在各大中型城市中一大批智能化小區、花園別墅、智能大型綜合體育設施等建筑拔地而起， 客觀上要求有與其相配套的高效能環保的照明設備的出現。LED 是發光二極管的統稱， 它工作在低電壓、小電流的狀態下， 所以具有發熱量小、功耗低的顯著特征。而且其使用方面， 可以根據不同場合的使用要求方便地進行多顆LED 的組合。所以在LED 技術基礎上發展起來的LED 光伏路燈是一種新型環保且具有高光效的節能設備， 具有安全抗震、使用方便、費用低、壽命長、節約能源、無污染等優點， 在許多領域可代替現在廣泛使用的白熾燈、日光燈等光效相對較低的照明設備。其工作原理就是通過太陽電池光伏陣列將太陽能轉化為電能， 給蓄電池進行充電， LED 驅動器則通過蓄電池為其提供工作電源， 完成對LED 燈的驅動和保護功能。其優點是克服了目前市場上所使用的其它照明設備普遍存在的耗能大、光效差、不穩定、蓄電池使用壽命短等多種弊端。大功率LED 路燈充電器設計的一個關鍵的部分就是光伏充電器的(de)(de)設計問(wen)題(ti)， 因(yin)為光伏(fu)充(chong)電(dian)器(qi)不(bu)僅完成了把(ba)太陽能(neng)(neng)轉換(huan)成電(dian)能(neng)(neng)的(de)(de)重任， 而且還對(dui)蓄電(dian)池提供了智能(neng)(neng)充(chong)電(dian)管理(li)， 因(yin)此光伏(fu)充(chong)電(dian)器(qi)的(de)(de)性能(neng)(neng)直(zhi)接決(jue)定了太陽能(neng)(neng)能(neng)(neng)量利用的(de)(de)效(xiao)率和系統使用的(de)(de)壽命。本文(wen)從原理(li)、控制策略和實際應用等幾個方(fang)面介紹一種光伏(fu)充(chong)電(dian)器(qi)及其控制系統的(de)(de)設計思(si)想。

　　1 系統構成

　　1.1 LED 的工作特(te)性

　　發光(guang)二極管LED（Light Emitting Diode）的(de)工作原(yuan)理是在半導(dao)體p-n 結上加(jia)一正向電(dian)壓， 從(cong)而使其電(dian)子(zi)與空(kong)穴(xue)復(fu)合（即結區變窄(zhai)）， 這種復(fu)合是電(dian)子(zi)從(cong)高(gao)能級的(de)導(dao)帶釋(shi)放能量回(hui)到價帶與空(kong)穴(xue)復(fu)合， 其釋(shi)放的(de)能量以光(guang)子(zi)的(de)形式出(chu)現， 即發光(guang)。

　　根(gen)據(ju)半導體物理(li)中的(de)(de)公式(shi)(shi)： λ=1.24/Eg式(shi)(shi)中： Eg 為(wei)半導體材料導帶與價帶之間(jian)的(de)(de)禁帶寬(kuan)度， λ為(wei)波(bo)(bo)(bo)長(chang)。從式(shi)(shi)中可(ke)以(yi)(yi)看出， 對于(yu)不(bu)同(tong)材料的(de)(de)半導體來(lai)說， 由于(yu)它們(men)的(de)(de)Eg 不(bu)同(tong)， 因(yin)此它們(men)的(de)(de)波(bo)(bo)(bo)長(chang)# 也(ye)不(bu)一樣， 所以(yi)(yi)發光(guang)(guang)(guang)(guang)(guang)(guang)(guang)的(de)(de)顏色不(bu)同(tong)。顯然， 一般LED 多為(wei)單顏色光(guang)(guang)(guang)(guang)(guang)(guang)(guang)， 如紅光(guang)(guang)(guang)(guang)(guang)(guang)(guang)、綠光(guang)(guang)(guang)(guang)(guang)(guang)(guang)、黃(huang)光(guang)(guang)(guang)(guang)(guang)(guang)(guang)、藍(lan)光(guang)(guang)(guang)(guang)(guang)(guang)(guang)等。所謂(wei)白光(guang)(guang)(guang)(guang)(guang)(guang)(guang)是多種顏色的(de)(de)光(guang)(guang)(guang)(guang)(guang)(guang)(guang)混(hun)合(he)而成， 以(yi)(yi)人類眼睛所能見到(dao)的(de)(de)白光(guang)(guang)(guang)(guang)(guang)(guang)(guang)形式(shi)(shi)至少必須兩種以(yi)(yi)上的(de)(de)光(guang)(guang)(guang)(guang)(guang)(guang)(guang)混(hun)合(he)， 一般有(you)下列(lie)兩種混(hun)合(he)方式(shi)(shi)： 二(er)波(bo)(bo)(bo)長(chang)光(guang)(guang)(guang)(guang)(guang)(guang)(guang)―――藍(lan)光(guang)(guang)(guang)(guang)(guang)(guang)(guang)與黃(huang)光(guang)(guang)(guang)(guang)(guang)(guang)(guang)混(hun)合(he)； 三(san)波(bo)(bo)(bo)長(chang)光(guang)(guang)(guang)(guang)(guang)(guang)(guang)―――紅光(guang)(guang)(guang)(guang)(guang)(guang)(guang)、綠光(guang)(guang)(guang)(guang)(guang)(guang)(guang)與藍(lan)光(guang)(guang)(guang)(guang)(guang)(guang)(guang)混(hun)合(he)。目前已經商品化的(de)(de)白光(guang)(guang)(guang)(guang)(guang)(guang)(guang)LED 產品多為(wei)二(er)波(bo)(bo)(bo)段藍(lan)光(guang)(guang)(guang)(guang)(guang)(guang)(guang)單晶(jing)片加上YAG 黃(huang)色熒光(guang)(guang)(guang)(guang)(guang)(guang)(guang)粉； 三(san)波(bo)(bo)(bo)長(chang)光(guang)(guang)(guang)(guang)(guang)(guang)(guang)以(yi)(yi)無機紫外線(xian)光(guang)(guang)(guang)(guang)(guang)(guang)(guang)晶(jing)片加R、G、B 三(san)顏色熒光(guang)(guang)(guang)(guang)(guang)(guang)(guang)粉。此外， 有(you)機單層三(san)波(bo)(bo)(bo)長(chang)型白光(guang)(guang)(guang)(guang)(guang)(guang)(guang)LED 也(ye)有(you)成本低、制作容易(yi)等優(you)點。

