單級功率因數校正開關電源
1、 引言
為(wei)(wei)減少辦公自動化設(she)備、計算機和家(jia)用(yong)電(dian)器等內部開關電(dian)源(yuan)對(dui)(dui)電(dian)網的(de)污染(ran),國際電(dian)工(gong)委員會和一些國家(jia)與地(di)區推(tui)出了IEC1000-3-2和EN61000-3-2等標準,對(dui)(dui)電(dian)流皆波(bo)作(zuo)出了限量規定。為(wei)(wei)滿足輸入電(dian)流諧波(bo)限制要求(qiu),最有(you)效的(de)技術手段就有(you)源(yuan)功率因數校正(有(you)源(yuan)PFC)。
目前被(bei)廣(guang)為采用的有(you)源PFC技術(shu)是兩級方案,即有(you)源PFC升壓變換器+DC-DC變換器,如圖(tu)1所示。
圖1 兩級(ji)PFC變換器電路級(ji)成框圖
兩級PFC變換器(qi)(qi)使(shi)用(yong)兩個(ge)(ge)開(kai)關(通常為MOSFET)和(he)兩個(ge)(ge)控(kong)制(zhi)器(qi)(qi),即一(yi)(yi)個(ge)(ge)功(gong)率因(yin)數(shu)控(kong)制(zhi)器(qi)(qi)和(he)一(yi)(yi)個(ge)(ge)PWM控(kong)制(zhi)器(qi)(qi)。只有(you)在采用(yong)PFC/PWM組合控(kong)制(zhi)器(qi)(qi)IC時,才能使(shi)用(yong)一(yi)(yi)個(ge)(ge)控(kong)制(zhi)器(qi)(qi),但仍需用(yong)兩個(ge)(ge)開(kai)關。兩級PFC在技術上十分成(cheng)熟(shu),早已獲得廣(guang)泛應用(yong),但該方案(an)存在電路拓樸復雜和(he)成(cheng)本較(jiao)高等缺點(dian)。
單級PFC AC-DC變換(huan)器中的PFC級和(he)DC-DC級共(gong)用(yong)一(yi)個開關管和(he)采用(yong)PWM方式的一(yi)套(tao)控制電路,同時實現(xian)功率因數校正(zheng)和(he)對(dui)輸出(chu)電壓(ya)的調節。
2、單級PFC變換器基本電路拓樸
2.1 單級PFC變換器基本電路
單級(ji)PFC變(bian)換(huan)器(qi)通(tong)(tong)常由升(sheng)(sheng)壓型(xing)PFC級(ji)和DC-DC變(bian)換(huan)器(qi)組合而成。其中(zhong)的DC-DC變(bian)換(huan)器(qi)又分正激(ji)(ji)式和反激(ji)(ji)式兩(liang)(liang)種類型(xing)。圖2所示為基本的單級(ji)隔離型(xing)正激(ji)(ji)式升(sheng)(sheng)壓PFC電(dian)路。兩(liang)(liang)部分電(dian)路共用一(yi)個開關(guan)(Q1),通(tong)(tong)過=極管D1的電(dian)流(liu)(liu)為儲能(neng)電(dian)容C1充電(dian),D2在Q1關(guan)斷(duan)時防(fang)止(zhi)電(dian)流(liu)(liu)倒流(liu)(liu)。通(tong)(tong)過控制Q1的通(tong)(tong)斷(duan),電(dian)路同時完成對(dui)AC輸(shu)(shu)入電(dian)流(liu)(liu)的整形和對(dui)輸(shu)(shu)出電(dian)壓的調節(jie)。
圖2 基本(ben)的(de)單級隔離(li)式升(sheng)壓型PFC電路
由于全波橋式整流電路輸入連接AC供電線路,瞬時輸入功率是隨時變化的,欲得到穩定的功率輸出,要依靠儲能電容實現功率平衡。對于DC-DC變換器,通(tong)常(chang)在連續模式(CCM)下工作,占空因(yin)數不隨頁栽變化。而全橋整流(liu)輸出(chu)電(dian)壓(ya)與頁載大小(xiao)無(wu)關,當頁栽減輕時(shi),輸出(chu)功率(lv)減小(xiao),但PFC級(ji)輸入(ru)功率(lv)同重載時(shi)一樣,使充入(ru)CI的能(neng)量等于(yu)從(cong)CI抽取(qu)的能(neng)量,別起直流(liu)總線電(dian)壓(ya)明顯上升,CI上的電(dian)壓(ya)應力(li)往往達1000V以上,對開(kai)關器件的耐壓(ya)要求非常(chang)高。由于(yu)開(kai)關器件的電(dian)壓(ya)高,電(dian)流(liu)應力(li)大,開(kai)關損耗大,并且(qie)功率(lv)從(cong)輸入(ru)到輸出(chu)要經兩次變換,故效率(lv)低。
2.2 改刊型單級PFC變換器電路
為降低儲能電容上的高壓和變換器效率,必須對圖2所示的單級PFC基本電路拓樸進行改進。
