Time-domain optimization of current THD for a single-phase three-level inverter modulation

The paper focuses on optimal current quality (minimal Total Harmonic Distortion - THD) for a single-phase three-level inverter modulation. Previous works addressed optimal THD problem in frequency domain accounting for a limited number of harmonics. The uniqueness of this work is in its time-domain formulation of minimal current THD problem, which facilitates optimization accounting for all harmonics. Moreover, new term of pattern selectivity is introduced for large angle counts. Pattern selectivity is used to reduce optimization time by eliminating unnecessary voltage patterns, which do not result in optimal current waveforms in any modulation index range. Optimal switching angles and respective minimal THD values are obtained for various switching angle counts for the whole fundamental voltage harmonic (modulation index) range. Simulations comply with theoretical optimization findings.