為了給設備提供足夠的(de)(de)電壓(ya)，鋰(li)電池(chi)包通常由(you)多個電池(chi)串聯而(er)成，但是如果電池(chi)之間的(de)(de)容量失(shi)配便會影響整(zheng)個電池(chi)包的(de)(de)容量。為此，我們需要(yao)對失(shi)配的(de)(de)電池(chi)進行均(jun)衡(heng)。本文(wen)討(tao)論了電池(chi)均(jun)衡(heng)的(de)(de)概(gai)念(nian)和一些注意(yi)事項。

      鋰電池包通常由(you)一個或幾個電(dian)池(chi)(chi)(chi)組(zu)并聯(lian)，每個電(dian)池(chi)(chi)(chi)組(zu)由(you)3到4個電(dian)池(chi)(chi)(chi)串聯(lian)構成。這種組(zu)合方式能(neng)同(tong)時滿足筆記本電(dian)腦、醫療設備、測試儀器及工業應用所需的(de)(de)(de)電(dian)壓和(he)功(gong)率(lv)要求。然而，這種應用普遍的(de)(de)(de)配(pei)置通常并不能(neng)發揮其(qi)最(zui)大功(gong)效，因(yin)為如果某個串聯(lian)電(dian)池(chi)(chi)(chi)的(de)(de)(de)容(rong)量與(yu)其(qi)它電(dian)池(chi)(chi)(chi)不匹配(pei)將會降低整個電(dian)池(chi)(chi)(chi)包的(de)(de)(de)容(rong)量。

電(dian)池(chi)(chi)容(rong)量(liang)(liang)的(de)(de)(de)不(bu)(bu)匹配包(bao)括(kuo)充電(dian)狀態(SOC)失(shi)配和容(rong)量(liang)(liang)/能量(liang)(liang)(C/E)失(shi)配。在兩(liang)種(zhong)情況(kuang)下，電(dian)池(chi)(chi)包(bao)的(de)(de)(de)總容(rong)量(liang)(liang)都只(zhi)能達到最(zui)弱電(dian)池(chi)(chi)的(de)(de)(de)容(rong)量(liang)(liang)。在大多數情況(kuang)下，引(yin)起(qi)電(dian)池(chi)(chi)失(shi)配的(de)(de)(de)原(yuan)因是工藝控制(zhi)和檢測手段的(de)(de)(de)不(bu)(bu)完善，而(er)不(bu)(bu)是鋰(li)離子本身的(de)(de)(de)化(hua)學(xue)屬性變化(hua)。棱柱形(xing)鋰(li)電(dian)池(chi)(chi)(LiIon prismatic cell)在生產(chan)時需要更(geng)強的(de)(de)(de)機械壓(ya)力，電(dian)池(chi)(chi)之(zhi)間(jian)更(geng)容(rong)易產(chan)生差異。此外(wai)，鋰(li)離子聚合物(wu)電(dian)池(chi)(chi)也會因為采用(yong)新的(de)(de)(de)工藝而(er)出現電(dian)池(chi)(chi)之(zhi)間(jian)的(de)(de)(de)差異。

      采用(yong)電池(chi)(chi)(chi)均(jun)衡處(chu)理技術可解決SOC和C/E失配問(wen)題(ti)(ti)，從而(er)改(gai)進(jin)串聯鋰電池(chi)(chi)(chi)包的性能。通(tong)過在(zai)初(chu)始調節過程中對電池(chi)(chi)(chi)進(jin)行均(jun)衡處(chu)理可以矯正電池(chi)(chi)(chi)失配問(wen)題(ti)(ti)，此(ci)后只需(xu)在(zai)充電過程中進(jin)行均(jun)衡即可，而(er)C/E失配則必(bi)須在(zai)充、放電過程都(dou)進(jin)行均(jun)衡。盡管對于某個(ge)電池(chi)(chi)(chi)廠商而(er)言其產品(pin)缺(que)陷率可能很低，但為(wei)了避免出現電池(chi)(chi)(chi)使用(yong)壽(shou)命 過短的問(wen)題(ti)(ti)，我們仍(reng)然有(you)必(bi)要提供進(jin)一(yi)步(bu)的質量保證(zheng)。

