近年來，直接轉矩控制法是相當活躍的研究課題之一，它是以解耦控制(direct decoupled control, DDC)為基礎的一種控制方法。直接轉矩控制法允許相當迅速及準確地控制馬達的磁通鏈及轉矩，而不需求助於複雜的磁場導向(field-oriented, FO)演算法與內部電流迴路調變計算；然而，為了將磁通鏈誤差及轉矩誤差限制在某一特定範圍、並且又要提供良好的追蹤表現，這種以切換表(switching table)為基礎的控制方法需要相當高的計算速度及取樣頻率。有時反流器的電晶體開關速度卻無法跟上這樣高的取樣控制頻率，這樣的情況通常造成很嚴重的速度及轉矩漣波。以上述的幾個課題為依據，本論文提出了三種新式的反流器切換策略，依序為：九階段轉矩磁滯比較策略、二十四分區磁通鏈磁滯比較策略，以及結合九階段轉矩比較與二十四分區磁通鏈圓的混合型切換策略。

藉由將轉矩磁滯比較的輸出由三種選擇增加至九種選擇，九階段轉矩磁滯比較策略可以讓馬達的正向加速轉矩與反向加速轉矩的大小變得更有彈性；相反地，藉由增加混合型的電壓向量，二十四分區磁通鏈比較策略使得磁通鏈的追蹤變得更圓滑平順。最後本論文將九階段轉矩比較套用在二十四分區磁通比較策略上，它混合了兩種新式切換策略的優點，明顯地減小了傳統方法難以解決的速度漣波及轉矩漣波問題。此外，經由寫入一個適當的電壓向量切換表至控制程式中，本文提出的混合式切換策略相當容易設計及實現。模擬結果與實驗結果將證實，在廣範圍的速度命令之下且無論加載與否，本文所提出的新式混合型切換策略提供了相較於傳統方法相當低的速度漣波及轉矩漣波，且不失去傳統方法快速響應之優點。

The direct torque control (DTC) is one of the actively researched control schemes which is based on the decoupled control of flux and torque. DTC allows a very quick and precise control of the flux and torque without calling for complex field-oriented algorithms and the inner current regulation loop. However, this switching-table-based DTC approach needs a very high sampling frequency for calculations of torque and flux in order to provide good tracking performance and limit the errors of torque and flux within the specified bands. Sometimes, the sampling frequency of control is too high as compared with the switching frequency of inverter, and therefore gives rise to significant speed and torque ripples. For coping with above-mentioned issues, three novel switching strategies for DTC-based drives have been proposed: the 9-level hysteresis torque comparator, the 24-sector flux comparator and the proposed hybrid switching strategy.

By increasing the output of torque comparator from three to nine choices, the 9-level torque comparator makes the control scheme having more flexibility in positive/negative accelerations. On the contrary, by increasing the choices of mixed voltage vectors, the 24-sector flux comparator leads to a smoother tracking of flux linkage command. Applying the 9-level torque comparator to the 24-sector case, the proposed DTC can significantly reduce the torque ripples and speed ripples in comparison with the conventional switching strategy. Furthermore, the proposed switching strategy can be easily designed by a table composed of hybrid space voltage vectors. Simulated and experimental results will confirm that, without losing the fast torque response of conventional switching-table-based DTC, the proposed switching strategy provides lower speed and torque ripple in very wide speed range despite load condition.

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