自放電是由電池的內在因素引起的，而受外在因素的影響。通常電池自放電性能由構成電池的正、負電極、聚華物隔膜和電解液性能決定，并且受制(zhi)造(zao)工藝及生產要求(qiu)的(de)(de)影響。而在電(dian)(dian)池(chi)壽命內自放(fang)電(dian)(dian)大(da)小并不(bu)是固定不(bu)變的(de)(de)，還與電(dian)(dian)池(chi)的(de)(de)老化程度(du)、SOC 和(he)電(dian)(dian)池(chi)所(suo)處環境(jing)的(de)(de)溫度(du)等因(yin)素(su)有(you)關系，惡劣的(de)(de)充放(fang)電(dian)(dian)制(zhi)度(du)和(he)工作條件(jian)也會對電(dian)(dian)池(chi)的(de)(de)自放(fang)電(dian)(dian)構成(cheng)影響。

除去制造工藝及錯誤的使用方式造成的自放電，影響電池自放電的因素就只有溫度、SOC 和電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)壽命(ming)了。其(qi)中(zhong)，溫度(du)(du)對電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)自(zi)(zi)放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)(de)(de)影響是(shi)顯而(er)易見的(de)(de)(de)(de)(de)，溫度(du)(du)越(yue)(yue)高(gao)，電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)內(nei)部(bu)的(de)(de)(de)(de)(de)化(hua)(hua)學(xue)反(fan)(fan)應越(yue)(yue)活躍，引起(qi)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)自(zi)(zi)放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)的(de)(de)(de)(de)(de)化(hua)(hua)學(xue)反(fan)(fan)應也(ye)(ye)隨(sui)溫度(du)(du)的(de)(de)(de)(de)(de)升(sheng)高(gao)而(er)加快。因此，溫度(du)(du)越(yue)(yue)高(gao)，電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)的(de)(de)(de)(de)(de)自(zi)(zi)放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)率將越(yue)(yue)大。在(zai)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)的(de)(de)(de)(de)(de)儲存(cun)和應用過程(cheng)當中(zhong)，應該保證(zheng)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)處于(yu)較低(di)的(de)(de)(de)(de)(de)溫度(du)(du)范圍內(nei)，避免由于(yu)外界或者電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)自(zi)(zi)身溫度(du)(du)升(sheng)高(gao)引起(qi)的(de)(de)(de)(de)(de)自(zi)(zi)放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)變(bian)大，電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)性(xing)能下降。SOC 表(biao)示的(de)(de)(de)(de)(de)是(shi)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)的(de)(de)(de)(de)(de)荷電(dian)(dian)(dian)(dian)(dian)狀(zhuang)態，當電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)處于(yu)不同 SOC 時，其(qi)自(zi)(zi)放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)大小也(ye)(ye)不相同。一般而(er)言，鋰電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)的(de)(de)(de)(de)(de) SOC 越(yue)(yue)大，其(qi)自(zi)(zi)放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)現象越(yue)(yue)明(ming)顯。壽命(ming)表(biao)示電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)的(de)(de)(de)(de)(de)劣化(hua)(hua)程(cheng)度(du)(du)，隨(sui)著(zhu)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)的(de)(de)(de)(de)(de)不斷老化(hua)(hua)，其(qi)內(nei)阻不斷變(bian)大，電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)的(de)(de)(de)(de)(de)荷電(dian)(dian)(dian)(dian)(dian)保持能力下降。我們常見的(de)(de)(de)(de)(de)手(shou)機(ji)(ji)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)待機(ji)(ji)時間越(yue)(yue)來越(yue)(yue)短(duan)，就(jiu)是(shi)由于(yu)電(dian)(dian)(dian)(dian)(dian)池(chi)(chi)(chi)(chi)(chi)老化(hua)(hua)導致的(de)(de)(de)(de)(de)，在(zai)這個過程(cheng)中(zhong)，除(chu)了內(nei)部(bu)極化(hua)(hua)現象嚴重外，自(zi)(zi)放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)也(ye)(ye)隨(sui)之(zhi)增大。