電池均衡的定義

     工作電(dian)(dian)壓(ya)為6V 或以上的(de)便攜(xie)(xie)式設備(bei)采用(yong)(yong)串(chuan)聯電(dian)(dian)池(chi)(chi)包供(gong)(gong)電(dian)(dian)，這種情(qing)況下電(dian)(dian)池(chi)(chi)包的(de)總電(dian)(dian)壓(ya)為各串(chuan)聯電(dian)(dian)池(chi)(chi)電(dian)(dian)壓(ya)之和。便攜(xie)(xie)式電(dian)(dian)腦的(de)電(dian)(dian)池(chi)(chi)包通常由(you)三(san)、四(si)個(ge)電(dian)(dian)池(chi)(chi)串(chuan)聯而(er)成，標稱電(dian)(dian)壓(ya)為 10.8V或14.4V。在大(da)(da)多數(shu)此類應用(yong)(yong)中(zhong)，單(dan)個(ge)串(chuan)聯電(dian)(dian)池(chi)(chi)包無法提供(gong)(gong)設備(bei)所需(xu)能(neng)(neng)量(liang)。目前最(zui)大(da)(da)的(de)電(dian)(dian)池(chi)(chi)(如18650)可提供(gong)(gong)2,000mAh(毫安(an) ?小時)能(neng)(neng)量(liang)，而(er)電(dian)(dian)腦需(xu)要50-60Whr(5,000-6,000mAh)的(de)能(neng)(neng)量(liang)，因此必須給(gei)串(chuan)聯的(de)每個(ge)電(dian)(dian)池(chi)(chi)并(bing)聯三(san)個(ge)電(dian)(dian)池(chi)(chi)。

     電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)均(jun)衡是(shi)(shi)指(zhi)對串聯電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)包中(zhong)不同的電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(或(huo)電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)組)采用差(cha)分電(dian)(dian)(dian)流(liu)(liu)。串聯電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)包中(zhong)每個電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)的電(dian)(dian)(dian)流(liu)(liu)通常是(shi)(shi)一樣(yang)的，因此(ci)必(bi)須給電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)包增(zeng)加額外的元件和電(dian)(dian)(dian)路來實現(xian) 電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)均(jun)衡。只有(you)當(dang)電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)包中(zhong)的電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)是(shi)(shi)串聯的，同時(shi)(shi)串聯電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)等于(yu)或(huo)大于(yu)三級(ji)時(shi)(shi)才會考慮(lv)電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)均(jun)衡問題。當(dang)電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)包中(zhong)所有(you)電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)都滿足下(xia)面(mian)兩個條件時(shi)(shi)，便實現(xian)了電(dian)(dian)(dian)池(chi)(chi)(chi)(chi)均(jun)衡：

