PIC單片機的數字式智能鉛酸電池充電器
鉛酸蓄電(dian)(dian)池由于其(qi)成本低、容量大、安全(quan)可靠等特點,在通信、電(dian)(dian)動汽車、軍(jun)事、航空(kong)航天(tian)等各(ge)個領域都有(you)廣泛(fan)的(de)(de)應用(yong)。電(dian)(dian)池的(de)(de)性能好(hao)壞、使用(yong)壽(shou)命的(de)(de)長短直接(jie)影響(xiang)到(dao)(dao)電(dian)(dian)子產品的(de)(de)使用(yong)壽(shou)命和(he)使用(yong)安全(quan);而充電(dian)(dian)器(qi)的(de)(de)好(hao)壞又直接(jie)影響(xiang)到(dao)(dao)電(dian)(dian)池的(de)(de)使用(yong)壽(shou)命。因此研究低成本又有(you)智能管理功能的(de)(de)充電(dian)(dian)器(qi)是有(you)實際(ji)應用(yong)價值的(de)(de)課題(ti)。
1 目前智能充電(dian)器的(de)幾(ji)種結(jie)構[1]
1.1 基于專用芯片的管理系統
現(xian)在(zai),UNITRODE 公司已開發出系列(lie)電(dian)(dian)(dian)(dian)池(chi)管理專(zhuan)用(yong)芯(xin)片(pian)(pian)。因為(wei)電(dian)(dian)(dian)(dian)池(chi)管理中(zhong)采(cai)用(yong)最多的(de)就(jiu)是控制充(chong)電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)壓及充(chong)放電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流,電(dian)(dian)(dian)(dian)池(chi)管理芯(xin)片(pian)(pian)正(zheng)是抓(zhua)住了(le)這一點,為(wei)VRLA 電(dian)(dian)(dian)(dian)池(chi)研制了(le)具有四(si)(si)狀態管理的(de)專(zhuan)用(yong)控制芯(xin)片(pian)(pian),可以智能地實(shi)現(xian)帶溫度補償(chang)的(de)四(si)(si)狀態管理方案:涓流充(chong)電(dian)(dian)(dian)(dian)模(mo)式(shi)、大功率充(chong)電(dian)(dian)(dian)(dian)模(mo)式(shi)、過充(chong)電(dian)(dian)(dian)(dian)模(mo)式(shi)和浮充(chong)電(dian)(dian)(dian)(dian)模(mo)式(shi)。不同(tong)的(de)電(dian)(dian)(dian)(dian)池(chi)要有不同(tong)的(de)芯(xin)片(pian)(pian)控制,因此,用(yong)專(zhuan)用(yong)芯(xin)片(pian)(pian)做管理系統其靈(ling)活性較差,
1.2 基于(yu)監(jian)控測量的蓄電池管理系統
在給電(dian)(dian)池充(chong)電(dian)(dian)的過程中,涉及到電(dian)(dian)池工(gong)作電(dian)(dian)壓(ya)、工(gong)作電(dian)(dian)流、溫度等參(can)數(shu),這(zhe)些都是表征電(dian)(dian)池狀態的重要參(can)數(shu)。采用傳感器提取這(zhe)些參(can)數(shu),然后再配合故障診斷、遙控遙測(ce)、自動報(bao)警和事(shi)故現場處理等功能,就可以(yi)組成(cheng)一個電(dian)(dian)池管理系統。如圖(tu)1所(suo)示。

1.3 與電源設備一起構成的蓄(xu)電池充放電管理系統
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。