　　1.2 太(tai)陽電池(chi)的(de)工(gong)作特性

　　圖(tu)(tu)1、圖(tu)(tu)2 分別給出(chu)了太陽(yang)電池溫度(du)在25 ℃時(shi)， 工作電壓、電流和日照（ W/m2） 的(de)關系(xi)曲(qu)線(xian)及(ji)太陽(yang)電池的(de)輸出(chu)功率和日照、電壓之間(jian)的(de)曲(qu)線(xian)。

　　從圖(tu)1 的(de)I/U 關系(xi)可以看出(chu)， 太(tai)陽電(dian)(dian)池(chi)陣列既非恒(heng)壓源(yuan)，也非恒(heng)流源(yuan)， 而是一(yi)種非線性直流電(dian)(dian)源(yuan)， 電(dian)(dian)池(chi)輸出(chu)電(dian)(dian)流在(zai)(zai)大(da)(da)部分工(gong)(gong)作(zuo)電(dian)(dian)壓范圍內相當恒(heng)定， 最(zui)終在(zai)(zai)一(yi)個足夠高的(de)電(dian)(dian)壓之(zhi)后，電(dian)(dian)流迅(xun)速下降至零。由(you)圖(tu)2 可知， 太(tai)陽電(dian)(dian)池(chi)的(de)工(gong)(gong)作(zuo)效率(lv)(lv)(lv)等(deng)于輸出(chu)功(gong)(gong)率(lv)(lv)(lv)與(yu)投(tou)射到太(tai)陽電(dian)(dian)池(chi)面積上的(de)功(gong)(gong)率(lv)(lv)(lv)之(zhi)比。因(yin)此， 為了(le)提(ti)高本系(xi)統的(de)工(gong)(gong)作(zuo)效率(lv)(lv)(lv)， 必須盡可能地(di)使太(tai)陽電(dian)(dian)池(chi)在(zai)(zai)最(zui)大(da)(da)功(gong)(gong)率(lv)(lv)(lv)點(dian)處工(gong)(gong)作(zuo)， 這樣就可以用功(gong)(gong)率(lv)(lv)(lv)盡可能小的(de)太(tai)陽電(dian)(dian)池(chi)獲得最(zui)大(da)(da)的(de)功(gong)(gong)率(lv)(lv)(lv)輸出(chu)， 這就是進行最(zui)大(da)(da)功(gong)(gong)率(lv)(lv)(lv)點(dian)跟蹤的(de)意(yi)義所在(zai)(zai)。如(ru)圖(tu)1 和(he)圖(tu)2 所示， 圖(tu)中的(de)A、B、C、D、E 點(dian)分別對應不同日照時的(de)最(zui)大(da)(da)功(gong)(gong)率(lv)(lv)(lv)點(dian)。

