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PIC單片機的數字式智能鉛酸電池充電器

    鉛酸蓄電(dian)池由(you)于其成本(ben)低(di)、容量大、安全可靠(kao)等特點,在通信(xin)、電(dian)動汽車、軍事、航空航天等各個(ge)領域都(dou)有(you)廣泛的(de)(de)(de)(de)應用(yong)(yong)(yong)。電(dian)池的(de)(de)(de)(de)性能好壞、使(shi)用(yong)(yong)(yong)壽命(ming)的(de)(de)(de)(de)長短直接影(ying)響(xiang)到電(dian)子產品的(de)(de)(de)(de)使(shi)用(yong)(yong)(yong)壽命(ming)和使(shi)用(yong)(yong)(yong)安全;而充(chong)電(dian)器的(de)(de)(de)(de)好壞又直接影(ying)響(xiang)到電(dian)池的(de)(de)(de)(de)使(shi)用(yong)(yong)(yong)壽命(ming)。因此研究低(di)成本(ben)又有(you)智(zhi)能管(guan)理功(gong)能的(de)(de)(de)(de)充(chong)電(dian)器是有(you)實(shi)際應用(yong)(yong)(yong)價值的(de)(de)(de)(de)課題。

  1 目前智(zhi)能充電器的幾種結構[1]

  1.1 基于專用芯片的管(guan)理系統

  現(xian)在,UNITRODE 公司已開(kai)發出系列電(dian)(dian)(dian)池(chi)(chi)管(guan)理專用芯片(pian)。因(yin)(yin)為(wei)電(dian)(dian)(dian)池(chi)(chi)管(guan)理中采用最多的(de)就是控制充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)壓(ya)及充(chong)放(fang)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu),電(dian)(dian)(dian)池(chi)(chi)管(guan)理芯片(pian)正(zheng)是抓住了這一點,為(wei)VRLA 電(dian)(dian)(dian)池(chi)(chi)研制了具有(you)四狀(zhuang)態管(guan)理的(de)專用控制芯片(pian),可以智能地實現(xian)帶(dai)溫度補償(chang)的(de)四狀(zhuang)態管(guan)理方案:涓流(liu)充(chong)電(dian)(dian)(dian)模式(shi)、大(da)功率充(chong)電(dian)(dian)(dian)模式(shi)、過充(chong)電(dian)(dian)(dian)模式(shi)和浮充(chong)電(dian)(dian)(dian)模式(shi)。不(bu)同的(de)電(dian)(dian)(dian)池(chi)(chi)要有(you)不(bu)同的(de)芯片(pian)控制,因(yin)(yin)此,用專用芯片(pian)做管(guan)理系統其(qi)靈活性較差,

  1.2 基于監(jian)控測量的蓄電池管理(li)系統(tong)

  在給電(dian)(dian)池(chi)(chi)充(chong)電(dian)(dian)的過程(cheng)中,涉及到電(dian)(dian)池(chi)(chi)工作(zuo)電(dian)(dian)壓(ya)、工作(zuo)電(dian)(dian)流、溫度(du)等參數(shu)(shu),這(zhe)些(xie)都是表征電(dian)(dian)池(chi)(chi)狀態的重要(yao)參數(shu)(shu)。采(cai)用傳感(gan)器(qi)提取這(zhe)些(xie)參數(shu)(shu),然(ran)后再配合(he)故(gu)障診斷、遙控遙測、自動報(bao)警和事故(gu)現(xian)場處理等功能,就(jiu)可以(yi)組成(cheng)一個電(dian)(dian)池(chi)(chi)管理系統。如圖1所示(shi)。

  

  1.3 與電源設備(bei)一起構成的(de)蓄電池充放電管(guan)理系統(tong)

  在通訊、供電系統中,為了保證電網掉電時蓄電池組能及時補充電能,在規定時間內向負載供電,保證通信或電力合閘系統的正常運轉,通常是將電池組直接掛接在電源模塊輸出端。當電網正常工作時,電池組工作在浮充狀態,起到平滑濾波和保持容量(補充自放電的容量損失)的作用。一旦電網掉電,蓄電池組立即投入工作,當電網恢復,電源模塊立即對電池進行充電。如圖2 所示。

