混合動力汽車充電關鍵是控制高電壓電池組
綠色革命可(ke)(ke)(ke)(ke)(ke)能(neng)不久就將迎來一(yi)場重大勝利。在大規模(mo)的(de)電能(neng)成為“可(ke)(ke)(ke)(ke)(ke)儲存”和“便攜(xie)式(shi)”能(neng)源(yuan)(yuan)之時(shi)(shi),能(neng)量效率將獲得顯著改善(shan),而(er)且(qie)可(ke)(ke)(ke)(ke)(ke)再生能(neng)源(yuan)(yuan)的(de)推動工作也(ye)將取得進展。可(ke)(ke)(ke)(ke)(ke)儲存性和便攜(xie)性是液(ye)體(ti)燃料的(de)主要(yao)優勢(shi),而(er)通過電池系統提供的(de)電力(li)(li)則擁(yong)有提供一(yi)種可(ke)(ke)(ke)(ke)(ke)行替代(dai)方(fang)案的(de)潛(qian)力(li)(li)。電能(neng)可(ke)(ke)(ke)(ke)(ke)在幾(ji)乎所有的(de)耗能(neng)設備中使用(yong),而(er)且(qie),電能(neng)也(ye)可(ke)(ke)(ke)(ke)(ke)以(yi)從幾(ji)乎所有的(de)可(ke)(ke)(ke)(ke)(ke)用(yong)能(neng)源(yuan)(yuan)來產生。核能(neng)、太陽能(neng)、風(feng)能(neng)、地(di)熱能(neng)和液(ye)體(ti)燃料(汽油、柴油、乙醇(chun)、氫等(deng)等(deng))都能(neng)很容(rong)易地(di)轉換(huan)成電能(neng)。因此,與(yu)石油燃料相比,電力(li)(li)的(de)重大優勢(shi)是可(ke)(ke)(ke)(ke)(ke)以(yi)利用(yong)最具(ju)成本(ben)效益的(de)解決(jue)方(fang)案隨時(shi)(shi)隨地(di)產生能(neng)量。
對電(dian)能(neng)(neng)的(de)(de)規范(fan)化可(ke)以同時實現(xian)規模經濟,并(bing)免除局部燃料消耗所需(xu)的(de)(de)基礎設施。優越(yue)的(de)(de)電(dian)能(neng)(neng)可(ke)儲存(cun)性(xing)便(bian)于發電(dian)(效率最高,且不是“按需(xu)”型的(de)(de)),目前的(de)(de)情況大體如此。例如:風力發電(dian)和太(tai)陽能(neng)(neng)發電(dian)未必與峰(feng)值(zhi)功率需(xu)求模式相吻(wen)合(he),而可(ke)儲存(cun)特(te)性(xing)則能(neng)(neng)緩(huan)解這個問題有所緩(huan)解。優越(yue)的(de)(de)便(bian)攜(xie)性(xing)允許(xu)電(dian)能(neng)(neng)作為(wei)汽(qi)車(耗能(neng)(neng)大戶(hu))的(de)(de)能(neng)(neng)源。隨著時間的(de)(de)推(tui)移(yi),其他(ta)傾向于使用綠色能(neng)(neng)源的(de)(de)應(ying)用肯定將(jiang)得益于此項技術。
電(dian)動汽車對(dui)電(dian)池系統的要求
電(dian)(dian)(dian)動(dong)(dong)汽(qi)(qi)車(che)為(wei)(wei)(wei)綠色革命提供了(le)一(yi)個巨大的(de)(de)(de)(de)發展機遇,原因(yin)有(you)(you)(you)很(hen)多。電(dian)(dian)(dian)動(dong)(dong)汽(qi)(qi)車(che)采用電(dian)(dian)(dian)網(wang)電(dian)(dian)(dian)力(li)(li)取代了(le)燃氣動(dong)(dong)力(li)(li)。電(dian)(dian)(dian)網(wang)電(dian)(dian)(dian)力(li)(li)的(de)(de)(de)(de)生(sheng)(sheng)成(cheng)(cheng)效(xiao)(xiao)(xiao)率很(hen)高(gao),可(ke)以(yi)從幾乎所(suo)有(you)(you)(you)的(de)(de)(de)(de)能(neng)(neng)(neng)源(yuan)來(lai)(lai)獲得。此外,電(dian)(dian)(dian)動(dong)(dong)汽(qi)(qi)車(che)的(de)(de)(de)(de)能(neng)(neng)(neng)源(yuan)使(shi)用效(xiao)(xiao)(xiao)率也高(gao)于(yu)燃油(you)(you)汽(qi)(qi)車(che)。大多數(shu)汽(qi)(qi)車(che)在運行時將(jiang)經歷一(yi)個“加(jia)(jia)速(su)(su)、減(jian)速(su)(su)和(he)空(kong)轉(zhuan)”的(de)(de)(de)(de)連續周期。相比之下,易變的(de)(de)(de)(de)負載(比如加(jia)(jia)速(su)(su)或減(jian)速(su)(su))更有(you)(you)(you)利于(yu)電(dian)(dian)(dian)動(dong)(dong)馬達(da)(da)(而(er)非(fei)燃油(you)(you)引擎),因(yin)為(wei)(wei)(wei)它在低速(su)(su)條件下提供了(le)高(gao)轉(zhuan)矩。