這樣(yang)的(de)(de)一個系統(tong)由于和電(dian)(dian)源模塊(kuai)聯系起(qi)來(lai)(lai),所以,可(ke)以從充放電(dian)(dian)過(guo)(guo)程(cheng)上(shang)來(lai)(lai)優(you)化電(dian)(dian)池(chi)(chi)工作(zuo)狀(zhuang)態,電(dian)(dian)池(chi)(chi)充電(dian)(dian)成為可(ke)控(kong)的(de)(de)過(guo)(guo)程(cheng),建立在這樣(yang)一個系統(tong)上(shang)的(de)(de)監控(kong)單元應該具有(you)第一種監控(kong)系統(tong)中所有(you)功能(neng),并且可(ke)以和電(dian)(dian)源模塊(kuai)直接“對話”,根據(ju)要求對電(dian)(dian)池(chi)(chi)進(jin)行管理,并且可(ke)以實(shi)時監控(kong)電(dian)(dian)池(chi)(chi)的(de)(de)放電(dian)(dian)狀(zhuang)態,對電(dian)(dian)池(chi)(chi)的(de)(de)工作(zuo)進(jin)行優(you)化[2]。因此,電(dian)(dian)池(chi)(chi)組的(de)(de)工作(zuo)會更加可(ke)靠,可(ke)控(kong)性和智能(neng)化程(cheng)度也會更高。但是(shi)這樣(yang)一個系統(tong)存在的(de)(de)主(zhu)要問(wen)題是(shi):
(1)沒(mei)有解(jie)決電池組串聯(lian)運行過程中不均衡 現(xian)象的問題,這也是電池失效的重(zhong)要原(yuan)因之一(yi);
(2)一般只完成了電(dian)(dian)池生(sheng)產廠家提(ti)供的充電(dian)(dian)曲線,對于電(dian)(dian)池在(zai)使用過程中發生(sheng)的其(qi)它問(wen)題控(kong)制不夠全面,例如深度放電(dian)(dian)后的涓充問(wen)題等。
在將來,充電器的(de)發(fa)展方向(xiang)是智能(neng)(neng)化(hua)、數(shu)字化(hua)、集(ji)成(cheng)化(hua)。智能(neng)(neng)化(hua)可(ke)以使電池的(de)管(guan)(guan)理做(zuo)到全自動,無(wu)需人(ren)員監管(guan)(guan),真正做(zuo)到免維護。數(shu)字化(hua)和集(ji)成(cheng)化(hua)可(ke)以減少管(guan)(guan)理系統的(de)體積和重量,減少系統的(de)復(fu)雜(za)度。
2 目前幾(ji)種充(chong)電方式[3]
鉛酸蓄電池的充電方法(fa)目前主要(yao)有恒流(liu)、恒壓、恒壓限流(liu)、脈(mo)沖充電、Reflex充電法(fa)。
2.1 恒(heng)流(liu)充(chong)電
恒流(liu)(liu)充(chong)電(dian)(dian)方式是一(yi)種簡單的充(chong)電(dian)(dian)方法(fa)。但是,恒流(liu)(liu)充(chong)電(dian)(dian)有其局限性:對(dui)電(dian)(dian)池過充(chong)電(dian)(dian)就會造(zao)成電(dian)(dian)池壽命的縮短(duan),而過小(xiao)電(dian)(dian)流(liu)(liu)又會延長充(chong)電(dian)(dian)時間。
2.2 恒壓(ya)充(chong)電
恒壓充(chong)(chong)(chong)電(dian)(dian)(dian)用簡單的(de)控制方(fang)法(fa)很(hen)容(rong)易就(jiu)(jiu)能實現。在充(chong)(chong)(chong)電(dian)(dian)(dian)的(de)初(chu)始階(jie)段,由于電(dian)(dian)(dian)池(chi)的(de)電(dian)(dian)(dian)壓很(hen)低(di)而(er)造(zao)成(cheng)充(chong)(chong)(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)(liu)很(hen)大,這對電(dian)(dian)(dian)池(chi)會造(zao)成(cheng)損害。當電(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)壓達到一(yi)定值之后,電(dian)(dian)(dian)流(liu)(liu)就(jiu)(jiu)會隨(sui)之減(jian)小。這種充(chong)(chong)(chong)電(dian)(dian)(dian)方(fang)法(fa)的(de)缺點就(jiu)(jiu)是會造(zao)成(cheng)溫度上(shang)升(sheng)和電(dian)(dian)(dian)池(chi)的(de)壽命減(jian)少(shao),并且在開始時電(dian)(dian)(dian)流(liu)(liu)很(hen)大,而(er)后來快充(chong)(chong)(chong)滿時電(dian)(dian)(dian)流(liu)(liu)又很(hen)小,就(jiu)(jiu)無法(fa)充(chong)(chong)(chong)分利用充(chong)(chong)(chong)電(dian)(dian)(dian)器(qi)的(de)容(rong)量。
