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(zhuan)(zhuan)(zhuan)差(cha)頻(pin)率(lv)(lv)控制轉(zhuan)(zhuan)(zhuan)差(cha)頻(pin)率(lv)(lv)是施(shi)加(jia)于(yu)電(dian)動(dong)機(ji)的(de)交流電(dian)源(yuan)頻(pin)率(lv)(lv)與電(dian)動(dong)機(ji)速度的(de)差(cha)頻(pin)率(lv)(lv)。根據異步電(dian)動(dong)機(ji)穩定(ding)數學模型可知，當(dang)頻(pin)率(lv)(lv)一定(ding)時(shi)，異步電(dian)動(dong)機(ji)的(de)電(dian)磁轉(zhuan)(zhuan)(zhuan)矩(ju)正比于(yu)轉(zhuan)(zhuan)(zhuan)差(cha)率(lv)(lv)，機(ji)械特性為直線。

　　轉(zhuan)差頻(pin)(pin)(pin)率(lv)(lv)控(kong)制(zhi)(zhi)就是通過(guo)控(kong)制(zhi)(zhi)轉(zhuan)差頻(pin)(pin)(pin)率(lv)(lv)來控(kong)制(zhi)(zhi)轉(zhuan)矩和(he)電流。轉(zhuan)差頻(pin)(pin)(pin)率(lv)(lv)控(kong)制(zhi)(zhi)需要(yao)檢出電動機的(de)轉(zhuan)速(su)(su)，構成速(su)(su)度(du)閉(bi)環(huan)(huan)，速(su)(su)度(du)調(diao)節器(qi)的(de)輸出為轉(zhuan)差頻(pin)(pin)(pin)率(lv)(lv)，然(ran)后以(yi)電動機速(su)(su)度(du)與(yu)轉(zhuan)差頻(pin)(pin)(pin)率(lv)(lv)之(zhi)和(he)作為變頻(pin)(pin)(pin)器(qi)的(de)給定頻(pin)(pin)(pin)率(lv)(lv)。與(yu)U/f控(kong)制(zhi)(zhi)相比(bi)，其加減速(su)(su)特性和(he)限制(zhi)(zhi)過(guo)電流的(de)能(neng)力得(de)到提高(gao)。另(ling)外，它(ta)有速(su)(su)度(du)調(diao)節器(qi)，利(li)用速(su)(su)度(du)反饋構成閉(bi)環(huan)(huan)控(kong)制(zhi)(zhi)，速(su)(su)度(du)的(de)靜(jing)態(tai)誤(wu)差小。然(ran)而要(yao)達到自動控(kong)制(zhi)(zhi)系(xi)統(tong)穩態(tai)控(kong)制(zhi)(zhi)，還(huan)達不到良好的(de)動態(tai)性能(neng)。

