變(bian)頻(pin)(pin)器(qi)大(da)體上可分為兩類：高壓(ya)變(bian)頻(pin)(pin)器(qi)和低(di)壓(ya)變(bian)頻(pin)(pin)器(qi)。

　　從用(yong)(yong)途來(lai)講(jiang)，適用(yong)(yong)對象不一樣(yang)，高(gao)(gao)壓(ya)電(dian)機從調(diao)速原理來(lai)講(jiang)，二(er)者都是一樣(yang)的(de)。從拓撲結構(gou)看(kan)，二(er)者差別很大(da)，主要是因(yin)為目前廣泛應用(yong)(yong)的(de)IGBT模塊耐壓(ya)不足(zu)造成(cheng)的(de)。高(gao)(gao)壓(ya)變頻(pin)器由于電(dian)壓(ya)高(gao)(gao)，對驅動電(dian)路(lu)等的(de)干擾也大(da)，通常都采(cai)用(yong)(yong)的(de)光纖進行隔離。

　　為(wei)什(shen)么變(bian)頻(pin)器的輸出電(dian)壓與頻(pin)率成(cheng)比(bi)例的改變(bian)?

　　異步電動機的轉矩是電機的磁通與轉子內流過的電流之間相互作用而產生的，在額定頻率下，如果電壓只降低頻率，那么磁通就過大，磁回路飽和，電機電流 ，嚴重時將燒毀電機。因此，頻率與電壓要成比例地改變，即改變頻率的同時控制變頻器的輸出電壓，使電動機的磁通保持定值，避免磁飽和現象的產生。這就是VVVF的定義。這里的電壓指的是電機的線電壓或者相電壓的 值。
　　電(dian)(dian)動機使(shi)用工(gong)頻(pin)電(dian)(dian)源驅(qu)動時，電(dian)(dian)壓下降則電(dian)(dian)流(liu)增加;對(dui)于變(bian)頻(pin)器(qi)驅(qu)動，如果頻(pin)率(lv)下降時電(dian)(dian)壓也下降，那么電(dian)(dian)流(liu)是否增加?

　　頻率(lv)下降(低速)時,如果輸出相同(tong)的功率(lv),則電(dian)流(liu)增加，但(dan)在轉矩規(gui)定(ding)的條件下,電(dian)流(liu)幾乎不變。

　　采用變頻(pin)器運轉時(shi)，電(dian)機(ji)的起動電(dian)流、起動轉矩怎樣(yang)?

　　采(cai)用變(bian)頻器(qi)運(yun)轉，隨著電(dian)(dian)(dian)機(ji)的加(jia)速相應提高頻率和電(dian)(dian)(dian)壓，起(qi)動(dong)(dong)(dong)(dong)電(dian)(dian)(dian)流被限制在(zai)150%額(e)定電(dian)(dian)(dian)流以(yi)下(根據(ju)機(ji)種不同(tong)，為125%～200%)。用工頻電(dian)(dian)(dian)源直接起(qi)動(dong)(dong)(dong)(dong)時，起(qi)動(dong)(dong)(dong)(dong)電(dian)(dian)(dian)流為6～7倍，因(yin)此，將(jiang)產生機(ji)械電(dian)(dian)(dian)氣上的沖擊。采(cai)用變(bian)頻器(qi)傳動(dong)(dong)(dong)(dong)可以(yi)平(ping)滑地起(qi)動(dong)(dong)(dong)(dong)(起(qi)動(dong)(dong)(dong)(dong)時間變(bian)長)。起(qi)動(dong)(dong)(dong)(dong)電(dian)(dian)(dian)流為額(e)定電(dian)(dian)(dian)流的1.2～1.5倍，起(qi)動(dong)(dong)(dong)(dong)轉矩(ju)為70%～120%額(e)定轉矩(ju);對(dui)于帶有轉矩(ju)自動(dong)(dong)(dong)(dong) 功能的變(bian)頻器(qi)，起(qi)動(dong)(dong)(dong)(dong)轉矩(ju)為 以(yi)上，可以(yi)帶全負載起(qi)動(dong)(dong)(dong)(dong)。