Study on short-term energy storage characteristics of accumulators of hydrostatic wind turbine system

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1 Available online Jounal of Chemical and Phamaceutical Reseach, 04, 6(7): Reseach Aticle ISSN : CODEN(USA) : JCPRC5 Study on shot-tem enegy stoage chaacteistics of accumulatos of hydostatic wind tubine system Fuzhu Li, Zhenzhi He, Wen Chen and Yuqin Guo 3 School of Mechanical and Electical Engineeing, Jiangsu Nomal Univesity, Xuzhou, China Division of Engineeing Technology of Wayne State Univesity, Detoit, MI, 480, USA 3 School of Mechanical Engineeing, Jiangsu Univesity, Zhenjiang, China ABSTRACT The imact of mico scale tubulence wind seed on wind owe geneation is studied in this ae. The elationshi between tubulence wind comonents and some key aametes, such as the accumulato effective volume, unit mass enegy stoage and state of chage, is analyzed when the mico scale tubulence wind seed is equal to the ated one. And then, a hydostatic wind tubine system and its coesonding contol method ae oosed, which can not only ealize the shot-tem enegy stoage, but also kee the wind tubine woking unde the ated owe condition. Finally, aimed at a 0 kw hydostatic wind tubine system with an accumulato to imlement shot-tem enegy stoage, the simulation analysis is caied out when the mico scale tubulence intensity is % of the ated wind seed. The esults showed that the outut enegy of the hydostatic wind tubine system with a shot-tem stoage accumulato is.3% lage than that of the coesonding system without accumulato. Keywods: Hydostatic System, Wind Powe Geneation, Accumulato, Shot-tem Stoage. INTRODUCTION Desite the low efficiency of the hydaulic system, the hydaulic vaiable seed constant fequency (VSCF) wind tubine system may avoid to use geabox and owe electonic devices, and also achieve shot-tem enegy stoage and elease easily though accumulato, which could stabilize owe quality of wind tubines [, ]. With the continuous imovement of the hydaulic technology and the evaluation eseach of its oveall cometitiveness, the hydostatic wind owe technology has attacted wide attention in the cuent wold wind owe counties [3]. It is qualified as one of the hot issues of next geneation of wind owe technology by United State Deatment of Enegy in June 00 [4]. Howeve, ecent eseaches ae mainly focused on the system contolling and efficiency imovement. The eseaches about influence of andom mico scale tubulent wind seed on wind owe, togethe with the chaacteistics and the effects of shot-tem enegy stoage of accumulatos of hydostatic wind tubine system, ae aely studied. Moeove, the utilization of accumulato in hydostatic wind tubine system not only imove the quality of wind owe, but also is an effective means of exanding the scoe of wind enegy, imoving the efficiency of wind enegy and making hydostatic wind tubine u. In wind tubine systems, the main uose of shot-tem enegy stoage device such as flywheels and sue caacito is to imove the owe quality, smooth owe fluctuations and imove the low-voltage ide-though caability [5,6]. The enegy stoage of accumulato of wind tubine system was studied in liteatue [7], howeve the chaacteistic and effect of enegy stoage of accumulato unde andom tubulence wind seed ae absent. In addition, the accumulato has been studied on the hybid vehicles as enegy stoage device, which mainly ecoves the baking enegy and imove the oveall efficiency of the engine [8]. 500

