為(wei)(wei)了給(gei)設備提供足夠的(de)(de)電(dian)(dian)(dian)(dian)壓(ya)，鋰(li)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包通常由多個電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)串聯而(er)成(cheng)，但是如果電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)之(zhi)間(jian)的(de)(de)容量(liang)失配便會(hui)影響整個電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包的(de)(de)容量(liang)。為(wei)(wei)此，我(wo)們(men)需要對失配的(de)(de)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)進行均衡(heng)。本文討(tao)論了電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)均衡(heng)的(de)(de)概念(nian)和一些注(zhu)意(yi)事(shi)項。

      鋰電池包通(tong)常(chang)(chang)由(you)一個(ge)或幾個(ge)電(dian)(dian)(dian)池(chi)(chi)組并(bing)聯(lian)，每(mei)個(ge)電(dian)(dian)(dian)池(chi)(chi)組由(you)3到4個(ge)電(dian)(dian)(dian)池(chi)(chi)串聯(lian)構(gou)成。這(zhe)種(zhong)組合方式能同時滿足筆(bi)記本電(dian)(dian)(dian)腦、醫(yi)療設備(bei)、測試儀(yi)器(qi)及(ji)工業應(ying)用所(suo)需的(de)電(dian)(dian)(dian)壓和功(gong)率(lv)要求。然而，這(zhe)種(zhong)應(ying)用普遍的(de)配置通(tong)常(chang)(chang)并(bing)不能發揮其(qi)最大(da)功(gong)效(xiao)，因為如(ru)果某個(ge)串聯(lian)電(dian)(dian)(dian)池(chi)(chi)的(de)容量(liang)(liang)與其(qi)它(ta)電(dian)(dian)(dian)池(chi)(chi)不匹(pi)配將會降(jiang)低整個(ge)電(dian)(dian)(dian)池(chi)(chi)包的(de)容量(liang)(liang)。

電池容(rong)(rong)(rong)量(liang)(liang)的(de)(de)不匹配(pei)包(bao)括(kuo)充電狀態(SOC)失(shi)配(pei)和容(rong)(rong)(rong)量(liang)(liang)/能量(liang)(liang)(C/E)失(shi)配(pei)。在(zai)(zai)兩種情(qing)況下(xia)，電池包(bao)的(de)(de)總容(rong)(rong)(rong)量(liang)(liang)都(dou)只能達到最弱電池的(de)(de)容(rong)(rong)(rong)量(liang)(liang)。在(zai)(zai)大多數情(qing)況下(xia)，引起(qi)電池失(shi)配(pei)的(de)(de)原因是工藝控(kong)制和檢測手段的(de)(de)不完善，而不是鋰離子本身的(de)(de)化(hua)學屬性變(bian)化(hua)。棱柱形鋰電池(LiIon prismatic cell)在(zai)(zai)生產(chan)時需要(yao)更強的(de)(de)機械壓力，電池之(zhi)間更容(rong)(rong)(rong)易(yi)產(chan)生差異(yi)。此外，鋰離子聚合物電池也(ye)會因為采用新的(de)(de)工藝而出現電池之(zhi)間的(de)(de)差異(yi)。

      采用電(dian)(dian)池(chi)(chi)均(jun)衡(heng)處理技術可解決SOC和C/E失(shi)配(pei)問(wen)題(ti)(ti)，從而改進串(chuan)聯鋰電(dian)(dian)池(chi)(chi)包(bao)的性能。通過(guo)(guo)在(zai)初(chu)始調節過(guo)(guo)程(cheng)中(zhong)對電(dian)(dian)池(chi)(chi)進行(xing)均(jun)衡(heng)處理可以矯正電(dian)(dian)池(chi)(chi)失(shi)配(pei)問(wen)題(ti)(ti)，此(ci)后只(zhi)需在(zai)充(chong)(chong)電(dian)(dian)過(guo)(guo)程(cheng)中(zhong)進行(xing)均(jun)衡(heng)即可，而C/E失(shi)配(pei)則必(bi)須(xu)在(zai)充(chong)(chong)、放電(dian)(dian)過(guo)(guo)程(cheng)都進行(xing)均(jun)衡(heng)。盡(jin)管(guan)對于某個電(dian)(dian)池(chi)(chi)廠商而言(yan)其產品(pin)缺陷率可能很低(di)，但為(wei)了避(bi)免出現電(dian)(dian)池(chi)(chi)使(shi)用壽命 過(guo)(guo)短的問(wen)題(ti)(ti)，我(wo)們仍然有必(bi)要提供進一步的質量(liang)保(bao)證。

