為(wei)了給設(she)備提供(gong)足夠的電(dian)(dian)(dian)壓，鋰電(dian)(dian)(dian)池(chi)包通常由(you)多個(ge)電(dian)(dian)(dian)池(chi)串聯而成(cheng)，但(dan)是(shi)如果(guo)電(dian)(dian)(dian)池(chi)之(zhi)間(jian)的容量失配(pei)便會影響整個(ge)電(dian)(dian)(dian)池(chi)包的容量。為(wei)此，我們需要對失配(pei)的電(dian)(dian)(dian)池(chi)進行均衡。本文討論了電(dian)(dian)(dian)池(chi)均衡的概念和一些注(zhu)意事項(xiang)。

      鋰電池包通常由一(yi)個或幾個電(dian)池(chi)(chi)(chi)組并(bing)聯，每個電(dian)池(chi)(chi)(chi)組由3到4個電(dian)池(chi)(chi)(chi)串(chuan)聯構成。這種(zhong)組合方(fang)式能同時滿足筆記本電(dian)腦、醫療設備、測試儀器(qi)及(ji)工業應用所需(xu)的(de)電(dian)壓(ya)和功率(lv)要求(qiu)。然而(er)，這種(zhong)應用普遍的(de)配(pei)置通常并(bing)不能發(fa)揮其最大功效，因為如果某個串(chuan)聯電(dian)池(chi)(chi)(chi)的(de)容量與(yu)其它電(dian)池(chi)(chi)(chi)不匹配(pei)將會降低整個電(dian)池(chi)(chi)(chi)包的(de)容量。

電(dian)(dian)(dian)池(chi)容(rong)量(liang)的(de)不匹(pi)配包括充電(dian)(dian)(dian)狀態(SOC)失(shi)配和容(rong)量(liang)/能(neng)量(liang)(C/E)失(shi)配。在(zai)兩種情況下，電(dian)(dian)(dian)池(chi)包的(de)總容(rong)量(liang)都(dou)只(zhi)能(neng)達到最弱電(dian)(dian)(dian)池(chi)的(de)容(rong)量(liang)。在(zai)大多數情況下，引起電(dian)(dian)(dian)池(chi)失(shi)配的(de)原因(yin)(yin)是工藝控制和檢測手段的(de)不完善，而不是鋰(li)離子本(ben)身的(de)化(hua)學屬(shu)性變化(hua)。棱柱形鋰(li)電(dian)(dian)(dian)池(chi)(LiIon prismatic cell)在(zai)生產時需要更(geng)強的(de)機械壓力，電(dian)(dian)(dian)池(chi)之間(jian)更(geng)容(rong)易(yi)產生差異。此外，鋰(li)離子聚合(he)物(wu)電(dian)(dian)(dian)池(chi)也會因(yin)(yin)為采用新(xin)的(de)工藝而出現電(dian)(dian)(dian)池(chi)之間(jian)的(de)差異。

      采用(yong)電(dian)(dian)池均衡(heng)處(chu)理技(ji)術(shu)可解決(jue)SOC和C/E失配(pei)問題，從而(er)改進串聯鋰電(dian)(dian)池包的(de)性能。通過在初始調節過程中對(dui)電(dian)(dian)池進行均衡(heng)處(chu)理可以矯正電(dian)(dian)池失配(pei)問題，此后只需在充(chong)電(dian)(dian)過程中進行均衡(heng)即可，而(er)C/E失配(pei)則(ze)必須在充(chong)、放電(dian)(dian)過程都進行均衡(heng)。盡管對(dui)于某個(ge)電(dian)(dian)池廠商而(er)言其產品缺陷率(lv)可能很低，但為了避免出現電(dian)(dian)池使用(yong)壽命 過短的(de)問題，我們仍(reng)然(ran)有必要提供進一步的(de)質量(liang)保證。

