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外文翻譯--一種先進(jìn)的應(yīng)用于分布式發(fā)電中的微型水電站的動態(tài)模型仿真和控制設(shè)計-閱讀頁

2025-01-31 12:08本頁面
  

【正文】 型的以上參數(shù)是在其額定工況下求得的,而且假定水是不可壓縮的。所轉(zhuǎn)換得到的機(jī)械能與水本身所具有的能量可以通過水輪機(jī)的效率 聯(lián)系起來,用方程表示如下: 由于所選用的進(jìn)行試驗(yàn)的水輪機(jī)幾乎要在轉(zhuǎn)輪允許轉(zhuǎn)速范圍內(nèi)各個數(shù)值進(jìn)行試驗(yàn),所以像通常文獻(xiàn)中那樣,假定轉(zhuǎn)矩和轉(zhuǎn)輪轉(zhuǎn)速之間為線性關(guān)系,是不可取的。事實(shí)上,與所獲得的機(jī)械能有關(guān)的水輪機(jī)效率在很大程度上依賴轉(zhuǎn)輪的設(shè)計與轉(zhuǎn)輪所處的運(yùn)行工況(如Q、H和轉(zhuǎn)輪的角速度)。所以,作者在文章進(jìn)行了一些近似計算以變計算出所選用進(jìn)行試驗(yàn)的水輪機(jī)的功率特性。書輪機(jī)的最高效率點(diǎn)設(shè)計在額定流量與額定水頭工況點(diǎn),該工況下,水輪機(jī)可以獲得最大的功率。因此,水輪機(jī)的控制關(guān)鍵在于可變轉(zhuǎn)速的操作機(jī)構(gòu)以便可以在某個特定的工況下實(shí)時跟蹤最大功率點(diǎn),這樣就可以源源不斷的從水流中提取最大的功率。本文提出的功率調(diào)節(jié)系統(tǒng)由背靠背式AC/DC/AC轉(zhuǎn)換器組成,它完全可以滿足上述對功率調(diào)節(jié)系統(tǒng)的要求。這種情況就需要一個額外的調(diào)節(jié)器來來滿足所并電網(wǎng)的幅值和頻率要求。不可控三相全波整流橋具有簡單,穩(wěn)固,便宜,不需要控制系統(tǒng)等優(yōu)點(diǎn)。首選三電平電壓源型逆變器而非其他類型逆變器,是因?yàn)槿娖诫妷涸葱湍孀兤鞅葌鹘y(tǒng)的不帶頻率切換功能的逆變器結(jié)構(gòu)的輸出電壓波形具有更好的正弦特性。與公共電網(wǎng)的連接是通過一臺升壓變壓和一臺低通濾波器,這樣做,可以減少對分布式電網(wǎng)系統(tǒng)的擾動。為了達(dá)到此目的,設(shè)置了一個中間級DC/DC 轉(zhuǎn)換器,用來連接三相全波整流橋的輸出端到逆變器的直流側(cè)總線。步進(jìn)式轉(zhuǎn)換器在連續(xù)導(dǎo)電模式下的穩(wěn)態(tài)電壓和電流的關(guān)系可以用下面的方程式表示: ; 其中: :斬波器的輸入電流(電感電流) :輸出電壓(直流鏈電壓) :步進(jìn)式轉(zhuǎn)換器的輸入電壓 :斬波器的輸出電流 :DC/DC 轉(zhuǎn)換器的占空比. 電壓源型逆變器 本文所使用的三相三電平電壓源型逆變器與采用正弦脈寬調(diào)制(PMW)技術(shù)的DC/AC開關(guān)電源逆變器是一致的[8]。這一完美的逆變器通過一個等價于升壓變壓器漏抗的電感和一組代表變壓器繞組電阻及電壓源型逆變器半導(dǎo)體導(dǎo)電損失的串聯(lián)電阻在公共耦合點(diǎn)(PCC)并入電網(wǎng)[9]。在逆變器的直流側(cè),損失源于電阻和直流總線電容器的等值電容。從而,在新的坐標(biāo)系中,瞬時電壓向量始終與直軸保持一致(即=,)。在交直軸坐標(biāo)系下,可以推導(dǎo)出控制電壓源型逆變器交流側(cè)輸出三相電壓瞬時值和與電網(wǎng)之間交換電流的動態(tài)方程,該方程如下[8,9]: 其中::拉普拉斯變量,定義0 :工頻電網(wǎng)電壓同步角速度 :電壓源型逆變器的調(diào)制指數(shù), = :變壓器的變比 :交直軸坐標(biāo)系下,電壓 源型逆變器的 平均轉(zhuǎn)換因素 :電壓源型逆變器的輸出電壓相對于參考點(diǎn)的相角 與三相電網(wǎng)相連的MHPP的多級控制框架 3. 控制測略 ,本文與三相電網(wǎng)相并列的微型水電站模型的控制由外層,中層,和內(nèi)層共三層構(gòu)成。電壓控制模式用來通過調(diào)整電壓源型逆變器輸出的無功電流(即交軸分量)控制逆變器公共耦合點(diǎn)的電壓。從而產(chǎn)生一個偏差信號,該偏差信號再輸入到衰減系數(shù)為的比例—積分控制器(PI)。為了達(dá)到這個目的,有功功率控制模式的作用在于使得輸入到電網(wǎng)中的有功功率與水輪發(fā)電機(jī)組發(fā)出的最大功率相一致。最大功率點(diǎn)跟蹤意味著微型水電站應(yīng)當(dāng)始終運(yùn)行在最大輸出電壓/電流工況。不幸的是,測量轉(zhuǎn)動著的水輪機(jī)中每時刻的水流速度是非常困難的;因此,為了避免使用測量的辦法來獲得水輪機(jī)的最優(yōu)轉(zhuǎn)速,有必要才用一種間接的方法。本控制算法采用了擾動觀察(Pamp。