為了(le)給(gei)設備提供足(zu)夠的電(dian)(dian)(dian)壓(ya)，鋰電(dian)(dian)(dian)池(chi)包(bao)通常由多個(ge)電(dian)(dian)(dian)池(chi)串聯(lian)而(er)成，但是如果電(dian)(dian)(dian)池(chi)之間的容量失(shi)配(pei)便會影響整個(ge)電(dian)(dian)(dian)池(chi)包(bao)的容量。為此，我們需要(yao)對失(shi)配(pei)的電(dian)(dian)(dian)池(chi)進行均衡。本文(wen)討論(lun)了(le)電(dian)(dian)(dian)池(chi)均衡的概念和一(yi)些注意事(shi)項(xiang)。

      鋰電池包通常(chang)由(you)(you)一個或幾個電(dian)池(chi)(chi)組(zu)并(bing)聯，每(mei)個電(dian)池(chi)(chi)組(zu)由(you)(you)3到4個電(dian)池(chi)(chi)串(chuan)聯構成。這(zhe)種組(zu)合方式能同時滿足筆記本電(dian)腦(nao)、醫療設備(bei)、測試儀器及(ji)工業應(ying)(ying)用所需(xu)的(de)(de)電(dian)壓和功率要求。然而(er)，這(zhe)種應(ying)(ying)用普遍的(de)(de)配置通常(chang)并(bing)不能發揮其(qi)最大功效，因為(wei)如果某個串(chuan)聯電(dian)池(chi)(chi)的(de)(de)容量與其(qi)它電(dian)池(chi)(chi)不匹配將會(hui)降低整個電(dian)池(chi)(chi)包的(de)(de)容量。

電(dian)(dian)(dian)池(chi)(chi)容(rong)(rong)量(liang)的(de)(de)不匹(pi)配(pei)(pei)包(bao)括充電(dian)(dian)(dian)狀態(tai)(SOC)失(shi)配(pei)(pei)和容(rong)(rong)量(liang)/能量(liang)(C/E)失(shi)配(pei)(pei)。在兩種(zhong)情況下，電(dian)(dian)(dian)池(chi)(chi)包(bao)的(de)(de)總容(rong)(rong)量(liang)都只(zhi)能達到最(zui)弱電(dian)(dian)(dian)池(chi)(chi)的(de)(de)容(rong)(rong)量(liang)。在大多數情況下，引起電(dian)(dian)(dian)池(chi)(chi)失(shi)配(pei)(pei)的(de)(de)原因(yin)是(shi)工(gong)(gong)藝(yi)控制和檢測手段的(de)(de)不完(wan)善，而(er)不是(shi)鋰離子(zi)本(ben)身的(de)(de)化學屬性變化。棱柱形鋰電(dian)(dian)(dian)池(chi)(chi)(LiIon prismatic cell)在生(sheng)產(chan)時需要更強的(de)(de)機械壓力(li)，電(dian)(dian)(dian)池(chi)(chi)之(zhi)間更容(rong)(rong)易產(chan)生(sheng)差異。此外，鋰離子(zi)聚合物電(dian)(dian)(dian)池(chi)(chi)也(ye)會(hui)因(yin)為采(cai)用新的(de)(de)工(gong)(gong)藝(yi)而(er)出現(xian)電(dian)(dian)(dian)池(chi)(chi)之(zhi)間的(de)(de)差異。

      采(cai)用電(dian)池(chi)均(jun)(jun)(jun)衡處理(li)技術可(ke)解決SOC和C/E失(shi)配問(wen)(wen)題(ti)，從而改(gai)進(jin)(jin)串聯鋰電(dian)池(chi)包的(de)性能(neng)。通過(guo)(guo)在(zai)初始調節過(guo)(guo)程中對電(dian)池(chi)進(jin)(jin)行均(jun)(jun)(jun)衡處理(li)可(ke)以矯正電(dian)池(chi)失(shi)配問(wen)(wen)題(ti)，此后只需在(zai)充電(dian)過(guo)(guo)程中進(jin)(jin)行均(jun)(jun)(jun)衡即可(ke)，而C/E失(shi)配則必須在(zai)充、放電(dian)過(guo)(guo)程都(dou)進(jin)(jin)行均(jun)(jun)(jun)衡。盡(jin)管對于某個電(dian)池(chi)廠商而言(yan)其產品缺陷率(lv)可(ke)能(neng)很低(di)，但為了避免出現電(dian)池(chi)使用壽命(ming) 過(guo)(guo)短的(de)問(wen)(wen)題(ti)，我們仍然(ran)有(you)必要提供進(jin)(jin)一(yi)步的(de)質量保證。