  

  這(zhe)樣(yang)的(de)(de)一(yi)個(ge)系統由于和(he)電(dian)(dian)(dian)源(yuan)模塊聯系起來(lai),所以(yi)(yi),可(ke)(ke)以(yi)(yi)從充放(fang)電(dian)(dian)(dian)過程上(shang)來(lai)優化電(dian)(dian)(dian)池(chi)工(gong)(gong)作狀態,電(dian)(dian)(dian)池(chi)充電(dian)(dian)(dian)成(cheng)為可(ke)(ke)控的(de)(de)過程,建立在這(zhe)樣(yang)一(yi)個(ge)系統上(shang)的(de)(de)監(jian)控單元應(ying)該(gai)具有第一(yi)種監(jian)控系統中(zhong)所有功能(neng)(neng),并且可(ke)(ke)以(yi)(yi)和(he)電(dian)(dian)(dian)源(yuan)模塊直接(jie)“對話(hua)”,根據要求對電(dian)(dian)(dian)池(chi)進行管理,并且可(ke)(ke)以(yi)(yi)實(shi)時監(jian)控電(dian)(dian)(dian)池(chi)的(de)(de)放(fang)電(dian)(dian)(dian)狀態,對電(dian)(dian)(dian)池(chi)的(de)(de)工(gong)(gong)作進行優化[2]。因此,電(dian)(dian)(dian)池(chi)組的(de)(de)工(gong)(gong)作會(hui)更加可(ke)(ke)靠(kao),可(ke)(ke)控性和(he)智能(neng)(neng)化程度(du)也會(hui)更高。但(dan)是這(zhe)樣(yang)一(yi)個(ge)系統存在的(de)(de)主要問題(ti)是:

  (1)沒有解(jie)決電池組串聯(lian)運(yun)行(xing)過(guo)程中不均衡 現(xian)象的(de)問題,這也是電池失效的(de)重要(yao)原因之一;

  (2)一般(ban)只完成了電(dian)池(chi)生產廠(chang)家提供的充電(dian)曲線,對于(yu)電(dian)池(chi)在使(shi)用(yong)過程中發(fa)生的其它問題控制不夠全面(mian),例如(ru)深度放(fang)電(dian)后的涓(juan)充問題等。

  在將來,充(chong)電器的(de)發展方向是智能化(hua)、數(shu)字化(hua)、集成(cheng)化(hua)。智能化(hua)可(ke)(ke)以使電池(chi)的(de)管理做到全自(zi)動,無需(xu)人(ren)員監管,真正做到免維護。數(shu)字化(hua)和(he)集成(cheng)化(hua)可(ke)(ke)以減少管理系(xi)(xi)統的(de)體積和(he)重量,減少系(xi)(xi)統的(de)復雜度。

  2 目前幾種充電(dian)方式[3]

  鉛酸蓄電(dian)池的充(chong)電(dian)方法目前主要有恒流、恒壓、恒壓限流、脈沖充(chong)電(dian)、Reflex充(chong)電(dian)法。

  2.1 恒(heng)流充電

  恒流(liu)充電(dian)(dian)方式是一種(zhong)簡(jian)單的充電(dian)(dian)方法。但是,恒流(liu)充電(dian)(dian)有其局限性:對電(dian)(dian)池過(guo)充電(dian)(dian)就會造成電(dian)(dian)池壽命的縮(suo)短(duan),而過(guo)小電(dian)(dian)流(liu)又會延長充電(dian)(dian)時間。

  2.2 恒壓充電(dian)

