一、內部主電路結構

采用“交-直(zhi)-交”結構(gou)的低壓(ya)變頻器，其(qi)內(nei)部(bu)主電路由整(zheng)(zheng)流(liu)和逆(ni)變兩大部(bu)分組成(cheng)(cheng)，如圖1所示。從R、S、T端輸入的三相交流(liu)電，經三相整(zheng)(zheng)流(liu)橋（由二(er)極(ji)管(guan)D1～D6構(gou)成(cheng)(cheng)）整(zheng)(zheng)流(liu)成(cheng)(cheng)直(zhi)流(liu)電，電壓(ya)為UD。電容(rong)器C1和C2是濾波電容(rong)器。6個(ge)IGBT管(guan)（絕(jue)緣柵雙(shuang)極(ji)性晶體管(guan)）V1～V6構(gou)成(cheng)(cheng)三相逆(ni)變橋，把直(zhi)流(liu)電逆(ni)變成(cheng)(cheng)頻率(lv)和電壓(ya)任意可(ke)調的三相交流(liu)電。

圖1 變(bian)頻器內部主電路

二、均壓電阻和限流電阻

圖(tu)1中，濾(lv)(lv)(lv)波(bo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)器(qi)(qi)C1和(he)C2兩端(duan)(duan)各并聯(lian)了(le)一(yi)個電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)，是(shi)為(wei)了(le)使兩只電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)器(qi)(qi)上(shang)的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)基本相等，防(fang)止電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)器(qi)(qi)在(zai)工(gong)作中損壞（目前，由于(yu)技術的(de)(de)進步，低(di)壓(ya)(ya)（380V）變頻(pin)器(qi)(qi)的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)解電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)大(da)多數(shu)可(ke)以不需要(yao)串(chuan)聯(lian)使用了(le)）。在(zai)整(zheng)流(liu)(liu)(liu)(liu)橋(qiao)和(he)濾(lv)(lv)(lv)波(bo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)器(qi)(qi)之(zhi)間接(jie)有一(yi)個電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)R和(he)一(yi)對接(jie)觸(chu)器(qi)(qi)觸(chu)點KM，其(qi)緣由是(shi)：變頻(pin)器(qi)(qi)剛(gang)接(jie)通(tong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源時(shi)，濾(lv)(lv)(lv)波(bo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)器(qi)(qi)上(shang)的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)為(wei)0V，而電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)為(wei)380V時(shi)的(de)(de)整(zheng)流(liu)(liu)(liu)(liu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)峰(feng)值是(shi)537V，這樣在(zai)接(jie)通(tong)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源的(de)(de)瞬間將有很大(da)的(de)(de)充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)沖(chong)擊電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)，有可(ke)能損壞整(zheng)流(liu)(liu)(liu)(liu)二(er)極管；另外，端(duan)(duan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)為(wei)0的(de)(de)濾(lv)(lv)(lv)波(bo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)器(qi)(qi)會(hui)使整(zheng)流(liu)(liu)(liu)(liu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)瞬間降低(di)至0V，形成對電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源網絡的(de)(de)干擾(rao)。為(wei)了(le)解決上(shang)述問(wen)題，在(zai)整(zheng)流(liu)(liu)(liu)(liu)橋(qiao)和(he)濾(lv)(lv)(lv)波(bo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)器(qi)(qi)之(zhi)間接(jie)入一(yi)個限(xian)流(liu)(liu)(liu)(liu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)R，可(ke)將濾(lv)(lv)(lv)波(bo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)器(qi)(qi)的(de)(de)充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)(liu)限(xian)制(zhi)在(zai)一(yi)個允許范圍內(nei)。但是(shi)，如果限(xian)流(liu)(liu)(liu)(liu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)R始終接(jie)在(zai)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)內(nei)，其(qi)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)降將影響變頻(pin)器(qi)(qi)的(de)(de)輸出(chu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)，也會(hui)降低(di)變頻(pin)器(qi)(qi)的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)能轉(zhuan)換效率，因(yin)此，濾(lv)(lv)(lv)波(bo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)器(qi)(qi)充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)完畢后，由接(jie)觸(chu)器(qi)(qi)KM將限(xian)流(liu)(liu)(liu)(liu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)R短接(jie)，使之(zhi)退出(chu)運(yun)行。