　　矢(shi)量(liang)(liang)控(kong)(kong)(kong)制(zhi)(zhi)矢(shi)量(liang)(liang)控(kong)(kong)(kong)制(zhi)(zhi)，也(ye)稱磁(ci)(ci)場(chang)定(ding)向控(kong)(kong)(kong)制(zhi)(zhi)。它是70年代(dai)初由西德F.Blasschke等人(ren)提(ti)(ti)出，以直(zhi)流(liu)(liu)(liu)(liu)電(dian)(dian)(dian)機和交(jiao)(jiao)(jiao)流(liu)(liu)(liu)(liu)電(dian)(dian)(dian)機比較的(de)(de)(de)方法(fa)闡述了這一(yi)原(yuan)理。由此(ci)開創了交(jiao)(jiao)(jiao)流(liu)(liu)(liu)(liu)電(dian)(dian)(dian)動(dong)(dong)(dong)機和等效直(zhi)流(liu)(liu)(liu)(liu)電(dian)(dian)(dian)動(dong)(dong)(dong)機的(de)(de)(de)先河。矢(shi)量(liang)(liang)控(kong)(kong)(kong)制(zhi)(zhi)變頻(pin)調速的(de)(de)(de)做法(fa)是將異(yi)步電(dian)(dian)(dian)動(dong)(dong)(dong)機在(zai)三(san)相(xiang)(xiang)坐(zuo)標(biao)系下的(de)(de)(de)定(ding)子交(jiao)(jiao)(jiao)流(liu)(liu)(liu)(liu)電(dian)(dian)(dian)流(liu)(liu)(liu)(liu)Ia、Ib、Ic。通過(guo)三(san)相(xiang)(xiang)-二相(xiang)(xiang)變換，等效成兩相(xiang)(xiang)靜止坐(zuo)標(biao)系下的(de)(de)(de)交(jiao)(jiao)(jiao)流(liu)(liu)(liu)(liu)電(dian)(dian)(dian)流(liu)(liu)(liu)(liu)Ia1、Ib1，再(zai)通過(guo)按轉子磁(ci)(ci)場(chang)定(ding)向旋轉變換，等效成同步旋轉坐(zuo)標(biao)系下的(de)(de)(de)直(zhi)流(liu)(liu)(liu)(liu)電(dian)(dian)(dian)流(liu)(liu)(liu)(liu)Im1、It1(Im1相(xiang)(xiang)當(dang)(dang)于直(zhi)流(liu)(liu)(liu)(liu)電(dian)(dian)(dian)動(dong)(dong)(dong)機的(de)(de)(de)勵磁(ci)(ci)電(dian)(dian)(dian)流(liu)(liu)(liu)(liu); It1相(xiang)(xiang)當(dang)(dang)于直(zhi)流(liu)(liu)(liu)(liu)電(dian)(dian)(dian)動(dong)(dong)(dong)機的(de)(de)(de)電(dian)(dian)(dian)樞電(dian)(dian)(dian)流(liu)(liu)(liu)(liu))，然后(hou)模仿直(zhi)流(liu)(liu)(liu)(liu)電(dian)(dian)(dian)動(dong)(dong)(dong)機的(de)(de)(de)控(kong)(kong)(kong)制(zhi)(zhi)方法(fa)，求得直(zhi)流(liu)(liu)(liu)(liu)電(dian)(dian)(dian)動(dong)(dong)(dong)機的(de)(de)(de)控(kong)(kong)(kong)制(zhi)(zhi)量(liang)(liang)，經過(guo)相(xiang)(xiang)應的(de)(de)(de)坐(zuo)標(biao)反變換實現對(dui)異(yi)步電(dian)(dian)(dian)動(dong)(dong)(dong)機的(de)(de)(de)控(kong)(kong)(kong)制(zhi)(zhi)。矢(shi)量(liang)(liang)控(kong)(kong)(kong)制(zhi)(zhi)方法(fa)的(de)(de)(de)出現，使異(yi)步電(dian)(dian)(dian)動(dong)(dong)(dong)機變頻(pin)調速在(zai)電(dian)(dian)(dian)動(dong)(dong)(dong)機的(de)(de)(de)調速領域里全fang位(wei)的(de)(de)(de)處于優勢地位(wei)。但是，矢(shi)量(liang)(liang)控(kong)(kong)(kong)制(zhi)(zhi)技(ji)術需要對(dui)電(dian)(dian)(dian)動(dong)(dong)(dong)機參數(shu)進行正確估算，如何提(ti)(ti)高參數(shu)的(de)(de)(de)準(zhun)確性是一(yi)直(zhi)研究(jiu)的(de)(de)(de)話題。

　　直接(jie)轉(zhuan)(zhuan)(zhuan)矩控(kong)(kong)(kong)制(zhi)1985年(nian)，德國魯(lu)爾(er)大學的(de)(de)DePenbrock教(jiao)授shou次提(ti)出了(le)直接(jie)轉(zhuan)(zhuan)(zhuan)矩控(kong)(kong)(kong)制(zhi)理(li)論，該(gai)技術(shu)在(zai)很大程(cheng)度(du)上解(jie)決了(le)矢量(liang)控(kong)(kong)(kong)制(zhi)的(de)(de)不足，它不是通過控(kong)(kong)(kong)制(zhi)電流，磁(ci)鏈等量(liang)間接(jie)控(kong)(kong)(kong)制(zhi)轉(zhuan)(zhuan)(zhuan)矩，而是把(ba)轉(zhuan)(zhuan)(zhuan)矩直接(jie)作為被控(kong)(kong)(kong)量(liang)來控(kong)(kong)(kong)制(zhi)。轉(zhuan)(zhuan)(zhuan)矩控(kong)(kong)(kong)制(zhi)的(de)(de)優越(yue)性(xing)在(zai)于:轉(zhuan)(zhuan)(zhuan)矩控(kong)(kong)(kong)制(zhi)是控(kong)(kong)(kong)制(zhi)定子(zi)磁(ci)鏈，在(zai)本質上并不需要轉(zhuan)(zhuan)(zhuan)速信息，控(kong)(kong)(kong)制(zhi)上對除定子(zi)電阻外的(de)(de)所有電機參數變(bian)化(hua)魯(lu)棒性(xing)良好(hao);所引入的(de)(de)定子(zi)磁(ci)鏈觀測器(qi)能很容易估(gu)算出同步速度(du)信息，因而能方便(bian)的(de)(de)實現無(wu)速度(du)傳(chuan)感器(qi)，這種(zhong)控(kong)(kong)(kong)制(zhi)被稱為無(wu)速度(du)傳(chuan)感器(qi)直接(jie)轉(zhuan)(zhuan)(zhuan)矩控(kong)(kong)(kong)制(zhi)。