一、內部主電路結構

采用“交(jiao)-直(zhi)(zhi)-交(jiao)”結(jie)構(gou)(gou)的(de)低壓(ya)變頻器，其內部主電(dian)路由整(zheng)(zheng)流(liu)(liu)和逆(ni)變兩大部分組(zu)成(cheng)，如(ru)圖1所示(shi)。從(cong)R、S、T端輸入的(de)三相交(jiao)流(liu)(liu)電(dian)，經(jing)三相整(zheng)(zheng)流(liu)(liu)橋(qiao)（由二極管D1～D6構(gou)(gou)成(cheng)）整(zheng)(zheng)流(liu)(liu)成(cheng)直(zhi)(zhi)流(liu)(liu)電(dian)，電(dian)壓(ya)為UD。電(dian)容器C1和C2是濾波電(dian)容器。6個IGBT管（絕(jue)緣(yuan)柵雙(shuang)極性晶體管）V1～V6構(gou)(gou)成(cheng)三相逆(ni)變橋(qiao)，把直(zhi)(zhi)流(liu)(liu)電(dian)逆(ni)變成(cheng)頻率和電(dian)壓(ya)任意可調(diao)的(de)三相交(jiao)流(liu)(liu)電(dian)。

圖1 變頻器(qi)內部主電(dian)路

二、均壓電阻和限流電阻

圖(tu)1中，濾波(bo)電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)器(qi)(qi)(qi)(qi)(qi)C1和(he)C2兩端各并(bing)聯了(le)一(yi)個電(dian)(dian)(dian)(dian)(dian)阻(zu)，是為(wei)了(le)使兩只電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)器(qi)(qi)(qi)(qi)(qi)上(shang)的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)壓(ya)基本相等，防止電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)器(qi)(qi)(qi)(qi)(qi)在工(gong)作中損(sun)壞（目前，由于技術的(de)(de)(de)進步，低(di)壓(ya)（380V）變頻器(qi)(qi)(qi)(qi)(qi)的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)解電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)大(da)多數可以不需要串聯使用了(le)）。在整流(liu)(liu)(liu)橋(qiao)和(he)濾波(bo)電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)器(qi)(qi)(qi)(qi)(qi)之(zhi)間(jian)(jian)接(jie)有一(yi)個電(dian)(dian)(dian)(dian)(dian)阻(zu)R和(he)一(yi)對接(jie)觸器(qi)(qi)(qi)(qi)(qi)觸點KM，其(qi)緣(yuan)由是：變頻器(qi)(qi)(qi)(qi)(qi)剛接(jie)通(tong)電(dian)(dian)(dian)(dian)(dian)源(yuan)時，濾波(bo)電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)器(qi)(qi)(qi)(qi)(qi)上(shang)的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)壓(ya)為(wei)0V，而(er)電(dian)(dian)(dian)(dian)(dian)源(yuan)電(dian)(dian)(dian)(dian)(dian)壓(ya)為(wei)380V時的(de)(de)(de)整流(liu)(liu)(liu)電(dian)(dian)(dian)(dian)(dian)壓(ya)峰值(zhi)是537V，這樣在接(jie)通(tong)電(dian)(dian)(dian)(dian)(dian)源(yuan)的(de)(de)(de)瞬間(jian)(jian)將(jiang)有很大(da)的(de)(de)(de)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)沖擊電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)，有可能(neng)損(sun)壞整流(liu)(liu)(liu)二極管；另外，端電(dian)(dian)(dian)(dian)(dian)壓(ya)為(wei)0的(de)(de)(de)濾波(bo)電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)器(qi)(qi)(qi)(qi)(qi)會(hui)使整流(liu)(liu)(liu)電(dian)(dian)(dian)(dian)(dian)壓(ya)瞬間(jian)(jian)降低(di)至0V，形成對電(dian)(dian)(dian)(dian)(dian)源(yuan)網絡的(de)(de)(de)干擾(rao)。為(wei)了(le)解決上(shang)述問題，在整流(liu)(liu)(liu)橋(qiao)和(he)濾波(bo)電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)器(qi)(qi)(qi)(qi)(qi)之(zhi)間(jian)(jian)接(jie)入一(yi)個限(xian)(xian)流(liu)(liu)(liu)電(dian)(dian)(dian)(dian)(dian)阻(zu)R，可將(jiang)濾波(bo)電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)器(qi)(qi)(qi)(qi)(qi)的(de)(de)(de)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)流(liu)(liu)(liu)限(xian)(xian)制在一(yi)個允許范圍(wei)內。但是，如果(guo)限(xian)(xian)流(liu)(liu)(liu)電(dian)(dian)(dian)(dian)(dian)阻(zu)R始終接(jie)在電(dian)(dian)(dian)(dian)(dian)路內，其(qi)電(dian)(dian)(dian)(dian)(dian)壓(ya)降將(jiang)影響變頻器(qi)(qi)(qi)(qi)(qi)的(de)(de)(de)輸(shu)出電(dian)(dian)(dian)(dian)(dian)壓(ya)，也(ye)會(hui)降低(di)變頻器(qi)(qi)(qi)(qi)(qi)的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)能(neng)轉換效率(lv)，因此，濾波(bo)電(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)器(qi)(qi)(qi)(qi)(qi)充(chong)(chong)電(dian)(dian)(dian)(dian)(dian)完畢后，由接(jie)觸器(qi)(qi)(qi)(qi)(qi)KM將(jiang)限(xian)(xian)流(liu)(liu)(liu)電(dian)(dian)(dian)(dian)(dian)阻(zu)R短接(jie)，使之(zhi)退出運(yun)行。

