高效压电能量回收系统的优化设计_英文_

第16卷　第12期
2008年12月 光学精密工程
　Optics and Precision Engineering Vol.16　No.12
　Dec.2008
R eceived d ate :2007209220;R evised d ate :2008205230.
Found ation item :Supported by the National Natural Science Foundation of China (No.50775110);the NUAA Foun 2
dation for Graduate Innovation (No.BCX J 08204)
文章编号　10042924X (2008)1222346206
高效压电能量回收系统的优化设计
季宏丽,马　勇,裘进浩,姜　皓,沈　辉,朱孔军
(南京航空航天大学智能材料与结构航空重点实验室,江苏南京210016)
摘要:提出了一种新型的压电能量回收器件,通过一个开关功率变换器的辅助,系统的能量转换效率可提高400%。

该功率变换器原型为Buck 2Boost 变压器,本项研究通过低功耗的控制电路对其进行了优化。

利用Pspice 软件对整个系统电路进行了建模和仿真,仿真结果显示,优化后的能量回收器件输出功率提高了3.4倍。

关　键　词:能量回收;压电系统;功率变换器;能量自给器件中图分类号:TN384 文献标识码:A
Optim al design of high eff iciency piezoelectric energy harvester
J I Hong 2li ,MA Y ong ,Q IU Jin 2hao ,J IAN G Hao ,SH EN Hui ,ZHU K ong 2jun
(A eronautic Key L aboratory f or S m art M ateri als &S t ruct ures ,
N anj i n g U ni verisit y of A eronautics &A st ronautics ,N anj i ng 210016,Chi na )
Abstract :A high efficiency piezoelectric energy harvester is designed and experiment result s show t hat t he power t ransformation efficiency of t he piezoelect ric energy harvester can be enhanced by more t han 400%by applying a switching power converter.This switching power converter is derived from Buck 2Boo st converter ,and it is optimized using a control circuit ry of low power consumption in t his work.The whole circuit ry is modeled and simulated in t he Pspice software.The simulation result s show t hat t he outp ut power of proposed energy harvester increases by 3.4times after optimization.K ey w ords :energy harvesting ;piezoelect ric system ;power converter ;self 2powered device
1　Int roduction
Piezoelect ric materials have elect romechani 2
cal p roperty by which piezoelectric materials can t ransform mechanical st rain into elect ric charge ,or transform electric charge into mechanical st rain.Piezoelect ric energy harvester is a device
using electric circuit to ext ract and store t he en 2
ergy induced by piezoelect ric materials ,and per 2pet ual power generation may be achieved by con 2verting ambient energy of mechanical vibration into elect rical energy.In order to obtain maxi 2mum outp ut power of piezoelect ric energy har 2vester ,some researchers focused on t he mechan 2ical design of t he harvester.However ,t he mo st
essential part affecting t he power efficiency is t he energy harvesting circuit which is usually a f ull 2wave rectifier ,and it s power efficiency is relatively low.Thus ,some researchers prefer to work on developing power co nditioning electrical interface t hat would maximaze t he power flow f rom t he piezoelect ric materials [122].
This paper present s a new type of energy harvester ,which is initially derived f rom t he de 2sign of Buck 2Boost converter [3].Wit h some im 2provement s t he converter is able to work in co 2ordinate wit h t he piezoelect ric device and act s as a power boo ster to t he energy harvester.To val 2idate t he efficiency of t he new energy harvester ,t he paper int roduces an elect ric simulation of t he energy harvester and present s t he result s of t he simulation.
2　Maximization t he power flow of
piezoelect ric energy harvester
As shown in Fig.1,a piezoelect ric element is attached to a clumped beam.The piezoelect
ric
Fig.1　Schematic of harvesting of vibration energy system
element has a t ransverse vibration due to t he st ruct ural vibration.The piezoelect ric equations of t he lengt h expander are given by Eq.(1),
D 3=e 31S 1+εS
33E 3
T 1=c E
11S 1-e 31E 3
,(1)
where subscript s ‘1’and ‘3’refer to t he x 2and
z 2direction ,respectively.In some literat ures t he