這種被廣泛應(yīng)用在太陽能光伏發(fā)電系統(tǒng)的具有良好結(jié)果的算法[7]結(jié)構(gòu)簡單,而且需要測量的變量較少。為了導(dǎo)出這一模塊的控制法則,需要使用一下由方程(6)所描述的電壓源型逆變器的動態(tài)模型。從方程(6)還可以看出,其中包含了直流電容電壓這一附加項。通過使用一個能夠消除直流母線上穩(wěn)態(tài)電壓變量的比例—積分(PI)控制器,這一問題的解決方法可以得到。這一級主要由一個同步組件,一個三相三電平正弦脈寬調(diào)制(SPWM)觸發(fā)脈沖發(fā)生器和一個作用于斬波器的脈寬調(diào)制脈沖發(fā)生器組成。由于該水電站有兩種控制策略,即有功功率控制模式(APCM)和電壓控制模式(VCM),所以要進(jìn)行兩套模擬仿真。流過水輪機(jī)轉(zhuǎn)子的流量按照圖片總給定的方式被強(qiáng)制改變(步長為1s),從而發(fā)電機(jī)的最大發(fā)出功率也相應(yīng)的改變。O)設(shè)計的最大功率跟蹤器(MPPT)在跟蹤微型水電站的最大功率點(diǎn)時是準(zhǔn)確的,設(shè)計時的最優(yōu)擾動步長要與斬波器的動態(tài)特性相一致。還可以觀察到DC/DC轉(zhuǎn)換器固定電壓控制的情況,即最大功率跟蹤器不參與控制,而且水輪機(jī)在幾乎恒定的轉(zhuǎn)速下運(yùn)作(圖中綠色虛線所示部分)。最后,由于電壓控制模式(VCM)沒有被激活,所以與電網(wǎng)之間沒有無功功率交換(圖中紅色實(shí)線所示部分)。正如看到的那樣,與僅有APCM被激活時的情況相同,微型水電站發(fā)出的有功功率除去部分損失外全部注入到電網(wǎng)中去了。無功功率的產(chǎn)生增加了電壓源型逆變器的損失,導(dǎo)致與先前用DC/DC轉(zhuǎn)換器雙重控制研究的情況(MPPT參與控制與不參與控制)相比,有功功率的交換有輕微的降低。模擬仿真研究和實(shí)驗(yàn)結(jié)果證明了所提出的在同步旋轉(zhuǎn)的交—直軸坐標(biāo)系下的多級控制方法的有效性,并展現(xiàn)了詳細(xì)的模型。2000.[2] Rahman S. Going green: the growth of renewable energy. IEEE Power amp。1(6):16–8.[3] Date A, Akbarzadeh A. Design and cost analysis of low head simple reaction hydro turbine for remote area power supply. Renewable Energy 2009。23(3):834–41.[5] Ansel A, Robyns B. Modelling and simulation of an autonomous variable speed micro hydropower station. Mathematics and Computers in Simulation June 2006。 n E, PortilloGuisado RC, Mart?180。53(4):1002–16.[7]Molina MG, Pontoriero DH, Mercado PE. An efficient maximumpowerpointtracking controller for gridconnected photovoltaic energy conversion system. Brazilian Journal of Power Electronics July 2007。 August 2006. p. 1–8.[9] OlsenBerenguer FA, Molina MG. Design of improved fuel cell controller for distributed generation systems. International Journal of Hydrogen Energy, in press, doi:[10] The MathWorks Inc.. SimPowerSystems for use with Simulink: user’s guide, updated for Simulink (Release 2009a). Available at: 。 so that to avoid using this measurement for determining the optimal rotor speed, an indirect approach needs to be implemented. The proposed MPPT strategy is based on directly adjusting the DC/DC converter duty cycle and thus the rotor speed, according to the result of the parison of successive output power measurements. The control algorithm uses a ‘‘Perturbation and Observation’’(Pamp。