電池均衡的定義

     工(gong)作(zuo)電(dian)(dian)(dian)(dian)壓為(wei)6V 或以上的便攜式設備采(cai)用(yong)(yong)串(chuan)聯電(dian)(dian)(dian)(dian)池(chi)包供電(dian)(dian)(dian)(dian)，這種情況下電(dian)(dian)(dian)(dian)池(chi)包的總(zong)電(dian)(dian)(dian)(dian)壓為(wei)各(ge)串(chuan)聯電(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)壓之和。便攜式電(dian)(dian)(dian)(dian)腦的電(dian)(dian)(dian)(dian)池(chi)包通常由(you)三(san)、四個(ge)(ge)電(dian)(dian)(dian)(dian)池(chi)串(chuan)聯而成(cheng)，標稱電(dian)(dian)(dian)(dian)壓為(wei) 10.8V或14.4V。在大(da)多數此類(lei)應用(yong)(yong)中，單個(ge)(ge)串(chuan)聯電(dian)(dian)(dian)(dian)池(chi)包無法提供設備所(suo)需能量。目(mu)前最大(da)的電(dian)(dian)(dian)(dian)池(chi)(如18650)可(ke)提供2,000mAh(毫安 ?小時)能量，而電(dian)(dian)(dian)(dian)腦需要(yao)50-60Whr(5,000-6,000mAh)的能量，因此必(bi)須給(gei)串(chuan)聯的每個(ge)(ge)電(dian)(dian)(dian)(dian)池(chi)并聯三(san)個(ge)(ge)電(dian)(dian)(dian)(dian)池(chi)。

     電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)均(jun)衡是(shi)(shi)指對串聯(lian)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)包中不同的(de)(de)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(或電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)組)采用差分電(dian)(dian)(dian)(dian)流(liu)(liu)。串聯(lian)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)包中每(mei)個電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)的(de)(de)電(dian)(dian)(dian)(dian)流(liu)(liu)通常(chang)是(shi)(shi)一(yi)樣的(de)(de)，因此必須給電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)包增(zeng)加(jia)額外的(de)(de)元(yuan)件和電(dian)(dian)(dian)(dian)路來(lai)實現 電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)均(jun)衡。只有(you)當電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)包中的(de)(de)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)是(shi)(shi)串聯(lian)的(de)(de)，同時(shi)串聯(lian)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)等(deng)于或大于三(san)級時(shi)才(cai)會考慮(lv)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)均(jun)衡問題。當電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)包中所有(you)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)都滿足下面(mian)兩(liang)個條件時(shi)，便(bian)實現了電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)均(jun)衡：