　　1.3 鉛酸蓄電池的工作特性

　　目(mu)前在(zai)光(guang)伏(fu)充電(dian)器系統中(zhong)(zhong)(zhong)大量使用的(de)(de)(de)是鉛(qian)酸(suan)(suan)(suan)蓄(xu)電(dian)池， 它的(de)(de)(de)工作原理(li)是依靠鉛(qian)酸(suan)(suan)(suan)正(zheng)極(ji)(ji)的(de)(de)(de)活(huo)性物質二氧化(hua)鉛(qian)（ PbO2） 和負極(ji)(ji)的(de)(de)(de)活(huo)性物質海綿狀鉛(qian)（ Pb） 與電(dian)解液硫(liu)(liu)酸(suan)(suan)(suan)（ H2SO4） 進行化(hua)學(xue)反應生成(cheng)硫(liu)(liu)酸(suan)(suan)(suan)鉛(qian)（ PbSO4） , 在(zai)此工作過程中(zhong)(zhong)(zhong)將(jiang)引起硫(liu)(liu)酸(suan)(suan)(suan)（ H2SO4） 的(de)(de)(de)減少， 而且在(zai)正(zheng)極(ji)(ji)板上(shang)(shang)不斷生成(cheng)水（ H2O） , 從而引起電(dian)解液的(de)(de)(de)密度(du)降低。在(zai)充電(dian)期(qi)間， 正(zheng)極(ji)(ji)極(ji)(ji)板上(shang)(shang)的(de)(de)(de)硫(liu)(liu)酸(suan)(suan)(suan)鉛(qian)（ PbSO4） 氧化(hua)成(cheng)了二氧化(hua)鉛(qian)（ PbO2） , 此時(shi)負極(ji)(ji)極(ji)(ji)板上(shang)(shang)的(de)(de)(de)硫(liu)(liu)酸(suan)(suan)(suan)鉛(qian)（ PbSO4） 還原成(cheng)鉛(qian)（ Pb） , 同時(shi)生成(cheng)硫(liu)(liu)酸(suan)(suan)(suan)（ H2SO4） , 耗去了蓄(xu)電(dian)池中(zhong)(zhong)(zhong)的(de)(de)(de)水（ H2O） , 使電(dian)池中(zhong)(zhong)(zhong)電(dian)解液的(de)(de)(de)密度(du)上(shang)(shang)升， 完成(cheng)充電(dian)過程。

　　2 系統(tong)的工作原理(li)

　　2.1 系統的主控制芯(xin)片介紹

　　充電(dian)器系統的(de)硬件框圖(tu)如圖(tu)3 所示。

　　主控(kong)芯片采用Microchip 公司的(de)PIC16F874, 它采用RISC 指令系(xi)統(tong)(tong)， 哈佛總線結構， 低功耗(hao)， 高(gao)速度。內(nei)部集成了(le)ADC、SPI 和Flash 程序存(cun)儲(chu)器(qi)等(deng)模塊， 具有10 位A/ D 轉換(huan)、PWM 輸(shu)出(chu)、LCD 驅動(dong)等(deng)功能(neng)， 此外它還帶有128 個字節的(de)E2PROM 存(cun)儲(chu)器(qi)， 能(neng)方便寫(xie)入調整(zheng)量以備后用。PIC16F874通過(guo)SPI 接口可以實現(xian)與CAN 控(kong)制器(qi)MCP2510 的(de)無縫連接， 且同時(shi)同步串行模塊（ SSP） 為(wei)以后與工(gong)控(kong)機聯網奠定(ding)了(le)基礎(chu)。PIC16F874 的(de)I/O 資源豐富， 共有A、B、C、D、E 五(wu)個I/O口， 每個I/O 口除了(le)基本用途外還有一些特殊功能(neng)。豐富的(de)資源和強大的(de)功能(neng)， 使(shi)之十分適(shi)合于作為(wei)控(kong)制系(xi)統(tong)(tong)的(de)控(kong)制核(he)心芯片。

　　2.2 系統的工作過程分析

　　充電器系統(tong)的(de)控制框圖如圖4 所示。

　　由(you)(you)圖4 可以看出(chu)， 在蓄(xu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)階段(duan)， 控制回路(lu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)環僅由(you)(you)太(tai)陽(yang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)構成。此(ci)時， 電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)環的(de)輸出(chu)為電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)環的(de)給(gei)定(ding)，通過(guo)檢測主電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)中(zhong)蓄(xu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池的(de)充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)與給(gei)定(ding)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)相比較來(lai)改變(bian)SG3525 的(de)輸出(chu)脈沖寬度， 使(shi)太(tai)陽(yang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)跟(gen)蹤(zong)給(gei)定(ding)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)。由(you)(you)圖1 可知， 當太(tai)陽(yang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)下降， 在穩態(tai)時， 太(tai)陽(yang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)等(deng)于(yu)(yu)給(gei)定(ding)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)， 電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)環的(de)給(gei)定(ding)亦(yi)為穩定(ding)值， 蓄(xu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池的(de)充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)等(deng)于(yu)(yu)給(gei)定(ding)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)； 反之， 當太(tai)陽(yang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)小于(yu)(yu)給(gei)定(ding)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)時，SG3525