LLC的大功率智能充電器
充電器與人們的日常生活密切相關,充電器充電性能的好壞與被充電池的使用壽命、充電效率等息息相關。 由于外界溫度變化,電網電壓波動,因而大大降低了充電器充電性能的穩定性,這就需要有一種能自我調節的系統,遇到外界的干擾能實時做出回應,保證充電的(de)(de)(de)穩定性,不(bu)損壞被充(chong)電(dian)(dian)的(de)(de)(de)電(dian)(dian)池(chi)(chi)。 智(zhi)能(neng)控制在此能(neng)提(ti)(ti)供一種很好的(de)(de)(de)解決(jue)方(fang)案(an)。電(dian)(dian)源行業已經開(kai)(kai)始在其產(chan)品中運用(yong)智(zhi)能(neng)控制,通過(guo)單片機的(de)(de)(de)編程(cheng)對(dui)過(guo)壓(ya)(ya)、過(guo)流(liu)情況做出判斷,為電(dian)(dian)池(chi)(chi)提(ti)(ti)供保護。 LLC 諧(xie)振(zhen)變換(huan)器(qi)在充(chong)電(dian)(dian)器(qi)的(de)(de)(de)運用(yong)也是(shi)越來(lai)越多(duo),LLC 諧(xie)振(zhen)變換(huan)器(qi)的(de)(de)(de)拓撲本身具(ju)有(you)一些(xie)優(you)越的(de)(de)(de)性能(neng),可以(yi)實現原邊開(kai)(kai)關管在全(quan)負載(zai)下的(de)(de)(de)零(ling)電(dian)(dian)壓(ya)(ya)軟開(kai)(kai)關( ZVS ( Zero VoltageSwitch) ) ,副邊整流(liu)二極管電(dian)(dian)壓(ya)(ya)應力低,因此高輸出電(dian)(dian)壓(ya)(ya)的(de)(de)(de)情況下可以(yi)實現較高的(de)(de)(de)效率(lv)等。 這使(shi)得LLC 諧(xie)振(zhen)變換(huan)器(qi)特別適合高輸出電(dian)(dian)壓(ya)(ya)的(de)(de)(de)應用(yong)場合。 今后(hou)電(dian)(dian)源的(de)(de)(de)發(fa)展方(fang)向是(shi)用(yong)單片機來(lai)完成所有(you)功能(neng),包括(kuo):脈(mo)寬(kuan)調控、反饋(kui)、過(guo)壓(ya)(ya)過(guo)流(liu)保護等等。
下面介紹的就是一款應比亞迪公司(B YD) 的要求,設計出的一種基于單片機的智能充電器。 該充電器對充電(dian)過(guo)程(cheng)進(jin)行智能控制,系統中的(de)管理電(dian)路還(huan)具有保護功能,可防(fang)止電(dian)池的(de)過(guo)充和過(guo)放對電(dian)池造成損壞。
1 LLC 諧振變換器
本充電器設計中要考慮整流濾波、能量轉換,電路保護、軟件設計等。 而LLC 諧振變換器是能量轉換中最重要的部分,關系到充電器性能的好壞。 下面著重介(jie)紹其基本結構、數學模型及(ji)時序分析。
1. 1 LLC 諧振(zhen)變換器的(de)基本結構
圖1 所示為LLC 諧(xie)振(zhen)(zhen)變換(huan)器(qi)的原理圖。 串聯(lian)諧(xie)振(zhen)(zhen)電(dian)(dian)感(gan)Lr 、串聯(lian)諧(xie)振(zhen)(zhen)電(dian)(dian)容Cr 和(he)并聯(lian)諧(xie)振(zhen)(zhen)電(dian)(dian)感(gan)Lm ,構(gou)成LLC 諧(xie)振(zhen)(zhen)網絡(luo), Cr 也(ye)起到隔(ge)直作(zuo)用[3 ] 。 在(zai)變壓(ya)器(qi)次級,整流二極(ji)管直接連接到輸(shu)出電(dian)(dian)容Co上(shang)。
圖(tu)(tu)1 LLC 諧振變換器(qi)的原理圖(tu)(tu)
當(dang)發生諧振(zhen)時,LC 的本征(zheng)諧振(zhen)頻率為:
當Lr , Cr 和(he)Lm發生諧振時,LLC 本征諧振頻率為:
由式(1) 、(2) 可知f1 》 f2 ,當負載RL 變(bian)化時,可以調節開關(Q1 、Q2 ) 頻率在f1 和f2 間變(bian)化,使品質因數(shu)達到最大。 利用(yong)這種特性,可以方便地實現脈沖頻率模式PFM( Pul se Frequency Model) ,品質因數(shu)表示如(ru)下(xia):
LLC 諧振(zhen)網(wang)絡需要(yao)兩(liang)個(ge)磁(ci)性元件Lr 和Lm。