two equations were used to obtain t he relation 2ship between t he lengt h variation of t he piezoe 2lect ric disk u ,t he force F P applied on t he disk ,t he voltage V acro ss t he disk elect rodes ,and t he outgoing
elect ric charge Q [4]
,as shown in Eq.
(2),
I =α u -C 0
V F P =K P u +αV
,
(2)
Eq.(3)defines t he clumped capacitor C 0,
t he force factor α,and t he stiff ness K PE of t he
disk in short circuit.A and L are respectively
t he cro ss 2section area and t hickness.
E 3=-V d ,S =u L
,I =A xy D ,F P =A yz T ,K P =c E 31A yz L ,C 0=εS
33A xy
d ,α=
e 31A yz L
.
(3)
The
classical improved piezoelect ric energy harvesting electric interface
are shown in Fig.2and Fig.3,respectively.The classical interface is simply to rectify and filter t he AC inp ut from
Fig.2　Classical energy harvesting circuit
Fig.3　Improved energy harvesting circuit
t he piezoelect ric element ,t hen outp ut a DC volt 2age [5].However ,t he working principle of t he imp roved electirc interface derived f rom Buck 2Boo st converter is quite different.The switch S is open during all duty circle except when t he voltage on t he piezoelect ric disk reaches maxi 2mum or minimun ,and at t he t ransient period when t he switch S is closed ,t he energy stored on t he piezoelect ric disk quickly flows to t he in 2ductor L .When t he energy t ransfer is done ,t he switch S becomes open again and t he energy stored on t he inductor L flows to t he energy storage device ,such as battery or super capaci 2tor.By repeating t hose step s ,t he energy in 2
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J I Hong 2li ,et al :Modelling ,simulation and optimization of high ……
duced by t he piezoelectric disk is ext racted con2 tinuously.
As t he vibrating piezoelect ric disk outp ut s an AC voltage,t he available outp ut power of t he classical circuit can be derived f rom Eq.(2)in combination wit h Kirchhoff’s Current Law,as it is given by a f unction of t he displacement ampli2 t ude U M and t he external loading R L,
P=V2DC
R L
=
4α2U2Mω2R L
(2R L C0ω+π)2
,(4)
In t he case t hat t he displacement amplit ude of t he piezoelect ric disk is fixed,t he average outp ut power reaches a maximum value P max at an optimal load resistance R opt,t hey are given by Eq.(5)and Eq.(6)respectively,
P max=ωα2U2
M
2πC0
,(5)
R opt=
π
2C0ω
,(6)
While,t he average outp ut power of t im2 proved energy harvesting circuit is given by Eq.
(7),
P avg=2ωα2
πC0U
2
M　.(7)
It is quite clear t hat t he average power of improved circuit doesn’t vary wit h t he load re2 sistance.Moreover,t he power is also enhanced by400%at t he same sit uation.All of t hose ad2 vantages make t he improved energy harvester po ssible to be stable and efficient.
3　Modeling and simulation of pie2 zoelect ric energy harvester
Mechanical vibrations are usually simulated by elect ric networks in some cases,and st udies on piezoelect ric equations indicate t hat piezoelec2 t ric materials also can be represented by equiva2 lent circuit s such as Msaon’s equivalent circuit s or KL M equivalent circuit s[6].To implement t he simulation,t he piezoelect ric energy harvester re2 presented by an elect ric network is a must.Herein a perfectly approximate equivalent circuit for t he piezoelect ric disk has been derived from t he Eq.(2
),as it is shown in Fig.4.
Fig.4　Equivalent circuit for a piezoelectric vibrator
