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)設(she)計問題， 因為光伏(fu)充電器不僅完成了把太(tai)(tai)陽能(neng)轉換(huan)成電能(neng)的(de)重(zhong)任， 而且還對蓄電池提供了智能(neng)充電管理(li)， 因此光伏(fu)充電器的(de)性能(neng)直(zhi)接(jie)決定(ding)了太(tai)(tai)陽能(neng)能(neng)量利(li)用的(de)效率和(he)系統(tong)使用的(de)壽命。本文從(cong)原理(li)、控制(zhi)策略和(he)實際應用等幾個方面介紹一種光伏(fu)充電器及其控制(zhi)系統(tong)的(de)設(she)計思想。

　　1 系統構成

　　1.1 LED 的工作(zuo)特性

　　發光(guang)二極管(guan)LED（Light Emitting Diode）的(de)工作原(yuan)理是(shi)在(zai)半導(dao)體p-n 結上加一正向電壓， 從(cong)而(er)使其電子(zi)與(yu)空(kong)穴復(fu)合（即(ji)結區變窄）， 這種復(fu)合是(shi)電子(zi)從(cong)高能級的(de)導(dao)帶釋(shi)放(fang)能量回到價(jia)帶與(yu)空(kong)穴復(fu)合， 其釋(shi)放(fang)的(de)能量以光(guang)子(zi)的(de)形式出現， 即(ji)發光(guang)。

　　根據半導(dao)體(ti)物理中的(de)公式(shi)： λ=1.24/Eg式(shi)中： Eg 為半導(dao)體(ti)材料導(dao)帶(dai)與價帶(dai)之間的(de)禁帶(dai)寬度(du)， λ為波長(chang)(chang)。從(cong)式(shi)中可以(yi)(yi)看出， 對于不(bu)同(tong)材料的(de)半導(dao)體(ti)來說， 由于它們(men)的(de)Eg 不(bu)同(tong)， 因此(ci)它們(men)的(de)波長(chang)(chang)# 也不(bu)一(yi)(yi)樣， 所(suo)以(yi)(yi)發(fa)光(guang)(guang)(guang)的(de)顏色不(bu)同(tong)。顯(xian)然， 一(yi)(yi)般LED 多(duo)為單(dan)顏色光(guang)(guang)(guang)， 如紅光(guang)(guang)(guang)、綠光(guang)(guang)(guang)、黃(huang)光(guang)(guang)(guang)、藍光(guang)(guang)(guang)等(deng)。所(suo)謂白光(guang)(guang)(guang)是多(duo)種顏色的(de)光(guang)(guang)(guang)混(hun)(hun)合(he)(he)(he)而成(cheng)， 以(yi)(yi)人類眼睛所(suo)能見到的(de)白光(guang)(guang)(guang)形式(shi)至(zhi)少必須兩種以(yi)(yi)上的(de)光(guang)(guang)(guang)混(hun)(hun)合(he)(he)(he)， 一(yi)(yi)般有下列兩種混(hun)(hun)合(he)(he)(he)方式(shi)： 二波長(chang)(chang)光(guang)(guang)(guang)―――藍光(guang)(guang)(guang)與黃(huang)光(guang)(guang)(guang)混(hun)(hun)合(he)(he)(he)； 三波長(chang)(chang)光(guang)(guang)(guang)―――紅光(guang)(guang)(guang)、綠光(guang)(guang)(guang)與藍光(guang)(guang)(guang)混(hun)(hun)合(he)(he)(he)。目前已(yi)經商(shang)品化的(de)白光(guang)(guang)(guang)LED 產品多(duo)為二波段藍光(guang)(guang)(guang)單(dan)晶片加上YAG 黃(huang)色熒光(guang)(guang)(guang)粉； 三波長(chang)(chang)光(guang)(guang)(guang)以(yi)(yi)無機(ji)紫外線光(guang)(guang)(guang)晶片加R、G、B 三顏色熒光(guang)(guang)(guang)粉。此(ci)外， 有機(ji)單(dan)層三波長(chang)(chang)型白光(guang)(guang)(guang)LED 也有成(cheng)本(ben)低、制作容易等(deng)優點。

