Optimum Design of Magnetic Inductive Energy Harvester and its AC-DC Converter

Transcription

1 Otmum Degn of Magnetc nductve Energy Harveter and t AC-DC Converter Qan Sun, Sumeet Patl, Stehen Stoute, Nan-Xang Sun, Brad Lehman Deartment of Electrcal and Comuter Engneerng Northeatern Unverty Boton, MA, 0115, USA Abtract The degn of a new-tye of nductve magnetc energy harvetng ytem wth hgh ermeablty magnetc materal combned wth a dual olarty boot converter reented. By ung the trong magnetotatc nteracton between the col and ermanent magnet, the outut ower and ower denty of the energy harveter enhanced comared to conventonal ar cored nductve harveter. n the rooed dual olarty boot converter, the col leakage nductor of the harveter utlzed to form the nut nductor of the boot converter to mnmze the converter ze. Therefore, the magnetc energy harveter and the ower converter hare the ame magnetc core. Otmum ytem degn become a balance of core ze, requred leakage nductance and requred magnetzng nductance n order to extract maxmum energy.. NTRODUCTON Vbraton and rotaton energy harvetng technologe have been develong radly, and have hown great otental n many dfferent alcaton. However, thee alcaton are often lmted by the amount of energy that can be harveted. Generally, ezoelectrc energy harvetng technologe are condered the mot commercally mature [1]-[3]. Alternatvely, nductve magnetc energy harveter wth ar cored col are alo avalable [4], but they have much lower ower denty than ther ezoelectrc baed counterart. However, there an emergng clafcaton of nductve energy harveter that rooe to relace the ar cored col wth hgh ermeablty magnetc materal [5]- [6]. Theoretcally th lead to energy denty tme that n ezoelectrc. The full otental of hgh ermeablty nductve magnetc energy harveter ha not yet been realzed. The man challenge to degn nductve magnetc energy harveter how to ncreae t outut ower and ower denty to hgher level. Although the outut voltage and ower can be ncreaed by makng a large ze harveter wth thouand of turn, t wll eventually lead to low effcency and low ower denty caued by hgh energy lo on ncreang col retance. The hgh ermeable core dramatcally ncreae the magntude of magnetc flux through the col. Thu, a larger flux change exected to be generated through each core, whch reult n larger nduced voltage. Ung trong magnetotatc nteracton between magnet and col wth hgh ermeablty magnetc materal core, the outut ower can be enhanced gnfcantly. Our rooed vbraton and rotaton energy harveter how enhanced outut ower and ower denty comared to ezoelectrc, a well a wden workng bandwdth [6]. A dffculty wth extractng energy n the majorty of nductve magnetc energy harveter that they roduce low AC voltage at low frequency (tycally around 100Hz), where te-u tranformer cannot be ued drectly becaue of ther large ze. At the ame tme, the voltage requrement for low voltage, low ower, electronc devce tycally 1.8~3.3VDC. Thu, rectfcaton loe cannot be avoded n ower roceng crcut of magnetc harveter. Recently, a number of hgh te u converter toologe have been reented, eecally for ezoelectc alcaton [3]-[4], [7]-[17]. Conventonal aroache to rectfy the AC harveter voltage to feed t to a dode brdge rectfer at the frt tage and then to a dc-dc converter n the econd tage [3]-[4]. However, th neffcent due to the ower loe n the frt tage to overcome the dode brdge voltage dro [16]. Th ha led to the begnnng of reearch to degn brdgele ower electronc and other crcut for ar cored nductve energy harveter to avod ome of the loe [4], [15]-[17]. A the frt work on nductve magnetc energy harvetng ytem, a drect AC/DC boot converter degned utlzng the harveter col leakage nductance. Snce the detaled analy on the