  恒壓充(chong)(chong)電(dian)(dian)用簡(jian)單的(de)控制方法很(hen)容(rong)易就(jiu)能實現。在(zai)(zai)充(chong)(chong)電(dian)(dian)的(de)初始(shi)階段(duan),由于(yu)電(dian)(dian)池的(de)電(dian)(dian)壓很(hen)低而造(zao)成充(chong)(chong)電(dian)(dian)電(dian)(dian)流(liu)很(hen)大,這(zhe)對電(dian)(dian)池會(hui)造(zao)成損害。當電(dian)(dian)池電(dian)(dian)壓達到(dao)一定值之(zhi)后,電(dian)(dian)流(liu)就(jiu)會(hui)隨(sui)之(zhi)減小(xiao)。這(zhe)種充(chong)(chong)電(dian)(dian)方法的(de)缺點就(jiu)是(shi)會(hui)造(zao)成溫度上升(sheng)和電(dian)(dian)池的(de)壽(shou)命減少(shao),并且(qie)在(zai)(zai)開始(shi)時電(dian)(dian)流(liu)很(hen)大,而后來快充(chong)(chong)滿時電(dian)(dian)流(liu)又很(hen)小(xiao),就(jiu)無法充(chong)(chong)分利(li)用充(chong)(chong)電(dian)(dian)器的(de)容(rong)量(liang)。

  2.3 恒壓限(xian)流法

  恒壓(ya)(ya)(ya)限流(liu)法(fa)實際上是將(jiang)恒壓(ya)(ya)(ya)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)和恒流(liu)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)相結(jie)合(he),又可稱(cheng)為混(hun)合(he)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)法(fa)。在(zai)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)開始階(jie)段,由(you)(you)于電(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)過低,為避免電(dian)(dian)(dian)(dian)(dian)流(liu)過大而損(sun)壞電(dian)(dian)(dian)(dian)(dian)池,就(jiu)采(cai)用恒流(liu)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)法(fa)來限制充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)。但電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)達到預定值時,進入恒壓(ya)(ya)(ya)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)方(fang)式(shi)。恒壓(ya)(ya)(ya)限流(liu)方(fang)式(shi)是大多數電(dian)(dian)(dian)(dian)(dian)池廠商推薦的(de)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)方(fang)式(shi)。由(you)(you)于蓄(xu)電(dian)(dian)(dian)(dian)(dian)池充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)較低,充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)后期電(dian)(dian)(dian)(dian)(dian)流(liu)很(hen)小,因此電(dian)(dian)(dian)(dian)(dian)解液中(zhong)產生的(de)氣泡(pao)很(hen)少,可以節省電(dian)(dian)(dian)(dian)(dian)能(neng)、降低蓄(xu)電(dian)(dian)(dian)(dian)(dian)池的(de)溫升,避免損(sun)壞電(dian)(dian)(dian)(dian)(dian)池的(de)極板(ban)。恒壓(ya)(ya)(ya)限流(liu)方(fang)式(shi)是一種(zhong)很(hen)有效(xiao)的(de)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)方(fang)式(shi),加上過充(chong)(chong)(chong)判(pan)斷、浮充(chong)(chong)(chong)控制、溫度補償等就(jiu)可以形成一個簡單的(de)充(chong)(chong)(chong)電(dian)(dian)(dian)(dian)(dian)管理系統(tong),蓄(xu)電(dian)(dian)(dian)(dian)(dian)池可以在(zai)這個系統(tong)下更好地工作。

  2.4 脈沖充(chong)電[4]

  在充(chong)電(dian)過(guo)程(cheng)中,只要充(chong)電(dian)電(dian)流(liu)不超過(guo)蓄(xu)(xu)電(dian)池可接(jie)受(shou)的電(dian)流(liu),蓄(xu)(xu)電(dian)池內部就不會產生(sheng)大(da)(da)量的氣泡。蓄(xu)(xu)電(dian)池中產生(sheng)的極(ji)化現象會阻礙(ai)充(chong)電(dian),并(bing)且使(shi)出氣率和溫(wen)升顯著升高。因(yin)此(ci),極(ji)化電(dian)壓是(shi)影(ying)響充(chong)電(dian)速度(du)的重要因(yin)素。用(yong)周期性的脈動(dong)電(dian)流(liu)給電(dian)池充(chong)電(dian)可以使(shi)電(dian)池有時間恢(hui)復其原來狀態,減小極(ji)化現象的影(ying)響,解決快(kuai)速充(chong)電(dian)面臨的難題(ti)。但是(shi)目前這種充(chong)電(dian)方式還在研究階(jie)段,對于(yu)采用(yong)多大(da)(da)的脈沖周期,占空比(bi)又是(shi)多少(shao)之(zhi)類的具體問題(ti)還沒有一個(ge)定論。