三、主電路的對外連接端子

各種(zhong)變頻(pin)器主電(dian)(dian)(dian)路的對外(wai)連接(jie)(jie)端(duan)(duan)(duan)子大(da)(da)致相同，如(ru)圖2所(suo)示。其中，R、S、T是(shi)變頻(pin)器的電(dian)(dian)(dian)源端(duan)(duan)(duan)子，接(jie)(jie)至(zhi)交流三相電(dian)(dian)(dian)源；U、V、W為變頻(pin)器的輸(shu)出(chu)端(duan)(duan)(duan)子，接(jie)(jie)至(zhi)電(dian)(dian)(dian)動機；P+是(shi)整流橋輸(shu)出(chu)的+端(duan)(duan)(duan)，出(chu)廠時P+端(duan)(duan)(duan)與P端(duan)(duan)(duan)之(zhi)間用(yong)一塊截面積足夠大(da)(da)的銅片(pian)短接(jie)(jie)，當需要接(jie)(jie)入(ru)直(zhi)流電(dian)(dian)(dian)抗器DL時，拆去(qu)銅片(pian)，將DL接(jie)(jie)在P+和P之(zhi)間；P、N是(shi)濾波后直(zhi)流電(dian)(dian)(dian)路的+、-端(duan)(duan)(duan)子，可以連接(jie)(jie)制(zhi)動單元和制(zhi)動電(dian)(dian)(dian)阻(zu)；PE是(shi)接(jie)(jie)地端(duan)(duan)(duan)子。