equvalent model of nductve magnetc harveter ha not been reented, there nuffcent reearch on how the harveter and converter degn nfluence each other. Furthermore, thee tye of converter requre bdrectonal wtche and addtonal external magnetc core for boot nductor. n th aer, a new dual olarty boot converter wth magnetc fully ntegrated nto the harveter rooed. By utlzng the leakage nductance of the rooed hgh ermeablty magnetc harveter, no external nductor core need to be added a the boot nductor of the AC/DC converter cacaded after the harveter. Further, by addng a dode n ere wth each center taed col, rectfcaton can be acheved wth low ower lo. The fact that nternal /1/$ EEE 394

2 v Fg. 1 nductve magnetc energy harveter. Vbraton harveter. Rotaton harveter leakage nductance utlzed to form nut nductance of boot converter, dramatcally reduce converter ze. Further, no b-drectonal wtch needed n the converter, whch lead to maller ower lo on control and drve crcut and mler control cheme. n Secton, the degn and modelng of the nductve magnetc energy harveter and t AC-DC converter reented. By analyzng an equvalent model of harveter, t hown how the dual olarty boot converter can utlze the leakage nductance of the harveter to acheve the maxmum extracted energy of the whole harvetng ytem. The exerment reult are reented n Secton. The effcency and ower lo of each wtchng devce are calculated n th ecton.. DESGN OF ENERGY HARVESTNG SYSTEM n th ecton, the degn and modelng of the nductve magnetc energy harveter and t dual olarty boot converter reented. The converter degned to utlze the nternal leakage nductance of the magnetc energy harveter n order to reduce the ze of harvetng ytem. A. nductve Magnetc Harveter Degn and Modelng Two nductve magnetc harveter are hown n Fg. 1 (vbraton harveter n Fg. 1 and rotaton harveter n Fg. 1). The nductve magnetc harveter tycally cont by magnet, col, and rotaton or vbraton mechancal tructure. Dete dfferent moton tye, the mechancal energy change to electrcal energy by the changng flux through magnetc core by vbratng or rotatng. Thu, they can be modeled by the ame equvalent model wth dfferent arameter. Fg. how the nductve magnetc energy harveter n equlbrum. The magnetc cored col exected to generate a much larger flux change than ar cored col (tycally degned a n [1]) by rovdng a hgh ermeablty ath for the flux. The key comonent of the harveter the hgh ermeablty (hgh- µ ) core nde the col. Th hgh ermeablty magnetc materal normally comoed of nckel-ron alloy (~77%), ron (16%), coer (5%) and other materal (%) and ha relatve ermeablty cloe to Tradtonally, the materal ha been ued to form thn heet of magnetc held for hell/rotecton of electrc ower v Fg. nductve magnetc energy harveter n equlbrum Lk R c L m m Lw Fg. 3 Equvalent model of nductve magnetc energy harveter tranformer, hard drve and magnetc reonance magng equment to revent magnetc feld from affectng nearby electronc equment. However, thee hgh ermeablty materal have the otental, a hown n th aer, to rovde gnfcantly enhanced nductance erformance wth hgh nductance, low volume, hgh qualty factor, etc. When ntroduced n nductve energy harveter, th lead to gnfcantly enhanced ower/energy denty comared to ar core col baed energy harveter [5]-[6]. Accordng to Faraday law, the electromotve force (EMF) nduced by the flux change through the col wndng, whch rereented by n the equvalent model. And the voltage meaured acro col wndng of the harveter. Snce the ermeablty of the core materal fnte, the magnetc reluctance non-zero. Accordng to Amere Law: v Hl ΦRm = = + = m + (1) n n ource current of equvalent model and exctaton current (Fg. 3). Th current can be modeled a magnetzng nductance n arallel. Due to fnte