作為多電平換流器的應用已經擴散出，其對系統的諧波影響可能是顯著並研究在各種情況下，包括那些不均衡諧波的影響是重要的。有許多方法來分析諧波，如蠻力時域，快時域和頻域。相對於其他方法，快速時域方法提供準確的解決方案來評估多電平變換器的諧波。然而，快速的時域方法的性能仍然有待改善，尤其是在大型稀疏矩陣處理，以減少計算時間。因此，本文提出利用Krylov子空間方法，以提高快速時域法。根據模擬結果，該方法的計算時間比PSCAD / EMTDC的短約兩倍。而且，從該方法得到的結果與PSCAD / EMTDC的一致

As the applications of multilevel converters have spread-out, their harmonic influence on system could be significant and it is important to study the harmonic impact under various situations including unbalanced ones. There are many methods to analyze the harmonics, such as brute-force time domain, fast-time domain, and frequency domain. Compared to other methods, fast-time domain method provides accurate solution to evaluate harmonics of multilevel converters. However, the performance of fast-time domain method still needs to be improved, especially in dealing with large and sparse matrix to reduce the computation time. Therefore, this thesis proposes to use Krylov subspace method to improve fast-time domain method. According to simulation results, the computation time of the proposed method is about two times shorter than that of PSCAD/EMTDC. Moreover, the results obtained from the proposed method are consistent with those of PSCAD/EMTDC.

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