為了給(gei)設備提供(gong)足夠的(de)電(dian)壓，鋰電(dian)池(chi)包通常由多個電(dian)池(chi)串聯而(er)成(cheng)，但(dan)是如(ru)果電(dian)池(chi)之間的(de)容(rong)量失配便(bian)會影響整(zheng)個電(dian)池(chi)包的(de)容(rong)量。為此，我們需要對失配的(de)電(dian)池(chi)進行均衡。本文討論了電(dian)池(chi)均衡的(de)概念(nian)和一些注意事項(xiang)。

      鋰電池包通常由(you)一個或幾個電(dian)池(chi)組并聯，每(mei)個電(dian)池(chi)組由(you)3到(dao)4個電(dian)池(chi)串(chuan)聯構(gou)成。這種組合(he)方(fang)式能同時滿足(zu)筆記(ji)本電(dian)腦、醫療設備、測試儀器及工業應(ying)用(yong)所需(xu)的電(dian)壓和功(gong)率(lv)要求(qiu)。然而(er)，這種應(ying)用(yong)普(pu)遍的配置(zhi)通常并不能發(fa)揮其(qi)最大功(gong)效，因(yin)為如果某個串(chuan)聯電(dian)池(chi)的容量(liang)與其(qi)它電(dian)池(chi)不匹配將會(hui)降低整個電(dian)池(chi)包的容量(liang)。

電(dian)池(chi)容量(liang)(liang)(liang)的(de)不匹配包括充電(dian)狀態(SOC)失配和容量(liang)(liang)(liang)/能量(liang)(liang)(liang)(C/E)失配。在(zai)兩種情況下，電(dian)池(chi)包的(de)總容量(liang)(liang)(liang)都只能達到最弱電(dian)池(chi)的(de)容量(liang)(liang)(liang)。在(zai)大多數情況下，引起電(dian)池(chi)失配的(de)原因是(shi)(shi)工藝(yi)控(kong)制和檢測手段的(de)不完善，而(er)不是(shi)(shi)鋰(li)離(li)子(zi)本身(shen)的(de)化(hua)學屬性變(bian)化(hua)。棱柱形鋰(li)電(dian)池(chi)(LiIon prismatic cell)在(zai)生(sheng)(sheng)產時需要(yao)更(geng)強(qiang)的(de)機械壓力，電(dian)池(chi)之(zhi)間更(geng)容易產生(sheng)(sheng)差異。此外，鋰(li)離(li)子(zi)聚合物電(dian)池(chi)也會因為采用新(xin)的(de)工藝(yi)而(er)出現電(dian)池(chi)之(zhi)間的(de)差異。

      采用電(dian)(dian)池(chi)(chi)均(jun)衡處理(li)技術可(ke)解決SOC和(he)C/E失(shi)配問題，從而(er)改進串聯鋰電(dian)(dian)池(chi)(chi)包的性能(neng)。通過在(zai)(zai)初始(shi)調節過程(cheng)(cheng)中對(dui)電(dian)(dian)池(chi)(chi)進行均(jun)衡處理(li)可(ke)以(yi)矯正電(dian)(dian)池(chi)(chi)失(shi)配問題，此后(hou)只需(xu)在(zai)(zai)充電(dian)(dian)過程(cheng)(cheng)中進行均(jun)衡即可(ke)，而(er)C/E失(shi)配則必須在(zai)(zai)充、放電(dian)(dian)過程(cheng)(cheng)都進行均(jun)衡。盡(jin)管對(dui)于某個電(dian)(dian)池(chi)(chi)廠(chang)商而(er)言其產品缺陷率可(ke)能(neng)很低，但(dan)為(wei)了避免出現電(dian)(dian)池(chi)(chi)使用壽命 過短(duan)的問題，我們仍然有必要(yao)提供進一步的質量保證。

