U/f恒定控制U/f控制是在改變電動機電源頻率的同時改變電動機電源的電壓，使電動機磁通保持一定，在較寬的調速范圍內，電動機的效率，功率因數不下降。因為是控制電壓(Voltage)與頻率(Frequency)之比，稱為U/f控制。恒定U/f控制存在的主要問題是低速性能較差，轉速極低時，電磁轉矩無法克服較大的靜摩擦力，不能恰當的調整電動機的轉矩補償和適應負載轉矩的變化; 其次是無法準確的控制電動機的實際轉速。由于恒U/f變頻器是轉速開環控制，由異步電動機的機械特性圖可知，設定值為定子頻率也就是理想空載轉速，而電動機的實際轉速由轉差率所決定，所以U/f恒定控制方式存在的穩定誤差不能控制，故無法準確控制電動機的實際轉速。

　　轉差(cha)頻(pin)率(lv)控(kong)制轉差(cha)頻(pin)率(lv)是施加(jia)于電(dian)動(dong)機(ji)的(de)交流(liu)電(dian)源頻(pin)率(lv)與電(dian)動(dong)機(ji)速(su)度(du)的(de)差(cha)頻(pin)率(lv)。根據異步電(dian)動(dong)機(ji)穩定數(shu)學模(mo)型可知，當頻(pin)率(lv)一定時，異步電(dian)動(dong)機(ji)的(de)電(dian)磁轉矩正比于轉差(cha)率(lv)，機(ji)械特性為直線。

　　轉差(cha)(cha)(cha)頻率(lv)控(kong)(kong)制(zhi)就是通過控(kong)(kong)制(zhi)轉差(cha)(cha)(cha)頻率(lv)來控(kong)(kong)制(zhi)轉矩和電流(liu)。轉差(cha)(cha)(cha)頻率(lv)控(kong)(kong)制(zhi)需(xu)要檢(jian)出電動機(ji)(ji)的(de)轉速(su)，構成速(su)度(du)閉環，速(su)度(du)調節器(qi)的(de)輸出為轉差(cha)(cha)(cha)頻率(lv)，然(ran)后以電動機(ji)(ji)速(su)度(du)與轉差(cha)(cha)(cha)頻率(lv)之和作為變頻器(qi)的(de)給定頻率(lv)。與U/f控(kong)(kong)制(zhi)相比，其加減速(su)特性(xing)和限制(zhi)過電流(liu)的(de)能(neng)力得到(dao)提高。另外，它有速(su)度(du)調節器(qi)，利用速(su)度(du)反饋構成閉環控(kong)(kong)制(zhi)，速(su)度(du)的(de)靜態誤差(cha)(cha)(cha)小。然(ran)而(er)要達到(dao)自動控(kong)(kong)制(zhi)系(xi)統穩態控(kong)(kong)制(zhi)，還達不到(dao)良好的(de)動態性(xing)能(neng)。

