為了給設備提供足夠的(de)(de)電(dian)(dian)壓，鋰(li)電(dian)(dian)池(chi)包通常由多個(ge)電(dian)(dian)池(chi)串聯而成，但是(shi)如果電(dian)(dian)池(chi)之(zhi)間的(de)(de)容量失配便會(hui)影響整個(ge)電(dian)(dian)池(chi)包的(de)(de)容量。為此，我們需要對失配的(de)(de)電(dian)(dian)池(chi)進(jin)行均(jun)衡(heng)。本文(wen)討(tao)論了電(dian)(dian)池(chi)均(jun)衡(heng)的(de)(de)概念和一些(xie)注意事項。

      鋰電池包通常由一(yi)個或幾個電池(chi)組并聯(lian)，每個電池(chi)組由3到4個電池(chi)串(chuan)(chuan)聯(lian)構成(cheng)。這種組合方式能同時滿足(zu)筆記本電腦(nao)、醫療設備(bei)、測試儀器及工(gong)業應(ying)用(yong)所需的電壓(ya)和功(gong)率要求(qiu)。然(ran)而，這種應(ying)用(yong)普遍的配置通常并不(bu)(bu)能發(fa)揮其(qi)最大(da)功(gong)效(xiao)，因(yin)為如(ru)果某個串(chuan)(chuan)聯(lian)電池(chi)的容量(liang)與其(qi)它(ta)電池(chi)不(bu)(bu)匹配將會降低(di)整個電池(chi)包的容量(liang)。

電(dian)(dian)池(chi)(chi)容量(liang)的不匹配(pei)(pei)包括(kuo)充電(dian)(dian)狀(zhuang)態(SOC)失(shi)(shi)配(pei)(pei)和容量(liang)/能量(liang)(C/E)失(shi)(shi)配(pei)(pei)。在(zai)兩種情況(kuang)下，電(dian)(dian)池(chi)(chi)包的總容量(liang)都只(zhi)能達到最弱電(dian)(dian)池(chi)(chi)的容量(liang)。在(zai)大多(duo)數情況(kuang)下，引起電(dian)(dian)池(chi)(chi)失(shi)(shi)配(pei)(pei)的原(yuan)因(yin)是工藝(yi)控制和檢測手段的不完善，而不是鋰(li)離(li)(li)子(zi)本身的化學(xue)屬性變化。棱柱形(xing)鋰(li)電(dian)(dian)池(chi)(chi)(LiIon prismatic cell)在(zai)生產時需要更強的機械壓力，電(dian)(dian)池(chi)(chi)之間(jian)更容易產生差異。此(ci)外(wai)，鋰(li)離(li)(li)子(zi)聚合物(wu)電(dian)(dian)池(chi)(chi)也會因(yin)為采用新的工藝(yi)而出現(xian)電(dian)(dian)池(chi)(chi)之間(jian)的差異。

      采(cai)用(yong)電(dian)池(chi)均衡處理(li)技術可解決SOC和C/E失(shi)配問題，從而改進串聯鋰(li)電(dian)池(chi)包(bao)的性能(neng)。通過(guo)在(zai)初(chu)始調節過(guo)程(cheng)中(zhong)對(dui)電(dian)池(chi)進行(xing)均衡處理(li)可以矯(jiao)正(zheng)電(dian)池(chi)失(shi)配問題，此后只需在(zai)充電(dian)過(guo)程(cheng)中(zhong)進行(xing)均衡即可，而C/E失(shi)配則(ze)必須在(zai)充、放(fang)電(dian)過(guo)程(cheng)都進行(xing)均衡。盡管對(dui)于某個電(dian)池(chi)廠商而言(yan)其(qi)產品缺(que)陷率(lv)可能(neng)很低，但為了(le)避免出現電(dian)池(chi)使用(yong)壽命 過(guo)短的問題，我們仍然有必要提供進一步的質量(liang)保證(zheng)。