然而,考慮到高頻變壓器實際結構,可以把磁性元件Lr 和Lm 集成在一個變壓器內,利用變壓器的漏感作為Lr , 利用變壓器的磁化電感作為Lm , 這樣一來,可以大大減少磁性元件數目。 在設計時,只要重點設計變壓器的漏感與變壓器磁化電感即可。 因此, 為增加漏感, 需要在變壓器中加入適當的氣隙,并且控制變壓器原、副邊的繞線方式可以提高品質因素。
1. 2 LLC 的數學模(mo)型(xing)分析(xi)
通過上述分析(xi),由圖(tu)1 的LLC 諧振變換(huan)器的原理圖(tu)得其LLC 等(deng)效模型如圖(tu)2 所示。
圖2 LLC 原(yuan)理圖的等效模型圖
電壓傳遞函(han)數(shu)為:
其中:
Q 為品質因數。
利用MA TIAB 對該模(mo)型進行(xing)仿真,可(ke)以(yi)初(chu)步分析出其(qi)(qi)工作特性如圖3 所(suo)示。 其(qi)(qi)中f s 為啟動頻率( Start Frequency) f r 為諧振(zhen)頻率( ResonantFrequency)。
圖3 LLC 諧振(zhen)工作特(te)性。
從圖3 中可(ke)(ke)以(yi)看到(dao),在(zai)(zai)整個頻率(lv)(lv)圍(wei)內(nei),既有(you)降(jiang)壓(ya)的(de)(de)(de)工(gong)(gong)(gong)(gong)作(zuo)(zuo)區(qu)(qu)域(yu)(M 《 1) ,也(ye)有(you)升(sheng)壓(ya)的(de)(de)(de)工(gong)(gong)(gong)(gong)作(zuo)(zuo)區(qu)(qu)域(yu)( M 》1) ,此LLC 諧(xie)振(zhen)有(you)著較(jiao)大(da)的(de)(de)(de)應用范圍(wei)。 在(zai)(zai)輕負載(zai)時(shi),工(gong)(gong)(gong)(gong)作(zuo)(zuo)頻率(lv)(lv)逐漸(jian)升(sheng)高(gao), 工(gong)(gong)(gong)(gong)作(zuo)(zuo)在(zai)(zai)降(jiang)壓(ya)區(qu)(qu)域(yu)內(nei); 而(er)(er)在(zai)(zai)重負載(zai)時(shi), 工(gong)(gong)(gong)(gong)作(zuo)(zuo)頻率(lv)(lv)逐漸(jian)降(jiang)低, 工(gong)(gong)(gong)(gong)作(zuo)(zuo)在(zai)(zai)升(sheng)壓(ya)區(qu)(qu)域(yu)內(nei)。 由圖3 可(ke)(ke)知, 串聯諧(xie)振(zhen)的(de)(de)(de)工(gong)(gong)(gong)(gong)作(zuo)(zuo)區(qu)(qu)域(yu)應該為(wei)(wei)f s / f r 》 1 ,才能(neng)工(gong)(gong)(gong)(gong)作(zuo)(zuo)在(zai)(zai)ZVS 的(de)(de)(de)狀(zhuang)態。 在(zai)(zai)不同(tong)負載(zai)下(xia),為(wei)(wei)獲(huo)得ZVS 的(de)(de)(de)工(gong)(gong)(gong)(gong)作(zuo)(zuo)條(tiao)件, 只要使之工(gong)(gong)(gong)(gong)作(zuo)(zuo)在(zai)(zai)f s / f r 》 1的(de)(de)(de)右(you)側即可(ke)(ke)。 而(er)(er)LLC 諧(xie)振(zhen)不僅僅局限于f s / f r 》 1 的(de)(de)(de)區(qu)(qu)域(yu), 在(zai)(zai)某些負載(zai)下(xia)可(ke)(ke)以(yi)工(gong)(gong)(gong)(gong)作(zuo)(zuo)在(zai)(zai)f s / f r 《 1區(qu)(qu)域(yu)。 同(tong)樣可(ke)(ke)以(yi)獲(huo)得零電(dian)壓(ya)轉換(huan)的(de)(de)(de)工(gong)(gong)(gong)(gong)作(zuo)(zuo)狀(zhuang)況。 并且與串聯諧(xie)振(zhen)相(xiang)比(bi),在(zai)(zai)不同(tong)負載(zai)時(shi)的(de)(de)(de)頻率(lv)(lv)變化范圍(wei)更小。
1. 3 LLC 諧振變(bian)換器的時(shi)序分析
LLC 諧振變(bian)換(huan)器(qi)(qi)由兩(liang)個主開(kai)關管Q1 和Q2 構(gou)成,其驅動(dong)信號是占(zhan)空(kong)比固定(ding)為0. 5 的(de)互補(bu)驅動(dong)信號。 為了(le)保證原邊(bian)功率MOS 管的(de)ZVS , 副(fu)邊(bian)二(er)極(ji)管的(de)ZCS(Zero Current Switch) 都可(ke)以實現,工作頻率在(zai)f 2 《 f ≤f 1 時, 其工作波(bo)形圖(tu)如圖(tu)4 所示(shi)。 從圖(tu)中(zhong)可(ke)以看出LLC 變(bian)換(huan)器(qi)(qi)工作在(zai)半個周期內可(ke)以分為三個工作模式(shi)。