2.3 恒壓限流法
恒(heng)壓(ya)(ya)限(xian)(xian)(xian)流(liu)(liu)法實際上是將恒(heng)壓(ya)(ya)充(chong)電(dian)(dian)(dian)和(he)恒(heng)流(liu)(liu)充(chong)電(dian)(dian)(dian)相結(jie)合,又可(ke)稱為混合充(chong)電(dian)(dian)(dian)法。在充(chong)電(dian)(dian)(dian)開始階段,由(you)(you)于電(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)壓(ya)(ya)過低(di),為避免電(dian)(dian)(dian)流(liu)(liu)過大(da)而損(sun)壞(huai)電(dian)(dian)(dian)池(chi),就采用恒(heng)流(liu)(liu)充(chong)電(dian)(dian)(dian)法來(lai)限(xian)(xian)(xian)制(zhi)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)(liu)。但電(dian)(dian)(dian)壓(ya)(ya)達到預定值時,進(jin)入恒(heng)壓(ya)(ya)充(chong)電(dian)(dian)(dian)方式。恒(heng)壓(ya)(ya)限(xian)(xian)(xian)流(liu)(liu)方式是大(da)多數電(dian)(dian)(dian)池(chi)廠商推(tui)薦的充(chong)電(dian)(dian)(dian)方式。由(you)(you)于蓄(xu)(xu)電(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)電(dian)(dian)(dian)壓(ya)(ya)較低(di),充(chong)電(dian)(dian)(dian)后期電(dian)(dian)(dian)流(liu)(liu)很(hen)小,因(yin)此電(dian)(dian)(dian)解(jie)液(ye)中(zhong)產生的氣(qi)泡很(hen)少(shao),可(ke)以節省電(dian)(dian)(dian)能、降低(di)蓄(xu)(xu)電(dian)(dian)(dian)池(chi)的溫升(sheng),避免損(sun)壞(huai)電(dian)(dian)(dian)池(chi)的極板。恒(heng)壓(ya)(ya)限(xian)(xian)(xian)流(liu)(liu)方式是一種很(hen)有效(xiao)的充(chong)電(dian)(dian)(dian)方式,加上過充(chong)判斷、浮充(chong)控制(zhi)、溫度補償(chang)等(deng)就可(ke)以形(xing)成一個(ge)簡(jian)單的充(chong)電(dian)(dian)(dian)管(guan)理系(xi)統,蓄(xu)(xu)電(dian)(dian)(dian)池(chi)可(ke)以在這個(ge)系(xi)統下(xia)更(geng)好地(di)工作(zuo)。
2.4 脈沖(chong)充電[4]
在(zai)充(chong)電(dian)(dian)過程中,只要(yao)充(chong)電(dian)(dian)電(dian)(dian)流不(bu)超(chao)過蓄電(dian)(dian)池(chi)可(ke)接受的(de)電(dian)(dian)流,蓄電(dian)(dian)池(chi)內部就(jiu)不(bu)會產生(sheng)大(da)量的(de)氣泡(pao)。蓄電(dian)(dian)池(chi)中產生(sheng)的(de)極化(hua)(hua)現象會阻礙充(chong)電(dian)(dian),并且使出氣率和(he)溫升顯(xian)著升高。因此,極化(hua)(hua)電(dian)(dian)壓是(shi)影響充(chong)電(dian)(dian)速度(du)的(de)重要(yao)因素。