and he peak curren of will be: where i (pk) Vin(pk) Co = Vin(pk) (9) Z o o Z o = (10) C uring he ime inerval 4 ~ 5 he inducor curren i already zero and he capacior i charged by he inpu ource curren. There are wo reaon for he incomplee commuaion. The fir one i he fac ha he commuaion ar afer he capacior volage ha already dropped during he inerval ~ 3. Therefore, during he nex inerval ( 3 ~ 4 ) le energy i available and he capacior volage canno be fully recovered o V +V. A econd reaon for he incomplee commuaion i he power lo during he ime duraion ( 3 ~ 4 ) becaue of he volage drop on and he iance of a well a he "on" iance of he wich. Thee power loe are replenihed by he power coming from he ource and evenually, he inpu volage will be clamped o V +V a ime 5 and a curren pah o he load i poible hrough diode B1 and B4 of he bridge. The operaion of he onan recifier i hu baed on he fac ha he inducor and he ZG oupu capacior form a onan nework ha i acivaed by cloing wiche (SW 1 ) or (SW ). The wiche are cloed a he end of each half cycle and hu he volage acro he capacior will auomaically, by virue of he onan curren, change polariy. Conequenly, excep for he need o overcome loe, he ZG curren i no required for commuaing he capacior volage, and a large porion of he curren will pa o he oupu. IV. EXERIMENTA RESUTS The circui diagram of he experimen e up i hown in Fig. 6. All he diode ued in he circui are Schoky diode (1N5817). The onan circui conied of paralleled MOSFET wiche (hree V0104 and hree VN0104) for implemening M p and M n pecively. The comparaor wa an ulra low power IC (MAX91, Maxim, USA). The bi-polar power upply for comparaor wa realized by wo exra diode ( S1, S ) and bu capacior (C S1, C S ). The derivaive of ( ) wa obained by a differeniaor circui C der -R der. In order o preven eiher erroneou or undeired rigger even, hyei wa inroduced by adding ior R hy. Two e of experimen were performed. The objecive of he fir e wa o ae he performance of he propoed recifier and for verifying he lo eimaion. In hi e we ued a dummy curren ource for modeling he generaor age. A high volage floaing ource V ex of 00V (pk) in erie wih 100KΩ ior R in produced a inuoidal curren ource of ma (pk). Thi curren wa moniored by a 1KΩ ene ior R en. A capacior of 330nF wa placed in parallel wih he inpu of he recifier o emulae he capaciive behavior of he AC ource. The fir meauremen e included hree recificaion cheme: he andard diode bridge recifier (Fig. ), he onan recifier (Fig. 6), and he onan recifier in which he comparaor wa fed by an auxiliary power upply (+/- 4V). The purpoe of he hird cheme wa o neuralize he power conumpion of he comparaor and o enure ufficien gae drive volage o he MOSFETS. In each cae he load wa adjued o maximize he oupu power. The ul are ummarized in Table 1 for he andard recifier, elf-powering onan recifier and onan recifier wih ±4V exernal upplie. A expeced, he laer yielded he highe power level of 3.16mW while he oupu of he 51

