Discontinuous Space Vector Modulation for Three-Phase Five-Levels Packed-U-Cell Converter

Abstract

This article proposes an optimal 3D space vector modulation algorithm for the three-phase five-levels packed U-cell converter. The algorithm consists of selecting a common-mode voltage that results in discontinuous modulation, as a result, the reference voltage vector is clamped to the external faces of the 3D space vector diagram and there is always a phase that does not switch for a certain period. Hence, the search for nearest vectors is reduced to a 2D plane and there are no redundancies in the abc coordinates. Moreover, the switching sequence is defined online in order to reduce the converter phase voltage transitions while ensuring half-wave symmetry. In addition, a cost function is proposed to optimize the number of commutations and maintain the capacitor voltages balanced. The proposed algorithm presents advantages when compared to other strategies, such as low computational effort, reduced switching losses, and smaller capacitors. Simulation results demonstrate the good performance and effectiveness of the proposed modulation compared to works previously published in the literature. Finally, experimental results from 2-kVA three-phase five-levels packed-U-cell converter are given to support the theoretical developments.