一(yi)種用變壓器(qi)雙線組(zu)(zu)實現頁反(fan)饋的單級(ji)PFC變換器(qi)電路如圖3所示。N1和N2繞組(zu)(zu)為(wei)變壓器(qi)T1的耦合繞組(zu)(zu)。
圖(tu)3 用雙繞組實現頁(ye)反饋的單級PFC變換(huan)器
當(dang)開關(guan)Q1導通時(shi),電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)VC1施(shi)加到T1初級繞組(zu)。當(dang)經整(zheng)的電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)大于N1上的電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)時(shi),升壓(ya)(ya)(ya)電(dian)(dian)(dian)(dian)感(gan)器L1上才會(hui)有電(dian)(dian)(dian)(dian)流(liu)通過(guo)。當(dang)Q1截止時(shi),加在L1上的反向電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)為VC1與(yu)N2上的電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)VN2之和(he)減去輸入(ru)電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)。N1和(he)N2兩個耦合線圈的加入(ru),提(ti)供了頁(ye)反饋電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya),減輕(qing)了C1上的電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)應力,提(ti)高了效率。但是(shi),加入(ru)N1和(he)N2后,會(hui)降低功率因數,增加電(dian)(dian)(dian)(dian)流(liu)諧波(bo)含(han)量。如(ru)果在D2與(yu)N1之間加入(ru)一個電(dian)(dian)(dian)(dian)感(gan),使輸入(ru)電(dian)(dian)(dian)(dian)流(liu)工作在CCM,C1上的電(dian)(dian)(dian)(dian)壓(ya)(ya)(ya)還可以降低。在圖3中。要求N1+N2<NP。
圖4示出了帶(dai)低頻輔助開(kai)關的(de)(de)CCM單級PFC變換器電(dian)(dian)(dian)(dian)(dian)路(lu)。Q1為(wei)主開(kai)關,Q2為(wei)輔助開(kai)關。在輸(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)流(liu)過(guo)零附(fu)近,Q2導通,使(shi)附(fu)加繞(rao)組N1短路(lu)當輸(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)壓(ya)大(da)于(yu)某一值時(shi),Q2關斷。由于(yu)Q2在輸(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)壓(ya)很(hen)小時(shi)才會(hui)導通,其余的(de)(de)時(shi)間阻斷,流(liu)過(guo)Q2的(de)(de)電(dian)(dian)(dian)(dian)(dian)流(liu)很(hen)小,Q2的(de)(de)功(gong)率(lv)損耗也就很(hen)小。這種(zhong)電(dian)(dian)(dian)(dian)(dian)路(lu)拓樸與圖3電(dian)(dian)(dian)(dian)(dian)路(lu)比較(jiao),減(jian)小了輸(shu)入(ru)(ru)電(dian)(dian)(dian)(dian)(dian)流(liu)的(de)(de)諧波含量,提高了功(gong)率(lv)因(yin)數和效率(lv),降低了電(dian)(dian)(dian)(dian)(dian)容(C1)上的(de)(de)電(dian)(dian)(dian)(dian)(dian)壓(ya)。
圖4 帶低(di)頻輔助開關的(de)CCM單級PFC變換器