2 Fuzhu Li et al J. Chem. Pham. Res., 04, 6(7): On the basis of the imact of mico scale tubulence wind seed on wind enegy outut of wind tubine system, the elationshi between tubulence wind comonents and some key chaacteistic aametes is analyzed in this ae, when the mico scale tubulence wind seed is equal to the ated wind seed. In addition, the effect of hydostatic wind tubine system with shot-tem enegy stoage accumulato is also studied. EXPERIMENTAL SECTION. Imact of mico scale tubulence wind seed on wind owe geneation. Model of mico scale tubulence wind seed Tubulence is a vey comlex hysical henomenon, and the wind seed of the sectal ga of wind-velocity sectum is consideed to be the mico scale tubulence wind seed, with the vaiation eiod fom 30 seconds to seveal minutes [9]. Sectal ga may not exist in many cases, but to the needs of engineeing alications and theoetical eseaches, it is assumed that thee is an obvious sectal ga, and that mico scale tubulence wind seed is the aveage wind seed sueimosed with a Gaussian andom vaiable with zeo mean, which is exessed as [9]. u = u + u () whee, u is the aveage wind seed, u is the Gaussian andom vaiable with zeo mean. The standad deviation could be witten as σ = ui, whee I is tubulence intensity. In ode to study the imact of mico scale tubulence wind seed on outut owe and enegy stoage of wind tubine, the actual o simulated wind seed can be used. The actual wind seed can eflect actual situation moe accuately, howeve it is difficult to measue, and is without univesality. Theefoe, based on the andom white noise and the Kalman Filte theoy, a two-dimensional mico scale tubulence wind seed geneated by MATLAB is selected as the eseach object, the sectum of which is 4 k Lk / uhub Sk ( f ) = σ () 5 6 flk 3 ( + ) u hub whee, f is the fequency, L k is the scale of Eule's integal, σ k is wind seed, vetical owe sectal density.. Imact of mico scale tubulence wind seed on wind owe geneation Assume that the owe of mico scale tubulent wind seed P is u hub is standad deviation, and S k is P ρ Au whee, ρ is the ai density, and A is the oto swet aea. The exected value of owe of mico scale tubulent wind seed E(P) is = 3 (3) 3 ( ( ) [ 3 ) 3 ( ) ( 3 E P = ρ A u + ue u + u E u + E u )] (4) whee, E (u ) is the exected value of andom vaiables with Gaussian distibution. Fo Gaussian distibution with E = σ =. Then, mico scale tubulent wind seed is zeo mean, E (u ) and ( 3 E u ) ae both zeo, and ( u ) ( ui ). times the owe of the aveage wind seed when the tubulence intensity I equals to 0%. In Figue, Figue (a) is the distibution of mico scale tubulent wind seed as the aveage wind seed is 0 m/s and the tubulence intensity is %. Figue (b) is the outut owe of wind tubine with the ated owe of 0 kw, the wind seed of which is shown in Figue (a). 50

3 Fuzhu Li et al J. Chem. Pham. Res., 04, 6(7): Wind seed(m/s) tubulence aveage seed Time(s) (a) Distibution of mico-scale wind seed as the aveage wind seed is 0 m/s and the tubulence intensity is % x 0 4 Roto owe with itch system Roto owe without itch system Rated oto owe Powe is the tubulent wind Stoage Enegy Powe(w) Release Enegy Time(s) (b) Outut owe of wind tubine as the aveage wind seed is 0 m/s and the tubulence intensity is % Fig. Imact of mico-scale tubulence wind seed on outut owe of 0 kw wind tubine When the wind seed exceeds the ated seed, the excess wind owe is geneally emoved though vaiable-itch stuctue in VSCF wind tubine system to ensue unning the wind tubine unde ated conditions. It is shown in Figue (a) that thee will be some mico scale tubulence wind seed exceeds the aveage ated one. Figue (b) shows that the theoetical outut owe of wind tubine should be 0 kw when the ated wind seed is 0 m/s. Howeve, the aveage outut owe of taditional VSCF wind tubine is only 8.9 kw with the action of mico scale tubulence wind seed of 0 m/s, that is % less than the theoetical value. It can be seen that the mico scale tubulent wind has a geat influence on the outut owe of wind machine. If stoing the exta tubulence wind owe when tubulent wind seed is moe than aveage value using the accumulato in hydostatic wind tubine systems, while eleasing wind owe when it is less, the utilization scoe of wind enegy can be effectively exanded and the outut owe of wind tubine can be imoved. The section headings ae in boldface caital and lowecase lettes. Second level headings ae tyed as at of the succeeding aagah (like the subsection heading of this aagah). All manuscits must be in English, also the table and figue texts, othewise we cannot ublish you ae. Please kee a second coy of you manuscit in you office. When eceiving the ae, we assume that the coesonding authos gant us the coyight to use the ae fo the book o jounal in question. When eceiving the ae, we assume that the coesonding authos gant us the coyight to use the ae fo the book o jounal in question. When eceiving the ae, we assume that the coesonding authos gant us the coyight to use.. Shot-tem enegy stoage scheme of hydostatic tubine system. Aoaches to acquie the excess enegy The chaacteistic cuve of the toque- otate seed of VSCF wind tubine with diffeent wind seeds is shown in Figue. T(Nm) Rated otation seed E C Toque limit D A v v B v4 v3 Rotating seed limit v7 v8 v 6 v 5 Powe limit Rated owe O ω(ad/s) Fig. Chaacteistics cuve of the toque- otate seed of wind tubine Geneally, VSCF wind tubine system extact wind enegy in the way of maximum owe tacking in the AB segment, and will un with constant toque afte eaching the ated owe of B-oint. Howeve, the mico scale tubulence in ated wind seed will affect the outut owe of wind tubine. The hydostatic wind tubine system does not use D' Cmax 50