1. 如果所(suo)(suo)有(you)(you)電(dian)(dian)(dian)(dian)(dian)(dian)池的(de)(de)(de)容(rong)量(liang)相同，那么當(dang)它們(men)的(de)(de)(de)相對充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)狀態(tai)一(yi)樣時便(bian)實現了電(dian)(dian)(dian)(dian)(dian)(dian)池均衡。SOC通(tong)(tong)常(chang)(chang)以(yi)當(dang)前容(rong)量(liang)與(yu)額定容(rong)量(liang)的(de)(de)(de)百分比(bi)來(lai)表示，因此，開路電(dian)(dian)(dian)(dian)(dian)(dian)壓(OCV)可(ke)作為SOC的(de)(de)(de)一(yi)個衡量(liang)標準。如果一(yi)個不均衡電(dian)(dian)(dian)(dian)(dian)(dian)池包中的(de)(de)(de)所(suo)(suo)有(you)(you)電(dian)(dian)(dian)(dian)(dian)(dian)池可(ke)以(yi)通(tong)(tong)過(guo)(guo)差分充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)達(da)到滿容(rong)量(liang)(均衡點)，它們(men)便(bian)可(ke)以(yi)進行正常(chang)(chang)的(de)(de)(de)充(chong)(chong)放(fang)電(dian)(dian)(dian)(dian)(dian)(dian)而無需任何(he)額外的(de)(de)(de)調整(zheng)(zheng)，通(tong)(tong)常(chang)(chang)這(zhe)(zhe)種調整(zheng)(zheng)是一(yi)次(ci)性的(de)(de)(de)。用(yong)戶在使用(yong)新電(dian)(dian)(dian)(dian)(dian)(dian)池時，通(tong)(tong)常(chang)(chang)需要(yao)求對電(dian)(dian)(dian)(dian)(dian)(dian)池進行長時間充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)，這(zhe)(zhe)個過(guo)(guo)程實際上包括一(yi)次(ci)完整(zheng)(zheng)的(de)(de)(de)放(fang)-充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)。該(gai)過(guo)(guo)程使負載(zai)最小化(hua)，并使電(dian)(dian)(dian)(dian)(dian)(dian)池充(chong)(chong) 電(dian)(dian)(dian)(dian)(dian)(dian)時間最長，降(jiang)低對電(dian)(dian)(dian)(dian)(dian)(dian)池均衡電(dian)(dian)(dian)(dian)(dian)(dian)路的(de)(de)(de)要(yao)求。

2. 如果電(dian)(dian)池的(de)(de)容量(liang)(liang)不同(tong)，當SOC相同(tong)時(shi)也(ye)認為(wei)它們是(shi)均衡的(de)(de)。但SOC只是(shi)一個(ge)(ge)相對值，每(mei)個(ge)(ge)電(dian)(dian)池容量(liang)(liang)的(de)(de)絕對值是(shi)不同(tong)的(de)(de)。為(wei)了使容量(liang)(liang)不同(tong)的(de)(de)電(dian)(dian)池的(de)(de)SOC相同(tong)，每(mei)次對串聯電(dian)(dian)池進行充放電(dian)(dian)時(shi)都必須使用差分電(dian)(dian)流。正常(chang)充放電(dian)(dian)的(de)(de)時(shi)間(jian)比初次充放電(dian)(dian)更(geng)短(duan)，并(bing)需要更(geng)大的(de)(de)電(dian)(dian)流。

     當電(dian)(dian)池(chi)(chi)(chi)包(bao)中(zhong)的電(dian)(dian)池(chi)(chi)(chi)不(bu)均衡時，它的可用(yong)容量將減少，串聯電(dian)(dian)池(chi)(chi)(chi)包(bao)中(zhong)容量最低的電(dian)(dian)池(chi)(chi)(chi)將決定電(dian)(dian)池(chi)(chi)(chi)包(bao)的總容量。在不(bu)均衡電(dian)(dian)池(chi)(chi)(chi)包(bao)中(zhong)，一(yi)個或(huo)幾個電(dian)(dian)池(chi)(chi)(chi)會在其(qi)它電(dian)(dian)池(chi)(chi)(chi)尚需(xu)充電(dian)(dian)時便已(yi)達到最大(da)容量。而(er)在放電(dian)(dian)時，未完全充電(dian)(dian)的電(dian)(dian)池(chi)(chi)(chi)又會比其(qi)它電(dian)(dian)池(chi)(chi)(chi)先放完電(dian)(dian)，使(shi)電(dian)(dian)池(chi)(chi)(chi)包(bao)因電(dian)(dian)壓不(bu)足而(er)提(ti)前停止供電(dian)(dian)。

通常，電池之間容量的差(cha)異低(di)于3%。如(ru)果串(chuan)聯鋰電池包的某(mou)個電池不(bu)合標準，或者在(zai)封裝前放(fang)置過久，在(zai)充電器(qi)充滿電后電壓(ya)差(cha)可達150mV，從而使(shi)電池包的總容量下(xia)降13-18%。