燃油(you)(you)引擎的(de)(de)(de)(de)工作效(xiao)(xiao)(xiao)率只在一(yi)個很(hen)窄(zhai)的(de)(de)(de)(de)速(su)(su)度/負載范圍內(nei)達(da)(da)到最高(gao),而(er)且為(wei)(wei)(wei)滿足峰值加(jia)(jia)速(su)(su)的(de)(de)(de)(de)需要(yao),它必須(xu)(xu)是(shi)超大型(xing)的(de)(de)(de)(de)。用于(yu)把汽(qi)(qi)油(you)(you)能(neng)(neng)(neng)量轉(zhuan)換(huan)為(wei)(wei)(wei)動(dong)(dong)能(neng)(neng)(neng)的(de)(de)(de)(de)引擎效(xiao)(xiao)(xiao)率通(tong)(tong)常為(wei)(wei)(wei) 20%,而(er)電(dian)(dian)(dian)動(dong)(dong)馬達(da)(da)將(jiang)電(dian)(dian)(dian)能(neng)(neng)(neng)轉(zhuan)換(huan)為(wei)(wei)(wei)動(dong)(dong)能(neng)(neng)(neng)的(de)(de)(de)(de)過程中可(ke)以(yi)實(shi)現 90% 的(de)(de)(de)(de)典型(xing)效(xiao)(xiao)(xiao)率。此外,電(dian)(dian)(dian)動(dong)(dong)馬達(da)(da)還無須(xu)(xu)在停靠時因(yin)為(wei)(wei)(wei)空(kong)轉(zhuan)而(er)無謂(wei)地消耗能(neng)(neng)(neng)量,而(er)且電(dian)(dian)(dian)動(dong)(dong)系統(tong)還具備通(tong)(tong)過再生(sheng)(sheng)制動(dong)(dong)來(lai)(lai)恢復機械能(neng)(neng)(neng)的(de)(de)(de)(de)潛(qian)力(li)(li)。通(tong)(tong)過電(dian)(dian)(dian)動(dong)(dong)汽(qi)(qi)車(che)的(de)(de)(de)(de)典型(xing)能(neng)(neng)(neng)耗成(cheng)(cheng)本僅(jin)為(wei)(wei)(wei)0.013美元/英里這(zhe)一(yi)事實(shi),便能(neng)(neng)(neng)看出能(neng)(neng)(neng)量效(xiao)(xiao)(xiao)率的(de)(de)(de)(de)整體改善情況。
遺憾的(de)(de)是(shi),在現今的(de)(de)市場上,純電(dian)(dian)動(dong)(dong)汽車(che)(che)(che)還不是(shi)一(yi)(yi)種可行(xing)的(de)(de)解決(jue)(jue)方案,因為其行(xing)駛(shi)距離(li)(li)受(shou)限于車(che)(che)(che)上所能(neng)儲存的(de)(de)能(neng)量。如今常見的(de)(de)電(dian)(dian)池組(zu)在充電(dian)(dian)8小時之后能(neng)夠(gou)讓(rang)一(yi)(yi)輛電(dian)(dian)動(dong)(dong)汽車(che)(che)(che)行(xing)駛(shi)100英里(li)。而一(yi)(yi)個普(pu)通(tong)的(de)(de)汽車(che)(che)(che)油箱則能(neng)為一(yi)(yi)輛標準(zhun)汽車(che)(che)(che)提供(gong)300英里(li)的(de)(de)行(xing)駛(shi)距離(li)(li),且只需幾(ji)分鐘(zhong)的(de)(de)時間(jian)就能(neng)完(wan)成加(jia)油。如果想得到美國消(xiao)費者的(de)(de)廣泛接受(shou),那么(me)電(dian)(dian)動(dong)(dong)汽車(che)(che)(che)必須延(yan)長行(xing)駛(shi)距離(li)(li)和(he)/或(huo)縮(suo)短再充電(dian)(dian)時間(jian)。應運而生的(de)(de)解決(jue)(jue)方案是(shi)“油電(dian)(dian)混(hun)(hun)合(he)動(dong)(dong)力車(che)(che)(che)”,它把燃油引(yin)(yin)擎(qing)(qing)和(he)電(dian)(dian)動(dong)(dong)傳動(dong)(dong)系(xi)統組(zu)合(he)起來(lai),以提供(gong)足夠(gou)的(de)(de)行(xing)駛(shi)距離(li)(li),同時仍然擁(yong)有綠(lv)色能(neng)源的(de)(de)大多數好處。油電(dian)(dian)混(hun)(hun)合(he)動(dong)(dong)力車(che)(che)(che)采(cai)用(yong)車(che)(che)(che)載燃氣引(yin)(yin)擎(qing)(qing)(用(yong)于電(dian)(dian)池充電(dian)(dian)),并在需要時在最有效的(de)(de)速度/轉矩范圍內操作該引(yin)(yin)擎(qing)(qing)。
