鋰離(li)子(zi)電(dian)(dian)池(chi)組充(chong)電(dian)(dian)主動均衡系統架構(gou)

鋰離子電池由于其(qi)性(xing)能(neng)(neng)有極(ji)大(da)(da)提高，因此其(qi)市場份額增(zeng)長非常(chang)迅速。鋰離(li)(li)子電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)的(de)(de)儲(chu)能(neng)(neng)容量非常(chang)驚人，但即便如此，單個(ge)(ge)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)單元(yuan)(yuan)的(de)(de)容量不論從(cong)電(dian)(dian)(dian)(dian)(dian)(dian)壓還是從(cong)電(dian)(dian)(dian)(dian)(dian)(dian)流方面仍(reng)都太(tai)低，不能(neng)(neng)滿(man)足一(yi)個(ge)(ge)混合動力(li)發動機的(de)(de)需要。并聯(lian)(lian)多個(ge)(ge)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)單元(yuan)(yuan)可以增(zeng)大(da)(da)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)所(suo)提供的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)流，串(chuan)(chuan)聯(lian)(lian)多個(ge)(ge)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)單元(yuan)(yuan)則可以增(zeng)大(da)(da)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)提供的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)壓。 電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)組(zu)(zu)裝商通常(chang)利用一(yi)些(xie)縮略(lve)短語來描述其(qi)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)產品，例如“3P50S”代表該電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)組(zu)(zu)中(zhong)(zhong)有3個(ge)(ge)并聯(lian)(lian)的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)單元(yuan)(yuan)、50個(ge)(ge)串(chuan)(chuan)聯(lian)(lian)的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)單元(yuan)(yuan)。 模塊(kuai)化結構在(zai)對(dui)包含(han)多個(ge)(ge)串(chuan)(chuan)聯(lian)(lian)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)單元(yuan)(yuan)的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)進行管理(li)時是很(hen)理(li)想的(de)(de)結構。例如，在(zai)一(yi)個(ge)(ge)3P12S的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)陣(zhen)列中(zhong)(zhong)，每12個(ge)(ge)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)單元(yuan)(yuan)串(chuan)(chuan)聯(lian)(lian)之后就(jiu)(jiu)組(zu)(zu)成了一(yi)個(ge)(ge)模塊(kuai)(block)。然后，這(zhe)些(xie)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)單元(yuan)(yuan)就(jiu)(jiu)可通過一(yi)塊(kuai)以微控(kong)制器(qi)為核心(xin)的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)子電(dian)(dian)(dian)(dian)(dian)(dian)路對(dui)其(qi)進行管理(li)和(he)平衡。 這(zhe)樣一(yi)個(ge)(ge)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)模塊(kuai)的(de)(de)輸(shu)出(chu)電(dian)(dian)(dian)(dian)(dian)(dian)壓取決(jue)于串(chuan)(chuan)聯(lian)(lian)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)單元(yuan)(yuan)的(de)(de)個(ge)(ge)數(shu)和(he)每個(ge)(ge)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)單元(yuan)(yuan)的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)壓。鋰離(li)(li)子電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)單元(yuan)(yuan)的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)壓通常(chang)在(zai)3.3V到(dao)3.6V之間(jian)，因此一(yi)個(ge)(ge)電(dian)(dian)(dian)(dian)(dian)(dian)池(chi)(chi)模塊(kuai)的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)壓約在(zai)30V到(dao)45V之間(jian)。

混(hun)合動(dong)力車的(de)驅動(dong)需要450V左右的(de)直流電(dian)(dian)(dian)源電(dian)(dian)(dian)壓。為(wei)(wei)了根據(ju)充電(dian)(dian)(dian)狀態來補償電(dian)(dian)(dian)池(chi)(chi)單元電(dian)(dian)(dian)壓的(de)變化，比較合適(shi)的(de)做法(fa)是在電(dian)(dian)(dian)池(chi)(chi)組和(he)發動(dong)機之間連接一個(ge)(ge)DC-DC轉換(huan)器(qi)(qi)(qi)。這個(ge)(ge)轉換(huan)器(qi)(qi)(qi)還可以限制電(dian)(dian)(dian)池(chi)(chi)組輸出的(de)電(dian)(dian)(dian)流。為(wei)(wei)確保(bao)DC-DC轉換(huan)器(qi)(qi)(qi)工(gong)作在最(zui)佳狀態，要求電(dian)(dian)(dian)池(chi)(chi)組電(dian)(dian)(dian)壓在150V到(dao)300V之間。因此，需要串(chuan)聯5到(dao)8個(ge)(ge)電(dian)(dian)(dian)池(chi)(chi)模塊。