　　1.2 太陽(yang)電池的(de)工作特性

　　圖(tu)1、圖(tu)2 分別給出(chu)了太(tai)陽電池溫(wen)度在(zai)25 ℃時， 工作電壓(ya)、電流和日照(zhao)（ W/m2） 的關系(xi)曲(qu)線及(ji)太(tai)陽電池的輸出(chu)功率(lv)和日照(zhao)、電壓(ya)之間的曲(qu)線。

　　從圖1 的(de)I/U 關系(xi)可(ke)(ke)(ke)以(yi)看(kan)出(chu)， 太陽(yang)電(dian)(dian)(dian)池陣列既非恒壓源，也非恒流源， 而是一種非線性直(zhi)流電(dian)(dian)(dian)源， 電(dian)(dian)(dian)池輸(shu)出(chu)電(dian)(dian)(dian)流在(zai)大(da)(da)部分(fen)工作電(dian)(dian)(dian)壓范(fan)圍內相(xiang)當(dang)恒定， 最(zui)(zui)終在(zai)一個足夠高的(de)電(dian)(dian)(dian)壓之(zhi)后(hou)，電(dian)(dian)(dian)流迅速下降(jiang)至零。由圖2 可(ke)(ke)(ke)知， 太陽(yang)電(dian)(dian)(dian)池的(de)工作效(xiao)率(lv)等(deng)于輸(shu)出(chu)功(gong)(gong)(gong)(gong)率(lv)與(yu)投射到(dao)太陽(yang)電(dian)(dian)(dian)池面(mian)積上的(de)功(gong)(gong)(gong)(gong)率(lv)之(zhi)比。因(yin)此， 為(wei)了(le)提高本系(xi)統的(de)工作效(xiao)率(lv)， 必須盡(jin)(jin)可(ke)(ke)(ke)能地使太陽(yang)電(dian)(dian)(dian)池在(zai)最(zui)(zui)大(da)(da)功(gong)(gong)(gong)(gong)率(lv)點(dian)處工作， 這樣(yang)就(jiu)可(ke)(ke)(ke)以(yi)用功(gong)(gong)(gong)(gong)率(lv)盡(jin)(jin)可(ke)(ke)(ke)能小的(de)太陽(yang)電(dian)(dian)(dian)池獲得最(zui)(zui)大(da)(da)的(de)功(gong)(gong)(gong)(gong)率(lv)輸(shu)出(chu)， 這就(jiu)是進行最(zui)(zui)大(da)(da)功(gong)(gong)(gong)(gong)率(lv)點(dian)跟蹤的(de)意義所在(zai)。如圖1 和(he)圖2 所示， 圖中的(de)A、B、C、D、E 點(dian)分(fen)別對應不同(tong)日照(zhao)時(shi)的(de)最(zui)(zui)大(da)(da)功(gong)(gong)(gong)(gong)率(lv)點(dian)。

　　1.3 鉛酸蓄電池(chi)的工作特性

　　目(mu)前在(zai)光伏充(chong)(chong)電(dian)器系統中(zhong)大量(liang)使用的(de)(de)(de)(de)是鉛酸(suan)蓄電(dian)池(chi)， 它的(de)(de)(de)(de)工(gong)(gong)作原(yuan)理是依靠鉛酸(suan)正(zheng)極(ji)的(de)(de)(de)(de)活(huo)性(xing)物(wu)質二氧(yang)化(hua)鉛（ PbO2） 和負(fu)極(ji)的(de)(de)(de)(de)活(huo)性(xing)物(wu)質海綿狀鉛（ Pb） 與電(dian)解(jie)液(ye)(ye)硫(liu)酸(suan)（ H2SO4） 進行化(hua)學(xue)反應生(sheng)(sheng)成(cheng)硫(liu)酸(suan)鉛（ PbSO4） , 在(zai)此(ci)工(gong)(gong)作過(guo)程(cheng)中(zhong)將引(yin)起硫(liu)酸(suan)（ H2SO4） 的(de)(de)(de)(de)減少， 而(er)且在(zai)正(zheng)極(ji)板上不斷生(sheng)(sheng)成(cheng)水（ H2O） , 從而(er)引(yin)起電(dian)解(jie)液(ye)(ye)的(de)(de)(de)(de)密度降(jiang)低。在(zai)充(chong)(chong)電(dian)期間， 正(zheng)極(ji)極(ji)板上的(de)(de)(de)(de)硫(liu)酸(suan)鉛（ PbSO4） 氧(yang)化(hua)成(cheng)了二氧(yang)化(hua)鉛（ PbO2） , 此(ci)時負(fu)極(ji)極(ji)板上的(de)(de)(de)(de)硫(liu)酸(suan)鉛（ PbSO4） 還(huan)原(yuan)成(cheng)鉛（ Pb） , 同時生(sheng)(sheng)成(cheng)硫(liu)酸(suan)（ H2SO4） , 耗去了蓄電(dian)池(chi)中(zhong)的(de)(de)(de)(de)水（ H2O） , 使電(dian)池(chi)中(zhong)電(dian)解(jie)液(ye)(ye)的(de)(de)(de)(de)密度上升， 完成(cheng)充(chong)(chong)電(dian)過(guo)程(cheng)。