  2.5 ReflexTM充電方式

  Reflex 充電方法是脈沖電流法的改進:一個周期是由一個正脈沖后加一個負脈沖,然后才是空閑時段。這樣就強制消除電池的極化現象,使得電池充電時可以更快而又不損害電池的使用壽命。這種充電方式與脈沖充電方式一樣,仍然處于研究階段。
. 3 數字式(shi)智(zhi)能充電器的(de)設計

  3.1 系統結(jie)構和充電方案的設計

  本(ben)文中(zhong)設計的系統是一個針對12 V/(200~500Ah)的鉛酸(suan)蓄(xu)電(dian)(dian)池智能(neng)充電(dian)(dian)系統。采用半橋作為主功率(lv)拓撲,開(kai)關(guan)頻(pin)率(lv)取80kHz左右。

  對于一個(ge)智能管理系(xi)統(tong),控制(zhi)模塊無異于它的(de)大腦。充電器(qi)的(de)所(suo)(suo)有(you)動作都是由它來決(jue)定和控制(zhi)的(de),所(suo)(suo)以控制(zhi)模塊的(de)選擇關系(xi)到整個(ge)系(xi)統(tong)的(de)優(you)劣。由于系(xi)統(tong)需要(yao)(yao)多個(ge)A/D 轉換(huan)器(qi),但不需要(yao)(yao)擴展存(cun)儲器(qi)也(ye)不需要(yao)(yao)通訊,根據以上特點我(wo)們選擇了MICROCHIP 公司的(de)PIC 系(xi)列(lie)PIC16C73 單片(pian)機。

  圖3 所示為智能充電器的(de)系統框圖。單(dan)片(pian)機是智能充電(dian)器的(de)核心部件,它根據電(dian)流、電(dian)壓采樣以(yi)及溫度(du)采樣做出溫度(du)補償后的(de)PWM波形輸出,經(jing)過驅動電(dian)路(lu)提供給功率電(dian)路(lu),并且(qie)決(jue)定了智能充電(dian)器的(de)工作狀態(tai),可(ke)以(yi)在必要的(de)情況下做出保(bao)護動作。意外故(gu)障(zhang)保(bao)護電(dian)路(lu)可(ke)以(yi)在單(dan)片(pian)機失效的(de)情況下對電(dian)路(lu)進行(xing)(xing)強制保(bao)護,起到雙重保(bao)險(xian)的(de)作用。報警顯示(shi)部分(fen)用若干(gan)個(ge)LED表(biao)示(shi)系統的(de)運行(xing)(xing)狀態(tai),簡單(dan)有效。

  

  充(chong)電(dian)方式采用恒(heng)壓(ya)限流(liu)法。恒(heng)壓(ya)限流(liu)充(chong)電(dian)模式分兩個階段(duan)(duan),第一階段(duan)(duan)是(shi)恒(heng)流(liu)階段(duan)(duan),即系(xi)統給定電(dian)流(liu)值,給電(dian)池(chi)以(yi)恒(heng)定電(dian)流(liu)充(chong)電(dian),當電(dian)池(chi)的電(dian)壓(ya)達到系(xi)統給定的轉化(hua)值,就轉為第二階段(duan)(duan)―――恒(heng)壓(ya)階段(duan)(duan)。恒(heng)壓(ya)轉化(hua)值會影響充(chong)入(ru)電(dian)量的多(duo)少。

  由圖4 可知,當恒(heng)(heng)壓(ya)轉(zhuan)化值(zhi)(zhi)(Vref)設置(zhi)的較(jiao)低時,充(chong)入(ru)的電(dian)量(liang)不足(圖中陰影部(bu)分(fen)就是(shi)少充(chong)入(ru)的容(rong)量(liang)),沒有充(chong)分(fen)利用(yong)電(dian)池(chi)(chi)的容(rong)量(liang),長期工作,會引起(qi)電(dian)池(chi)(chi)容(rong)量(liang)丟失,這(zhe)就要求把(ba)恒(heng)(heng)壓(ya)轉(zhuan)化值(zhi)(zhi)設高(gao)。但是(shi)恒(heng)(heng)壓(ya)值(zhi)(zhi)較(jiao)高(gao),容(rong)易(yi)在充(chong)電(dian)末(mo)期引起(qi)過充(chong)電(dian),這(zhe)同樣會導致電(dian)池(chi)(chi)容(rong)量(liang)丟失。