4 Fuzhu Li et al J. Chem. Pham. Res., 04, 6(7): owe- limited hydaulic owe electonic convete equiment, thus the wind tubine may un in owe limit mode which is exceed the B-oint when ensuing the geneato in ated owe oeation. Thee ae two diffeent ways to incease the outut enegy of wind tubine, one is to kee toque constant and incease otation seed which is along BD', the othe is to kee otation seed constant and incease toque which is along BD... Rotation seed inceasing while toque is constant The otation seed of wind tubine is limited by the blade ti seed atio which is the main facto of wind tubine noise and geneally less than 65 m/s, theefoe, the method to obtain tubine wind enegy though inceasing otation seed while toque is constant is not consideed in this ae... Toque inceasing while otation seed is constant The ated owe of oto is as following, P T ω = ρac λ β u 3 = (, ) (5) whee, T is the ated toque, ω is the ated seed, λ and β ae the itch angle and the blade ti seed atio esectively, with ωr / u, and C (λ,β) is the owe facto of the wind tubine. λ = Then the total owe outut when inceasing toque while otation seed is constant can be witten as P = T ω + Tω (6) t whee, P t is the total owe outut of the wind tubine, and T is the toque incement.. Relationshi between mico scale tubulence and system essue Afte ignoing the fiction, daming and leakage losses of the oto and um, the following elationshi can be obtained accoding to enegy balance, P t = P + P = P + Tω (7) whee, P and P ae the ated owe of um and the owe incement of wind tubine esectively, with P =P. The hydaulic system essue will be ose when the toque inceasing while the oto seed of wind tubine is constant. P = D ω = ) D ω = Tω ( (8) whee, and ae the ated essue and the system essue afte toque inceasing esectively, and D is the ated caacity of um. By substituting the equations (5) and (6) into equation (8), it becomes: D 3 (, )( u u 3 β λ = ρac ω (9) By substituting the equation () into equation (9), the elationshi between system essue vaiation and tubulence can be exessed as = D ω ( 3 ρac u u + uu + 3u 3. Relationshi between chaacteistic aametes of accumulato and tubulence 3. Effective volume Boh gas law gives the following equation n n n V = V = ava = const () ) ) (0) whee, V V and V a, ae the volume coesond esectively to the lowest essue, the highest essue and the andom essue a of the accumulato, n is the olytoic exonent of gas. 503

5 ( ) Fuzhu Li et al J. Chem. Pham. Res., 04, 6(7): Effective volume V is the amount of volume changed coesonding to the change of gas essue within the accumulato, i.e., V = V V () V and V can be obtained fom equation (). By letting = /( + ) and combining equations (0) and (), elationshi between the effective volume V of accumulato of the hydostatic wind tubine system and the mico scale tubulence wind seed can be exessed as V = V ( n ) (3) Figue 3 shows the elationshi between the effective volume V of accumulato and tubulence comonent u. Effective volume(l) Local amlication n=.0 n= B=0Ma C=5Ma Fig.3 Relationshi between the accumulato effective volume and tubulence wind comonents It can be seen that the effective volume of accumulato changes aidly when the tubulence comonent u < 0. m/s with the same initial volume, which is mainly due to that the gas with fee state in the accumulato is comessed quickly. Convesely, the volume changes smoothly when tubulent comonent u >. 5 m/s. And it also can be seen that the effective volume deceases as the system ated essue and olytoic exonent n inceases. 3. Unit mass enegy stoage Assuming E is the total enegy stoed in the accumulato, the unit mass enegy stoage of accumulato will be E m =E/(ρ a V ). Afte combining equations (0) and (), it gives E m / n / n ρ av ( ρo + ρ0)( ) + ρ g u ( + ) / n ( ) E = = n (4) whee, ρ a ρ o ρ o andρ g ae the densities of accumulato and its ai bags, hydaulic fluid and gas esectively. The elationshi between the accumulato unit mass enegy stoage and the tubulence comonents u is shown in Figue 4. Kg KJ Uint mass stoage enegy n=.0 A=5Ma n=. n=. n=.3 n=.4 n=.0 n=. n=. n=.3 n=.4 5 n=.4 C=5Ma n=.0 n=. B=0Ma n=. n= u Fig.4 Relationshi between the accumulato unit mass enegy stoage and tubulence wind comonents It can be seen that the accumulato unit mass enegy stoage is essentially indeendent of multilateal index when the tubulent comonent u <0., and only elates to the system ated essue. The geate the essue the geate the unit mass enegy stoage. It inceases as the tubulent comonent inceases when u >

