電池管理可視為是電源管理的一部分。電池管理中,電量計是負責估計電池容量。其基本功能為監測電壓,充電/放電電流和電池溫度,并估計電池荷電狀態(SOC)及電池的完全充電容量(FCC)。有兩種典型估計電池荷電狀態的方法:開路電壓法(OCV)和庫侖計量法。另一種方法是由RICHTEK所設計的動態電壓算法。

1、開路電壓(ya)法(fa)的電池電量計算(suan)方法(fa)

用開路(lu)電(dian)壓(ya)法的電(dian)量(liang)計,其實(shi)現方法較容易,可借著(zhu)開路(lu)電(dian)壓(ya)對(dui)應荷(he)電(dian)狀態查表而得到。開路(lu)電(dian)壓(ya)的假設(she)條件(jian)是(shi)電(dian)池(chi)休息約(yue)超(chao)過30分鐘時的電(dian)池(chi)端電(dian)壓(ya)。

不(bu)(bu)同(tong)(tong)的負載(zai),溫(wen)度,及電(dian)池老化情(qing)況下,電(dian)池電(dian)壓(ya)曲(qu)線也會有所(suo)不(bu)(bu)同(tong)(tong)。所(suo)以一個固(gu)定的開(kai)路電(dian)壓(ya)表(biao)無(wu)法(fa)完全(quan)代表(biao)荷(he)電(dian)狀(zhuang)態(tai);不(bu)(bu)能單靠查表(biao)來估計(ji)(ji)荷(he)電(dian)狀(zhuang)態(tai)。換言之,荷(he)電(dian)狀(zhuang)態(tai)若只靠查表(biao)來估計(ji)(ji),誤差將會很(hen)大。

同樣的電池電壓分別在充放電之下,透過開路(lu)電壓法所查得的荷電狀態(tai)差異(yi)很(hen)大。

放電(dian)(dian)(dian)時不同負載之下,荷電(dian)(dian)(dian)狀態的差異也是很大。所(suo)以基本上(shang),開(kai)路電(dian)(dian)(dian)壓法只適合對(dui)荷電(dian)(dian)(dian)狀態準確性要求低的系統,像汽車(che)使用鉛酸(suan)電(dian)(dian)(dian)池或不間斷電(dian)(dian)(dian)源(yuan)等。

放電(dian)時不同負載之下,荷(he)電(dian)狀(zhuang)態的(de)差異(yi)也是很大

2、庫侖計量(liang)法的電池電量(liang)計算方法

庫侖計量法的操作原理是(shi)在電(dian)(dian)(dian)(dian)(dian)池的充電(dian)(dian)(dian)(dian)(dian)/放(fang)電(dian)(dian)(dian)(dian)(dian)路徑上的連接一個檢(jian)測(ce)(ce)電(dian)(dian)(dian)(dian)(dian)阻。ADC量測(ce)(ce)在檢(jian)測(ce)(ce)電(dian)(dian)(dian)(dian)(dian)阻上的電(dian)(dian)(dian)(dian)(dian)壓,轉換成電(dian)(dian)(dian)(dian)(dian)池正在充電(dian)(dian)(dian)(dian)(dian)或放(fang)電(dian)(dian)(dian)(dian)(dian)的電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)值。實時(shi)計數器(RTC)則供應把該電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)值對時(shi)間作積分,從而得知流(liu)(liu)過多少(shao)庫倫。

庫侖計量法(fa)