電池均衡的定義

     工作電(dian)(dian)(dian)(dian)壓(ya)為6V 或以上的(de)便攜式設備采用串(chuan)聯電(dian)(dian)(dian)(dian)池(chi)包供(gong)電(dian)(dian)(dian)(dian)，這種情況下電(dian)(dian)(dian)(dian)池(chi)包的(de)總(zong)電(dian)(dian)(dian)(dian)壓(ya)為各串(chuan)聯電(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)壓(ya)之和。便攜式電(dian)(dian)(dian)(dian)腦的(de)電(dian)(dian)(dian)(dian)池(chi)包通常由三、四(si)個電(dian)(dian)(dian)(dian)池(chi)串(chuan)聯而成(cheng)，標(biao)稱電(dian)(dian)(dian)(dian)壓(ya)為 10.8V或14.4V。在(zai)大多數此(ci)類應用中，單(dan)個串(chuan)聯電(dian)(dian)(dian)(dian)池(chi)包無法提供(gong)設備所需能(neng)(neng)量。目前最大的(de)電(dian)(dian)(dian)(dian)池(chi)(如18650)可提供(gong)2,000mAh(毫安 ?小時(shi))能(neng)(neng)量，而電(dian)(dian)(dian)(dian)腦需要50-60Whr(5,000-6,000mAh)的(de)能(neng)(neng)量，因此(ci)必(bi)須給(gei)串(chuan)聯的(de)每個電(dian)(dian)(dian)(dian)池(chi)并聯三個電(dian)(dian)(dian)(dian)池(chi)。

     電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)均衡是(shi)指對串(chuan)聯電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包中不同的(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(yong)差分電(dian)(dian)(dian)(dian)(dian)(dian)流。串(chuan)聯電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包中每個電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)流通常是(shi)一樣的(de)，因(yin)此必須給電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包增(zeng)加額外的(de)元(yuan)件和(he)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)來實現 電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)均衡。只有當電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包中的(de)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)是(shi)串(chuan)聯的(de)，同時(shi)(shi)串(chuan)聯電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)等(deng)于(yu)或大(da)于(yu)三級(ji)時(shi)(shi)才會考(kao)慮(lv)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)均衡問(wen)題。當電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包中所(suo)有電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)都滿(man)足下面(mian)兩個條件時(shi)(shi)，便實現了電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)均衡：

1. 如果(guo)(guo)所有電(dian)(dian)(dian)(dian)池的(de)(de)(de)(de)容(rong)(rong)量(liang)(liang)相(xiang)同，那么當它們(men)的(de)(de)(de)(de)相(xiang)對(dui)充(chong)電(dian)(dian)(dian)(dian)狀態一(yi)(yi)樣時便(bian)實現了(le)電(dian)(dian)(dian)(dian)池均(jun)(jun)衡(heng)。SOC通(tong)(tong)常以當前容(rong)(rong)量(liang)(liang)與(yu)額定(ding)容(rong)(rong)量(liang)(liang)的(de)(de)(de)(de)百分比來表示，因此，開(kai)路電(dian)(dian)(dian)(dian)壓(OCV)可(ke)(ke)作為SOC的(de)(de)(de)(de)一(yi)(yi)個(ge)衡(heng)量(liang)(liang)標(biao)準。如果(guo)(guo)一(yi)(yi)個(ge)不均(jun)(jun)衡(heng)電(dian)(dian)(dian)(dian)池包(bao)中的(de)(de)(de)(de)所有電(dian)(dian)(dian)(dian)池可(ke)(ke)以通(tong)(tong)過差分充(chong)電(dian)(dian)(dian)(dian)達(da)到滿(man)容(rong)(rong)量(liang)(liang)(均(jun)(jun)衡(heng)點)，它們(men)便(bian)可(ke)(ke)以進(jin)(jin)行正常的(de)(de)(de)(de)充(chong)放電(dian)(dian)(dian)(dian)而無需任(ren)何額外的(de)(de)(de)(de)調(diao)整(zheng)(zheng)，通(tong)(tong)常這種調(diao)整(zheng)(zheng)是一(yi)(yi)次(ci)(ci)性的(de)(de)(de)(de)。用(yong)戶在使(shi)用(yong)新電(dian)(dian)(dian)(dian)池時，通(tong)(tong)常需要(yao)求對(dui)電(dian)(dian)(dian)(dian)池進(jin)(jin)行長(chang)時間充(chong)電(dian)(dian)(dian)(dian)，這個(ge)過程實際(ji)上包(bao)括一(yi)(yi)次(ci)(ci)完整(zheng)(zheng)的(de)(de)(de)(de)放-充(chong)電(dian)(dian)(dian)(dian)。該過程使(shi)負載(zai)最小(xiao)化，并使(shi)電(dian)(dian)(dian)(dian)池充(chong) 電(dian)(dian)(dian)(dian)時間最長(chang)，降低(di)對(dui)電(dian)(dian)(dian)(dian)池均(jun)(jun)衡(heng)電(dian)(dian)(dian)(dian)路的(de)(de)(de)(de)要(yao)求。