ermeablty, a mall amount of flux doe not go through magnetc core, whch called leakage flux (Fg.). The leakage flux from two art. One art from ermanent magnet can be modeled a ere leakage nductor. manly related to the ermeablty of the magnetc core materal, and the ga between magnet and col. The leakage flux generated by col wndng can be modeled a a ere nductor, whch generally neglgble comared to. Once the core materal ha been decded, leakage nductance and magnetzng nductance are manly decded by the ga between ermanent magnet and col (Fg. ). When the ga ncreae, v L m m v 395

3 = 0 = 0 n v v = v v Fg.4 Oen and hort crcut of harveter 5 x 10-3 Leakage nductance n Leakage nductance (H) π T t 1 D T f 0.5 DT Frequency (Hz) Fg. 5 Leakage nductance ncreae and decreae. By choong a ga mall enough, can be made to become a large quantty and can be neglected. The followng ecton of converter degn wll be under th lmted ga range. A hown n Fg. 3, n ere wth rereent wndng retance. n order to ncreae the outut voltage of the harveter, the harveter wndng uually made u of large number of turn. Thu, generally, the wndng retance cannot be gnored and t key factor that affect the effcency of the harvetng ytem. The wndng retance hould be a mall a oble to acheve le ower lo. Snce the magnetc core hghly ermeable, there ext core lo. A retor n arallel wth rereent eddy current lo and hytere lo. Comared to and, the effect of core lo neglgble. Thu, large enough to be neglected n followng analy. t can be een from Fg. 3 that the leakage nductance one of the key arameter affectng outut ower of harveter. At the ame tme, the leakage nductance ued a the nut nductance of dual olarty boot converter n the converter degn. The value of alo nfluence the converter ower lo. n order to gan maxmum energy out from the energy harvetng ytem, need to be controlled to an otmum value. Theoretcally, the leakage nductance can be only calculated by fnte element analy. However, t can be roughly etmated wth the mlfed equvalent model. Fg. 6 Prooed crcut and nut current Oen and hort crcut tet can be done wth the harveter under certan frequency. Oen crcut voltage and hort crcut current can be meaured wth the etu hown n Fg. 4. Snce there no current gong through the harveter n oen crcut condton, we can get: v = v () n hort crcut condton, the wndng retance and the leakage nductance can be een a the load of the harveter. For a general load comoed of RL element under nuodal-teady-tate exctaton follow the followng equaton: ( SC ) v = jωl ( OS ) k + R Thu, the leakage nductance can be etmated under each fxed frequency wth known wndng retance. t can be een n Fg. 5 that the leakage nductance of rooed nductve magnetc harveter around mh. B. Dual Polarty Boot Converter We rooe to center ta the harveter col n Fg. 1. Then accordng to the harveter equvalent model, we ntroduce a new tye of converter, n Fg. 6, that a dual olarty boot converter that utlze the leakage nductance of the center taed col a the two boot nductor. Snce w (3) 396

4 1 v 1 v 1 v 1 D 1 D D 1 dramatcally reduce the converter ze nce no external nductor needed. Further, wth a center taed col, rectfcaton acheved by addng the two dode n Fg. 6, ntead of a dode brdge rectfer. Therefore, rectfcaton voltage dro wll lower by 50%, and further, there no bdrectonal wtch needed (mlfyng and mrovng the effcency of the control and drve). The man loe n the crcut are due to the wndng retance of col, ON-tate retance of the MOSFET, and the nut and outut dode: P = R + V + V + R (4) lo ( rm) w f dn ( avg ) f dout ( avg ) SW ( rm) d v Lk D 1 D 1 where,,, and are nut current, nut dode current ( and ), outut dode current ( ) and MOSFET current, reectvely. Conder the k th wtchng cycle for