1. 如(ru)果所有電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)的(de)(de)(de)(de)容量(liang)相同，那么當它們的(de)(de)(de)(de)相對充(chong)(chong)電(dian)(dian)(dian)(dian)狀態(tai)一(yi)(yi)樣時(shi)(shi)便(bian)實(shi)現了電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)均衡(heng)。SOC通(tong)常(chang)以(yi)當前容量(liang)與額定(ding)容量(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)作為SOC的(de)(de)(de)(de)一(yi)(yi)個衡(heng)量(liang)標(biao)準。如(ru)果一(yi)(yi)個不均衡(heng)電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)包中的(de)(de)(de)(de)所有電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)可(ke)以(yi)通(tong)過(guo)差分充(chong)(chong)電(dian)(dian)(dian)(dian)達(da)到滿容量(liang)(均衡(heng)點)，它們便(bian)可(ke)以(yi)進(jin)行(xing)正常(chang)的(de)(de)(de)(de)充(chong)(chong)放電(dian)(dian)(dian)(dian)而無需(xu)任(ren)何額外的(de)(de)(de)(de)調(diao)(diao)整，通(tong)常(chang)這(zhe)種調(diao)(diao)整是一(yi)(yi)次性的(de)(de)(de)(de)。用(yong)戶在使用(yong)新電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)時(shi)(shi)，通(tong)常(chang)需(xu)要求(qiu)對電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)進(jin)行(xing)長(chang)時(shi)(shi)間充(chong)(chong)電(dian)(dian)(dian)(dian)，這(zhe)個過(guo)程實(shi)際上包括一(yi)(yi)次完整的(de)(de)(de)(de)放-充(chong)(chong)電(dian)(dian)(dian)(dian)。該過(guo)程使負載最小化，并(bing)使電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)充(chong)(chong) 電(dian)(dian)(dian)(dian)時(shi)(shi)間最長(chang)，降低對電(dian)(dian)(dian)(dian)池(chi)(chi)(chi)均衡(heng)電(dian)(dian)(dian)(dian)路的(de)(de)(de)(de)要求(qiu)。

2. 如果電(dian)(dian)(dian)池(chi)的(de)容量(liang)不同(tong)(tong)(tong)，當SOC相(xiang)同(tong)(tong)(tong)時也認為它們是均衡的(de)。但SOC只(zhi)是一個(ge)相(xiang)對(dui)(dui)值，每個(ge)電(dian)(dian)(dian)池(chi)容量(liang)的(de)絕對(dui)(dui)值是不同(tong)(tong)(tong)的(de)。為了使(shi)容量(liang)不同(tong)(tong)(tong)的(de)電(dian)(dian)(dian)池(chi)的(de)SOC相(xiang)同(tong)(tong)(tong)，每次對(dui)(dui)串聯(lian)電(dian)(dian)(dian)池(chi)進行(xing)充放(fang)電(dian)(dian)(dian)時都必須使(shi)用(yong)差分電(dian)(dian)(dian)流。正常(chang)充放(fang)電(dian)(dian)(dian)的(de)時間(jian)比初次充放(fang)電(dian)(dian)(dian)更短，并需要(yao)更大的(de)電(dian)(dian)(dian)流。

     當電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)包中(zhong)的電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)不均(jun)衡(heng)時(shi)，它的可用容量(liang)(liang)將減(jian)少，串聯電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)包中(zhong)容量(liang)(liang)最低的電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)將決定電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)包的總(zong)容量(liang)(liang)。在(zai)不均(jun)衡(heng)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)包中(zhong)，一(yi)個或幾個電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)會在(zai)其它電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)尚需充電(dian)(dian)(dian)(dian)(dian)時(shi)便已達(da)到最大容量(liang)(liang)。而在(zai)放(fang)電(dian)(dian)(dian)(dian)(dian)時(shi)，未完(wan)全充電(dian)(dian)(dian)(dian)(dian)的電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)又(you)會比其它電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)先放(fang)完(wan)電(dian)(dian)(dian)(dian)(dian)，使電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)包因電(dian)(dian)(dian)(dian)(dian)壓不足而提前停(ting)止供電(dian)(dian)(dian)(dian)(dian)。

通常，電池之間容(rong)量的(de)差(cha)異低于3%。如果串聯鋰電池包(bao)(bao)的(de)某(mou)個電池不(bu)合(he)標(biao)準，或者在封(feng)裝前放置過久，在充電器(qi)充滿電后電壓(ya)差(cha)可達(da)150mV，從而(er)使電池包(bao)(bao)的(de)總(zong)容(rong)量下降13-18%。

SOC均衡處理

如(ru)果電(dian)(dian)池包中所有電(dian)(dian)池的容量(liang)相(xiang)同，我們(men)便(bian)采用SOC均衡(heng)處理(li)。當所有電(dian)(dian)池的SOC值相(xiang)同時我們(men)認(ren)為電(dian)(dian)池是(shi)均衡(heng)的。