The equivalent circuit consist s of capaci2 tors,current2cont rolled current source,and voltage2controlled voltage source,while t he ca2 pacitor C1,current2cont rolled current source F1 and voltage2controlled voltage source E1respec2 tively refer to t he clumped capacitor,t he direct piezoelect ricity and t he converse piezoelect ricity of t he piezoelectric disk.While t he vibration is simulated by t he voltage source V1,inductor L m,resistor R m and capacitor C m,which respec2 tively rep resent t he external excitation,equiva2 lent mass,damping and stiff ness of t he struc2 t ure.
Anot her part of t his energy harvester is t he cont rol circuit for t he switch which is open and clo sed synchronously wit h t he vibration of t he piezoelect ric disk.The integrated control circuit consist s of two ult ra2low power voltage compa2 rators and an XOR logical gate,and t hey are shown in Fig.5.
The inp ut signal for t he control circuit is f rom anot her piezoelect ric disk sensitive to t he vibration of t he harvesting disk,and t he sensing signal varies proportionally wit h t he displace2 ment of t he harvesting disk.Wit h t he sensing signal flows into t he cont rol circuit,t he two comparators generate two square waves which rise and fall at t he peak of t he wave of t he sig2
8432 光学　精密工程 第16卷　
Fig.5　Control circuit
for generating switch signal
nal ,and it is wort h noting t hat t here is a little p hase difference between t he two square waves.Then t he two square waves flow into t he XOR gate and at t he end a periodic p ulse is generated.
The sensing signal and generated p ulse are shown in Fig.
6.
Fig.6　Sensing signal and generated control signal
The generated signal drives a power MOS 2
FET which act s as a switch ,and t he time needed to switch t he MOSFET between on and off state is dependent upon t he impedance of t he cont rol circuit.It is very important t hat t he cont rol cir 2cuit be bypassed wit h a capacitor t hat will keep t he drive voltage constant over t he drive
period.
Fig.7　Schematic of whole system
Fig.7shows t he integrated circuit of t he improved piezoelect ric energy harvester.The ul 2t ra 2low power co st of t he chip s and component s rest s on t he nanopower technology ,t hus t he chip s and component s are able to meet t he re 2quirement s in power cost of t he energy harvest 2er.
To check t he compatibility between t he modules wit hin t he harvester and validate it s ef 2ficiency ,t he elect rical simulation software called Orcad is used to perform t he simulations.Mo st of t he spice models are gotten f rom t he soft 2ware ’s own libraries except t he ones of t he volt 2age comparator ,t he MOSFET and t he Schott ky
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J I Hong 2li ,et al :Modelling ,simulation and optimization of high ……
diode ,which are only available from t he web 2page of t heir p roducers.
T ab.1　P aram eters of electric components in energy h arvester Voltage amplitude U of voltage source V 1(V )0.5Frequency f of voltage source V 1(Hz )30.33Inductance of inductor L m (H )
0.1292Resistance of resistor R m (Ω)
0.3376Capacitance of capacitor C m (
μF )214
Clumped capacitance C 0of piezoelectric disk (nF )91.2
Force factor αof piezoelectric disk 0.001298
Capacitance C r of filter capacitor (μF )10Inductance of inductor L (H ) 1.6Serial resistance of inductor L (Ω)
18
Forward voltage drop V f of Schottky diodes (mV )410Reverse breakdown voltage V r of Schottky diode (V )
70
4　Result s and discussion
The comparison of two types of piezoelec 2t ric energy harvesters is p resented ,t he classical one and t he imp roved o ne.The simulation re 2sult s of t he classical energy harvester are shown in Fig.8.The upper curve is t he voltage acro ss on t he piezoelectric disk elect rodes ,while t he lower one is t he harvested power in t he