the converter, the nut voltage can be een a contant, nce vbraton erod. v 1 v Lk D Lk1 D1 T vk = V n( π k ) T vk DT k = L where the eak voltage of harveter. The RMS value of the ource current over a wtch cycle can be derved a: k (5) v 1 v vk D T 1 k = k ( D + Df ) = ( DCM ) 3 3 Lk 1 vk / Vo v D T = + ( CCM ) k k k ( avg) 1Lk (6) D Fg. 7 Prncle of Oeraton. Potve half cycle of AC voltage. Negatve half cycle of AC voltage the dode are located after the leakage nductance, ther voltage dro wll not have domnant ower lo, and hence th toology utable for ultra-low voltage, low ower alcaton. Snce the outut voltage of the harveter mlar to a ne waveform, the EMF wll be condered a nuod n the analy to mlfy the roce. The rncle of oeraton hown n Fg. 7. Each wndng oerate durng a half cycle of the nut AC voltage, wth the control cheme each half cycle mlar to a fxed duty rato boot converter. The converter can work n both contnuou (CCM) and dcontnuou (DCM) current mode. A hown n Fg. 6, when the nut voltage low, the converter work n DCM and when the nut voltage buld u, the converter tranfer to CCM. The rooed converter degned to be ntegrated to the nductve magnetc energy harveter by ung leakage nductance a the nut nductance of boot converter. The leakage nductance can be degned o that t large enough to be ued for the nut nductance, whch can Suoe the converter work n CCM durng. The RMS value of nut current can be calculated by takng average of half cycle ntegraton: V D T V D T θ ( ) (1 ) 3 π θ 4 c n θ (1 D) n c ( rm ) = dθ + 0 3L θ + + k π θ c 1 V n RL 1Lk Vo 3 4 V D T nθ (1 D) V V D T c n = (1 ) + (1 ) + + 6Lk π RL 4Lk DCM CCM Smlarly, the MOSFET current, nut dode current ( and ) and outut dode current ( ) can be calculated: V D T DV D T (1 ) (1 ) 3 D 1 n( ) n( ) ( avg) VD T V D = = ( ) + L π θ R (1 D) θ 4 4 n (1 D) n SW ( rm) = D ( rm ) = Lk π RL 1Lk dn ( avg ) k c L c dout ( avg ) V 1 n( ) n( ) D T V = ( ) + L (1 D) π θ R (1 D) θ k c L c (7) (8) (9) (10) t can be een from (7), (8), (9) and (10), the ower lo on the MOSFET wtche, wndng retance and dode decreae when the leakage nductance ncreae. And f the harveter enter CCM, the ower lo reduce. However, 397

5 Harveter Outut Power Converter Outut Power Sytem Outut Power TABLE. Parameter PARAMETER OF MAGNETC HARVESTER Value Outut Power (W) nduced voltage (RMS) Ga mm Magnet dameter 8mm Col number 4 Col nductance 1mH Col retance 4.5 Ω 1V Leakage nductance (H) Fg. 8 Varaton of harveter and converter outut ower wth Outut Power (W) Fg. 9 Exermental etu Frequency (Hz) Frequency (Hz) Fg. 10 Harveter outut ower veru frequency a mentoned revouly, hgh outut ower of harveter requre low. A tradeoff mut be made on degnng of a value of value to obtan maxmum ytem energy extracton. A mentoned before, leakage nductance gnfcantly affected by ga between col and magnet. That mean, there a tradeoff between ower lo n the wtche and magnetc core energy harveter outut. C. Otmum Leakage nductance Tradtonally, magnetc harveter degn and converter degn are earated. However, the maxmum outut cannot be acheved for both harveter and converter at the ame. MATLAB/Smulnk model are bult accordng to Fg. 3 and Fg. 6 n order to oberve how the harveter and converter outut ower change wth leakage nductance. The harveter outut ower meaured under otmal retance n order to gan maxmum ower tranfer. Fg. 8 how the mulaton reult. The outut energy of magnetc energy harveter dro wth the ncreae of. The outut ower of the converter re wth the ncreae of due to lower ower lo, whch verfe (7)-(10). The energy harvetng ytem net energy outut hown n the red curve. When the leakage nductance mall, the ytem outut ower lmted by hgh ower lo of converter. And when the large, the outut ower