電池均衡的定義

     工作電(dian)(dian)(dian)壓(ya)為(wei)(wei)6V 或以上(shang)的便攜式設(she)(she)備采用(yong)串(chuan)聯(lian)(lian)(lian)電(dian)(dian)(dian)池(chi)(chi)(chi)包供電(dian)(dian)(dian)，這種情況下電(dian)(dian)(dian)池(chi)(chi)(chi)包的總電(dian)(dian)(dian)壓(ya)為(wei)(wei)各串(chuan)聯(lian)(lian)(lian)電(dian)(dian)(dian)池(chi)(chi)(chi)電(dian)(dian)(dian)壓(ya)之和。便攜式電(dian)(dian)(dian)腦(nao)的電(dian)(dian)(dian)池(chi)(chi)(chi)包通常(chang)由三(san)、四個(ge)電(dian)(dian)(dian)池(chi)(chi)(chi)串(chuan)聯(lian)(lian)(lian)而(er)成，標稱電(dian)(dian)(dian)壓(ya)為(wei)(wei) 10.8V或14.4V。在(zai)大多數此(ci)(ci)類應(ying)用(yong)中，單個(ge)串(chuan)聯(lian)(lian)(lian)電(dian)(dian)(dian)池(chi)(chi)(chi)包無法提供設(she)(she)備所需(xu)能(neng)量(liang)。目前最大的電(dian)(dian)(dian)池(chi)(chi)(chi)(如18650)可提供2,000mAh(毫安(an) ?小時)能(neng)量(liang)，而(er)電(dian)(dian)(dian)腦(nao)需(xu)要50-60Whr(5,000-6,000mAh)的能(neng)量(liang)，因此(ci)(ci)必須給串(chuan)聯(lian)(lian)(lian)的每個(ge)電(dian)(dian)(dian)池(chi)(chi)(chi)并聯(lian)(lian)(lian)三(san)個(ge)電(dian)(dian)(dian)池(chi)(chi)(chi)。

     電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)均(jun)衡(heng)是指對串(chuan)聯電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包中不同(tong)的(de)(de)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(或電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)組)采用差分電(dian)(dian)(dian)(dian)流(liu)(liu)。串(chuan)聯電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包中每個(ge)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)的(de)(de)電(dian)(dian)(dian)(dian)流(liu)(liu)通(tong)常是一樣的(de)(de)，因此必須給電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包增加額外的(de)(de)元件(jian)和(he)電(dian)(dian)(dian)(dian)路(lu)來實現 電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)均(jun)衡(heng)。只有當電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包中的(de)(de)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)是串(chuan)聯的(de)(de)，同(tong)時(shi)(shi)串(chuan)聯電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)等(deng)于或大于三級時(shi)(shi)才會(hui)考慮電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)均(jun)衡(heng)問題。當電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包中所有電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)都(dou)滿足下面兩個(ge)條件(jian)時(shi)(shi)，便實現了電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)均(jun)衡(heng)：

1. 如(ru)果(guo)所有電(dian)(dian)池(chi)(chi)的(de)(de)(de)(de)(de)容量(liang)(liang)相同，那么(me)當它(ta)(ta)們(men)的(de)(de)(de)(de)(de)相對充電(dian)(dian)狀態(tai)一(yi)樣時(shi)便實(shi)現了電(dian)(dian)池(chi)(chi)均(jun)衡(heng)。SOC通(tong)常(chang)以當前容量(liang)(liang)與額(e)(e)定容量(liang)(liang)的(de)(de)(de)(de)(de)百(bai)分比來表示，因(yin)此(ci)，開路(lu)電(dian)(dian)壓(OCV)可(ke)作為(wei)SOC的(de)(de)(de)(de)(de)一(yi)個衡(heng)量(liang)(liang)標準。如(ru)果(guo)一(yi)個不均(jun)衡(heng)電(dian)(dian)池(chi)(chi)包中(zhong)的(de)(de)(de)(de)(de)所有電(dian)(dian)池(chi)(chi)可(ke)以通(tong)過(guo)(guo)差分充電(dian)(dian)達到滿容量(liang)(liang)(均(jun)衡(heng)點)，它(ta)(ta)們(men)便可(ke)以進行正常(chang)的(de)(de)(de)(de)(de)充放電(dian)(dian)而無需(xu)任何額(e)(e)外的(de)(de)(de)(de)(de)調整，通(tong)常(chang)這(zhe)種調整是一(yi)次性的(de)(de)(de)(de)(de)。用戶在(zai)使(shi)用新電(dian)(dian)池(chi)(chi)時(shi)，通(tong)常(chang)需(xu)要求(qiu)(qiu)對電(dian)(dian)池(chi)(chi)進行長時(shi)間充電(dian)(dian)，這(zhe)個過(guo)(guo)程實(shi)際上(shang)包括一(yi)次完整的(de)(de)(de)(de)(de)放-充電(dian)(dian)。該過(guo)(guo)程使(shi)負載最小化，并使(shi)電(dian)(dian)池(chi)(chi)充 電(dian)(dian)時(shi)間最長，降低對電(dian)(dian)池(chi)(chi)均(jun)衡(heng)電(dian)(dian)路(lu)的(de)(de)(de)(de)(de)要求(qiu)(qiu)。