毫無疑問(wen),電(dian)(dian)(dian)動汽車的(de)(de)(de)成功(gong)將有助于其它應用的(de)(de)(de)高(gao)性能電(dian)(dian)(dian)池(chi)(chi)(chi)系(xi)(xi)統(tong)(tong)找到屬于自己的(de)(de)(de)生存(cun)空間,從而推進其價格的(de)(de)(de)下降(jiang)和性能的(de)(de)(de)提升。對于局(ju)部(bu)發電(dian)(dian)(dian)(包括小型(xing)光伏(fu)或(huo)風力發電(dian)(dian)(dian)系(xi)(xi)統(tong)(tong)),電(dian)(dian)(dian)池(chi)(chi)(chi)可以起到至關(guan)重要(yao)的(de)(de)(de)平衡作用,且(qie)當可以使用電(dian)(dian)(dian)網電(dian)(dian)(dian)力時,它還能充當一個后備電(dian)(dian)(dian)源系(xi)(xi)統(tong)(tong)。目(mu)前的(de)(de)(de)電(dian)(dian)(dian)池(chi)(chi)(chi)系(xi)(xi)統(tong)(tong)相當昂貴而且(qie)龐大,且(qie)存(cun)在可靠(kao)性和安全方(fang)面的(de)(de)(de)問(wen)題。下一代電(dian)(dian)(dian)池(chi)(chi)(chi)系(xi)(xi)統(tong)(tong)將提供(gong)較(jiao)高(gao)的(de)(de)(de)能量密度,旨(zhi)在實現外形較(jiao)小、價格較(jiao)低、可靠(kao)性和安全性更高(gao)的(de)(de)(de)解決方(fang)案。
高電(dian)壓電(dian)池(chi)組的設(she)計挑戰
對于大功率電池應用而言,鋰離電池可作為首選的化(hua)學電(dian)池(chi)(chi)(chi),主要因為它(ta)的能(neng)量密(mi)度高。當今的電(dian)動汽車(che)和油(you)電(dian)混合動力車(che)采用的是(shi)NiMH電(dian)池(chi)(chi)(chi),如(ru)果采用鋰離子電(dian)池(chi)(chi)(chi)將使(shi)其(qi)能(neng)量儲存密(mi)度提高400%。然而,為了使(shi)鋰離子電(dian)池(chi)(chi)(chi)在多(duo)達數千次的充放(fang)電(dian)循環(huan)過程中保持可靠,電(dian)池(chi)(chi)(chi)系(xi)統(tong)必(bi)須解決諸(zhu)多(duo)技術難(nan)題。
鋰離子電池的性能取決于電池溫度和使用期限、電池充電和放電速率以及充電狀態(SOC)。這些因素并不是獨立的。例如:鋰離子電池在放電時將產生熱量,從而增加放電電流。這有可能形成熱失控狀態,并導致災難性故障的發生。此外,把鋰離子電池充(chong)電(dian)至100% SOC或放電(dian)至0% SOC將(jiang)迅速降低其容(rong)量。因此,必(bi)須將(jiang)鋰離(li)子電(dian)池(chi)的操作限制在(zai)某(mou)個SOC范圍(wei)內(nei),比(bi)如20%至80%,此時的可(ke)用容(rong)量僅為規定(ding)容(rong)量的60%。不僅如此,鋰離(li)子電(dian)池(chi)還具有平(ping)坦(tan)的放電(dian)曲線(圖1),其中1%的SOC變化可(ke)能僅表(biao)現為數毫(hao)伏的電(dian)壓差異。為充(chong)分利(li)用電(dian)池(chi)的可(ke)用電(dian)壓范圍(wei),電(dian)池(chi)系統(tong)必(bi)須非常(chang)準確地監視電(dian)池(chi)電(dian)壓(它(ta)直接對應于SOC)。
除了鋰離子電(dian)(dian)池(chi)的(de)敏(min)感特性之外,把電(dian)(dian)池(chi)組(zu)合在一起的(de)方法也是一個重要的(de)考慮因素。如欲(yu)從一個電(dian)(dian)氣系(xi)統(tong)(比如用于(yu)給車(che)輛加速所(suo)需(xu)(xu)的(de)電(dian)(dian)氣系(xi)統(tong))來(lai)提供有效的(de)功率,則(ze)需(xu)(xu)高(gao)達數百伏的(de)電(dian)(dian)壓(ya)(ya)(ya)。舉例來(lai)說,在1V電(dian)(dian)壓(ya)(ya)(ya)條件(jian)下輸送(song)1kW功率需(xu)(xu)要1,000A電(dian)(dian)流,而在100V電(dian)(dian)壓(ya)(ya)(ya)條件(jian)下輸送(song)1kW功率則(ze)僅需(xu)(xu)10A電(dian)(dian)流。系(xi)統(tong)布線(xian)和(he)互連線(xian)中(zhong)的(de)固有電(dian)(dian)阻將轉換(huan)成IR損耗,因此設計師需(xu)(xu)采用切(qie)實可行的(de)最(zui)高(gao)電(dian)(dian)壓(ya)(ya)(ya)/最(zui)低電(dian)(dian)流。