電池均衡的定義

     工(gong)作(zuo)電(dian)(dian)(dian)(dian)(dian)壓(ya)為6V 或(huo)以(yi)上的(de)(de)便攜式設(she)備采用串聯(lian)電(dian)(dian)(dian)(dian)(dian)池(chi)包(bao)供電(dian)(dian)(dian)(dian)(dian)，這種情況下電(dian)(dian)(dian)(dian)(dian)池(chi)包(bao)的(de)(de)總(zong)電(dian)(dian)(dian)(dian)(dian)壓(ya)為各串聯(lian)電(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)壓(ya)之和。便攜式電(dian)(dian)(dian)(dian)(dian)腦的(de)(de)電(dian)(dian)(dian)(dian)(dian)池(chi)包(bao)通(tong)常由三、四個電(dian)(dian)(dian)(dian)(dian)池(chi)串聯(lian)而成，標稱電(dian)(dian)(dian)(dian)(dian)壓(ya)為 10.8V或(huo)14.4V。在(zai)大(da)多(duo)數(shu)此(ci)類應用中(zhong)，單(dan)個串聯(lian)電(dian)(dian)(dian)(dian)(dian)池(chi)包(bao)無法提供設(she)備所需能(neng)量(liang)。目前最(zui)大(da)的(de)(de)電(dian)(dian)(dian)(dian)(dian)池(chi)(如18650)可提供2,000mAh(毫(hao)安 ?小時(shi))能(neng)量(liang)，而電(dian)(dian)(dian)(dian)(dian)腦需要50-60Whr(5,000-6,000mAh)的(de)(de)能(neng)量(liang)，因此(ci)必須給串聯(lian)的(de)(de)每個電(dian)(dian)(dian)(dian)(dian)池(chi)并聯(lian)三個電(dian)(dian)(dian)(dian)(dian)池(chi)。

     電(dian)(dian)(dian)(dian)池(chi)均(jun)衡是(shi)指對串(chuan)聯電(dian)(dian)(dian)(dian)池(chi)包(bao)中不(bu)同的電(dian)(dian)(dian)(dian)池(chi)(或電(dian)(dian)(dian)(dian)池(chi)組)采用差分電(dian)(dian)(dian)(dian)流。串(chuan)聯電(dian)(dian)(dian)(dian)池(chi)包(bao)中每個電(dian)(dian)(dian)(dian)池(chi)的電(dian)(dian)(dian)(dian)流通(tong)常(chang)是(shi)一樣的，因此(ci)必須給電(dian)(dian)(dian)(dian)池(chi)包(bao)增加(jia)額外的元(yuan)件(jian)和電(dian)(dian)(dian)(dian)路來實現 電(dian)(dian)(dian)(dian)池(chi)均(jun)衡。只(zhi)有當電(dian)(dian)(dian)(dian)池(chi)包(bao)中的電(dian)(dian)(dian)(dian)池(chi)是(shi)串(chuan)聯的，同時串(chuan)聯電(dian)(dian)(dian)(dian)池(chi)等于或大于三級時才(cai)會考慮電(dian)(dian)(dian)(dian)池(chi)均(jun)衡問(wen)題。當電(dian)(dian)(dian)(dian)池(chi)包(bao)中所有電(dian)(dian)(dian)(dian)池(chi)都滿足(zu)下面(mian)兩個條件(jian)時，便實現了電(dian)(dian)(dian)(dian)池(chi)均(jun)衡：

1. 如果所(suo)有電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)的容量相(xiang)同，那(nei)么當它們(men)的相(xiang)對(dui)充電(dian)(dian)(dian)(dian)狀(zhuang)態(tai)一樣時便實(shi)現(xian)了電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)均(jun)衡。SOC通(tong)常以當前容量與額(e)定容量的百分比來表示，因(yin)此(ci)，開路電(dian)(dian)(dian)(dian)壓(OCV)可作為SOC的一個(ge)衡量標準(zhun)。如果一個(ge)不均(jun)衡電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包(bao)中的所(suo)有電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)可以通(tong)過差(cha)分充電(dian)(dian)(dian)(dian)達到(dao)滿容量(均(jun)衡點(dian))，它們(men)便可以進行(xing)正常的充放(fang)(fang)電(dian)(dian)(dian)(dian)而無需任何額(e)外的調整(zheng)，通(tong)常這種調整(zheng)是一次(ci)性的。用戶在使用新電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)時，通(tong)常需要求(qiu)對(dui)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)進行(xing)長時間充電(dian)(dian)(dian)(dian)，這個(ge)過程實(shi)際上(shang)包(bao)括一次(ci)完(wan)整(zheng)的放(fang)(fang)-充電(dian)(dian)(dian)(dian)。該(gai)過程使負載最(zui)小化，并(bing)使電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)充 電(dian)(dian)(dian)(dian)時間最(zui)長，降低對(dui)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)均(jun)衡電(dian)(dian)(dian)(dian)路的要求(qiu)。

