本文主要利用輸出變壓器曲折繞接線(zig-zag transformer)及選擇諧波消除脈波寬度調變(Selective Harmonics Elimination PWM, SHE PWM)來控制三階層反流器系統。因輸出變壓器之特性，其脈波寬度調變波形被設計成四分之ㄧ對稱波形，該波形利用牛頓-瑞福森法(Newton-Raphson method)求開關之切換角度精確解曲線資料，再將曲線資料利用最小平方差法(Least Squares Solutions)來獲得曲線近似方程式。由於曲線近似化的優點能夠讓數位處理器做即時運算來控制基本波大小及改變系統頻率。最後，本文將實驗證明該系統。

This thesis applies the zig-zag transformer and the selective harmonics elimination PWM (SHEPWM) scheme to control a three-level inverter system. The PWM is designed to a quarter symmetry wave due the transformer’s characteristics. The wave applies the Newton-Raphson method to solve the exact curves, and then used the least squares solutions to obtain curve fitting equations. Due to the advantage property of curve fitting, the digital signal processor is able to control the fundamental value and change systematic frequency. Finally, experimental results confirm the system.

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