用周期性的(de)脈動(dong)電(dian)(dian)流給電(dian)(dian)池(chi)充(chong)電(dian)(dian)可(ke)以使電(dian)(dian)池(chi)有時間(jian)恢(hui)復其原來狀(zhuang)態(tai),減小(xiao)極化(hua)(hua)現象的(de)影響,解決快(kuai)速充(chong)電(dian)(dian)面臨的(de)難題。但是(shi)目(mu)前(qian)這種充(chong)電(dian)(dian)方(fang)式還在(zai)研(yan)究階段(duan),對于采用多大(da)的(de)脈沖周期,占空比(bi)又是(shi)多少之類的(de)具體(ti)問題還沒有一個定(ding)論。
2.5 ReflexTM充電(dian)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 數字式智能(neng)充電器(qi)的設計
3.1 系統結構和充電方(fang)案(an)的設計(ji)
本(ben)文中設計的(de)系(xi)統是一個針對(dui)12 V/(200~500Ah)的(de)鉛(qian)酸蓄電池智能充電系(xi)統。采用半橋作為主(zhu)功(gong)率(lv)拓撲,開關(guan)頻率(lv)取(qu)80kHz左右(you)。
對于一個智(zhi)能管理系(xi)統,控(kong)制模(mo)塊(kuai)無(wu)異(yi)于它(ta)的(de)(de)大腦。充(chong)電器(qi)的(de)(de)所有動作(zuo)都是由它(ta)來決定和(he)控(kong)制的(de)(de),所以(yi)控(kong)制模(mo)塊(kuai)的(de)(de)選擇關系(xi)到整個系(xi)統的(de)(de)優劣。由于系(xi)統需(xu)要多個A/D 轉換器(qi),但(dan)不需(xu)要擴展存儲(chu)器(qi)也不需(xu)要通(tong)訊,根據以(yi)上(shang)特點我們選擇了MICROCHIP 公(gong)司的(de)(de)PIC 系(xi)列PIC16C73 單片機。
圖3 所示為智能充電器的(de)(de)(de)系統框圖。單(dan)片機是智能充電(dian)器的(de)(de)(de)核心部件,它根據電(dian)流、電(dian)壓采樣以(yi)及溫(wen)度采樣做(zuo)(zuo)出溫(wen)度補償后(hou)的(de)(de)(de)PWM波形輸出,經過驅動(dong)(dong)電(dian)路(lu)提供給功率電(dian)路(lu),并且(qie)決定了(le)智能充電(dian)器的(de)(de)(de)工作狀態(tai)(tai),可以(yi)在(zai)必要的(de)(de)(de)情(qing)況下(xia)做(zuo)(zuo)出保(bao)護動(dong)(dong)作。意外(wai)故障保(bao)護電(dian)路(lu)可以(yi)在(zai)單(dan)片機失效的(de)(de)(de)情(qing)況下(xia)對電(dian)路(lu)進行(xing)強制保(bao)護,起到雙重保(bao)險的(de)(de)(de)作用。報警顯(xian)示部分用若干個LED表示系統的(de)(de)(de)運(yun)行(xing)狀態(tai)(tai),簡單(dan)有(you)效。

充(chong)電(dian)方式采用恒(heng)(heng)壓(ya)限(xian)流(liu)法。恒(heng)(heng)壓(ya)限(xian)流(liu)充(chong)電(dian)模式分兩(liang)個階段(duan)(duan)(duan),第一階段(duan)(duan)(duan)是恒(heng)(heng)流(liu)階段(duan)(duan)(duan),即系統給定(ding)電(dian)流(liu)值(zhi),給電(dian)池以恒(heng)(heng)定(ding)電(dian)流(liu)充(chong)電(dian),當電(dian)池的(de)電(dian)壓(ya)達到系統給定(ding)的(de)轉化值(zhi),就轉為第二階段(duan)(duan)(duan)―――恒(heng)(heng)壓(ya)階段(duan)(duan)(duan)。恒(heng)(heng)壓(ya)轉化值(zhi)會影響充(chong)入電(dian)量的(de)多少。