4 R in Vex R en C der R der R hy Mn Mp B C V R 1 3 S C S S1 C S1 + V S COM. + V S Vc Figure 7. Experimen waveform of he andard recifier. Meaured inpu power: 1.7mW. Verical cale: -5V/div; -ma/div. Figure 6. Circui diagram of experimen e up wih dummy curren ource. andard recifier wa only 1.6mW. The onan recifier howed a ignifican improvemen (51%) compared wih convenional recificaion oupu power. Fig 7 and 8 how he experimen waveform of he andard recifier and he onan recifier wih exernal upplie pecively. Boh figu are marked by he ime even corponding o one dicued in Secion II and III. Neglecing comparaor loe, oal loe of propoed circui were eimaed o be 1.mW for he experimenal parameer: (pk) =3.5V, =1mH, =330nF, R r =1Ω, V =0.5V, f =185Hz, C =1µF and I =0.8mA. The meaured oal lo of he onan recifier wih exernal upplie wa 0.8mW (Fig. 8.a and Table 1), lower han he eimaed one. In he econd e of experimen a Z wa ued a a generaor (Fig. 9) for he ame hree recificaion circui, while eing procedure remained he ame. The generaor wa buil by connecing longiudinally wo piezoelecric bimorph van elemen (RB1-006 model, iezo Syem, Inc, USA). One wa ued a an acuaor and he oher a a randucer. The acuaor wa excied by inuoidal volage ource of 40V p-p. Thi arrangemen provided he required mechanical exciaion for he econd van ha wa ued a he generaor. The oupu capaciance of he randucer wa eimaed o be 60nF uing he echnique of [1]. Two adjumen were needed here for maximizing he oupu power, one for locaing he onance frequency of he Z device (approximaely 185Hz), and he econd adjumen for elecing he opimal Table 1. Experimen ul wih ma (pk) ource. CIRCUIT TOOOGY VOTAGE (C) OTIMA OA OWER GAIN (%) COMARE WITH RECTIFIER RECTIFIER 1.6V.1KΩ 1.6mW - RECTIFIER.V.75KΩ 1.79mW 14% RECTIFIER WITH EXTERNA SUIES V S =±4V 3.34V 3.51KΩ 3.16mW 51% (a) (b) Vin Figure 8. Experimen waveform of he propoed onan recifier. Meaured inpu power: 3.96mW. Verical cale: (a) -5V/div; -ma/div; (b) V/div. load of he recificaion circui under e (for a given frequency). The meaured exraced power for he hree recificaion circui are ummarized in Table. Maximum exraced oupu power produced by he onan recifier wih exernal upplie wa 30% of he power produced by he convenional recifier. V. ISCUSSION AN CONCUSIONS A new onan recifier circui i inroduced. The operaion of he circui i baed on a highly efficien onan energy ranfer beween a capaciive ource uch a a ZG and an inducor. Thi mechanim, conrolled by elf-imed circuiry, faciliae he commuaion of he volage acro inpu capacior. Thi wa hown o lead o a ignifican oupu power improvemen of 51% compared o a convenional recifier for dummy ource and 30% for a piezoelecric generaor. 5

5 V ex Acuaor Tranducer S S1 C S C S1 C der R hy R der Mn + V S COM. + V S Mp Vc B C V R inducor one hould conider he wo facor: (1) he oupu power lo during he commuaion period and () he power lo due o he onan curren. In pracice, one hould rive o make a mall a poible while keeping he conducion loe a reaonable fracion of he expeced oal power. Conidering all non-idealiie and limiaion dicued above, he onan recifier exhibi an impive improvemen compared o he convenional recifier. Addiional improvemen could be achieved by replacing he diode bridge by a ynchronou recificaion cheme in a elfpowering yem uiable for mobile applicaion. Figure 9. Circui diagram of experimen e up wih piezoelecric generaor. Table. Experimen ul wih he piezoelecric generaor. CIRCUIT TOOOGY VOTAGE (C) OTIMA OA OWER GAIN (%) COMARE WITH RECTIFIER RECTIFIER 1.779V 5.89KΩ 0.537mW - RECTIFIER 1.818V 5.19KΩ 0.636mW 118% RECTIFIER WITH EXTERNA SUIES V S =±4V 3.75V 11.43KΩ 1.3mW 30% The fir experimen reveal oal loe of 0.8mW for he recifier circui wih exernal upplie, while he heoreically eimaed loe were 1.mW. A coniderable porion of hee loe i due o forward volage drop of he bridge diode ( B ). Thi problem can be alleviaed by uing a ynchronou recificaion cheme in which he diode ( B ) are replaced by a wich wih low on iance and