電池均衡的定義

     工作電(dian)(dian)(dian)(dian)壓(ya)為6V 或以上(shang)的(de)(de)(de)便(bian)攜(xie)式設備采用串(chuan)(chuan)聯(lian)(lian)(lian)(lian)(lian)電(dian)(dian)(dian)(dian)池(chi)包供(gong)(gong)電(dian)(dian)(dian)(dian)，這種情(qing)況下電(dian)(dian)(dian)(dian)池(chi)包的(de)(de)(de)總電(dian)(dian)(dian)(dian)壓(ya)為各串(chuan)(chuan)聯(lian)(lian)(lian)(lian)(lian)電(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)壓(ya)之(zhi)和。便(bian)攜(xie)式電(dian)(dian)(dian)(dian)腦(nao)的(de)(de)(de)電(dian)(dian)(dian)(dian)池(chi)包通常由(you)三、四個電(dian)(dian)(dian)(dian)池(chi)串(chuan)(chuan)聯(lian)(lian)(lian)(lian)(lian)而成，標稱電(dian)(dian)(dian)(dian)壓(ya)為 10.8V或14.4V。在(zai)大多(duo)數此類應用中，單(dan)個串(chuan)(chuan)聯(lian)(lian)(lian)(lian)(lian)電(dian)(dian)(dian)(dian)池(chi)包無法提(ti)供(gong)(gong)設備所需能量。目前最(zui)大的(de)(de)(de)電(dian)(dian)(dian)(dian)池(chi)(如18650)可(ke)提(ti)供(gong)(gong)2,000mAh(毫(hao)安(an) ?小時)能量，而電(dian)(dian)(dian)(dian)腦(nao)需要50-60Whr(5,000-6,000mAh)的(de)(de)(de)能量，因此必須(xu)給串(chuan)(chuan)聯(lian)(lian)(lian)(lian)(lian)的(de)(de)(de)每(mei)個電(dian)(dian)(dian)(dian)池(chi)并聯(lian)(lian)(lian)(lian)(lian)三個電(dian)(dian)(dian)(dian)池(chi)。

     電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)均衡是指對串聯電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包(bao)中(zhong)(zhong)不同的(de)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(或電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)組)采用差分電(dian)(dian)(dian)(dian)(dian)(dian)流。串聯電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包(bao)中(zhong)(zhong)每個電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)流通常(chang)是一樣的(de)，因(yin)此必須給電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包(bao)增(zeng)加額外的(de)元件和電(dian)(dian)(dian)(dian)(dian)(dian)路來實(shi)現(xian) 電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)均衡。只(zhi)有(you)當(dang)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包(bao)中(zhong)(zhong)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)是串聯的(de)，同時串聯電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)等于或大(da)于三級(ji)時才(cai)會(hui)考慮電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)均衡問題。當(dang)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包(bao)中(zhong)(zhong)所(suo)有(you)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)都(dou)滿足下面(mian)兩(liang)個條(tiao)件時，便(bian)實(shi)現(xian)了電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)均衡：

1. 如果所有電(dian)池(chi)(chi)(chi)(chi)的(de)(de)(de)(de)(de)(de)容(rong)量相同，那么(me)當它們的(de)(de)(de)(de)(de)(de)相對(dui)充電(dian)狀態(tai)一(yi)(yi)樣(yang)時(shi)便(bian)實(shi)現了電(dian)池(chi)(chi)(chi)(chi)均衡(heng)。SOC通(tong)常(chang)以當前容(rong)量與額(e)定(ding)容(rong)量的(de)(de)(de)(de)(de)(de)百(bai)分比來表示(shi)，因此(ci)，開路電(dian)壓(OCV)可(ke)作為SOC的(de)(de)(de)(de)(de)(de)一(yi)(yi)個衡(heng)量標準。如果一(yi)(yi)個不均衡(heng)電(dian)池(chi)(chi)(chi)(chi)包中的(de)(de)(de)(de)(de)(de)所有電(dian)池(chi)(chi)(chi)(chi)可(ke)以通(tong)過差(cha)分充電(dian)達到滿(man)容(rong)量(均衡(heng)點)，它們便(bian)可(ke)以進行正常(chang)的(de)(de)(de)(de)(de)(de)充放(fang)電(dian)而無(wu)需任何(he)額(e)外的(de)(de)(de)(de)(de)(de)調整，通(tong)常(chang)這種調整是一(yi)(yi)次性(xing)的(de)(de)(de)(de)(de)(de)。用(yong)戶在使(shi)(shi)用(yong)新電(dian)池(chi)(chi)(chi)(chi)時(shi)，通(tong)常(chang)需要求(qiu)對(dui)電(dian)池(chi)(chi)(chi)(chi)進行長(chang)時(shi)間(jian)充電(dian)，這個過程(cheng)實(shi)際上包括一(yi)(yi)次完整的(de)(de)(de)(de)(de)(de)放(fang)-充電(dian)。該過程(cheng)使(shi)(shi)負(fu)載最小化，并使(shi)(shi)電(dian)池(chi)(chi)(chi)(chi)充 電(dian)時(shi)間(jian)最長(chang)，降低對(dui)電(dian)池(chi)(chi)(chi)(chi)均衡(heng)電(dian)路的(de)(de)(de)(de)(de)(de)要求(qiu)。