模式1 (t0 - t1):兩個開(kai)關管(guan)(Q1 、Q2 ) 都截止(zhi),Q1 的(de)反向(xiang)二(er)級管(guan)導(dao)通(tong)續流, Lr 上的(de)電(dian)(dian)流逐漸減(jian)小,變壓器產生感生電(dian)(dian)流,向(xiang)負載供電(dian)(dian)。 反向(xiang)二(er)極管(guan)的(de)導(dao)通(tong)將Q1兩端的(de)電(dian)(dian)壓鉗位(wei)在零。
模式2 (t1 - t2):Lr 上的電流在t1 時(shi)(shi)刻減(jian)小到零,Q1 在此(ci)時(shi)(shi)刻導(dao)通, Lr 上的電流反向增大(da), 達到峰值后減(jian)小。 Lm 上的電流先減(jian)小,然后反向增加。
可(ke)以(yi)看(kan)出,t1 時刻由于Q1 的(de)反向(xiang)二極(ji)管的(de)鉗位作用,Q1 的(de)導通電壓(ya)為零。 此階段只有Lr 和Cr 進行諧(xie)振。
圖4 工作(zuo)時序(xu)波形圖
模式(shi)3 (t2 - t3):Lm 上(shang)的(de)(de)電流(liu)在(zai)t2 時(shi)刻(ke)與Lr上(shang)的(de)(de)電流(liu)相等(deng),此(ci)時(shi)流(liu)過變(bian)壓器的(de)(de)電流(liu)為零,負載(zai)與變(bian)壓器被隔離開。Q1 在(zai)此(ci)時(shi)刻(ke)關斷,Q2的(de)(de)反向二極管導通續流(liu)。 此(ci)階段Lm 也加入到諧振部(bu)分, 與Lr 和(he)Cr 串聯組成諧振回(hui)路。
在(zai)下半(ban)個(ge)(ge)周(zhou)(zhou)期中(zhong), 電(dian)(dian)(dian)路(lu)的工(gong)作與上半(ban)個(ge)(ge)周(zhou)(zhou)期剛剛相似(si),只是方向相反(fan)。整個(ge)(ge)周(zhou)(zhou)期的電(dian)(dian)(dian)路(lu)工(gong)作波形:在(zai)上半(ban)個(ge)(ge)周(zhou)(zhou)期中(zhong),開(kai)關(guan)(guan)管(guan)(guan)Q1 為(wei)零(ling)電(dian)(dian)(dian)壓導通, 而(er)Q1 在(zai)t3 時(shi)刻的關(guan)(guan)斷(duan)電(dian)(dian)(dian)流(liu)(liu)im 很小; 在(zai)下半(ban)個(ge)(ge)周(zhou)(zhou)期中(zhong),開(kai)關(guan)(guan)管(guan)(guan)Q2 為(wei)零(ling)電(dian)(dian)(dian)壓導通,而(er)Q2 在(zai)t6 時(shi)刻的關(guan)(guan)斷(duan)電(dian)(dian)(dian)流(liu)(liu)im 很小,所以Q1 、Q2 工(gong)作時(shi)的開(kai)關(guan)(guan)損耗很小。
2 充電器(qi)硬(ying)件設計
經過上面的(de)(de)分(fen)析(xi),設計中采用電流(liu)、電壓(ya)負反饋的(de)(de)方法(fa)來達到恒流(liu)、恒壓(ya)充(chong)(chong)電的(de)(de)目(mu)的(de)(de),充(chong)(chong)電器(qi)硬件原理框圖如圖5 所示(shi)。
圖5 充電器的硬(ying)件原理框圖
交流(liu)電(dian)(dian)(dian)經過濾波整(zheng)流(liu)后(hou),流(liu)向NCP1653,由其提(ti)供PFC(Power Factor Correction) 操作(zuo),NCP1653是一款連續導通(tong)(tong)型(CCM) 的(de)(de)功(gong)率(lv)(lv)因數校正( PFC) 升(sheng)壓(ya)(ya)式的(de)(de)上升(sheng)控(kong)制電(dian)(dian)(dian)路(lu), 它的(de)(de)外圍元器(qi)(qi)(qi)件數量很(hen)少,有(you)效地減少了(le)(le)(le)升(sheng)壓(ya)(ya)電(dian)(dian)(dian)感的(de)(de)體(ti)積(ji), 減小了(le)(le)(le)功(gong)率(lv)(lv)MOS管的(de)(de)電(dian)(dian)(dian)流(liu)應(ying)(ying)力,從而(er)降低(di)了(le)(le)(le)成本,且極大地簡化了(le)(le)(le)CCM 型的(de)(de)PFC 的(de)(de)操作(zuo),它還集成了(le)(le)(le)高可靠(kao)的(de)(de)保護功(gong)能。 