　　2 系(xi)統的工作原理

　　2.1 系(xi)統的主控制芯(xin)片介紹

　　充電(dian)器(qi)系統的硬件框圖如圖3 所示。

　　主控(kong)(kong)(kong)芯片采用(yong)Microchip 公司的(de)PIC16F874, 它(ta)采用(yong)RISC 指令系(xi)統， 哈佛總線(xian)結構， 低功(gong)耗， 高(gao)速度(du)。內部集成了ADC、SPI 和Flash 程(cheng)序(xu)存(cun)儲器(qi)等(deng)模塊(kuai)， 具有10 位A/ D 轉換、PWM 輸出、LCD 驅(qu)動等(deng)功(gong)能(neng)， 此(ci)外(wai)它(ta)還(huan)帶有128 個(ge)(ge)字節的(de)E2PROM 存(cun)儲器(qi)， 能(neng)方便寫入調(diao)整量以(yi)備(bei)后用(yong)。PIC16F874通過SPI 接口(kou)可以(yi)實現與(yu)CAN 控(kong)(kong)(kong)制器(qi)MCP2510 的(de)無(wu)縫(feng)連接， 且同(tong)時(shi)同(tong)步串行模塊(kuai)（ SSP） 為(wei)以(yi)后與(yu)工(gong)控(kong)(kong)(kong)機聯網奠定了基(ji)礎。PIC16F874 的(de)I/O 資源豐富， 共有A、B、C、D、E 五個(ge)(ge)I/O口(kou)， 每個(ge)(ge)I/O 口(kou)除了基(ji)本用(yong)途外(wai)還(huan)有一些特(te)殊功(gong)能(neng)。豐富的(de)資源和強大(da)的(de)功(gong)能(neng)， 使之十分適合于作(zuo)為(wei)控(kong)(kong)(kong)制系(xi)統的(de)控(kong)(kong)(kong)制核心芯片。

　　2.2 系統的工作過程(cheng)分(fen)析

　　充電器系統的控制框圖(tu)如圖(tu)4 所示。

　　由(you)圖4 可以看(kan)出(chu)， 在蓄(xu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)階段， 控(kong)制回路電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)環(huan)僅由(you)太(tai)(tai)陽(yang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)構成。此時(shi)， 電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)環(huan)的輸出(chu)為電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)環(huan)的給(gei)定(ding)(ding)，通過檢測主電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路中蓄(xu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)的充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)與給(gei)定(ding)(ding)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)相比(bi)較來(lai)改變(bian)SG3525 的輸出(chu)脈沖寬度， 使太(tai)(tai)陽(yang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)的電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)跟蹤給(gei)定(ding)(ding)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)。由(you)圖1 可知， 當(dang)太(tai)(tai)陽(yang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)下(xia)降， 在穩態時(shi)， 太(tai)(tai)陽(yang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)等(deng)于給(gei)定(ding)(ding)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)， 電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)環(huan)的給(gei)定(ding)(ding)亦為穩定(ding)(ding)值， 蓄(xu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)的充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)等(deng)于給(gei)定(ding)(ding)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)； 反之， 當(dang)太(tai)(tai)陽(yang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)小(xiao)于給(gei)定(ding)(ding)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)時(shi)，SG3525