三、主電路的對外連接端子

各種變(bian)(bian)頻器主電(dian)路的(de)(de)對外連接端(duan)(duan)子(zi)(zi)(zi)大致相同，如(ru)圖2所示。其中，R、S、T是變(bian)(bian)頻器的(de)(de)電(dian)源端(duan)(duan)子(zi)(zi)(zi)，接至交流(liu)三(san)相電(dian)源；U、V、W為變(bian)(bian)頻器的(de)(de)輸出端(duan)(duan)子(zi)(zi)(zi)，接至電(dian)動機；P+是整流(liu)橋輸出的(de)(de)+端(duan)(duan)，出廠(chang)時P+端(duan)(duan)與(yu)P端(duan)(duan)之(zhi)間(jian)用一塊截面積足夠(gou)大的(de)(de)銅片(pian)(pian)短接，當需要接入直流(liu)電(dian)抗器DL時，拆去銅片(pian)(pian)，將DL接在P+和P之(zhi)間(jian)；P、N是濾波(bo)后直流(liu)電(dian)路的(de)(de)+、-端(duan)(duan)子(zi)(zi)(zi)，可以連接制(zhi)(zhi)動單(dan)元和制(zhi)(zhi)動電(dian)阻(zu)；PE是接地端(duan)(duan)子(zi)(zi)(zi)。

圖2 主電路(lu)對外連接端子

四、變頻系統的共用直流母線

電(dian)(dian)(dian)動(dong)(dong)(dong)(dong)機(ji)在(zai)制(zhi)(zhi)(zhi)動(dong)(dong)(dong)(dong)（發電(dian)(dian)(dian)）狀(zhuang)態(tai)時(shi)(shi)，變頻(pin)(pin)器從電(dian)(dian)(dian)動(dong)(dong)(dong)(dong)機(ji)吸(xi)收(shou)的(de)(de)(de)能(neng)(neng)(neng)量(liang)都會(hui)保(bao)存在(zai)變頻(pin)(pin)器直流(liu)(liu)環節(jie)的(de)(de)(de)電(dian)(dian)(dian)解(jie)電(dian)(dian)(dian)容中(zhong)，并(bing)導(dao)致變頻(pin)(pin)器中(zhong)的(de)(de)(de)直流(liu)(liu)母(mu)線(xian)電(dian)(dian)(dian)壓升高(gao)。如(ru)果(guo)變頻(pin)(pin)器配備制(zhi)(zhi)(zhi)動(dong)(dong)(dong)(dong)單(dan)元(yuan)和(he)制(zhi)(zhi)(zhi)動(dong)(dong)(dong)(dong)電(dian)(dian)(dian)阻(zu)（這兩種(zhong)(zhong)元(yuan)件(jian)屬于(yu)選配件(jian)），變頻(pin)(pin)器就(jiu)(jiu)可(ke)(ke)以(yi)(yi)通過短時(shi)(shi)間接通電(dian)(dian)(dian)阻(zu)，使再生電(dian)(dian)(dian)能(neng)(neng)(neng)以(yi)(yi)熱方(fang)式消耗(hao)掉，稱做能(neng)(neng)(neng)耗(hao)制(zhi)(zhi)(zhi)動(dong)(dong)(dong)(dong)。當然(ran)，采取再生能(neng)(neng)(neng)量(liang)回(hui)饋(kui)(kui)方(fang)案也可(ke)(ke)解(jie)決變頻(pin)(pin)調(diao)速系統的(de)(de)(de)再生能(neng)(neng)(neng)量(liang)問題，并(bing)可(ke)(ke)達(da)到節(jie)約能(neng)(neng)(neng)源的(de)(de)(de)目(mu)的(de)(de)(de)。而標準(zhun)通用PWM變頻(pin)(pin)器沒有設計(ji)使再生能(neng)(neng)(neng)量(liang)反(fan)饋(kui)(kui)到三相(xiang)電(dian)(dian)(dian)源的(de)(de)(de)功能(neng)(neng)(neng)。如(ru)果(guo)將多臺變頻(pin)(pin)器的(de)(de)(de)直流(liu)(liu)環節(jie)通過共(gong)(gong)用直流(liu)(liu)母(mu)線(xian)互(hu)連，則一(yi)(yi)臺或多臺電(dian)(dian)(dian)動(dong)(dong)(dong)(dong)機(ji)產生的(de)(de)(de)再生能(neng)(neng)(neng)量(liang)就(jiu)(jiu)可(ke)(ke)以(yi)(yi)被(bei)(bei)其他電(dian)(dian)(dian)動(dong)(dong)(dong)(dong)機(ji)以(yi)(yi)電(dian)(dian)(dian)動(dong)(dong)(dong)(dong)的(de)(de)(de)方(fang)式消耗(hao)吸(xi)收(shou)。或者，在(zai)直流(liu)(liu)母(mu)線(xian)上設置(zhi)一(yi)(yi)組一(yi)(yi)定容量(liang)的(de)(de)(de)制(zhi)(zhi)(zhi)動(dong)(dong)(dong)(dong)單(dan)元(yuan)和(he)制(zhi)(zhi)(zhi)動(dong)(dong)(dong)(dong)電(dian)(dian)(dian)阻(zu)，用以(yi)(yi)吸(xi)收(shou)不能(neng)(neng)(neng)被(bei)(bei)電(dian)(dian)(dian)動(dong)(dong)(dong)(dong)狀(zhuang)態(tai)電(dian)(dian)(dian)動(dong)(dong)(dong)(dong)機(ji)吸(xi)收(shou)的(de)(de)(de)再生能(neng)(neng)(neng)量(liang)。若共(gong)(gong)用直流(liu)(liu)母(mu)線(xian)與能(neng)(neng)(neng)量(liang)回(hui)饋(kui)(kui)單(dan)元(yuan)組合，就(jiu)(jiu)可(ke)(ke)以(yi)(yi)將直流(liu)(liu)母(mu)線(xian)上的(de)(de)(de)多余能(neng)(neng)(neng)量(liang)直接反(fan)饋(kui)(kui)到電(dian)(dian)(dian)網中(zhong)來，從而提高(gao)系統的(de)(de)(de)節(jie)能(neng)(neng)(neng)效果(guo)。綜上所述，在(zai)具有多臺電(dian)(dian)(dian)動(dong)(dong)(dong)(dong)機(ji)的(de)(de)(de)變頻(pin)(pin)調(diao)速系統中(zhong)，選用共(gong)(gong)用直流(liu)(liu)母(mu)線(xian)方(fang)案，配置(zhi)一(yi)(yi)組制(zhi)(zhi)(zhi)動(dong)(dong)(dong)(dong)單(dan)元(yuan)、制(zhi)(zhi)(zhi)動(dong)(dong)(dong)(dong)電(dian)(dian)(dian)阻(zu)和(he)能(neng)(neng)(neng)量(liang)回(hui)饋(kui)(kui)單(dan)元(yuan)，是(shi)一(yi)(yi)種(zhong)(zhong)提高(gao)系統性能(neng)(neng)(neng)并(bing)節(jie)約投資(zi)的(de)(de)(de)較好方(fang)案。