NCP1396 電(dian)(dian)(dian)路(lu)為整(zheng)個硬件電(dian)(dian)(dian)路(lu)提(ti)供保護(包括(kuo)有(you)反饋環(huan)路(lu)失效偵測、快速(su)(su)與低(di)速(su)(su)事件輸(shu)入(ru),以及可以避(bi)免在低(di)輸(shu)入(ru)電(dian)(dian)(dian)壓(ya)(ya)下工(gong)作(zuo)的(de)(de)電(dian)(dian)(dian)源電(dian)(dian)(dian)壓(ya)(ya)過低(di)偵測等) ,NCP1396 的(de)(de)獨特架構(gou)(gou)包括(kuo)一個500 kHz 的(de)(de)壓(ya)(ya)控(kong)振蕩(dang)器(qi)(qi)(qi),由于在諧(xie)振電(dian)(dian)(dian)路(lu)結(jie)構(gou)(gou)中避(bi)開(kai)諧(xie)振尖(jian)峰相當重要(yao),因此為了(le)(le)(le)將轉換器(qi)(qi)(qi)安排在正確的(de)(de)工(gong)作(zuo)區(qu),NCP1396 內置了(le)(le)(le)可調整(zheng)且精(jing)確的(de)(de)最低(di)開(kai)關頻率(lv)(lv),通(tong)(tong)過專有(you)高電(dian)(dian)(dian)壓(ya)(ya)技(ji)術支持(chi)。 應(ying)(ying)用S3F84K4 單片機(ji)實(shi)現(xian)智(zhi)能充電(dian)(dian)(dian)器(qi)(qi)(qi)控(kong)制。
3 軟(ruan)件設計
為滿足充(chong)電要求, 該充(chong)電器(qi)軟件(jian)設計除了完成充(chong)放電控(kong)制外, 還具有過流保(bao)護(hu)、過壓保(bao)護(hu)、過溫保(bao)護(hu)、短路報警等(deng)功能(neng)模(mo)塊。主程序流程圖如圖6 所示(shi)。
圖6 主程(cheng)序(xu)流程(cheng)圖。
程序開始執行(xing)后(hou), 首先進行(xing)初始化并檢測電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)、電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)、溫度等(deng)信息是否正(zheng)(zheng)常(chang)。 如正(zheng)(zheng)常(chang)則(ze)(ze)進入下一步。 否則(ze)(ze)報警并關閉電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)。 如果(guo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)在(zai)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)終(zhong)止(zhi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)和(he)放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)終(zhong)止(zhi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)之間, 說明(ming)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)既可充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)也可放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)。 此時(shi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)將(jiang)(jiang)判斷接上(shang)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)機(ji)還是接上(shang)負(fu)載(zai)。 以進行(xing)相應的(de)(de)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)和(he)放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)。 