單個電池的充電狀態定義為：

SOC=C/CTOTAL%

單個(ge)電池的容量(liang)定義為(wei)：

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)(dian)，并在(zai)電(dian)(dian)池充電(dian)(dian)器充電(dian)(dian)過程中的(de)不同時間(jian)進行電(dian)(dian)流測量，直到達到4.20V的(de)開路電(dian)(dian)壓。最(zui)佳性能電(dian)(dian)池在(zai)該狀態下的(de)SOC為100%，SOC為50%的(de)OCV電(dian)(dian)壓通(tong)常稱為VMID，其典型值為3.67V。

為了(le)給容(rong)量不(bu)同的(de)電(dian)(dian)池(chi)充(chong)(chong)電(dian)(dian)使它(ta)們達到同樣的(de)SOC，要(yao)求一些電(dian)(dian)池(chi)的(de)充(chong)(chong)/放電(dian)(dian)量必須比其它(ta)電(dian)(dian)池(chi)多(duo)，這(zhe)必須使用差(cha)分電(dian)(dian)流。我們將這(zhe)個過程稱之為容(rong)量/能(neng)量最(zui)大化。

容量/能量最大化

容(rong)(rong)量(liang)(liang)/能(neng)量(liang)(liang)最(zui)大(da)化是指將(jiang)電(dian)池(chi)(chi)(chi)包中所(suo)有(you)串聯(lian)電(dian)池(chi)(chi)(chi)設置為相同的(de)(de)SOC，即(ji)使它們的(de)(de)容(rong)(rong)量(liang)(liang)不(bu)同。在所(suo)有(you)時間內管(guan)理SOC，使電(dian)池(chi)(chi)(chi)包的(de)(de)輸(shu)出能(neng)量(liang)(liang)達到(dao)最(zui)大(da)。為了使輸(shu)出能(neng)量(liang)(liang)最(zui)大(da)化，所(suo)有(you)的(de)(de)電(dian)池(chi)(chi)(chi)都必須(xu)充滿電(dian)。即(ji)，所(suo)有(you)電(dian)池(chi)(chi)(chi)的(de)(de)SOC必須(xu)為100%。如果電(dian)池(chi)(chi)(chi)的(de)(de)容(rong)(rong)量(liang)(liang)不(bu)同，一些電(dian)池(chi)(chi)(chi)的(de)(de)充/放電(dian)就會比其(qi)它電(dian)池(chi)(chi)(chi)更(geng)多。例如，假設一個電(dian)池(chi)(chi)(chi)包有(you)三個串聯(lian)電(dian)池(chi)(chi)(chi)，C1＞C2=C3。均衡這個電(dian)池(chi)(chi)(chi)包的(de)(de)唯(wei)一方(fang)法是給(gei)容(rong)(rong)量(liang)(liang)較高的(de)(de)電(dian)池(chi)(chi)(chi)(C1)施(shi)加一個差分充電(dian)電(dian)流。

在電(dian)(dian)池包(bao)放電(dian)(dian)時(shi)也必須如此(ci)，否則當容(rong)量最小的電(dian)(dian)池達到關斷電(dian)(dian)壓時(shi)，整個(ge)(ge)電(dian)(dian)池包(bao)便會(hui)停止放電(dian)(dian)，而此(ci)時(shi)其它(ta)電(dian)(dian)池仍有剩余容(rong)量，這樣(yang)使總容(rong)量降低。長此(ci)以往，容(rong)量最小的電(dian)(dian)池便會(hui)比其它(ta)電(dian)(dian)池性能(neng)衰退更快，經(jing)過多(duo)個(ge)(ge)充/放電(dian)(dian)周期后將加速容(rong)量損耗(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(tong)常圓柱形鋰(li)離子電(dian)池(chi)(chi)(cylindrical cell)的(de)質量控制(zhi)通(tong)常都較好，電(dian)池(chi)(chi)容量差(cha)別(bie)(bie)不超過±3%。輸入容量基(ji)本上比較精確，差(cha)別(bie)(bie)不超過幾(ji)個mAs(毫安?秒)。因此，電(dian)池(chi)(chi)容量絕對值(zhi)也基(ji)本準確，SOC的(de)差(cha)異在(zai)幾(ji)個百分點以內。