first 20s after t he energy harvester is started.The aver 2age power is able to reach to 160μW at last.
Fig.8　Simulation results of classical energy harvest 2
er
The simulation result s of t he improved en 2ergy harvester are shown in Fig.9.The upper curve is t he voltage acro ss on t he piezoelectric disk elect rodes ,while t he lower one is t he har 2vested power in t he first 4.5s after t he energy harvester is started.The average power is able to reach to 550μW ,3.4times higher t han t hat of t he classical energy harvester.
Moreover ,t he calculation by t he software indicates t hat t he total power cost
of all t he com 2ponent s is merely 66μW which is much lower t han t he power gain.
Fig.9　Simulation results of improved energy har 2
vester
5　Conclusions
The imp rovement of Buck 2Boost converter is usef ul in piezoelect ric energy harvesting sys 2tem wit h p roper designs ,t he improved energy harvester has good compatibility inside and shows high efficiency gain compared wit h t he classical energy harvester.
An ult ra 2low power co st circuit used to switch t he converter of energy harvester is pro 2po sed in t his paper ,t he simulation result s indi 2cate t hat t he circuit has very low power co st
while enhances t he harvested power by 3.4times.Being in good agreement wit h t he t heo 2
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第16卷　
ries ,t hese result s confirm t he f ut ure applica 2tio ns for piezoelect ric energy harvester.
R eferences :
[1]　O T TMAN C K ,HOFMANN H F ,B HA T T A C ,et al ..Adaptive piezoelectric energy harvesting circuit for wire 2
less eemote power supply[J ].T ransaction on Power Elect ronics ,2002,17:6692676.
[2]　MARZENC KI M ,BASROUR S ,CHARLO T B ,et al ..Design and fabrication of piezoelectric micro power genera 2
tors for autonomous microsystems [C ].Proc.S y m p.on Desi gn ,Test ,I nteg ration and Packaging of M EM S /MO EM S ,Mont reux ,S w itzerland :D T I P 05,2005:.
[3]　MAR T Y B.Power S up pl y Cookbook [M ].Charlotte :Baker &Taylor Books ,2001.
[4]　BADEL A ,ABDEL MJ ID B ,EL IE L ,et al ..Single crystals and nonlinear process for outstanding vibration 2pow 2
ered electrical generators[J ].T ransaction on Ult rasonics ,Ferroelect rics ,and Frequency Cont rol ,2006,53:6732684.
[5]　SODANO H A ,PAR K G and INMAN D J.Estimation of electric charge output for piezoelectric energy harvesting
[J ].S t rain ,2004,40:49258.
[6]　TIL MANS H A C.Equivalent circuit representation of electromechanical transducers :I.L umped 2parameter sys 2
tems[J ].M icromech.M icroeng ,1996,6:1572176.
Authors ’biographies :J I Hong 2li (1983-),famale ,Ph.D.student ,her interests focus on vibration damping ,noise suppres 2
sion and energy harvesting.E -mail :jihongli @
Q IU Jin 2hao (1963-),male ,Professor ,Ph.D.,his present research interests are in the field of smart materials and systems :vibration control ,noise isolation ,energy harvesting ,piezo 2transformers and nonlinear/hysteretic modeling of these materials.E 2mail :qiu @
●下期预告
空间双光路的红外CO 2气体传感器及测量模型
李亚萍,张广军,李庆波
(北京航空航天大学精密光机电一体化技术教育部重点实验室,北京100083)
提出了一种基于空间双光路结构的红外CO 2气体传感器。

阐述了传感器光学探头的结构和工作
原理,并给出气室的几何形状和相应的尺寸参数,以朗伯2比尔定律为理论依据,结合空间双光路结构的工作机理,以及红外光源周期性开关的工作方式,推导出了该传感器的线性测量模型,并采用最小二乘法对建立的测量模型进行标定。

在静态下对该传感器的传感特性进行了测试,测试结果表明:在0～3%测量时,该传感器的实验值与真实值符合较好,其精度为2.42%;系统运行良好,可无故障连续在线测量30天以上。

该传感器能有效消除温度信号和背景光信号的干扰,能够在5～40℃的温度内、不同杂光背景下正常工作,基本满足CO 2气体浓度测量的功耗低、精度高、稳定性好等要求。

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532第12期
J I Hong 2li ,et al :Modelling ,simulation and optimization of high ……。