圖5所示為帶有(you)源(yuan)(yuan)箱(xiang)(xiang)信和(he)(he)(he)(he)軟(ruan)開(kai)關(guan)(guan)(guan)(guan)的(de)(de)單級隔離(li)式PFC變(bian)(bian)換器(qi)(qi)電(dian)路(lu)。圖中(zhong),Q1為主開(kai)關(guan)(guan)(guan)(guan),Q2為輔助(zhu)開(kai)關(guan)(guan)(guan)(guan),C1為儲能電(dian)容,C2為箱(xiang)(xiang)位(wei)電(dian)容,C2為Q1、Q2和(he)(he)(he)(he)電(dian)路(lu)中(zhong)寄生電(dian)容之(zhi)和(he)(he)(he)(he)。電(dian)路(lu)的(de)(de)升(sheng)壓(ya)級工作在DCM,從(cong)而保證(zheng)有(you)較(jiao)高的(de)(de)功率因數。反激式變(bian)(bian)換器(qi)(qi)級設計工作在CCM,,從(cong)而避免了(le)(le)產生較(jiao)高的(de)(de)電(dian)流(liu)應力(li)。電(dian)路(lu)采(cai)用有(you)源(yuan)(yuan)箱(xiang)(xiang)位(wei)和(he)(he)(he)(he)軟(ruan)開(kai)關(guan)(guan)(guan)(guan)技術來限制(zhi)開(kai)關(guan)(guan)(guan)(guan)MOSFET的(de)(de)電(dian)壓(ya)應力(li)。存儲在變(bian)(bian)壓(ya)器(qi)(qi)漏感中(zhong)的(de)(de)再生能量,為主開(kai)關(guan)(guan)(guan)(guan)Q1和(he)(he)(he)(he)輔助(zhu)開(kai)關(guan)(guan)(guan)(guan)Q2提供了(le)(le)軟(ruan)開(kai)關(guan)(guan)(guan)(guan)條(tiao)件(jian),從(cong)而減(jian)少(shao)了(le)(le)開(kai)關(guan)(guan)(guan)(guan)損(sun)耗,提高了(le)(le)變(bian)(bian)換器(qi)(qi)效率。Q1和(he)(he)(he)(he)Q2采(cai)用同一控制(zhi)電(dian)路(lu)和(he)(he)(he)(he)驅動電(dian)路(lu),從(cong)而使(shi)拓(tuo)樸(pu)結(jie)構(gou)簡(jian)化。
圖(tu)5 帶(dai)有源箱位和軟開關的單級隔離(li)式PFC變換器
3、基于Flyboost模塊的單級PFC AC-DC變換器
基于Flyboost模塊(kuai)的(de)單級PFC AC-DC變(bian)(bian)換(huan)器(qi)(qi)(qi)電(dian)(dian)(dian)(dian)路(lu)如圖6所(suo)示。該變(bian)(bian)換(huan)器(qi)(qi)(qi)建立在(zai)反(fan)(fan)(fan)激式升壓(ya)拓(tuo)樸基礎上(shang),工作狀(zhuang)態(tai)分反(fan)(fan)(fan)激式變(bian)(bian)壓(ya)器(qi)(qi)(qi)狀(zhuang)態(tai)和(he)升壓(ya)狀(zhuang)態(tai)兩個工作狀(zhuang)態(tai)。若Vin(t)為(wei)Ac輸(shu)(shu)入電(dian)(dian)(dian)(dian)壓(ya)的(de)瞬時值,Vc1為(wei)儲能(neng)電(dian)(dian)(dian)(dian)容C1上(shang)的(de)電(dian)(dian)(dian)(dian)壓(ya),n為(wei)變(bian)(bian)壓(ya)器(qi)(qi)(qi)T1的(de)電(dian)(dian)(dian)(dian)壓(ya)比,在(zai)反(fan)(fan)(fan)激式變(bian)(bian)壓(ya)器(qi)(qi)(qi)狀(zhuang)態(tai)的(de)一(yi)個開(kai)(kai)關周期內,當開(kai)(kai)關Q1導(dao)通時,T1被充電(dian)(dian)(dian)(dian),儲存能(neng)量(liang);當Q1截止時,由于(Vin(t))<(Vc1-nVo),D6不能(neng)導(dao)通,儲存在(zai)T1中的(de)能(neng)量(liang)全部傳送到輸(shu)(shu)出端(duan)。在(zai)這種工作狀(zhuang)態(tai),全橋整(zheng)流輸(shu)(shu)出端(duan)的(de)變(bian)(bian)換(huan)器(qi)(qi)(qi)輸(shu)(shu)入電(dian)(dian)(dian)(dian)流Iin波形(xing)(xing)為(wei)直(zhi)角三角形(xing)(xing),平均輸(shu)(shu)入電(dian)(dian)(dian)(dian)流Iin(avg)為(wei):