2. 如果電(dian)池(chi)的容(rong)量不(bu)同(tong)(tong)(tong)(tong)，當SOC相同(tong)(tong)(tong)(tong)時(shi)(shi)也認為它們(men)是均衡的。但SOC只(zhi)是一個相對(dui)(dui)值，每(mei)個電(dian)池(chi)容(rong)量的絕對(dui)(dui)值是不(bu)同(tong)(tong)(tong)(tong)的。為了使容(rong)量不(bu)同(tong)(tong)(tong)(tong)的電(dian)池(chi)的SOC相同(tong)(tong)(tong)(tong)，每(mei)次(ci)對(dui)(dui)串聯電(dian)池(chi)進行充(chong)(chong)放(fang)(fang)電(dian)時(shi)(shi)都必須使用差分電(dian)流。正常(chang)充(chong)(chong)放(fang)(fang)電(dian)的時(shi)(shi)間比初次(ci)充(chong)(chong)放(fang)(fang)電(dian)更(geng)(geng)短(duan)，并需要更(geng)(geng)大的電(dian)流。

     當電(dian)(dian)(dian)(dian)池(chi)(chi)包中(zhong)的(de)電(dian)(dian)(dian)(dian)池(chi)(chi)不(bu)(bu)均衡時，它的(de)可用容(rong)量(liang)將減少(shao)，串聯電(dian)(dian)(dian)(dian)池(chi)(chi)包中(zhong)容(rong)量(liang)最低(di)的(de)電(dian)(dian)(dian)(dian)池(chi)(chi)將決定電(dian)(dian)(dian)(dian)池(chi)(chi)包的(de)總容(rong)量(liang)。在不(bu)(bu)均衡電(dian)(dian)(dian)(dian)池(chi)(chi)包中(zhong)，一個或幾個電(dian)(dian)(dian)(dian)池(chi)(chi)會(hui)在其(qi)它電(dian)(dian)(dian)(dian)池(chi)(chi)尚需充(chong)(chong)電(dian)(dian)(dian)(dian)時便已達到最大容(rong)量(liang)。而在放電(dian)(dian)(dian)(dian)時，未完全充(chong)(chong)電(dian)(dian)(dian)(dian)的(de)電(dian)(dian)(dian)(dian)池(chi)(chi)又會(hui)比其(qi)它電(dian)(dian)(dian)(dian)池(chi)(chi)先放完電(dian)(dian)(dian)(dian)，使電(dian)(dian)(dian)(dian)池(chi)(chi)包因電(dian)(dian)(dian)(dian)壓不(bu)(bu)足(zu)而提前(qian)停(ting)止供電(dian)(dian)(dian)(dian)。

通常(chang)，電(dian)池之間(jian)容量(liang)的(de)差(cha)異低(di)于3%。如果(guo)串聯鋰電(dian)池包的(de)某(mou)個(ge)電(dian)池不(bu)合標準(zhun)，或者在封(feng)裝前放置(zhi)過久，在充(chong)電(dian)器充(chong)滿電(dian)后電(dian)壓(ya)差(cha)可達150mV，從而使電(dian)池包的(de)總(zong)容量(liang)下降13-18%。

SOC均衡處理

如果(guo)電(dian)(dian)(dian)池包中所有電(dian)(dian)(dian)池的容量(liang)相(xiang)同，我(wo)們便采用(yong)SOC均衡(heng)處理。當所有電(dian)(dian)(dian)池的SOC值相(xiang)同時我(wo)們認為電(dian)(dian)(dian)池是(shi)均衡(heng)的。