自(zi)(zi)放(fang)電(dian)(dian)(dian)檢(jian)測(ce)(ce)(ce)電(dian)(dian)(dian)路是自(zi)(zi)放(fang)電(dian)(dian)(dian)檢(jian)測(ce)(ce)(ce)方法(fa)的核(he)心體(ti)現，按照容(rong)量保持法(fa)，需(xu)監測(ce)(ce)(ce)維(wei)持電(dian)(dian)(dian)池 SOC 或電(dian)(dian)(dian)壓不變所需(xu)電(dian)(dian)(dian)荷量，因(yin)此在自(zi)(zi)放(fang)電(dian)(dian)(dian)檢(jian)測(ce)(ce)(ce)電(dian)(dian)(dian)路中需(xu)要搭建(jian)出(chu)對電(dian)(dian)(dian)池的充放(fang)電(dian)(dian)(dian)控制電(dian)(dian)(dian)路，以便于電(dian)(dian)(dian)壓穩定時(shi)檢(jian)測(ce)(ce)(ce)充電(dian)(dian)(dian)電(dian)(dian)(dian)流大小。自(zi)(zi)放(fang)電(dian)(dian)(dian)檢(jian)測(ce)(ce)(ce)模塊(kuai)功(gong)能(neng)框圖如下圖1所示。

基(ji)(ji)準電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)作為(wei)自放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)檢測(ce)(ce)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)的(de)輸入，來源于 D/A 轉(zhuan)換模塊按照MSP430F149 給定的(de)數(shu)字量轉(zhuan)換而成(cheng)的(de)模擬電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)。該基(ji)(ji)準電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)值(zhi)可以通(tong)過(guo)人為(wei)按鍵設定，以便(bian)測(ce)(ce)出電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)不同(tong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)下的(de)自放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)大(da)小。首先基(ji)(ji)準電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)要經過(guo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)比較(jiao)環節(jie)，與(yu)實際(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)的(de)實時(shi)(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)進(jin)行(xing)(xing)比較(jiao)，判(pan)斷(duan)此時(shi)(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)與(yu)基(ji)(ji)準電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)之(zhi)間的(de)差(cha)值(zhi)。電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)若高(gao)于基(ji)(ji)準電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)，則充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)停止(zhi)工作，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)自動(dong)通(tong)過(guo)負載電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)進(jin)行(xing)(xing)放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)；若低于基(ji)(ji)準電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)，則充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)開始工作，對(dui)其(qi)進(jin)行(xing)(xing)充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)動(dong)作，直至電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)穩定為(wei)止(zhi)。此時(shi)(shi)的(de)充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)為(wei)充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)與(yu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)通(tong)過(guo)負載電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)的(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)與(yu)自放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)之(zhi)和(he)，測(ce)(ce)出此時(shi)(shi)的(de)充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)大(da)小，并通(tong)過(guo)計算得到(dao)放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)值(zhi)，那么兩者之(zhi)差(cha)即為(wei)該電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)芯的(de)自放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)值(zhi)。

另外，雖然從(cong)基準電(dian)壓模塊送來的(de)電(dian)壓在原理上已(yi)經是直(zhi)流，但仍不可(ke)避免混有雜(za)波，可(ke)能(neng)導致(zhi)檢(jian)測電(dian)路發生(sheng)震(zhen)蕩，因此需要設置低通(tong)(tong)濾波器(qi)，濾掉高(gao)頻(pin)干擾。考慮到當f > f0，即信號頻(pin)率(lv)大于通(tong)(tong)帶截止(zhi)頻(pin)率(lv)時，一階低通(tong)(tong)濾波器(qi)的(de)對數幅頻(pin)特性(xing)只是以(yi)-20dB/十倍(bei)頻(pin)的(de)緩慢速(su)度(du)下降(jiang)，電(dian)壓放大倍(bei)數并不能(neng)立即降(jiang)為零，存在較(jiao)寬的(de)過(guo)渡(du)帶，濾波性(xing)能(neng)較(jiao)差。因此采用二階低通(tong)(tong)濾波電(dian)路，在保證通(tong)(tong)頻(pin)帶增(zeng)益的(de)同時，高(gao)頻(pin)段(duan)幅頻(pin)特性(xing)能(neng)夠以(yi)-40dB/十倍(bei)頻(pin)的(de)速(su)度(du)快速(su)衰減，濾波效果較(jiao)好。