outut ower wth lmted by the harveter outut caacty. The maxmum ytem net energy occur when two curve cro each other. Generally, magnetc energy harveter are degned to be oerated cloe to the vertcal ax ( a mall a oble) to gan hgher voltage and ower outut. However, th no longer derable f no external nductor added. There no need to mantan the mnmum ga, whch often lead to a hgh requrement on the mechancal degn of magnetc energy harveter [1],[7]-[8]. Near the maxmum ont of ytem outut ower n Fg. 7, ytem outut ower dro lowly wth ncreang. Thu, there a tolerance on for magnetc harveter degn. Therefore, the ga can be mantaned n a mall range, and need not be a rece value, addng more convenence on harveter mechancal degn. n the rooed harvetng ytem, the col are mounted on the holder of nductve magnetc energy harveter wth uerglue (Fg. 1 ). Snce the ga can hardly be adjuted by changng the oton of col once they are fxed to the harveter, everal et of harveter were bult wth dfferent mechancal and electrcal arameter. The exerment reult are baed on one et of harveter whch ha better erformance. 398

6 TABLE. CRCUT PARAMETERS AND LOSS OF THE CONVERTER Fg. 11 Outut voltage (V/dv). nut current (00mA/dv) Fg. 1 Gate Sgnal (V/dv). Outut voltage (V/dv).. EXPERMENT RESULT The nductve magnetc energy harveter (Fg. 1 ) and dual olarty boot converter degned accordng to above analy. The block dagram of exerment etu hown n Fg. 9. A mllng machne ued to roduce rotaton for the harveter. The harveter fxed to the bae of the mllng machne wth the rotaton wheel cloe to ndle, o that the wheel can rotate wth the ndle. The rotaton eed of the harveter controlled by the mllng machne. The exerment reult reented under both condton when the harveter connected wth and wthout converter. A. nductve Magnetc Energy harveter The harveter degn arameter are hown n TABLE. The frequency of harveter outut voltage can be changed from 0 to 10Hz wth the mllng machne. The harveter outut ower teted under the otmal retance 4.9Ω. The curve of harveter outut energy varaton wth frequency hown n Fg. 10. The curve obtaned by changng the rotaton eed of the mllng Parameter Value Etmated Lo Leakage nductance 1, mh Wndng Retance 4.7Ω 0.113mW MOSFET R d_on 0.Ω mW Outut Caactor C 100µF nut Dode V f 0.3V 5.3mW Outut Dode 4.5mW Outut Voltage V o 3.3V machne. The outut ower of the harveter calculated from the voltage acro the load retance. The maxmum ower 130mW at 110Hz. B. Energy Harvetng Sytem n th ecton, the exerment reult of energy harvetng ytem are reented. The degn arameter of the converter are hown n TABLE. A MOSFET wth low gate drve voltage (FDV305N from Farchld) elected a the man wtchng devce. Schottky dode (NSR030 from ONemconductor) wth low forward voltage dro choen to be nut and outut dode. The tycal forward voltage dro 0.3V. The converter oerated n oen loo wth fxed duty rato =0.85 at the wtchng frequency 5kHz. A nomnal load of = 00 Ω connected to the converter. The magntude of the outut voltage around 3.3V, whch mean the outut ower around 54mW. The nut current of otve de hown n Fg. 11. t can be een that the nut current blocked by the nut dode durng negatve half cycle. Due to the large value of nut nductance (around mh), there mall current rle. The gate gnal hown n Fg. 1. Snce the nut voltage cannot be meaured drectly, the nut ower and converter effcency can hardly be found from the nut voltage and current. A hown n TABLE, the ower lo etmated accordng to (7)-(10). The converter condered to work under contnuou current mode and the effect of nut dode voltage dro alo ncluded. t can be een that the mot gnfcant ower lo from nut and outut dode. The converter effcency etmated to be around 64.4%. However, the harveter ha maxmum outut ower 130mW at 110Hz under otmal retance 4.9Ω. There no medance matchng n the converter degn. f the harveter maxmum outut ower condered a nut ower, the effcency of the harvetng ytem 41.5%. V. CONCLUSON n th work, the rooed energy harvetng ytem for extractng more energy from nductve magnetc energy harveter. The reented nductve magnetc energy harveter ue hgh ermeablty materal core to acheve 399