庫侖計(ji)量(liang)法(fa)可精確(que)計(ji)算(suan)出充電(dian)(dian)(dian)或放(fang)電(dian)(dian)(dian)過程(cheng)中實時(shi)的(de)荷電(dian)(dian)(dian)狀態。藉由充電(dian)(dian)(dian)庫侖計(ji)數器和(he)放(fang)電(dian)(dian)(dian)庫侖計(ji)數器,它可計(ji)算(suan)剩余(yu)電(dian)(dian)(dian)容(rong)量(liang)(RM)及完(wan)全充電(dian)(dian)(dian)容(rong)量(liang)(FCC)。同(tong)時(shi)也可用剩余(yu)電(dian)(dian)(dian)容(rong)量(liang)(RM)及完(wan)全充電(dian)(dian)(dian)容(rong)量(liang)(FCC)來計(ji)算(suan)出荷電(dian)(dian)(dian)狀態,即(SOC=RM/FCC)。此(ci)外,它還可預估剩余(yu)時(shi)間(jian),如電(dian)(dian)(dian)力耗竭(TTE)和(he)電(dian)(dian)(dian)力充滿(TTF)。

剩余電容量(liang)(RM)及完全充電容量(liang)(FCC)

重要有(you)兩個因素(su)造成庫倫計量(liang)法準(zhun)確度偏(pian)差(cha)。第一是(shi)電流感測及ADC量(liang)測中(zhong)(zhong)偏(pian)移誤(wu)差(cha)的(de)累(lei)積(ji)。雖然(ran)以目(mu)前(qian)的(de)技術此量(liang)測的(de)誤(wu)差(cha)還算(suan)小,但(dan)若沒有(you)消(xiao)除它的(de)好(hao)方法,則此誤(wu)差(cha)會隨時間新(xin)增而新(xin)增。下圖顯示(shi)了在實際應用中(zhong)(zhong),假如(ru)時間持續(xu)中(zhong)(zhong)的(de)未有(you)任何的(de)修正,則累(lei)積(ji)的(de)誤(wu)差(cha)是(shi)無上限的(de)。

實(shi)際應用中,假如時間持續中的未有任何的修正,則(ze)累積的誤差(cha)是(shi)無(wu)上限的

為(wei)消(xiao)除累積誤差(cha),在正(zheng)(zheng)常(chang)的(de)電(dian)池(chi)(chi)(chi)操作中有(you)三個可(ke)(ke)能可(ke)(ke)使(shi)(shi)用(yong)(yong)的(de)時間點(dian):充(chong)電(dian)結(jie)束(EOC),放(fang)電(dian)結(jie)束(EOD)和休(xiu)息(Relax)。充(chong)電(dian)結(jie)束條件(jian)達(da)到表示電(dian)池(chi)(chi)(chi)已(yi)充(chong)滿電(dian)且荷(he)電(dian)狀(zhuang)(zhuang)態(tai)(SOC)應為(wei)100%。放(fang)電(dian)結(jie)束條件(jian)則表示電(dian)池(chi)(chi)(chi)已(yi)完(wan)全放(fang)電(dian),且荷(he)電(dian)狀(zhuang)(zhuang)態(tai)(SOC)應該(gai)為(wei)0%;它可(ke)(ke)以(yi)(yi)是(shi)一個絕對的(de)電(dian)壓(ya)值(zhi)或者是(shi)隨(sui)負載而(er)改(gai)變。達(da)到休(xiu)息狀(zhuang)(zhuang)態(tai)時,則是(shi)電(dian)池(chi)(chi)(chi)旣沒(mei)有(you)充(chong)電(dian)也沒(mei)有(you)放(fang)電(dian),而(er)且保持這種狀(zhuang)(zhuang)態(tai)很長(chang)一段時間。若(ruo)使(shi)(shi)用(yong)(yong)者想用(yong)(yong)電(dian)池(chi)(chi)(chi)休(xiu)息狀(zhuang)(zhuang)態(tai)來作庫侖計量法的(de)誤差(cha)修(xiu)正(zheng)(zheng),則此時必須搭配開路(lu)電(dian)壓(ya)表。下(xia)圖顯(xian)示了在上(shang)述(shu)狀(zhuang)(zhuang)態(tai)下(xia)的(de)荷(he)電(dian)狀(zhuang)(zhuang)態(tai)誤差(cha)是(shi)可(ke)(ke)以(yi)(yi)被修(xiu)正(zheng)(zheng)的(de)。