平衡的必要性

如果(guo)(guo)電壓(ya)(ya)超(chao)出允許的(de)(de)(de)范(fan)圍，鋰(li)離(li)子電池(chi)(chi)單元就很容易損壞。如果(guo)(guo)電壓(ya)(ya)超(chao)出了上、下限(xian)(以納米磷酸鹽型鋰(li)離(li)子電池(chi)(chi)為例，下限(xian)電壓(ya)(ya)為2V，上限(xian)電壓(ya)(ya)為3.6V)，電池(chi)(chi)就可能出現(xian)不(bu)可逆轉的(de)(de)(de)損壞。其結果(guo)(guo)至少(shao)是加快電池(chi)(chi)的(de)(de)(de)自放電速度(du)。電池(chi)(chi)輸(shu)出電壓(ya)(ya)在一個(ge)很寬(kuan)的(de)(de)(de)充電狀態(SOC)范(fan)圍內都(dou)是穩定的(de)(de)(de)，電壓(ya)(ya)偏離(li)安全(quan)范(fan)圍的(de)(de)(de)風險很小。但在安全(quan)范(fan)圍的(de)(de)(de)兩端，充電曲(qu)線的(de)(de)(de)起伏相對比較陡峭。因此，為預(yu)防起見，必須嚴(yan)密監(jian)控電壓(ya)(ya)。

如果(guo)電(dian)(dian)壓達到(dao)一(yi)(yi)個(ge)臨界值，就(jiu)必(bi)需立即停止放(fang)電(dian)(dian)或充電(dian)(dian)過程(cheng)。在一(yi)(yi)個(ge)強大的平(ping)衡電(dian)(dian)路的幫助下(xia)，相(xiang)關(guan)電(dian)(dian)池單元(yuan)的電(dian)(dian)壓可以返回安全范圍(wei)內。但為達到(dao)這一(yi)(yi)目(mu)的，該電(dian)(dian)路必(bi)需能在電(dian)(dian)池組中任(ren)何一(yi)(yi)個(ge)單元(yuan)的電(dian)(dian)壓開(kai)始與其他單元(yuan)出現差異時馬(ma)上在各(ge)單元(yuan)之間轉移能量。

充電平衡法

1.傳統的被(bei)動(dong)方(fang)法：在(zai)一(yi)(yi)般的電(dian)(dian)(dian)池管理系統中，每個(ge)電(dian)(dian)(dian)池單元都通過(guo)一(yi)(yi)個(ge)開關連接到一(yi)(yi)個(ge)負(fu)載電(dian)(dian)(dian)阻。這種被(bei)動(dong)電(dian)(dian)(dian)路(lu)可以對個(ge)別被(bei)選中的單元放(fang)電(dian)(dian)(dian)。但(dan)該方(fang)法只適(shi)用(yong)于在(zai)充(chong)電(dian)(dian)(dian)模式下抑制最強電(dian)(dian)(dian)池單元的電(dian)(dian)(dian)壓攀(pan)升(sheng)。為限制功耗，此類電(dian)(dian)(dian)路(lu)一(yi)(yi)般只允許以100mA左右的小(xiao)電(dian)(dian)(dian)流放(fang)電(dian)(dian)(dian)，從而(er)導(dao)致(zhi)充(chong)電(dian)(dian)(dian)平(ping)衡(heng)耗時可高達幾小(xiao)時。

2.主(zhu)動(dong)平衡法(fa)：相關資料中有很(hen)多種主(zhu)動(dong)平衡法(fa)，均(jun)需要一個用(yong)于轉移能量的(de)存(cun)儲(chu)元件(jian)。如果用(yong)電(dian)容(rong)來做存(cun)儲(chu)元件(jian)，將(jiang)其與(yu)所有電(dian)池單元相連就(jiu)需要龐大的(de)開關陣(zhen)列。更有效(xiao)的(de)方法(fa)是將(jiang)能量存(cun)儲(chu)在(zai)一個磁(ci)場中。

在電池(chi)單元之間轉移(yi)能(neng)量(liang)