7 more flux change through the col, whch lead to hgher outut voltage. The rooed dual olarty boot converter combned wth the harveter can dramatcally reduce the rectfcaton voltage dro comared to conventonal dodebrdge rectfer. The leakage nductance of col utlzed to form the nut nductance of the boot converter to reduce the converter ze. Snce hgh ermeablty core are emloyed, the leakage nductance hgh enough and can be adjuted to acheve hgher effcency of the harvetng ytem. REFERENCES [1] Y.J. Wang, C.-D. Chen, C.-K. Sung, Sytem Degn of a Weghted- Pendulum-Tye Electromagnetc Generator for Harvetng Energy From a Rotatng Wheel, EEE/ASME Tran. Mechatronc, Vol. PP, no. 99, PP. 1-10, 01. [] G.K. Ottman, H.F.Hofmann, A.C. Bhatt, and G.A. Leeutre, Adatve ezoelectrc energy harvetng crcut for wrele remote ower uly, EEE Tran. Power Electron., vol.17, no. 5, , Se. 00. [3] E. Lefeuvre, D. Audger, C. Rchard, and D. Guyomar, Buck boot converter for enorle ower otmzaton of ezoelectrc energy harveter, EEE Tran. Power Electron., vol., no.5, , Se [4] R. Dayal, S. Dwar, and L. Para. A New Degn for Vbraton- Baed Electromagnetc Energy Harvetng Sytem Ung Col nductance of Mcrogenerator, EEE Tran. nd. Electron., vol. 47, no., [5] X. Xng, J. Lou, G. M. Yang, O. Ob, C. Drcoll, and N. X. Sun, Wdeband vbraton energy harveter wth hgh ermeablty magnetc materal, Aled Phyc Letter, Vol. 95, ue 13, d , 009. [6] X. Xng, G. M. Yang, M. Lu, J. Lou, O. Ob, and N. X. Sun, Hgh ower denty vbraton energy harveter wth hgh ermeablty magnetc materal, J. A. Phy.,Vol. 109, d , Feb [7] N. Kong, D. Ha, "Low-Power Degn of a Self-owered Pezoelectrc Energy Harvetng Sytem Wth Maxmum Power Pont Trackng," EEE Tran. Power Electron., vol.7, no.5, , May 01. [8] Shuo Cheng; Yng Jn; Yuan Rao; D.P. Arnold, An Actve Voltage Doublng AC/DC Converter for Low-Voltage Energy Harvetng Alcaton, EEE Tran. Power Electron., vol.6, no.8,.58-65, Aug [9] N. Golbon, G. Mochooulo, A Low-Power AC DC Sngle-Stage Converter Wth Reduced DC BuVoltage Varaton, EEE Tran. Power Electron., vol.7, no.8, , Aug. 01 [10] K.. Hwu, Y. T. Yau, Hgh Ste-U Converter Baed on Charge Pum and Boot Converter," EEE Tran. Power Electron., vol.7, no.5, , May 01 [11] J. Lee, J. Park, H. Jeon, Sere-Connected Forward Flyback Converter for Hgh Ste-U Power Converon, EEE Tran. Power Electron., vol.6, no.1, , Dec [1] Tun-Hao Ha, Hen-Y Ta, Dan Chen, M. Lee, Chun-Shh Huang, nterleaved Actve-Clamng converter wth ZVS/ZCS Feature, EEE Tran. Power Electron., vol.6, no.1,.9-37, Jan [13] K-Bum Park, Gun-Woo Moon, Myung-Joong Youn, Nonolated Hgh Ste-U Stacked Converter Baed on Boot-ntegrated olated Converter, EEE Tran. Power Electron., vol.6, no., , Feb [14] Y. P. Heh, J.-F. Chen,T. J. Lang, L. S. Yang, "A Novel Hgh Ste- U DC DC Converter for a Mcrogrd Sytem EEE Tran. Power Electron., vol.6, no.4, , Arl 011. [15] P. D. Mcheon, T.C. Green, E. M. Yeatman, and A.S. Holme, Power Proceng Crcut for Electromagnetc, Electrotatc and Pezoelectrc nertal Energy Scavenger, Mcroytem Technologe, Vol. 13, , May 007. [16] R. Dayal, S. Dwar, and L. Para, Degn and mlementaton of a drect ac-dc boot converter for low voltage energy harvetng, EEE Tran. nd. Electron., 010. [17] S. Dwar and L. Para, An effcent AC-DC te-u converter for low-voltage energy harvetng, EEE Tran. Power Electron., vol. 5, no. 8,