hereby reducing he forward volage drop o a negligible value. The circui wa alo eed in elf-powering mode. I howed 14% oupu power improvemen compared o he andard recifier wih dummy ource and 118% oupu power improvemen wih piezoelecric generaor. The main reaon for hi mode improvemen i he low power level ha wa available from he experimenal ZG. The relaively low power level uled in a low oupu and auxiliary upply volage which, in urn, wa no ufficien o drive M n and M p ino he range of low on iance R d(on). Conequenly, power diipaion of he circui wa increaed in addiion o already exiing loe due o he iance of he inducor, power conumpion of he comparaor and due o he paraiic gae capaciance of he ranior. The oal loe of he onan recifier are a funcion of he paraiic iance and he volage drop on he diode. The maller he iance and he volage drop, he lower will be he loe. Opimizaion of he onan inducor i le obviou. One migh hink ha a reducion in inducance of value will minimize he commuaion period (Eq. (8)) and hence will increae oupu power. In realiy, a decreae in he value of will increae he onan curren (Eq. (9)) which migh lead o a larger power diipaion by 1,, M n, M p and he iance of he inducor. Therefore, in he elecion of he ACKNOWEGMENT Thi earch wa uppored by THE ISRAE SCIENCE FOUNATION (gran # 113/0-1) and by he aul Ivanier Cener for Roboic and roducion managemen. REFERENCES [1] J. Kymii, C. Kendall, J. aradio and N. Gerhenfeld, araiic power harveing in hoe, in roc. nd IEEE In. Symp. Wearable Compu., 1998, pp [] J. M. Rabaey, M. J. Ammer, J.. da Silva Jr,. ael and S. Roundy, icoradio uppor ad hoc ulra-low power wirele neworking, Compu., vol. 33, no.7, pp. 4-48, July 000. [3] W. Shu-Yau, iezoelecric hun wih a parallel R- circui for rucural damping and vibraion conrol, roc. SIE Smar Srucu and Maerial Conf., vol. 70, pp , [4] S. Behren, A. J. Fleming and S. O. R. Moheimani, A broadband conroller for hun piezoelecric damping of rucural vibraion, Smar Maerial and Srucu, vol. 1, pp. 18-8, 003. [5] F. dell Iola, C. Maurini and M. orfiri, aive damping of beam vibraion hrough diribued elecric nework and piezoelecric randucer: prooype deign and experimenal validaion, Smar Maerial and Srucu, vol. 13, pp , 004. [6] A. J. Fleming, S. Behren and S. O. R. Moheimani, Reducing he inducance requiremen of piezoelecric hun damping yem, Smar Maerial and Srucu, vol. 1, pp , 003. [7] G. K. Oman, H. F. Hofmann, A. C. Bha and G. A. eieure, Adapive piezoelecric energy harveing circui for wirele remoe power upply, IEEE Tranacion on ower Elecronic, vol. 17, no. 5, pp , Sepember 00. [8] G. K. Oman, H. F. Hofmann and G. A. eieure, Opimized piezoelecric energy harveing circui uing ep-down converer in diconinuou conducion mode, IEEE Tranacion on ower Elecronic, vol. 18, no., pp , March 003. [9] A. Kayap, Ji-Song im,. Johnon, S. Horowiz, T. Nihida, Khai Ngo, M. Sheplak and. Caafea, Energy reclamaion from a vibraing piezoceramic compoie beam, 9h Inernaional Cong on Sound and Vibraion, Orlando, F, July 00. [10] F. u, H.. ee and S.. im, Modeling and analyi of micro piezoelecric power generaor for micro-elecromechanicalyem applicaion, Smar Maerial and Srucu, vol. 13, pp , 004. [11] J. Han, A. V. Jouanne, T. e, K. Mayaram, T. S. Fiez, Novel power condiioning circui for piezoelecric micro power generaor, IEEE Applied ower Elecronic Conf., 004, pp [1] S. Ben-Yaakov and N. Krihely, Modeling and driving piezoelecric onan blade elemen, IEEE Applied ower Elecronic Conf., 004, pp