將(jiang)多個單獨的(de)電(dian)池單元(yuan)電(dian)壓復接至一個基于地電(dian)壓的(de)模數轉換器(ADC)輸入端

該(gai)電路(lu)是按(an)照回(hui)掃變壓(ya)器(qi)原理構造的。這(zhe)類變壓(ya)器(qi)能(neng)(neng)夠將能(neng)(neng)量存儲在磁場中(zhong)(zhong)。其(qi)鐵氧體磁心中(zhong)(zhong)的氣隙(xi)增大了磁阻，因此可以(yi)避免磁心材料出現(xian)磁飽和。該(gai)變壓(ya)器(qi)兩側的電路(lu)是不(bu)同的：

初(chu)級線圈與整個(ge)電池(chi)組相連

次級線圈與每(mei)個電池單(dan)元相連

由于(yu)變壓(ya)(ya)器可以(yi)雙(shuang)向工作(zuo)，因此我們可以(yi)根據(ju)情況采(cai)取兩種不同的平(ping)(ping)(ping)衡(heng)方法。在對所有(you)電(dian)(dian)池(chi)單元(yuan)進行電(dian)(dian)壓(ya)(ya)掃描(miao)(miao)之(zhi)后(電(dian)(dian)壓(ya)(ya)掃描(miao)(miao)的細節(jie)將在后面(mian)介紹)，計算平(ping)(ping)(ping)均(jun)值(zhi)(zhi)，然后檢查電(dian)(dian)壓(ya)(ya)偏(pian)離平(ping)(ping)(ping)均(jun)值(zhi)(zhi)最大的電(dian)(dian)池(chi)單元(yuan)。如果(guo)其電(dian)(dian)壓(ya)(ya)低于(yu)平(ping)(ping)(ping)均(jun)值(zhi)(zhi)，就(jiu)采(cai)用底部平(ping)(ping)(ping)衡(heng)法(bottom-balancing)，如果(guo)其電(dian)(dian)壓(ya)(ya)高(gao)于(yu)平(ping)(ping)(ping)均(jun)值(zhi)(zhi)，就(jiu)采(cai)用頂(ding)部平(ping)(ping)(ping)衡(heng)法(top-balancing)。

1.底部平衡(heng)法：采(cai)用的(de)(de)底部平衡(heng)法對(dui)電(dian)池(chi)(chi)單元最弱(ruo)的(de)(de)單元，必須對(dui)其進行增強。電(dian)池(chi)(chi)組開始對(dui)最弱(ruo)的(de)(de)單元充電(dian)，能量就可以轉移至選(xuan)定的(de)(de)弱(ruo)電(dian)池(chi)(chi)單元。

每個周(zhou)期(qi)均(jun)包含兩個主動(dong)脈沖和一個暫停(ting)。在本例中，40毫秒的(de)周(zhou)期(qi)轉換(huan)為(wei)頻率就是25kHz。在設計變壓器時，其工(gong)作頻段應(ying)在20kHz以上，以避免出現人類聽覺頻率范圍內可感知(zhi)的(de)嘯叫(jiao)噪音(yin)。這種(zhong)聲音(yin)是由變壓器鐵氧體磁心的(de)磁致(zhi)(zhi)伸(shen)縮導(dao)致(zhi)(zhi)的(de)。

尤其是當某個電(dian)(dian)(dian)池單元的(de)(de)(de)電(dian)(dian)(dian)壓已經達(da)到(dao)SoC的(de)(de)(de)下(xia)限(xian)時，底(di)部平衡法(fa)能夠幫助延長整(zheng)個電(dian)(dian)(dian)池組(zu)的(de)(de)(de)工作時間。只要電(dian)(dian)(dian)池組(zu)提供的(de)(de)(de)電(dian)(dian)(dian)流(liu)低(di)于(yu)平均(jun)平衡電(dian)(dian)(dian)流(liu)，車輛就能繼續工作，直到(dao)最后一塊(kuai)電(dian)(dian)(dian)池單元也被耗盡。

2.頂部(bu)平衡(heng)法：如(ru)果某個電池單(dan)(dan)元(yuan)的(de)電壓(ya)高(gao)于其他單(dan)(dan)元(yuan)，那么就(jiu)需要將其中的(de)能(neng)量(liang)導出(chu)，這在充(chong)電模式下尤其必(bi)要。如(ru)果不進行平衡(heng)，充(chong)電過程(cheng)在第一塊電池單(dan)(dan)元(yuan)充(chong)滿之(zhi)后就(jiu)不得不立即停止(zhi)。采用平衡(heng)之(zhi)后則可以通過保持所有(you)電池單(dan)(dan)元(yuan)的(de)電壓(ya)相等而避(bi)免發生過早停止(zhi)充(chong)電的(de)情況(kuang)。