2. 如果電(dian)(dian)(dian)(dian)池(chi)(chi)的(de)(de)容(rong)量不(bu)同(tong)，當SOC相同(tong)時(shi)(shi)也認為它們(men)是(shi)均衡的(de)(de)。但SOC只是(shi)一個(ge)相對(dui)值(zhi)，每個(ge)電(dian)(dian)(dian)(dian)池(chi)(chi)容(rong)量的(de)(de)絕(jue)對(dui)值(zhi)是(shi)不(bu)同(tong)的(de)(de)。為了使(shi)容(rong)量不(bu)同(tong)的(de)(de)電(dian)(dian)(dian)(dian)池(chi)(chi)的(de)(de)SOC相同(tong)，每次對(dui)串聯電(dian)(dian)(dian)(dian)池(chi)(chi)進行充(chong)放(fang)電(dian)(dian)(dian)(dian)時(shi)(shi)都(dou)必須(xu)使(shi)用差分電(dian)(dian)(dian)(dian)流。正常(chang)充(chong)放(fang)電(dian)(dian)(dian)(dian)的(de)(de)時(shi)(shi)間比初次充(chong)放(fang)電(dian)(dian)(dian)(dian)更短，并需(xu)要更大的(de)(de)電(dian)(dian)(dian)(dian)流。

     當電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包(bao)(bao)中(zhong)的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)不(bu)均(jun)衡時(shi)，它(ta)的(de)(de)可(ke)用容量(liang)將減少，串聯(lian)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包(bao)(bao)中(zhong)容量(liang)最低的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)將決(jue)定電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包(bao)(bao)的(de)(de)總容量(liang)。在(zai)(zai)不(bu)均(jun)衡電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包(bao)(bao)中(zhong)，一(yi)個(ge)或(huo)幾個(ge)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)會(hui)在(zai)(zai)其它(ta)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)尚需充電(dian)(dian)(dian)(dian)(dian)(dian)時(shi)便已(yi)達到最大容量(liang)。而(er)在(zai)(zai)放電(dian)(dian)(dian)(dian)(dian)(dian)時(shi)，未完全充電(dian)(dian)(dian)(dian)(dian)(dian)的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)又會(hui)比(bi)其它(ta)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)先放完電(dian)(dian)(dian)(dian)(dian)(dian)，使電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包(bao)(bao)因電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)不(bu)足而(er)提前(qian)停止供電(dian)(dian)(dian)(dian)(dian)(dian)。

通常，電(dian)池(chi)(chi)之間(jian)容量的差異低于3%。如果串(chuan)聯鋰電(dian)池(chi)(chi)包(bao)的某個電(dian)池(chi)(chi)不合標準(zhun)，或者在(zai)封裝前(qian)放置過(guo)久，在(zai)充電(dian)器(qi)充滿(man)電(dian)后電(dian)壓差可達150mV，從而使(shi)電(dian)池(chi)(chi)包(bao)的總容量下降(jiang)13-18%。

SOC均衡處理

如果電池(chi)包中所(suo)有電池(chi)的(de)容量相(xiang)同(tong)，我(wo)們(men)便采用SOC均衡處理(li)。當所(suo)有電池(chi)的(de)SOC值相(xiang)同(tong)時(shi)我(wo)們(men)認為電池(chi)是均衡的(de)。

