Common and Differential Mode Harmonic Analyses of Modulations for Three-Phase Three-Level Converter With Unbalanced DC Link Voltages

This paper presents comprehensive harmonic analyses of sinusoidal pulse width modulations (SPWM) for the three-phase three-level converter with unbalanced dc-link voltages. An analytical model is established to calculate the precise harmonics of common-mode (CM) and differential-mode (DM) voltages. With the developed model, the impacts of unbalanced dc-link voltages on harmonic characteristics for the phase disposition (PD) method and alternative phase opposition disposition (APOD) method are studied. The analysis provides guidelines for the balance control based on the harmonic mechanism with unbalanced dc-link voltages. The analysis is confirmed by extensive simulation and experimental studies.