整(zheng)個電(dian)池(chi)組(zu)中(zhong)電(dian)壓(ya)最高的(de)單(dan)(dan)元(yuan)，電(dian)流從電(dian)池(chi)流向變壓(ya)器，由(you)于自(zi)感(gan)的(de)存在，電(dian)流隨時間線性增大。而由(you)于自(zi)感(gan)是變壓(ya)器的(de)一個固有特性，因(yin)此開(kai)(kai)關的(de)導(dao)通時間就決(jue)定了能(neng)夠(gou)達(da)到的(de)最大電(dian)流值。電(dian)池(chi)單(dan)(dan)元(yuan)中(zhong)轉(zhuan)移(yi)出的(de)能(neng)量以磁場的(de)形(xing)式(shi)得到存儲(chu)。在開(kai)(kai)關斷開(kai)(kai)后，必(bi)須閉合主開(kai)(kai)關。此時，變壓(ya)器就從儲(chu)能(neng)模(mo)(mo)式(shi)進入(ru)了能(neng)量輸出模(mo)(mo)式(shi)。能(neng)量通過巨大的(de)初(chu)級線圈送入(ru)整(zheng)個電(dian)池(chi)組(zu)。

頂部(bu)平衡法(fa)中的(de)電(dian)流(liu)和時序(xu)條件與(yu)底部(bu)平衡法(fa)非常(chang)類似，只是順(shun)序(xu)和電(dian)流(liu)的(de)方向與(yu)底部(bu)平衡法(fa)相反。

為了(le)管理每個電(dian)(dian)(dian)池單元(yuan)的(de)(de)充電(dian)(dian)(dian)狀態，必須測量(liang)它(ta)們各自(zi)的(de)(de)電(dian)(dian)(dian)壓。由于只有(you)單元(yuan)1在微控制器的(de)(de)ADC范圍內，因此模塊中其他單元(yuan)的(de)(de)電(dian)(dian)(dian)壓無法直接測量(liang)。一種可能的(de)(de)方案是采(cai)用一組(zu)差(cha)分放大器陣列，而(er)且它(ta)們必須支(zhi)持整個電(dian)(dian)(dian)池模塊的(de)(de)電(dian)(dian)(dian)壓。

下文(wen)中(zhong)描(miao)述的方(fang)法(fa)只需增加很少量(liang)(liang)的額(e)外(wai)硬(ying)件(jian)就能(neng)測量(liang)(liang)所有(you)電池單元的電壓(ya)。在該方(fang)法(fa)中(zhong)，主要任務是進行充電平衡的變(bian)壓(ya)器同時也被用(yong)做一個復(fu)用(yong)器。

在(zai)電(dian)壓(ya)掃(sao)描模式中沒(mei)有(you)使用變(bian)壓(ya)器的(de)回掃(sao)模式。當S1到Sn這些(xie)開關(guan)中有(you)一個閉(bi)合(he)時，與(yu)其相連(lian)的(de)電(dian)池單元的(de)電(dian)壓(ya)就(jiu)轉(zhuan)換(huan)到變(bian)壓(ya)器的(de)所有(you)繞組中。

在經過(guo)一個離散濾波(bo)器(qi)的(de)(de)簡單預處理之(zhi)后，被測(ce)信號就被送入微控制器(qi)的(de)(de)ADC輸入端口。開關(guan)S1到Sn中(zhong)的(de)(de)某個開關(guan)閉合時所(suo)產(chan)生的(de)(de)測(ce)量脈沖(chong)持(chi)續時間可(ke)能(neng)(neng)非(fei)常(chang)短(duan)，實際導通時間為(wei)4us。因此，通過(guo)這個脈沖(chong)存(cun)儲至變壓器(qi)中(zhong)的(de)(de)能(neng)(neng)量很少。而且無論如何在開關(guan)斷開之(zhi)后，存(cun)儲在磁場中(zhong)的(de)(de)能(neng)(neng)量都會通過(guo)初級晶體管(guan)流回(hui)整個電(dian)(dian)池模(mo)塊(kuai)。因此電(dian)(dian)池模(mo)塊(kuai)的(de)(de)能(neng)(neng)量多少并不受(shou)影(ying)響。在對所(suo)有電(dian)(dian)池單元(yuan)進行完一個周期的(de)(de)掃(sao)描之(zhi)后，系(xi)統又回(hui)到初始狀(zhuang)態。