荷電(dian)狀態誤差被修正(zheng)

造成庫倫計量(liang)法(fa)(fa)準確(que)度(du)偏差的(de)第二重要因素是完全(quan)(quan)充(chong)電(dian)(dian)容量(liang)(FCC)誤差,它(ta)是由電(dian)(dian)池設計容量(liang)的(de)值(zhi)和(he)電(dian)(dian)池真正(zheng)的(de)完全(quan)(quan)充(chong)電(dian)(dian)容量(liang)的(de)差異。完全(quan)(quan)充(chong)電(dian)(dian)容量(liang)(FCC)會受到(dao)溫度(du),老化,負載等因素影響(xiang)。所以(yi),完全(quan)(quan)充(chong)電(dian)(dian)容量(liang)的(de)再(zai)學習和(he)補償方法(fa)(fa)對庫侖計量(liang)法(fa)(fa)是非(fei)常關(guan)鍵重要的(de)。

完全(quan)充電容量被高估和被低(di)估時荷(he)電狀態誤差的趨勢(shi)現象

3、動態電(dian)壓算法的電(dian)池(chi)電(dian)量計算方法

動態電(dian)(dian)(dian)(dian)壓(ya)算法(fa)電(dian)(dian)(dian)(dian)量(liang)(liang)計(ji)僅根據(ju)電(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)壓(ya)即可計(ji)算鋰(li)離子電(dian)(dian)(dian)(dian)池的(de)荷電(dian)(dian)(dian)(dian)狀(zhuang)(zhuang)態。此(ci)法(fa)是根據(ju)電(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)壓(ya)和電(dian)(dian)(dian)(dian)池的(de)開路電(dian)(dian)(dian)(dian)壓(ya)之(zhi)間的(de)差值,來估計(ji)荷電(dian)(dian)(dian)(dian)狀(zhuang)(zhuang)態的(de)遞增量(liang)(liang)或遞減量(liang)(liang)。動態電(dian)(dian)(dian)(dian)壓(ya)的(de)信息可以有效地仿真鋰(li)離子電(dian)(dian)(dian)(dian)池的(de)行(xing)為,進而決定荷電(dian)(dian)(dian)(dian)狀(zhuang)(zhuang)態SOC(%),但此(ci)方法(fa)并不能估計(ji)電(dian)(dian)(dian)(dian)池容量(liang)(liang)值(mAh)。

它的(de)計(ji)(ji)(ji)算(suan)方(fang)式是(shi)根據(ju)電(dian)(dian)(dian)池電(dian)(dian)(dian)壓(ya)和開(kai)路電(dian)(dian)(dian)壓(ya)之間(jian)的(de)動態(tai)(tai)(tai)差(cha)異(yi),借著使(shi)用迭代算(suan)法(fa)(fa)來計(ji)(ji)(ji)算(suan)每次新(xin)增或減少(shao)的(de)荷(he)電(dian)(dian)(dian)狀態(tai)(tai)(tai),以(yi)估計(ji)(ji)(ji)荷(he)電(dian)(dian)(dian)狀態(tai)(tai)(tai)。相較于庫侖計(ji)(ji)(ji)量(liang)(liang)法(fa)(fa)電(dian)(dian)(dian)量(liang)(liang)計(ji)(ji)(ji)的(de)解決方(fang)法(fa)(fa),動態(tai)(tai)(tai)電(dian)(dian)(dian)壓(ya)算(suan)法(fa)(fa)電(dian)(dian)(dian)量(liang)(liang)計(ji)(ji)(ji)不會隨(sui)時間(jian)和電(dian)(dian)(dian)流累(lei)積誤(wu)差(cha)。庫侖計(ji)(ji)(ji)量(liang)(liang)法(fa)(fa)電(dian)(dian)(dian)量(liang)(liang)計(ji)(ji)(ji)通常會因為電(dian)(dian)(dian)流感測誤(wu)差(cha)及(ji)電(dian)(dian)(dian)池自放電(dian)(dian)(dian)而(er)(er)造成(cheng)荷(he)電(dian)(dian)(dian)狀態(tai)(tai)(tai)估計(ji)(ji)(ji)不準。即使(shi)電(dian)(dian)(dian)流感測誤(wu)差(cha)非常小,庫侖計(ji)(ji)(ji)數(shu)器(qi)卻(que)會持續累(lei)積誤(wu)差(cha),而(er)(er)所累(lei)積的(de)誤(wu)差(cha)只有在完全充電(dian)(dian)(dian)或完全放電(dian)(dian)(dian)才能消除。