6 Fuzhu Li et al J. Chem. Pham. Res., 04, 6(7): Chage and dischage of accumulato Accumulato state of chage (SOC) eesents the atio of fluid volume in accumulato and the initial volume of accumulato. Accoding to equations (0) and (), it can be exessed as SOC / n = (5) The elationshi between the accumulato state of chage and tubulence comonents u is shown in Figue Local amlication n=.3 n=. n=. n=.0 A =5Ma Tubulence wind comonent u (m/s) n=.4 n=. n=. n=.0 C=5Ma B=0Ma n=.3 n=.4 n=.0 n=. n=. n=.3 n=.4 Fig.5 Relationshi between the accumulato state of chage and tubulence wind comonents It can be seen that the accumulato state of chage will make u to 40% even when thee is small tubulent comonent, and then inceased slowly. Its state of chage deceases as the initial essue of accumulato o system ated essue incease. 4. Case study 4. Shot-tem enegy stoage hydostatic wind tubine system The seed egulating system adoted in cuent hydostatic wind tubine system is mainly the quantitative umvaiable moto systems o vaiable um- quantitative moto systems, the disadvantages of which ae eflected in lage oveflow losses, low system esonse, limited seed ange [,]. Theefoe, accoding to the method to obtain moe enegy by toque inceasing while otation seed is constant, and the equiements to un the geneato unde ated conditions, the stuctue of hydostatic wind tubine system with shot-tem enegy stoage is shown in Figue 6. A + B C u ω T+ T ωm Tm GM β D Contolle Dm Fig. 6 Shot-tem stoage enegy stuctue of a hydostatic wind owe geneation system When the wind seed is highe than the ated mico scale tubulence wind seed, the valve C is tuned on while valve B disconnected, meanwhile, the wind tubine will kee the seed constant and incease toque to obtain moe wind enegy until the accumulato is full of enegy, in which the function of educing valve is to ensue the owe of hydaulic motos constant. On the contay, when the wind seed is lowe than the ated wind seed, the accumulato will elease enegy. When the inlet essue of educing valve eaches to the ated essue, valve B will be disconnected while valve C tuned on, then the system unning nomally. 4. Contol stategy When the aveage wind seed equals to the ated one, the dynamics equation of hydaulic ums and wind machine can be exessed as following T ω D = J & ω + Bω t t (6) 505

7 Fuzhu Li et al J. Chem. Pham. Res., 04, 6(7): whee, T t =T + T=P t /ω, J t is the sum of otational inetia of wind tubine and um, and B is the daming coefficient of the toque. By substituting the equation (5) into equation (6), the equation becomes: ω R = [ ρac (, ) ] 3 P λ β J & ω Bω (7) D λ In ode to ensue the otate seed ω constant, it is only needed to contol the hydaulic system essue to tack the changes of tubulent wind seed. 4.3 Simulation esults A wind tubine system with the owe of 0 kw is adoted in this case study, the main technical aametes of which ae:r=4m ω =00m P =0kw u =0m/s,D =68cc/ev, length of ie l=m, diamete of ie d=5mm, the volume of accumulato V =40L, nominal essue =0MPa,J t =8kg.m,B= 0.09N m/(ad s - ), ρ=.5kg/m 3. Figue 7shows the distibution of mico scale wind seed within 600s as the tubulence intensity is % and the aveage wind seed is 0 m/s Times(s) 时时 Fig.7 Distibution of wind seed as the tubulence intensity is % and the aveage wind seed is 0m/s The Comaison of outut owe of wind tubines with and without accumulato is shown in Figue 8. Fig. 8 Comaison of outut owe of wind tubines with/without accumulato Thanks to the shot-tem enegy stoage of accumulato, the outut enegy of hydostatic wind tubine system is aoximately J with accumulatos, while about J without accumulatos. So the enegy stoed by accumulato is about J. The outut enegy of the hydostatic wind tubine system with accumulato is.3% lage than that of the coesonding system without accumulato. CONCLUSION ) Mico scale tubulent wind seed is. times the owe of the aveage wind seed when the tubulence intensity I equals to 0%, that is to say that the mico scale tubulent wind has a geat influence on the wind tubine system. ) The elationshi between tubulence wind comonents and some key efomance aametes of accumulato in hydostatic wind tubine system, such as the effective volume, secific enegy and state of chage, is given when the mico scale tubulence wind seed is equal to the ated wind seed. 3) A hydostatic wind tubine system with the shot-tem enegy stoage accumulato and its coesonding contol method ae oosed. The esults showed that the outut enegy of the hydostatic wind tubine system with a shot-tem stoage accumulato is.3% lage than that of the coesonding system without accumulato, when the initial volume of accumulato V equals to 40L and the tubulence intensity I equals to %. 506

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