圖(tu)2 主電(dian)路(lu)對外連接端子

四、變頻系統的共用直流母線

電(dian)(dian)動(dong)(dong)(dong)(dong)(dong)機(ji)(ji)在(zai)制(zhi)動(dong)(dong)(dong)(dong)(dong)（發電(dian)(dian)）狀(zhuang)態時，變(bian)(bian)頻(pin)(pin)(pin)器(qi)(qi)從(cong)電(dian)(dian)動(dong)(dong)(dong)(dong)(dong)機(ji)(ji)吸收的(de)(de)能(neng)(neng)(neng)量(liang)(liang)(liang)都會保存(cun)在(zai)變(bian)(bian)頻(pin)(pin)(pin)器(qi)(qi)直(zhi)流(liu)(liu)環節(jie)的(de)(de)電(dian)(dian)解(jie)電(dian)(dian)容中，并(bing)導致變(bian)(bian)頻(pin)(pin)(pin)器(qi)(qi)中的(de)(de)直(zhi)流(liu)(liu)母(mu)(mu)線電(dian)(dian)壓升(sheng)高。如果變(bian)(bian)頻(pin)(pin)(pin)器(qi)(qi)配備制(zhi)動(dong)(dong)(dong)(dong)(dong)單元和制(zhi)動(dong)(dong)(dong)(dong)(dong)電(dian)(dian)阻(zu)（這兩種元件(jian)屬于選配件(jian)），變(bian)(bian)頻(pin)(pin)(pin)器(qi)(qi)就可(ke)以通(tong)過短時間接通(tong)電(dian)(dian)阻(zu)，使(shi)再(zai)生電(dian)(dian)能(neng)(neng)(neng)以熱方(fang)式消(xiao)耗(hao)掉(diao)，稱做能(neng)(neng)(neng)耗(hao)制(zhi)動(dong)(dong)(dong)(dong)(dong)。當然，采取再(zai)生能(neng)(neng)(neng)量(liang)(liang)(liang)回饋方(fang)案也可(ke)解(jie)決(jue)變(bian)(bian)頻(pin)(pin)(pin)調(diao)速系統(tong)的(de)(de)再(zai)生能(neng)(neng)(neng)量(liang)(liang)(liang)問題，并(bing)可(ke)達到(dao)(dao)節(jie)約能(neng)(neng)(neng)源(yuan)的(de)(de)目的(de)(de)。而(er)標(biao)準通(tong)用(yong)(yong)(yong)PWM變(bian)(bian)頻(pin)(pin)(pin)器(qi)(qi)沒(mei)有(you)設(she)(she)計使(shi)再(zai)生能(neng)(neng)(neng)量(liang)(liang)(liang)反(fan)饋到(dao)(dao)三相電(dian)(dian)源(yuan)的(de)(de)功(gong)能(neng)(neng)(neng)。如果將多(duo)臺(tai)(tai)變(bian)(bian)頻(pin)(pin)(pin)器(qi)(qi)的(de)(de)直(zhi)流(liu)(liu)環節(jie)通(tong)過共用(yong)(yong)(yong)直(zhi)流(liu)(liu)母(mu)(mu)線互(hu)連，則一(yi)(yi)臺(tai)(tai)或多(duo)臺(tai)(tai)電(dian)(dian)動(dong)(dong)(dong)(dong)(dong)機(ji)(ji)產生的(de)(de)再(zai)生能(neng)(neng)(neng)量(liang)(liang)(liang)就可(ke)以被其他電(dian)(dian)動(dong)(dong)(dong)(dong)(dong)機(ji)(ji)以電(dian)(dian)動(dong)(dong)(dong)(dong)(dong)的(de)(de)方(fang)式消(xiao)耗(hao)吸收。或者，在(zai)直(zhi)流(liu)(liu)母(mu)(mu)線上設(she)(she)置一(yi)(yi)組一(yi)(yi)定容量(liang)(liang)(liang)的(de)(de)制(zhi)動(dong)(dong)(dong)(dong)(dong)單元和制(zhi)動(dong)(dong)(dong)(dong)(dong)電(dian)(dian)阻(zu)，用(yong)(yong)(yong)以吸收不(bu)能(neng)(neng)(neng)被電(dian)(dian)動(dong)(dong)(dong)(dong)(dong)狀(zhuang)態電(dian)(dian)動(dong)(dong)(dong)(dong)(dong)機(ji)(ji)吸收的(de)(de)再(zai)生能(neng)(neng)(neng)量(liang)(liang)(liang)。若(ruo)共用(yong)(yong)(yong)直(zhi)流(liu)(liu)母(mu)(mu)線與能(neng)(neng)(neng)量(liang)(liang)(liang)回饋單元組合，就可(ke)以將直(zhi)流(liu)(liu)母(mu)(mu)線上的(de)(de)多(duo)余能(neng)(neng)(neng)量(liang)(liang)(liang)直(zhi)接反(fan)饋到(dao)(dao)電(dian)(dian)網中來，從(cong)而(er)提(ti)高系統(tong)的(de)(de)節(jie)能(neng)(neng)(neng)效果。綜上所述，在(zai)具有(you)多(duo)臺(tai)(tai)電(dian)(dian)動(dong)(dong)(dong)(dong)(dong)機(ji)(ji)的(de)(de)變(bian)(bian)頻(pin)(pin)(pin)調(diao)速系統(tong)中，選用(yong)(yong)(yong)共用(yong)(yong)(yong)直(zhi)流(liu)(liu)母(mu)(mu)線方(fang)案，配置一(yi)(yi)組制(zhi)動(dong)(dong)(dong)(dong)(dong)單元、制(zhi)動(dong)(dong)(dong)(dong)(dong)電(dian)(dian)阻(zu)和能(neng)(neng)(neng)量(liang)(liang)(liang)回饋單元，是一(yi)(yi)種提(ti)高系統(tong)性能(neng)(neng)(neng)并(bing)節(jie)約投(tou)資的(de)(de)較好方(fang)案。