  

  為了(le)解決這(zhe)(zhe)個矛盾,系統引(yin)進(jin)了(le)第三個階(jie)段―――浮充(chong)(chong)階(jie)段,這(zhe)(zhe)樣就可(ke)以把恒壓轉化值設置的比普通恒壓限流(liu)模式高(gao),這(zhe)(zhe)樣可(ke)以保證充(chong)(chong)入足夠的電量,在充(chong)(chong)電末(mo)期(qi)轉入浮充(chong)(chong)階(jie)段,用稍低的電壓浮充(chong)(chong)充(chong)(chong)電,從而保證不會過充(chong)(chong)電。

  三階段充(chong)電(dian)(dian)方法保證了充(chong)電(dian)(dian)末期不(bu)過充(chong),同時又能達到滿充(chong)的目的,是一(yi)種成本較低的通用蓄電(dian)(dian)池(chi)充(chong)電(dian)(dian)解決方案(an)。

  3.2 軟件系(xi)統(tong)的設計

  圖5 為系統(tong)軟(ruan)件(jian)的程序流程圖。根(gen)據電(dian)池的端(duan)電(dian)壓決定充(chong)(chong)電(dian)器(qi)工作在何種充(chong)(chong)電(dian)狀(zhuang)態(tai)。

  

  我們做(zuo)的(de)是全數(shu)字化(hua)的(de)改(gai)良型PI 調節(jie)環,由于(yu)PI 調節(jie)的(de)積(ji)(ji)分(fen)環在前期對誤(wu)差(cha)進(jin)行(xing)積(ji)(ji)累,為了不讓積(ji)(ji)累的(de)誤(wu)差(cha)影響系統的(de)穩(wen)定性,所(suo)以我們在誤(wu)差(cha)等(deng)于(yu)0 時,對原有積(ji)(ji)累的(de)誤(wu)差(cha)清零。當誤(wu)差(cha)等(deng)于(yu)±1 時,只進(jin)行(xing)積(ji)(ji)分(fen)運算,減慢調整速度(du),避免(mian)產(chan)生(sheng)振蕩。

  鉛酸(suan)蓄(xu)電池的(de)充電電壓需要根據環境(jing)溫(wen)度進(jin)行調整,以-4 mV/℃的(de)補(bu)償系數來(lai)調整。因此我們加(jia)入了(le)溫(wen)度補(bu)償的(de)功能。

  4 實驗結果

  圖6 為(wei)用電子負載(zai)模擬電池(chi)三階段充(chong)電過(guo)程的(de)波(bo)形圖。從圖6 中我(wo)們可以看出智(zhi)能(neng)充(chong)電系統能(neng)夠方(fang)便(bian)地(di)實現各(ge)個充(chong)電狀態(tai)的(de)轉換。

  

  5 結語

  用(yong)PIC 單(dan)片機可以(yi)實現全數字化的電(dian)池充(chong)電(dian)管理(li),結構(gou)簡單(dan),成本較低,并(bing)且具(ju)有很高的靈活性,通過改(gai)(gai)變軟件內(nei)設置的恒(heng)(heng)流參考(kao)值(zhi)和(he)(he)恒(heng)(heng)壓參考(kao)值(zhi)就可以(yi)改(gai)(gai)變系統的恒(heng)(heng)流電(dian)流和(he)(he)恒(heng)(heng)壓電(dian)壓值(zhi),使得系統在(zai)不改(gai)(gai)變系統硬件設計的情況下(xia)實現給多(duo)種不同容量(liang)的鉛(qian)酸蓄電(dian)池充(chong)電(dian)。另外可以(yi)實現有效的電(dian)池充(chong)電(dian)管理(li)和(he)(he)保護功(gong)能,達(da)到智能化控制。

 
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