Three-Level Optimized Pulse Patterns for Grid-Connected Converters with LCL Filters

Abstract

This paper presents the computation of three-level optimized pulse patterns (OPPs) for converters connected to the grid via LCL filters. To meet the relevant harmonic grid codes, the OPP optimization problem considers the transfer function from the switching function harmonics to the grid current harmonics, while respecting the constraints that relate to the current harmonic limits. Moreover, the proposed problem relaxes the restrictions that are traditionally imposed on the switching signals, i.e., the quarter-wave symmetry and unipolar switch positions. In doing so, the current distortions are less than those of the conventional constrained OPPs, while they are occasionally even lower than those of the OPPs without constraints on the current harmonics. The presented numerical results demonstrate the superior harmonic performance of the computed OPPs compared with conventional modulation techniques, such as space vector modulation (SVM).