圖3所示為應用比較廣泛的共用直流母線方案，該方案包括以(yi)下幾個(ge)部分(fen)。

圖3 變頻(pin)器的公用直流(liu)母線(xian)

1.三相交流電源進線?

各變(bian)頻(pin)(pin)器(qi)(qi)(qi)(qi)(qi)的(de)電(dian)源輸(shu)入端(duan)并聯(lian)于(yu)同(tong)一交流母(mu)線(xian)上，并保證各變(bian)頻(pin)(pin)器(qi)(qi)(qi)(qi)(qi)的(de)輸(shu)入端(duan)電(dian)源相位一致。圖3中，斷路器(qi)(qi)(qi)(qi)(qi)QF是每(mei)臺變(bian)頻(pin)(pin)器(qi)(qi)(qi)(qi)(qi)的(de)進線(xian)保護裝置。LR是進線(xian)電(dian)抗器(qi)(qi)(qi)(qi)(qi)，當多臺變(bian)頻(pin)(pin)器(qi)(qi)(qi)(qi)(qi)在同(tong)一環境中運行時(shi)，相鄰變(bian)頻(pin)(pin)器(qi)(qi)(qi)(qi)(qi)會互相干擾(rao)，為了消除或減輕這種干擾(rao)，同(tong)時(shi)為了提高變(bian)頻(pin)(pin)器(qi)(qi)(qi)(qi)(qi)輸(shu)入側的(de)功率因數(shu)，接入LR是必須的(de)。

2.直流母線?

KM是變頻(pin)器(qi)的直流(liu)(liu)環節與(yu)公用直流(liu)(liu)母線連接的控制(zhi)開關。FU是半(ban)導體快速熔斷器(qi)，其額定電(dian)壓可選700V，額定電(dian)流(liu)(liu)必(bi)須考慮驅動電(dian)動機(ji)在(zai)電(dian)動或制(zhi)動時的最大電(dian)流(liu)(liu)，一般情況(kuang)下，可以選擇(ze)額定負載電(dian)流(liu)(liu)的125%。

3.公共制動單元和（或）能量回饋裝置?

回饋到公(gong)共直(zhi)流母線上的(de)再生(sheng)能(neng)(neng)量(liang)，在不能(neng)(neng)完(wan)全被吸收的(de)情況下(xia)，可通過共用(yong)的(de)制動電(dian)阻消耗未(wei)被吸收的(de)再生(sheng)能(neng)(neng)量(liang)。若(ruo)采用(yong)能(neng)(neng)量(liang)回饋裝置，則這部分再生(sheng)能(neng)(neng)量(liang)將被回饋到電(dian)網中，從(cong)而提(ti)高節(jie)能(neng)(neng)的(de)效(xiao)率。

4.控制單元?

各變頻器(qi)根(gen)據控制(zhi)單元的指令，通(tong)過KM將其直流(liu)環節(jie)并聯到共用直流(liu)母(mu)(mu)線上，或是在變頻器(qi)故障后快速地與共用直流(liu)母(mu)(mu)線斷開。