單個電池的充電狀態定義(yi)為：

SOC=C/CTOTAL%

單個電(dian)池的容量定(ding)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)充電器充電過程中(zhong)的不(bu)同時間進(jin)行電流測量(liang)，直(zhi)到(dao)達到(dao)4.20V的開路電壓。最(zui)佳(jia)性能電池(chi)在(zai)該狀態下的SOC為(wei)(wei)100%，SOC為(wei)(wei)50%的OCV電壓通常稱為(wei)(wei)VMID，其典(dian)型(xing)值為(wei)(wei)3.67V。

為了給容量不同的(de)電(dian)(dian)池充(chong)(chong)電(dian)(dian)使(shi)它(ta)們(men)(men)達(da)到(dao)同樣(yang)的(de)SOC，要求一些電(dian)(dian)池的(de)充(chong)(chong)/放電(dian)(dian)量必須比其它(ta)電(dian)(dian)池多(duo)，這(zhe)必須使(shi)用差分電(dian)(dian)流。我們(men)(men)將這(zhe)個(ge)過程稱(cheng)之為容量/能量最大化。

容量/能量最大化

容(rong)(rong)量/能(neng)量最大化是指(zhi)將(jiang)電(dian)(dian)池(chi)包(bao)(bao)中所(suo)有(you)串聯電(dian)(dian)池(chi)設(she)置為相同的(de)(de)(de)SOC，即使(shi)它們的(de)(de)(de)容(rong)(rong)量不(bu)同。在(zai)所(suo)有(you)時間(jian)內管理(li)SOC，使(shi)電(dian)(dian)池(chi)包(bao)(bao)的(de)(de)(de)輸出能(neng)量達到最大。為了使(shi)輸出能(neng)量最大化，所(suo)有(you)的(de)(de)(de)電(dian)(dian)池(chi)都必(bi)(bi)須(xu)充滿電(dian)(dian)。即，所(suo)有(you)電(dian)(dian)池(chi)的(de)(de)(de)SOC必(bi)(bi)須(xu)為100%。如(ru)果電(dian)(dian)池(chi)的(de)(de)(de)容(rong)(rong)量不(bu)同，一些電(dian)(dian)池(chi)的(de)(de)(de)充/放(fang)電(dian)(dian)就會比其它電(dian)(dian)池(chi)更多(duo)。例如(ru)，假設(she)一個(ge)電(dian)(dian)池(chi)包(bao)(bao)有(you)三個(ge)串聯電(dian)(dian)池(chi)，C1＞C2=C3。均衡這個(ge)電(dian)(dian)池(chi)包(bao)(bao)的(de)(de)(de)唯一方法是給容(rong)(rong)量較高的(de)(de)(de)電(dian)(dian)池(chi)(C1)施加一個(ge)差分充電(dian)(dian)電(dian)(dian)流(liu)。

在電(dian)池(chi)包放電(dian)時(shi)也(ye)必須(xu)如(ru)此，否則當(dang)容(rong)量(liang)最小(xiao)的(de)電(dian)池(chi)達(da)到關斷電(dian)壓時(shi)，整(zheng)個電(dian)池(chi)包便會(hui)停(ting)止放電(dian)，而此時(shi)其它電(dian)池(chi)仍有剩余容(rong)量(liang)，這樣使總容(rong)量(liang)降低。長此以往，容(rong)量(liang)最小(xiao)的(de)電(dian)池(chi)便會(hui)比其它電(dian)池(chi)性能衰退更快，經過(guo)多個充/放電(dian)周期(qi)后(hou)將加速容(rong)量(liang)損耗(hao)。

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(yuan)柱形(xing)鋰(li)離子電池(cylindrical cell)的質量(liang)控制(zhi)通常都較好，電池容量(liang)差別不超(chao)過(guo)(guo)±3%。輸入容量(liang)基(ji)本上比較精確，差別不超(chao)過(guo)(guo)幾個mAs(毫安?秒)。因(yin)此(ci)，電池容量(liang)絕對值也基(ji)本準確，SOC的差異(yi)在幾個百分點以內。