　　矢量(liang)(liang)控(kong)制(zhi)矢量(liang)(liang)控(kong)制(zhi)，也稱磁(ci)場定向控(kong)制(zhi)。它(ta)是(shi)(shi)(shi)70年代初由西德(de)F.Blasschke等人(ren)提出(chu)，以直(zhi)(zhi)(zhi)流(liu)(liu)電(dian)(dian)(dian)(dian)機(ji)(ji)(ji)(ji)和(he)交(jiao)(jiao)流(liu)(liu)電(dian)(dian)(dian)(dian)機(ji)(ji)(ji)(ji)比較的(de)(de)(de)(de)(de)方(fang)(fang)法(fa)闡述了(le)(le)這一(yi)原(yuan)理。由此開創了(le)(le)交(jiao)(jiao)流(liu)(liu)電(dian)(dian)(dian)(dian)動機(ji)(ji)(ji)(ji)和(he)等效(xiao)直(zhi)(zhi)(zhi)流(liu)(liu)電(dian)(dian)(dian)(dian)動機(ji)(ji)(ji)(ji)的(de)(de)(de)(de)(de)先河。矢量(liang)(liang)控(kong)制(zhi)變(bian)(bian)頻(pin)調速的(de)(de)(de)(de)(de)做法(fa)是(shi)(shi)(shi)將異(yi)步(bu)(bu)電(dian)(dian)(dian)(dian)動機(ji)(ji)(ji)(ji)在(zai)(zai)三相(xiang)坐(zuo)標系下的(de)(de)(de)(de)(de)定子(zi)交(jiao)(jiao)流(liu)(liu)電(dian)(dian)(dian)(dian)流(liu)(liu)Ia、Ib、Ic。通過三相(xiang)-二相(xiang)變(bian)(bian)換，等效(xiao)成兩相(xiang)靜(jing)止坐(zuo)標系下的(de)(de)(de)(de)(de)交(jiao)(jiao)流(liu)(liu)電(dian)(dian)(dian)(dian)流(liu)(liu)Ia1、Ib1，再(zai)通過按轉(zhuan)子(zi)磁(ci)場定向旋轉(zhuan)變(bian)(bian)換，等效(xiao)成同(tong)步(bu)(bu)旋轉(zhuan)坐(zuo)標系下的(de)(de)(de)(de)(de)直(zhi)(zhi)(zhi)流(liu)(liu)電(dian)(dian)(dian)(dian)流(liu)(liu)Im1、It1(Im1相(xiang)當(dang)于直(zhi)(zhi)(zhi)流(liu)(liu)電(dian)(dian)(dian)(dian)動機(ji)(ji)(ji)(ji)的(de)(de)(de)(de)(de)勵磁(ci)電(dian)(dian)(dian)(dian)流(liu)(liu); It1相(xiang)當(dang)于直(zhi)(zhi)(zhi)流(liu)(liu)電(dian)(dian)(dian)(dian)動機(ji)(ji)(ji)(ji)的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)樞電(dian)(dian)(dian)(dian)流(liu)(liu))，然后(hou)模仿直(zhi)(zhi)(zhi)流(liu)(liu)電(dian)(dian)(dian)(dian)動機(ji)(ji)(ji)(ji)的(de)(de)(de)(de)(de)控(kong)制(zhi)方(fang)(fang)法(fa)，求(qiu)得(de)直(zhi)(zhi)(zhi)流(liu)(liu)電(dian)(dian)(dian)(dian)動機(ji)(ji)(ji)(ji)的(de)(de)(de)(de)(de)控(kong)制(zhi)量(liang)(liang)，經過相(xiang)應的(de)(de)(de)(de)(de)坐(zuo)標反(fan)變(bian)(bian)換實現對異(yi)步(bu)(bu)電(dian)(dian)(dian)(dian)動機(ji)(ji)(ji)(ji)的(de)(de)(de)(de)(de)控(kong)制(zhi)。矢量(liang)(liang)控(kong)制(zhi)方(fang)(fang)法(fa)的(de)(de)(de)(de)(de)出(chu)現，使異(yi)步(bu)(bu)電(dian)(dian)(dian)(dian)動機(ji)(ji)(ji)(ji)變(bian)(bian)頻(pin)調速在(zai)(zai)電(dian)(dian)(dian)(dian)動機(ji)(ji)(ji)(ji)的(de)(de)(de)(de)(de)調速領域里全(quan)fang位(wei)的(de)(de)(de)(de)(de)處(chu)于優勢地(di)位(wei)。但是(shi)(shi)(shi)，矢量(liang)(liang)控(kong)制(zhi)技術需要(yao)對電(dian)(dian)(dian)(dian)動機(ji)(ji)(ji)(ji)參(can)數進行正(zheng)確估算，如何提高(gao)參(can)數的(de)(de)(de)(de)(de)準確性是(shi)(shi)(shi)一(yi)直(zhi)(zhi)(zhi)研究的(de)(de)(de)(de)(de)話(hua)題。

　　直(zhi)(zhi)接(jie)(jie)轉(zhuan)矩(ju)控(kong)(kong)(kong)(kong)(kong)(kong)制(zhi)(zhi)1985年，德國魯爾(er)大學的DePenbrock教(jiao)授shou次提出(chu)了直(zhi)(zhi)接(jie)(jie)轉(zhuan)矩(ju)控(kong)(kong)(kong)(kong)(kong)(kong)制(zhi)(zhi)理論，該(gai)技術在(zai)很(hen)大程(cheng)度上(shang)解決了矢量控(kong)(kong)(kong)(kong)(kong)(kong)制(zhi)(zhi)的不(bu)足(zu)，它不(bu)是(shi)通過(guo)控(kong)(kong)(kong)(kong)(kong)(kong)制(zhi)(zhi)電流(liu)，磁(ci)鏈(lian)等量間(jian)接(jie)(jie)控(kong)(kong)(kong)(kong)(kong)(kong)制(zhi)(zhi)轉(zhuan)矩(ju)，而是(shi)把轉(zhuan)矩(ju)直(zhi)(zhi)接(jie)(jie)作為(wei)被(bei)控(kong)(kong)(kong)(kong)(kong)(kong)量來(lai)控(kong)(kong)(kong)(kong)(kong)(kong)制(zhi)(zhi)。轉(zhuan)矩(ju)控(kong)(kong)(kong)(kong)(kong)(kong)制(zhi)(zhi)的優(you)越性在(zai)于:轉(zhuan)矩(ju)控(kong)(kong)(kong)(kong)(kong)(kong)制(zhi)(zhi)是(shi)控(kong)(kong)(kong)(kong)(kong)(kong)制(zhi)(zhi)定子磁(ci)鏈(lian)，在(zai)本質上(shang)并不(bu)需要轉(zhuan)速信(xin)息，控(kong)(kong)(kong)(kong)(kong)(kong)制(zhi)(zhi)上(shang)對(dui)除(chu)定子電阻(zu)外的所有(you)電機參數變化魯棒性良(liang)好;所引入的定子磁(ci)鏈(lian)觀測器(qi)能很(hen)容(rong)易估(gu)算出(chu)同步速度信(xin)息，因而能方便的實(shi)現無速度傳感器(qi)，這種控(kong)(kong)(kong)(kong)(kong)(kong)制(zhi)(zhi)被(bei)稱為(wei)無速度傳感器(qi)直(zhi)(zhi)接(jie)(jie)轉(zhuan)矩(ju)控(kong)(kong)(kong)(kong)(kong)(kong)制(zhi)(zhi)。