圖3所示為應用比(bi)較廣泛的共(gong)用直流母線方(fang)案(an)，該(gai)方(fang)案(an)包括(kuo)以下(xia)幾個部分。

圖3 變(bian)頻器的公用直(zhi)流母(mu)線

1.三相交流電源進線?

各(ge)變(bian)頻(pin)器(qi)(qi)(qi)的(de)(de)(de)(de)電源輸(shu)入(ru)端(duan)并聯于(yu)同(tong)一(yi)交流母線(xian)上，并保證(zheng)各(ge)變(bian)頻(pin)器(qi)(qi)(qi)的(de)(de)(de)(de)輸(shu)入(ru)端(duan)電源相位(wei)一(yi)致(zhi)。圖3中(zhong)，斷路(lu)器(qi)(qi)(qi)QF是(shi)每臺(tai)變(bian)頻(pin)器(qi)(qi)(qi)的(de)(de)(de)(de)進線(xian)保護裝置。LR是(shi)進線(xian)電抗器(qi)(qi)(qi)，當(dang)多臺(tai)變(bian)頻(pin)器(qi)(qi)(qi)在同(tong)一(yi)環境中(zhong)運(yun)行時(shi)，相鄰(lin)變(bian)頻(pin)器(qi)(qi)(qi)會(hui)互相干擾，為了消除或減輕這種干擾，同(tong)時(shi)為了提高變(bian)頻(pin)器(qi)(qi)(qi)輸(shu)入(ru)側的(de)(de)(de)(de)功率因數(shu)，接入(ru)LR是(shi)必須的(de)(de)(de)(de)。

2.直流母線?

KM是變頻器的直(zhi)流環節與(yu)公用直(zhi)流母線連接的控制(zhi)開關。FU是半導體快速熔斷器，其額(e)(e)定電(dian)壓可選(xuan)700V，額(e)(e)定電(dian)流必須考慮驅動(dong)(dong)電(dian)動(dong)(dong)機(ji)在(zai)電(dian)動(dong)(dong)或制(zhi)動(dong)(dong)時的最大電(dian)流，一般情(qing)況下，可以選(xuan)擇(ze)額(e)(e)定負載電(dian)流的125%。

3.公共制動單元和（或）能量回饋裝置?

回(hui)饋(kui)到公共直流母線上的再生(sheng)能(neng)量(liang)(liang)，在不能(neng)完全(quan)被(bei)吸(xi)收(shou)的情況(kuang)下，可通過共用的制動電阻消耗(hao)未被(bei)吸(xi)收(shou)的再生(sheng)能(neng)量(liang)(liang)。若采(cai)用能(neng)量(liang)(liang)回(hui)饋(kui)裝置，則這部分再生(sheng)能(neng)量(liang)(liang)將(jiang)被(bei)回(hui)饋(kui)到電網中，從而提高節能(neng)的效率。

4.控制單元?

各變頻(pin)器(qi)(qi)根據控制(zhi)單元的指令，通(tong)過KM將其直流環節(jie)并聯到共用(yong)直流母線上，或(huo)是在變頻(pin)器(qi)(qi)故障后快速地與共用(yong)直流母線斷開。