變(bian)頻器(qi)轉矩提(ti)升原因和調試方法

　　1、轉(zhuan)矩提升的原因

　　設置好轉(zhuan)矩(ju)(ju)提升功能很重要(yao)。變(bian)頻器(qi)應用廣泛的是V/F控(kong)制(zhi)模式，當電(dian)(dian)動(dong)機(ji)(ji)的電(dian)(dian)源頻率下(xia)(xia)(xia)降時，電(dian)(dian)動(dong)機(ji)(ji)的轉(zhuan)速也會(hui)下(xia)(xia)(xia)降，如果(guo)負載(zai)轉(zhuan)矩(ju)(ju)不(bu)變(bian)，則其輸(shu)出(chu)功率也是下(xia)(xia)(xia)降的。根據 守恒的原理，如果(guo)負載(zai)的轉(zhuan)矩(ju)(ju)不(bu)變(bian)，電(dian)(dian)流(liu)是不(bu)能減小(xiao)的， 減小(xiao)電(dian)(dian)壓來(lai)保持輸(shu)入與(yu)輸(shu)出(chu)間的 平衡。設電(dian)(dian)動(dong)機(ji)(ji)輸(shu)入的對應電(dian)(dian)壓為Ux，頻率下(xia)(xia)(xia)降為fx，則：

　　①電壓調節比Ku=Ux/Un

　　②頻(pin)率調(diao)節比Kf=fx/fn

　　式中，Un和fn。分別是(shi)(shi)額(e)定(ding)電(dian)(dian)(dian)(dian)壓(ya)(ya)和額(e)定(ding)頻率。當Ku=Kf時(shi)，電(dian)(dian)(dian)(dian)壓(ya)(ya)和頻率是(shi)(shi)成正比下(xia)降(jiang)的(de)(de)(de)。由(you)于電(dian)(dian)(dian)(dian)動機(ji)的(de)(de)(de)轉(zhuan)速是(shi)(shi)由(you)頻率決(jue)定(ding)的(de)(de)(de)，故輸出(chu)功率所占比例減小的(de)(de)(de)具體反映便是(shi)(shi)電(dian)(dian)(dian)(dian)磁轉(zhuan)矩(ju)的(de)(de)(de)減小，這就降(jiang)低(di)了電(dian)(dian)(dian)(dian)動機(ji)帶(dai)負載(zai)(zai)的(de)(de)(de)能力，如要(yao)不降(jiang)低(di)電(dian)(dian)(dian)(dian)動機(ji)帶(dai)負載(zai)(zai)的(de)(de)(de)能力，當電(dian)(dian)(dian)(dian)壓(ya)(ya)和頻率同時(shi)下(xia)降(jiang)時(shi)，應該在Ku=Kf的(de)(de)(de)基礎(chu)上適當加(jia)大一點電(dian)(dian)(dian)(dian)壓(ya)(ya)，使Ku>Kf。由(you)于加(jia)大電(dian)(dian)(dian)(dian)壓(ya)(ya)的(de)(de)(de)目的(de)(de)(de)是(shi)(shi)為了 轉(zhuan)矩(ju)，所以(yi)稱(cheng)為轉(zhuan)矩(ju)提(ti)升(sheng)(sheng)，又叫(jiao)轉(zhuan)矩(ju)補償。轉(zhuan)矩(ju)提(ti)升(sheng)(sheng)的(de)(de)(de)多少反映了電(dian)(dian)(dian)(dian)壓(ya)(ya)與頻率比值的(de)(de)(de)大小，調試(shi)轉(zhuan)矩(ju)提(ti)升(sheng)(sheng)實際上就是(shi)(shi)調節U/f比

　　2、轉矩(ju)提升(sheng)的(de)U/f曲線

　　變頻器產(chan)(chan)品幾(ji)乎都提供了數(shu)十(shi)條U/f曲(qu)線，供用戶選擇(ze)使用。由于產(chan)(chan)品型號不同(tong)，其U/f曲(qu)線大致有直線形、折(zhe)線形、任(ren)意折(zhe)線形幾(ji)種。具(ju)體可(ke)按電動(dong)機所(suo)帶負載的特性，及(ji)變頻器用戶手(shou)冊的說(shuo)明進行(xing)選擇(ze)即可(ke)。