2. 如果電(dian)(dian)池的(de)容量(liang)不(bu)同(tong)，當SOC相同(tong)時也認為它們是(shi)均衡的(de)。但(dan)SOC只是(shi)一個(ge)相對(dui)值，每個(ge)電(dian)(dian)池容量(liang)的(de)絕對(dui)值是(shi)不(bu)同(tong)的(de)。為了使容量(liang)不(bu)同(tong)的(de)電(dian)(dian)池的(de)SOC相同(tong)，每次對(dui)串聯電(dian)(dian)池進(jin)行充(chong)(chong)(chong)放電(dian)(dian)時都必須(xu)使用差分電(dian)(dian)流。正(zheng)常充(chong)(chong)(chong)放電(dian)(dian)的(de)時間比初次充(chong)(chong)(chong)放電(dian)(dian)更短(duan)，并需要更大(da)的(de)電(dian)(dian)流。

     當電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)包中的電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)不均衡時，它(ta)的可用容(rong)量(liang)將(jiang)減少，串聯電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)包中容(rong)量(liang)最低的電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)將(jiang)決定電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)包的總容(rong)量(liang)。在不均衡電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)包中，一個或幾個電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)會在其它(ta)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)尚需充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)時便(bian)已達到最大(da)容(rong)量(liang)。而在放(fang)電(dian)(dian)(dian)(dian)(dian)(dian)時，未完全充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)(dian)的電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)又會比(bi)其它(ta)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)先放(fang)完電(dian)(dian)(dian)(dian)(dian)(dian)，使電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)包因電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)不足而提前停止供電(dian)(dian)(dian)(dian)(dian)(dian)。

通常，電(dian)(dian)(dian)池(chi)之間(jian)容量的差異低于3%。如果串聯鋰電(dian)(dian)(dian)池(chi)包(bao)的某(mou)個(ge)電(dian)(dian)(dian)池(chi)不合標準，或者在封裝前放置(zhi)過久，在充(chong)電(dian)(dian)(dian)器充(chong)滿電(dian)(dian)(dian)后電(dian)(dian)(dian)壓差可達150mV，從(cong)而(er)使電(dian)(dian)(dian)池(chi)包(bao)的總容量下(xia)降13-18%。

SOC均衡處理

如果(guo)電(dian)池包中所有(you)電(dian)池的(de)容量相(xiang)同(tong)，我們(men)便采(cai)用SOC均衡(heng)處理。當所有(you)電(dian)池的(de)SOC值(zhi)相(xiang)同(tong)時我們(men)認為(wei)電(dian)池是均衡(heng)的(de)。

單個電池(chi)的充電狀態定義(yi)為：

SOC=C/CTOTAL%

單個電池(chi)的(de)容(rong)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)電(dian)(dian)，并在電(dian)(dian)池充(chong)電(dian)(dian)器(qi)充(chong)電(dian)(dian)過程中的(de)(de)不(bu)同(tong)時間(jian)進(jin)行(xing)電(dian)(dian)流測量，直到(dao)達到(dao)4.20V的(de)(de)開路電(dian)(dian)壓。最佳性能(neng)電(dian)(dian)池在該狀態(tai)下的(de)(de)SOC為(wei)100%，SOC為(wei)50%的(de)(de)OCV電(dian)(dian)壓通常(chang)稱為(wei)VMID，其典型值為(wei)3.67V。

