本論文主要目的為研究感應馬達在直接轉矩控制情況下分析轉矩漣波。方法上利用每一取樣時間使轉矩漣波均方根值最小化，再以此轉矩漣波均方根最小化之準則，獲得各向量之最佳切換時間。此最佳切換時間則是實際與參考轉矩間的轉矩誤差函數，這意謂著控制最佳切換時間是屬於區域性初始轉矩誤差函數，而不是全域性的。論文所提出的最佳轉矩漣波控制及初始轉矩誤差包含三個問題:(1)最佳漣波控制隨時間增加，初始轉矩誤差的演化情形；(2)尋求一種最佳初始轉矩誤差，可使得使全域性轉矩漣波最小化；(3)可使全域性轉矩漣波最小化的設計。針對這些問題，本論文發現能使全域性轉矩漣波最小化之準則，並證明全域性轉矩存在最小漣波。另外，有關非全域性轉矩漣波控制隨時間增加，初始轉矩誤差的演化情形，論文研究證明區域性最小漣波將會收斂到全域性最小漣波。本論文也提出藉由二階段控制可得到全域性最小轉矩漣波的結果。第一階段控制可驅使初始轉矩誤差為零值，並使轉矩漣波最小化。第二階段控制可使轉矩漣波最小化。最後經由模擬及實驗證明區域性轉矩漣波初始轉矩誤差，隨時間之演化可收斂至全域性轉矩漣波之最小漣波值。比較區域性轉矩漣波與全域性轉矩漣波後可得到，全域性轉矩漣波有效降低馬達運轉時所產生的轉矩漣波之結果。The purpose of this dissertation is to investigate a novel direct torque control for induction motors. To theoretically analyze the torque ripple, a criterion for the torque ripple should be firstly defined. This dissertation aims to minimize the torque ripple criteria defined by the root mean square (RMS) over a sampling period. By minimizing the RMS torque ripple criteria, one could obtain the optimal switching time for zero and nonzero vectors. However, the optimal switching time is a function of the starting torque error between the reference and actual torques. This means this controlled optimal torque ripple is local but global because of the dependence of starting toque error.Three interesting problems are raised from this starting torque error based optimal torque ripple control. The first one is the evolution of the starting torque error based optimal torque ripple when time increases. The next problem is the existence of global optimal torque ripple, which should not be a function of the starting torque error. The last one is to design a control input such that the torque ripple is the global minimum.Aiming at three problems mentioned above, this dissertation firstly not only proves the existence but also finds the formula of the global minimum torque ripple. Then, starting from a local minimum torque ripple, this dissertation deeply investigates the evolution of the local minimum torque ripple as time increases. A very interesting fact has been found is the convergence from local to global minimum torque ripple when time goes to infinite. Moreover, because of the existence of global minimum torque ripple, this dissertation proposes a two-phase control to obtain the global minimum torque ripple. The first phase control drives the torque error to zero. Therefore, the second phase control enables the global minimum torque ripple. Finally both simulation and experimental results are provided to verify the feasibility of the new-type direct torque control for induction motor drive system.