同時，由于本設(she)計中的負載(zai)為實際電(dian)池(chi)，而 D/A 轉換模塊提供(gong)的基準電(dian)壓并不(bu)能(neng)作(zuo)為充電(dian)源使(shi)用，所(suo)以自放(fang)(fang)電(dian)檢測電(dian)路模塊還應該具有功(gong)率(lv)放(fang)(fang)大的功(gong)能(neng)，以實現對(dui)電(dian)池(chi)的充電(dian)動作(zuo)。自放(fang)(fang)電(dian)檢測電(dian)路原理(li)圖(tu)如圖(tu)所(suo)示。

在該圖中(zhong)，信(xin)號 DA_Vout 即(ji)為(wei) D/A 轉換(huan)模塊產(chan)生的(de)基(ji)準(zhun)電(dian)(dian)(dian)(dian)(dian)壓(ya)信(xin)號，整個電(dian)(dian)(dian)(dian)(dian)路以 DA_Vout 作為(wei)系(xi)統輸入(ru)量，電(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)壓(ya)作為(wei)輸出(chu)量和反饋(kui)(kui)量，從而(er)構成了一個反饋(kui)(kui)系(xi)統，最終將電(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)壓(ya)穩定在基(ji)準(zhun)電(dian)(dian)(dian)(dian)(dian)壓(ya)，通(tong)(tong)過(guo)測量此時采樣電(dian)(dian)(dian)(dian)(dian)阻Sample Res 兩端的(de)電(dian)(dian)(dian)(dian)(dian)壓(ya)即(ji)可求(qiu)出(chu)電(dian)(dian)(dian)(dian)(dian)池的(de)自(zi)放(fang)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)值。為(wei)了防止電(dian)(dian)(dian)(dian)(dian)池通(tong)(tong)過(guo)比例運算放(fang)大(da)器等其它(ta)回路放(fang)電(dian)(dian)(dian)(dian)(dian)，而(er)造成自(zi)放(fang)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)值求(qiu)取(qu)不(bu)精確，引入(ru)了光電(dian)(dian)(dian)(dian)(dian)開(kai)關，由單(dan)片機的(de)引腳直接進行開(kai)通(tong)(tong)和關斷控(kong)制。

需要注意(yi)的(de)是(shi)，一般正常鋰電(dian)(dian)(dian)池的(de)自(zi)放電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)均為(wei)微安級別(bie)(bie)，而采樣(yang)電(dian)(dian)(dian)阻(zu)阻(zu)值(zhi)為(wei) 1KW，則其兩(liang)端(duan)電(dian)(dian)(dian)壓保(bao)持在(zai)毫伏級別(bie)(bie)，因此(ci)需要測量精(jing)度(du)較高的(de)電(dian)(dian)(dian)壓表(biao)才能保(bao)證(zheng)得到(dao)的(de)自(zi)放電(dian)(dian)(dian)流(liu)的(de)準確度(du)。MSP430F159 芯(xin)片自(zi)帶的(de) A/D 轉換器為(wei)12 位，可以對采樣(yang)電(dian)(dian)(dian)壓精(jing)確到(dao) 1.2mV，對應于電(dian)(dian)(dian)流(liu)值(zhi)即為(wei) 1.2μA，精(jing)度(du)較低。因此(ci)本(ben)設計直接應用了美(mei)國安捷倫公司生產的(de) Agilent34401A 六位半數(shu)字萬用表(biao)顯示采樣(yang)電(dian)(dian)(dian)阻(zu)兩(liang)端(duan)電(dian)(dian)(dian)壓值(zhi)，該表(biao)可穩定顯示 0.1mV，此(ci)時對自(zi)放電(dian)(dian)(dian)電(dian)(dian)(dian)流(liu)的(de)檢測精(jing)度(du)可達到(dao) 0.1μA。