為了給容量(liang)不同的電(dian)池(chi)充電(dian)使(shi)它們(men)達到(dao)同樣(yang)的SOC，要求一些(xie)電(dian)池(chi)的充/放電(dian)量(liang)必須(xu)比其它電(dian)池(chi)多，這必須(xu)使(shi)用差分電(dian)流。我們(men)將這個過程稱之為容量(liang)/能量(liang)最大(da)化。

容量/能量最大化

容(rong)量(liang)(liang)/能(neng)(neng)量(liang)(liang)最(zui)大(da)化是(shi)指(zhi)將(jiang)電(dian)(dian)池(chi)(chi)(chi)(chi)包(bao)中所有串聯電(dian)(dian)池(chi)(chi)(chi)(chi)設(she)置為相(xiang)同的(de)(de)(de)(de)SOC，即使(shi)它(ta)(ta)們的(de)(de)(de)(de)容(rong)量(liang)(liang)不同。在所有時間內管(guan)理SOC，使(shi)電(dian)(dian)池(chi)(chi)(chi)(chi)包(bao)的(de)(de)(de)(de)輸(shu)出(chu)(chu)能(neng)(neng)量(liang)(liang)達(da)到最(zui)大(da)。為了使(shi)輸(shu)出(chu)(chu)能(neng)(neng)量(liang)(liang)最(zui)大(da)化，所有的(de)(de)(de)(de)電(dian)(dian)池(chi)(chi)(chi)(chi)都必(bi)須(xu)充滿電(dian)(dian)。即，所有電(dian)(dian)池(chi)(chi)(chi)(chi)的(de)(de)(de)(de)SOC必(bi)須(xu)為100%。如(ru)果(guo)電(dian)(dian)池(chi)(chi)(chi)(chi)的(de)(de)(de)(de)容(rong)量(liang)(liang)不同，一些電(dian)(dian)池(chi)(chi)(chi)(chi)的(de)(de)(de)(de)充/放電(dian)(dian)就(jiu)會(hui)比其(qi)它(ta)(ta)電(dian)(dian)池(chi)(chi)(chi)(chi)更多(duo)。例如(ru)，假(jia)設(she)一個電(dian)(dian)池(chi)(chi)(chi)(chi)包(bao)有三個串聯電(dian)(dian)池(chi)(chi)(chi)(chi)，C1＞C2=C3。均衡這個電(dian)(dian)池(chi)(chi)(chi)(chi)包(bao)的(de)(de)(de)(de)唯一方法是(shi)給(gei)容(rong)量(liang)(liang)較高(gao)的(de)(de)(de)(de)電(dian)(dian)池(chi)(chi)(chi)(chi)(C1)施加(jia)一個差分充電(dian)(dian)電(dian)(dian)流。

在電(dian)(dian)(dian)池包放電(dian)(dian)(dian)時也必須如此，否則當容(rong)量(liang)最(zui)(zui)小(xiao)(xiao)的電(dian)(dian)(dian)池達(da)到關(guan)斷電(dian)(dian)(dian)壓時，整個電(dian)(dian)(dian)池包便會停止放電(dian)(dian)(dian)，而此時其它電(dian)(dian)(dian)池仍有剩余容(rong)量(liang)，這(zhe)樣使(shi)總(zong)容(rong)量(liang)降低。長此以往，容(rong)量(liang)最(zui)(zui)小(xiao)(xiao)的電(dian)(dian)(dian)池便會比其它電(dian)(dian)(dian)池性能衰(shuai)退(tui)更(geng)快，經過多個充(chong)/放電(dian)(dian)(dian)周期(qi)后將加速容(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(tong)常圓柱形鋰離子電池(cylindrical cell)的質量(liang)控制通(tong)常都(dou)較好，電池容量(liang)差別不超過±3%。輸入容量(liang)基(ji)(ji)本上比較精確，差別不超過幾個(ge)mAs(毫安?秒(miao))。因此，電池容量(liang)絕對(dui)值(zhi)也基(ji)(ji)本準確，SOC的差異在幾個(ge)百(bai)分點以內。