在升壓電感狀態,當>(Vc1-Vo)時(shi),T1相(xiang)(xiang)當于一(yi)(yi)個(ge)升壓(ya)電感(gan)。在(zai)一(yi)(yi)個(ge)開關周期內,當Q1導(dao)能時(shi),T1初級(ji)繞組電感(gan)LP經D5充(chong)電儲(chu)能;當Q1關斷時(shi),D6導(dao)通,在(zai)LP中(zhong)的儲(chu)能向C1放(fang)電,工作情況與一(yi)(yi)般升壓(ya)電感(gan)型單級(ji)PFC變換器相(xiang)(xiang)同。在(zai)此(ci)狀態(tai)下,平均輸入電流可表示為(wei):
式(shi)中:D為(wei)開關5空比,Ts為(wei)開關周期。
從式(1)和(2)可知,在兩(liang)種工作(zuo)狀(zhuang)態下,平均輸入(ru)電(dian)(dian)(dian)流均與輸入(ru)電(dian)(dian)(dian)壓成正比,從而實現(xian)功率因數校正。C1上的(de)電(dian)(dian)(dian)壓被箱位在(Vin(peak)+n.Vo)電(dian)(dian)(dian)平上,通(tong)常不超過(guo)400Vo此(ci)電(dian)(dian)(dian)路拓樸的(de)功率因數一般可達0.95以上,效(xiao)率超過(guo)80%。
圖(tu)6 基于Flyboost模塊(kuai)的單級PFC AC-DC變(bian)換器(qi)
4、基于:W2202的數字單級PFC電路
圖7所示為基于數字控制器iw2202的(de)單級(ji)PFC變換(huan)器電(dian)路。Iw2202與本刊(kan)2005年第(di)11期《一(yi)種全數字高效率開關(guan)電(dian)源(yuan)》一(yi)文(wen)中介紹的(de)iw2201一(yi)樣(yang),采(cai)用了脈沖串(pulseTainTM)專有技(ji)術(shu)和實時波(bo)形分析及智能跳(tiao)越(SmartSkip)技(ji)術(shu)。但是,iw2201不具有PFC功(gong)能,而iw2202集成了單級(ji)PFC變換(huan)器控制功(gong)能。
圖7 基于數字控制(zhi)器(qi)iw2202的單(dan)級(ji)PFC變換器(qi)
圖7所(suo)示的電(dian)路橋式(shi)整流(liu)后邊(bian)拓樸,為PFC升(sheng)壓與反激式(shi)整流(liu)器相結(jie)合/能量儲存/DC-DC(BoostintegratedwithFlybackRectifier/Energy Storage/DC-DC,簡寫為(BIFRED)拓樸,利(li)用不連續(xu)模式(shi)(DCM)升(sheng)壓變(bian)換器實(shi)現功率因數校正。變(bian)壓器初級繞組(WP)串(chuan)聯的儲能電(dian)容C1,用作驅(qu)動反激式(shi)變(bian)換器。電(dian)路的工作原理如下:
當開關Q1導(dao)通時,來自AC線(xian)路的(de)能(neng)量(liang)被(bei)(bei)儲(chu)存在升(sheng)壓電(dian)感(gan)器L1中。與此同時,來自C1的(de)能(neng)量(liang)被(bei)(bei)儲(chu)存在反激式變壓器T1的(de)初級繞組中。
當Q1關斷時(shi),在T1初級儲存(cun)的(de)能量傳送到輸出。同時(shi),在升壓(ya)電(dian)感(gan)器L1中(zhong)的(de)能量傳輸到電(dian)容(rong)C1,對(dui)C1進行充電(dian)。
在AC線路輸入的(de)(de)半周期內,兩個(ge)電(dian)(dian)感器(L1和(he)LP)儲(chu)存的(de)(de)能(neng)(neng)量平(ping)均值相等(deng),從(cong)而使C1上的(de)(de)電(dian)(dian)壓保(bao)持不變。用iw2202作為(wei)控(kong)制器,解(jie)決了(le)儲(chu)能(neng)(neng)電(dian)(dian)容上電(dian)(dian)壓應力(li)過(guo)高的(de)(de)問(wen)題。在通(tong)常情況下,C1上的(de)(de)電(dian)(dian)壓不會超(chao)過(guo)400V,從(cong)而C1可(ke)選用400V的(de)(de)標準電(dian)(dian)容器。基于iw2202的(de)(de)全(quan)數字(zi)SMPS,可(ke)以實現單位功率因數(即PF=1)和(he)小于5%的(de)(de)總(zong)諧波失真(THD)
5、結束語
單(dan)級PFC變換器電(dian)(dian)路簡(jian)單(dan),但PFC和對輸(shu)入(ru)電(dian)(dian)流諧波抑(yi)制的效果不(bu)如兩級PFC變換器。基于(yu)全數(shu)字控(kong)制器iw2202的單(dan)級全數(shu)字PFC變換器,可以(yi)實現接近于(yu)I的功率因數(shu),輸(shu)入(ru)電(dian)(dian)流達到(dao)低失(shi)真指標(biao),滿足(zu)IEC1000-3-2規(gui)定限值。