O MPPT method proves to be accurate in following the MPP of the microhydro power station, designed with an optimum duty cycle perturbation step in accordance with the chopper dynamics. As can be noted, all the active power generated by the MHPP (shown in blue dashed lines) is injected into the electric grid, except losses, with small delays in the dynamic response. It can be also seen the case with fixed voltage control of the DC/DC converter, . with no MPPT control and consequently with near constant rotor speed operation (shown in green dotted lines). In this case, the power injected into the electric grid is much lesser than with MPPT, about an average 30% lower. Eventually, no reactive power is exchanged with the electric grid since VCM is not activated (shown in red solid lines). Fig. 7–Simulation results for active and reactive power exchange (APCM and VCM) Simulations of Fig. 7 show the case with active and reactive power exchange with the utility grid, . the APCM is activated all the time while the VCM is activated at t= . As can be seen, all the active power generated by the MHPP is injected into the electric grid, except losses, in the same way than the case with only APCM activated. The rapid injection of almost 300 var of reactive capacitive power into the electric system (shown in red solid lines) when the VCM is activated aims at regulating the PCC voltage at 1 . This reactive power generation increases the VSI losses, which causes a slightly lower exchange of active power than the previous casestudied with both controls of the DC/DC converter (with and without MPPT).5. Conclusion In this paper, a novel control approach of a threephase gridconnected MHPP, incorporating a MPPT for dynamic active power generation jointly with reactive power pensation of distribution systems has been presented. Simulation studiesand experimental results demonstrate the effectiveness of the proposed multilevel control approaches in the synchronousrotating dq reference frame and the detailed models presented.References[1] Willis HL, Scott WG. Distributed power generation – planning and evaluation. 1st ed. Marcel Dekker, ISBN 0824703367。 Energy Magazine Nov/Dec 20
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