由圖4 可知(zhi),當恒(heng)(heng)壓(ya)(ya)轉化(hua)值(Vref)設置(zhi)的較低時,充(chong)(chong)入(ru)的電(dian)量(liang)不足(圖中陰(yin)影部(bu)分(fen)就(jiu)是(shi)少充(chong)(chong)入(ru)的容量(liang)),沒有(you)充(chong)(chong)分(fen)利用電(dian)池(chi)的容量(liang),長(chang)期(qi)工作,會(hui)引起電(dian)池(chi)容量(liang)丟失(shi),這就(jiu)要求把(ba)恒(heng)(heng)壓(ya)(ya)轉化(hua)值設高(gao)。但是(shi)恒(heng)(heng)壓(ya)(ya)值較高(gao),容易在充(chong)(chong)電(dian)末期(qi)引起過(guo)充(chong)(chong)電(dian),這同樣會(hui)導致電(dian)池(chi)容量(liang)丟失(shi)。

為了(le)(le)解決這(zhe)個矛盾(dun),系統引進了(le)(le)第三個階(jie)段―――浮充(chong)階(jie)段,這(zhe)樣就可(ke)以把恒(heng)壓(ya)(ya)(ya)轉(zhuan)化(hua)值設置的比普通恒(heng)壓(ya)(ya)(ya)限流模式高(gao),這(zhe)樣可(ke)以保證充(chong)入足夠(gou)的電(dian)(dian)量,在充(chong)電(dian)(dian)末期轉(zhuan)入浮充(chong)階(jie)段,用稍低的電(dian)(dian)壓(ya)(ya)(ya)浮充(chong)充(chong)電(dian)(dian),從而保證不會過充(chong)電(dian)(dian)。
三階段充電(dian)(dian)方法保證了充電(dian)(dian)末期不過充,同時(shi)又能達到滿充的目(mu)的,是(shi)一(yi)種成本(ben)較低的通(tong)用(yong)蓄電(dian)(dian)池充電(dian)(dian)解決(jue)方案。
3.2 軟件系統的設計(ji)
圖5 為系統軟(ruan)件的程(cheng)(cheng)序流程(cheng)(cheng)圖。根(gen)據電池的端電壓(ya)決定(ding)充(chong)電器工作在(zai)何種充(chong)電狀態。

我們做的是(shi)全(quan)數字(zi)化的改良型PI 調(diao)節環(huan)(huan),由于PI 調(diao)節的積分環(huan)(huan)在(zai)前期對(dui)誤(wu)差進行積累(lei),為了不讓積累(lei)的誤(wu)差影響(xiang)系(xi)統的穩定性,所(suo)以我們在(zai)誤(wu)差等(deng)于0 時(shi),對(dui)原有積累(lei)的誤(wu)差清零。當誤(wu)差等(deng)于±1 時(shi),只(zhi)進行積分運算,減慢調(diao)整速度(du),避免(mian)產生振(zhen)蕩。
鉛酸(suan)蓄電(dian)池的(de)充電(dian)電(dian)壓(ya)需要(yao)根據環(huan)境溫度進行調(diao)(diao)整,以-4 mV/℃的(de)補償(chang)系數來調(diao)(diao)整。因此我(wo)們(men)加(jia)入了(le)溫度補償(chang)的(de)功能。
4 實驗結果
圖6 為用電(dian)子負載(zai)模(mo)擬電(dian)池三階(jie)段充(chong)電(dian)過程的(de)波形圖。從圖6 中我們可(ke)以(yi)看出智能(neng)充(chong)電(dian)系(xi)統能(neng)夠方便地實(shi)現各個充(chong)電(dian)狀(zhuang)態的(de)轉換。

5 結語
用PIC 單片機可以(yi)實(shi)現全數字化(hua)的(de)電(dian)池充電(dian)管理,結構簡單,成本(ben)較低,并且具(ju)有很高的(de)靈活(huo)性,通過改(gai)(gai)變軟(ruan)件內設(she)置(zhi)的(de)恒(heng)流參(can)(can)考值(zhi)和(he)恒(heng)壓(ya)參(can)(can)考值(zhi)就可以(yi)改(gai)(gai)變系統(tong)的(de)恒(heng)流電(dian)流和(he)恒(heng)壓(ya)電(dian)壓(ya)值(zhi),使得系統(tong)在不(bu)改(gai)(gai)變系統(tong)硬件設(she)計的(de)情況下實(shi)現給多種(zhong)不(bu)同容(rong)量的(de)鉛酸(suan)蓄電(dian)池充電(dian)。另外可以(yi)實(shi)現有效的(de)電(dian)池充電(dian)管理和(he)保護功能(neng),達到智能(neng)化(hua)控制。