2. 如果電(dian)(dian)池的(de)容(rong)量(liang)不(bu)同，當SOC相(xiang)同時(shi)也(ye)認(ren)為它們(men)是均衡的(de)。但(dan)SOC只是一(yi)個相(xiang)對值(zhi)，每個電(dian)(dian)池容(rong)量(liang)的(de)絕對值(zhi)是不(bu)同的(de)。為了(le)使(shi)容(rong)量(liang)不(bu)同的(de)電(dian)(dian)池的(de)SOC相(xiang)同，每次對串(chuan)聯電(dian)(dian)池進行充放電(dian)(dian)時(shi)都必(bi)須使(shi)用差(cha)分(fen)電(dian)(dian)流。正常充放電(dian)(dian)的(de)時(shi)間比初次充放電(dian)(dian)更短，并需要更大的(de)電(dian)(dian)流。

     當電(dian)(dian)池(chi)(chi)包(bao)(bao)中的(de)電(dian)(dian)池(chi)(chi)不均(jun)衡(heng)時，它的(de)可用容(rong)量將減(jian)少(shao)，串聯電(dian)(dian)池(chi)(chi)包(bao)(bao)中容(rong)量最低(di)的(de)電(dian)(dian)池(chi)(chi)將決(jue)定電(dian)(dian)池(chi)(chi)包(bao)(bao)的(de)總容(rong)量。在不均(jun)衡(heng)電(dian)(dian)池(chi)(chi)包(bao)(bao)中，一個或幾個電(dian)(dian)池(chi)(chi)會在其它電(dian)(dian)池(chi)(chi)尚需充(chong)電(dian)(dian)時便已達(da)到最大容(rong)量。而在放(fang)(fang)電(dian)(dian)時，未完(wan)全(quan)充(chong)電(dian)(dian)的(de)電(dian)(dian)池(chi)(chi)又會比其它電(dian)(dian)池(chi)(chi)先放(fang)(fang)完(wan)電(dian)(dian)，使(shi)電(dian)(dian)池(chi)(chi)包(bao)(bao)因電(dian)(dian)壓(ya)不足而提前(qian)停(ting)止供電(dian)(dian)。

通常，電池(chi)(chi)之間容量的差異低(di)于3%。如果(guo)串聯鋰(li)電池(chi)(chi)包的某個電池(chi)(chi)不(bu)合標準，或者在封(feng)裝前放置過久(jiu)，在充電器(qi)充滿電后電壓差可達150mV，從而使電池(chi)(chi)包的總容量下降13-18%。

SOC均衡處理

如果電池(chi)包中所有電池(chi)的容量相同，我們(men)便(bian)采(cai)用(yong)SOC均衡(heng)處理。當所有電池(chi)的SOC值相同時我們(men)認(ren)為電池(chi)是均衡(heng)的。

單個(ge)電(dian)池的(de)充(chong)電(dian)狀態定義為：

SOC=C/CTOTAL%

單(dan)個(ge)電池的容量(liang)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電，并在(zai)電池(chi)充電器充電過程(cheng)中的(de)不同(tong)時(shi)間進行電流測量，直(zhi)到(dao)達到(dao)4.20V的(de)開路電壓。最(zui)佳性能電池(chi)在(zai)該(gai)狀(zhuang)態下的(de)SOC為(wei)100%，SOC為(wei)50%的(de)OCV電壓通(tong)常稱(cheng)為(wei)VMID，其(qi)典型值(zhi)為(wei)3.67V。