　　3、U/f比的(de)大小對(dui)負載(zai)的(de)影(ying)響

　　轉矩提升是為了補償(chang)因電(dian)動(dong)(dong)機(ji)(ji)定子繞組電(dian)阻所(suo)引起的低(di)速時轉矩降低(di)，而把低(di)頻率(lv)范圍U/f 。U/f比太小，低(di)頻率(lv)時電(dian)動(dong)(dong)機(ji)(ji)難以啟(qi)(qi)動(dong)(dong)或者可啟(qi)(qi)動(dong)(dong)但帶(dai)不了負載。U/f比太大，電(dian)動(dong)(dong)機(ji)(ji)在(zai)低(di)頻率(lv)運行時不節能(neng)，甚至(zhi)會由于電(dian)動(dong)(dong)機(ji)(ji)磁(ci)路高度飽和而使(shi)變頻器過流跳閘。

　　上述所說(shuo)只(zhi)是(shi)基(ji)本的(de)影響情況(kuang)，在現(xian)(xian)(xian)場要根據電(dian)動(dong)(dong)(dong)機所帶負(fu)載的(de)特性(xing)(xing)，進行(xing)(xing)具體考(kao)慮、設(she)(she)(she)定和調整。對(dui)(dui)于調速(su)(su)范圍(wei)較(jiao)寬的(de)恒轉矩(ju)(ju)(ju)負(fu)載，如帶運輸機等，在設(she)(she)(she)定時(shi)要考(kao)慮在低頻(pin)率運行(xing)(xing)時(shi)能(neng)否帶得動(dong)(dong)(dong)負(fu)載，應把(ba)U/f設(she)(she)(she)置大些。對(dui)(dui)于輕(qing)負(fu)載啟動(dong)(dong)(dong)，重(zhong)負(fu)載運行(xing)(xing)的(de)對(dui)(dui)象(xiang)，對(dui)(dui)轉矩(ju)(ju)(ju)可(ke)不(bu)提(ti)(ti)升或(huo)(huo)少提(ti)(ti)升;對(dui)(dui)于風機、泵類負(fu)載，在低頻(pin)率時(shi)應少提(ti)(ti)升或(huo)(huo)者選(xuan)用(yong)(yong)弱減特性(xing)(xing)的(de)曲線。變頻(pin)器對(dui)(dui)轉矩(ju)(ju)(ju)提(ti)(ti)升都設(she)(she)(she)計有“自(zi)(zi)動(dong)(dong)(dong)”供用(yong)(yong)戶使(shi)用(yong)(yong)，如果(guo)設(she)(she)(she)定為自(zi)(zi)動(dong)(dong)(dong)時(shi)，可(ke)使(shi)加(jia)速(su)(su)時(shi)的(de)電(dian)壓自(zi)(zi)動(dong)(dong)(dong)提(ti)(ti)升以補償啟動(dong)(dong)(dong)轉矩(ju)(ju)(ju)，使(shi)電(dian)動(dong)(dong)(dong)機加(jia)速(su)(su)順利進行(xing)(xing)，對(dui)(dui)于調試(shi)經驗不(bu)足的(de)新手(shou)，或(huo)(huo)者對(dui)(dui)負(fu)載特性(xing)(xing)不(bu)太清楚時(shi)，使(shi)用(yong)(yong)“自(zi)(zi)動(dong)(dong)(dong)”是(shi)種(zhong)不(bu)錯的(de)選(xuan)擇(ze)。如采用(yong)(yong)手(shou)動(dong)(dong)(dong)補償時(shi)，根據負(fu)載特性(xing)(xing)，尤其是(shi)負(fu)載的(de)啟動(dong)(dong)(dong)特性(xing)(xing)，通過試(shi)驗可(ke)選(xuan)出(chu)較(jiao)佳曲線。對(dui)(dui)于變轉矩(ju)(ju)(ju)負(fu)載，如選(xuan)擇(ze)不(bu)當會出(chu)現(xian)(xian)(xian)低速(su)(su)時(shi)的(de)輸出(chu)電(dian)壓過高，而浪費(fei)電(dian)能(neng)的(de)現(xian)(xian)(xian)象(xiang)，甚至還會出(chu)現(xian)(xian)(xian)電(dian)動(dong)(dong)(dong)機帶負(fu)載啟動(dong)(dong)(dong)時(shi)電(dian)流大，而轉速(su)(su)上不(bu)去的(de)現(xian)(xian)(xian)象(xiang)。