如果(guo)兩者(zhe)都(dou)沒有接則(ze)(ze)循(xun)環檢測過(guo)程。 若電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)已經(jing)到達(da)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)終(zhong)止(zhi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)。 則(ze)(ze)等(deng)待負(fu)載(zai)的(de)(de)接入進行(xing)放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian);同樣若電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)己(ji)經(jing)達(da)到放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)終(zhong)止(zhi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)(ya),則(ze)(ze)等(deng)待充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)器的(de)(de)接入以進行(xing)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)。 在(zai)整個(ge)過(guo)程中(zhong),該電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)將(jiang)(jiang)始終(zhong)實時(shi)檢測電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)池(chi)信息,若有異常(chang)情況發生(sheng),則(ze)(ze)立即利(li)用中(zhong)斷信號終(zhong)止(zhi)正(zheng)(zheng)在(zai)進行(xing)的(de)(de)充(chong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)或者(zhe)放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)過(guo)程,關斷充(chong)放(fang)(fang)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)回路(lu),同時(shi)進行(xing)報警并提示報警原因。
4 測試結果
本充電器的各項指標如下:
(1) 輸入電流:50/ 60 Hz。
(2) AC/ DC 輸(shu)出電壓48 :V , AC/ DC 輸(shu)出電流:5. 0 A。
(3) 恒流充電電流:4. 5 A。
(4) 恒(heng)壓充電電壓:45 V (AC)。
(5) 環境(jing)溫度: - 5~45 ℃。
經分析, 按上述設計和(he)分析結果, 最(zui)后選定LLC 的參數Cr = 0. 043 055μF,Lr = 72. 636 09μH,Lm = 435. 816 5μH。
本智能充電器經測試,充電保護措施可靠,充電狀態準確,充電時間約為6 h ,如果需要進一步縮短充電時間,只需在初始化時設定更大的充電電流即可。 因為采用PWM 控制器(qi),所以(yi),充電(dian)效率可以(yi)達到(dao)92 %以(yi)上,最低時在85 %左右。根據實際(ji)需要,要想(xiang)達到(dao)理想(xiang)的充電(dian)效率,對充器(qi)件做進(jin)一步(bu)的精確要求(qiu)。
在智能充電器控制系統設計過程中,主要側重點是保證充電器對充電(dian)(dian)(dian)電(dian)(dian)(dian)池電(dian)(dian)(dian)壓的(de)精確(que)控制(zhi),設(she)計中元(yuan)器件的(de)選型(xing)也都是圍繞著(zhu)這(zhe)個(ge)重(zhong)點(dian)來完成的(de)經過實驗(yan)電(dian)(dian)(dian)路(lu)(lu)的(de)實際(ji)測試,由電(dian)(dian)(dian)源變(bian)壓器、整流電(dian)(dian)(dian)路(lu)(lu)、濾波電(dian)(dian)(dian)路(lu)(lu)及穩(wen)壓電(dian)(dian)(dian)路(lu)(lu)構成AC/ DC 變(bian)換(huan)電(dian)(dian)(dian)路(lu)(lu)。 在NCP1653 、NCP1396 與S3F84 K4 的(de)配合控制(zhi)下可實現很高的(de)系統(tong)精度。