為了給容量不(bu)同的(de)電(dian)池充電(dian)使它(ta)們達到同樣的(de)SOC，要(yao)求一(yi)些電(dian)池的(de)充/放(fang)電(dian)量必(bi)須(xu)比其它(ta)電(dian)池多，這(zhe)必(bi)須(xu)使用差分(fen)電(dian)流。我們將這(zhe)個(ge)過程稱(cheng)之為容量/能(neng)量最大化(hua)。

容量/能量最大化

容(rong)量/能量最(zui)大化是指將電(dian)(dian)(dian)(dian)池(chi)包(bao)中所(suo)有(you)(you)串聯電(dian)(dian)(dian)(dian)池(chi)設置(zhi)為(wei)相同的(de)(de)SOC，即使(shi)它(ta)們的(de)(de)容(rong)量不同。在所(suo)有(you)(you)時間(jian)內管理SOC，使(shi)電(dian)(dian)(dian)(dian)池(chi)包(bao)的(de)(de)輸(shu)出(chu)能量達到(dao)最(zui)大。為(wei)了使(shi)輸(shu)出(chu)能量最(zui)大化，所(suo)有(you)(you)的(de)(de)電(dian)(dian)(dian)(dian)池(chi)都必(bi)須充滿電(dian)(dian)(dian)(dian)。即，所(suo)有(you)(you)電(dian)(dian)(dian)(dian)池(chi)的(de)(de)SOC必(bi)須為(wei)100%。如果電(dian)(dian)(dian)(dian)池(chi)的(de)(de)容(rong)量不同，一(yi)(yi)些(xie)電(dian)(dian)(dian)(dian)池(chi)的(de)(de)充/放(fang)電(dian)(dian)(dian)(dian)就(jiu)會比其它(ta)電(dian)(dian)(dian)(dian)池(chi)更多。例(li)如，假設一(yi)(yi)個(ge)(ge)電(dian)(dian)(dian)(dian)池(chi)包(bao)有(you)(you)三個(ge)(ge)串聯電(dian)(dian)(dian)(dian)池(chi)，C1＞C2=C3。均衡這個(ge)(ge)電(dian)(dian)(dian)(dian)池(chi)包(bao)的(de)(de)唯一(yi)(yi)方法是給容(rong)量較高(gao)的(de)(de)電(dian)(dian)(dian)(dian)池(chi)(C1)施加(jia)一(yi)(yi)個(ge)(ge)差分充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流。

在(zai)電(dian)(dian)池(chi)(chi)包放(fang)電(dian)(dian)時(shi)也必須如此，否則當(dang)容量(liang)最小的電(dian)(dian)池(chi)(chi)達到關斷電(dian)(dian)壓時(shi)，整個(ge)電(dian)(dian)池(chi)(chi)包便會(hui)停止放(fang)電(dian)(dian)，而此時(shi)其它電(dian)(dian)池(chi)(chi)仍有(you)剩余(yu)容量(liang)，這樣使(shi)總容量(liang)降低。長此以往(wang)，容量(liang)最小的電(dian)(dian)池(chi)(chi)便會(hui)比其它電(dian)(dian)池(chi)(chi)性能衰(shuai)退更快，經(jing)過多個(ge)充(chong)/放(fang)電(dian)(dian)周(zhou)期后將加速容量(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(tong)常(chang)圓柱形鋰離子電池(cylindrical cell)的質(zhi)量(liang)控制通(tong)常(chang)都較好，電池容(rong)量(liang)差(cha)(cha)別不(bu)超過(guo)±3%。輸入容(rong)量(liang)基本(ben)上比(bi)較精確，差(cha)(cha)別不(bu)超過(guo)幾(ji)個(ge)mAs(毫安(an)?秒)。因此，電池容(rong)量(liang)絕對值(zhi)也基本(ben)準確，SOC的差(cha)(cha)異在幾(ji)個(ge)百分點以內。