動(dong)態電(dian)(dian)(dian)(dian)壓算(suan)(suan)法(fa)電(dian)(dian)(dian)(dian)量計(ji)僅由電(dian)(dian)(dian)(dian)壓信(xin)息來(lai)估計(ji)電(dian)(dian)(dian)(dian)池(chi)的(de)(de)荷(he)電(dian)(dian)(dian)(dian)狀態;因為(wei)它不是由電(dian)(dian)(dian)(dian)池(chi)的(de)(de)電(dian)(dian)(dian)(dian)流信(xin)息來(lai)估計(ji),所(suo)以不會累積誤差。若要提高荷(he)電(dian)(dian)(dian)(dian)狀態的(de)(de)精確度,動(dong)態電(dian)(dian)(dian)(dian)壓算(suan)(suan)法(fa)要用實際的(de)(de)裝置,根據它在完全(quan)充電(dian)(dian)(dian)(dian)和完全(quan)放(fang)電(dian)(dian)(dian)(dian)的(de)(de)情況下,由實際的(de)(de)電(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)壓曲線來(lai)調整出一優化的(de)(de)算(suan)(suan)法(fa)的(de)(de)參數。

動態(tai)電壓算法電量計

下面(mian)是(shi)(shi)動態電壓算(suan)法在不(bu)同(tong)放(fang)電速率條件(jian)(jian)下,荷電狀態的表現。由圖(tu)可知,它的荷電狀態精確度良好。不(bu)論是(shi)(shi)在C/2,C/4,C/7和C/10等的放(fang)電條件(jian)(jian)下,此法整(zheng)體(ti)的荷電狀態誤差都(dou)小于3%。

動(dong)態電(dian)(dian)壓算法在不(bu)同放電(dian)(dian)速率條件下荷電(dian)(dian)狀態的表現

電池短充短放情(qing)況下(xia)荷電狀態的表現

相較(jiao)于庫侖(lun)計(ji)量法電(dian)(dian)(dian)量計(ji)通常會因(yin)為(wei)電(dian)(dian)(dian)流(liu)感測誤差(cha)及電(dian)(dian)(dian)池自放電(dian)(dian)(dian)而造成荷電(dian)(dian)(dian)狀態的(de)不(bu)準的(de)情形,動態電(dian)(dian)(dian)壓(ya)算法它(ta)不(bu)會隨時間和電(dian)(dian)(dian)流(liu)累(lei)積誤差(cha),這是一個大(da)優點(dian)。因(yin)為(wei)沒有充(chong)/放電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)的(de)信息,動態電(dian)(dian)(dian)壓(ya)算法在短時間精(jing)確(que)度上較(jiao)差(cha),且(qie)反應時間較(jiao)慢。此(ci)外,它(ta)也無法估(gu)計(ji)完全充(chong)電(dian)(dian)(dian)容量。然而,它(ta)在長期精(jing)確(que)度上卻表現良好,因(yin)為(wei)電(dian)(dian)(dian)池電(dian)(dian)(dian)壓(ya)最終會直(zhi)接反應它(ta)的(de)荷電(dian)(dian)(dian)狀態。