單個電(dian)池的(de)充電(dian)狀態定義為：

SOC=C/CTOTAL%

單個電池(chi)的(de)容量定義為：

C=(i×t)mAh

為了確定某個電池的容量，我們將該電池完全放電然后再用鋰電池充電器充(chong)(chong)電(dian)(dian)，并在電(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)器充(chong)(chong)電(dian)(dian)過(guo)程中的(de)不(bu)同時間(jian)進行電(dian)(dian)流測(ce)量，直到(dao)達到(dao)4.20V的(de)開路(lu)電(dian)(dian)壓。最佳性能電(dian)(dian)池(chi)在該狀(zhuang)態下(xia)的(de)SOC為(wei)(wei)100%，SOC為(wei)(wei)50%的(de)OCV電(dian)(dian)壓通(tong)常稱(cheng)為(wei)(wei)VMID，其典型值為(wei)(wei)3.67V。

為了給容(rong)量不同(tong)的電(dian)池充電(dian)使(shi)它們(men)達到同(tong)樣(yang)的SOC，要求一些電(dian)池的充/放電(dian)量必(bi)須比其它電(dian)池多，這必(bi)須使(shi)用(yong)差分電(dian)流。我們(men)將(jiang)這個過程稱之為容(rong)量/能量最大化(hua)。

容量/能量最大化

容量(liang)/能量(liang)最大化是(shi)指將電(dian)(dian)(dian)(dian)池(chi)(chi)包中(zhong)所有串聯(lian)電(dian)(dian)(dian)(dian)池(chi)(chi)設置為(wei)相同的(de)SOC，即使(shi)它(ta)(ta)們(men)的(de)容量(liang)不(bu)同。在所有時(shi)間內管理SOC，使(shi)電(dian)(dian)(dian)(dian)池(chi)(chi)包的(de)輸(shu)出能量(liang)達到最大。為(wei)了使(shi)輸(shu)出能量(liang)最大化，所有的(de)電(dian)(dian)(dian)(dian)池(chi)(chi)都必須(xu)充滿電(dian)(dian)(dian)(dian)。即，所有電(dian)(dian)(dian)(dian)池(chi)(chi)的(de)SOC必須(xu)為(wei)100%。如(ru)果電(dian)(dian)(dian)(dian)池(chi)(chi)的(de)容量(liang)不(bu)同，一(yi)些電(dian)(dian)(dian)(dian)池(chi)(chi)的(de)充/放電(dian)(dian)(dian)(dian)就會比其它(ta)(ta)電(dian)(dian)(dian)(dian)池(chi)(chi)更多。例如(ru)，假設一(yi)個(ge)電(dian)(dian)(dian)(dian)池(chi)(chi)包有三個(ge)串聯(lian)電(dian)(dian)(dian)(dian)池(chi)(chi)，C1＞C2=C3。均衡這個(ge)電(dian)(dian)(dian)(dian)池(chi)(chi)包的(de)唯一(yi)方法是(shi)給容量(liang)較高的(de)電(dian)(dian)(dian)(dian)池(chi)(chi)(C1)施加(jia)一(yi)個(ge)差分充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流。

在電(dian)(dian)池(chi)包放(fang)電(dian)(dian)時(shi)也必須如此(ci)，否則當容(rong)(rong)量(liang)最小的電(dian)(dian)池(chi)達到關斷(duan)電(dian)(dian)壓時(shi)，整個(ge)電(dian)(dian)池(chi)包便會(hui)停(ting)止放(fang)電(dian)(dian)，而此(ci)時(shi)其它電(dian)(dian)池(chi)仍有剩余容(rong)(rong)量(liang)，這樣使總容(rong)(rong)量(liang)降低。長(chang)此(ci)以往，容(rong)(rong)量(liang)最小的電(dian)(dian)池(chi)便會(hui)比其它電(dian)(dian)池(chi)性能(neng)衰退更快(kuai)，經過多個(ge)充/放(fang)電(dian)(dian)周期后(hou)將加速容(rong)(rong)量(liang)損耗。

通過匹配串聯電池的電壓，將從高容量電池汲取更多電流。放電時要求通過均衡消耗掉一些額外的電壓，在最后當所有電池都達到0SOC時，從電池包中獲得的總電能相對于均衡前仍然會增加。
通常圓柱形鋰(li)離子電池(cylindrical cell)的(de)質量控制通常都較(jiao)好，電池容(rong)量差(cha)別不超過±3%。輸(shu)入容(rong)量基本上比較(jiao)精(jing)確，差(cha)別不超過幾個mAs(毫安?秒)。因此，電池容(rong)量絕對值也基本準確，SOC的(de)差(cha)異在(zai)幾個百分點以內。