This paper presents the optimization technique for minimizing the voltage and current total\nharmonic distortion (THD) in a single-phase multilevel inverter controlled by staircase modulation.\nThe previously reported research generally considered the optimal THD problem in the frequency\ndomain, taking into account a limited harmonic number. The novelty of the suggested approach\nis that voltage and current minimal THD problems are being formulated in the time domain as\nconstrained optimization ones, making it possible to determine the optimal switching angles. In\nthis way, all switching harmonics can be considered. The target function expression becomes very\ncompact and existing efficient solvers for this kind of optimization problems can find a solution\nin negligible processor time. Current THD is understood as voltage frequency weighted THD that\nassumes pure inductive loadââ?¬â?this approximation is practically accurate for inductively dominant\nRL-loads. In this study, the optimal switching angles and respective minimal THD values were\nobtained for different inverter level counts and overall fundamental voltage magnitude (modulation\nindex) dynamic range. Developments are easily modified to cover multilevel inverter grid-connected\napplications. The results have been verified by experimental tests.
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