SOC均衡處理

如果電池(chi)(chi)包中所(suo)有(you)電池(chi)(chi)的容量相(xiang)同，我(wo)們便采用SOC均衡處(chu)理(li)。當所(suo)有(you)電池(chi)(chi)的SOC值相(xiang)同時我(wo)們認為(wei)電池(chi)(chi)是均衡的。

單個電(dian)池的充電(dian)狀態定義為(wei)：

SOC=C/CTOTAL%

單個電池的(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電(dian)，并(bing)在電(dian)池充電(dian)器(qi)充電(dian)過程中(zhong)的不同(tong)時間進(jin)行電(dian)流(liu)測量，直(zhi)到(dao)(dao)達到(dao)(dao)4.20V的開路電(dian)壓。最佳(jia)性能(neng)電(dian)池在該狀態下的SOC為(wei)100%，SOC為(wei)50%的OCV電(dian)壓通常稱為(wei)VMID，其典型值為(wei)3.67V。

為了(le)給容量不同的電(dian)(dian)(dian)池(chi)充(chong)電(dian)(dian)(dian)使(shi)它們達到同樣(yang)的SOC，要求一些電(dian)(dian)(dian)池(chi)的充(chong)/放電(dian)(dian)(dian)量必(bi)須比其它電(dian)(dian)(dian)池(chi)多，這(zhe)必(bi)須使(shi)用差(cha)分電(dian)(dian)(dian)流。我們將這(zhe)個過程稱之為容量/能(neng)量最大(da)化。

容量/能量最大化

容量(liang)(liang)/能(neng)(neng)量(liang)(liang)最(zui)大(da)化是(shi)指將(jiang)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)包中所有串(chuan)聯電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)設(she)置為相(xiang)同的(de)(de)(de)SOC，即(ji)(ji)使(shi)(shi)它們的(de)(de)(de)容量(liang)(liang)不(bu)同。在所有時間(jian)內管理SOC，使(shi)(shi)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)包的(de)(de)(de)輸出能(neng)(neng)量(liang)(liang)達(da)到最(zui)大(da)。為了(le)使(shi)(shi)輸出能(neng)(neng)量(liang)(liang)最(zui)大(da)化，所有的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)都必須充滿電(dian)(dian)(dian)(dian)(dian)。即(ji)(ji)，所有電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)的(de)(de)(de)SOC必須為100%。如果電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)的(de)(de)(de)容量(liang)(liang)不(bu)同，一(yi)(yi)些電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)的(de)(de)(de)充/放(fang)電(dian)(dian)(dian)(dian)(dian)就(jiu)會比其它電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)更多。例如，假設(she)一(yi)(yi)個電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)包有三個串(chuan)聯電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)，C1＞C2=C3。均衡這個電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)包的(de)(de)(de)唯一(yi)(yi)方(fang)法是(shi)給(gei)容量(liang)(liang)較高的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(C1)施加一(yi)(yi)個差分充電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)。

在電池(chi)包(bao)放電時(shi)(shi)也必(bi)須如此，否則當容量(liang)最小(xiao)的電池(chi)達到關斷電壓(ya)時(shi)(shi)，整(zheng)個電池(chi)包(bao)便會(hui)停(ting)止放電，而(er)此時(shi)(shi)其(qi)(qi)它電池(chi)仍有剩余容量(liang)，這樣使總容量(liang)降(jiang)低。長此以往(wang)，容量(liang)最小(xiao)的電池(chi)便會(hui)比其(qi)(qi)它電池(chi)性能衰退更快，經(jing)過多(duo)個充(chong)/放電周期后將加速容量(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。
通常(chang)圓柱形鋰(li)離(li)子電池(cylindrical cell)的質量控(kong)制通常(chang)都較(jiao)好，電池容(rong)量差(cha)別(bie)不超過(guo)(guo)±3%。輸(shu)入容(rong)量基本(ben)上比較(jiao)精確(que)，差(cha)別(bie)不超過(guo)(guo)幾個mAs(毫安?秒)。因此(ci)，電池容(rong)量絕對值也基本(ben)準確(que)，SOC的差(cha)異在幾個百分點以內。