Dc-link current and voltage ripple harmonics in three-phase three-level flying capacitor inverters with sinusoidal carrier-based PWM

This paper concerns with the analysis and calculation of the low-frequency DC-link input current and voltage ripple harmonic components in three-phase three-level flying capacitor inverter topologies. As a first simplified approach, reference is made to sinusoidal carrier-based PWM, and sinusoidal load currents with unity power factor, well representing most of the grid-connected applications. The proposed method can be straight-forwardly extended to centered PWM with any output power factor angle. Based on the ripple requirements of DC-link voltage, an original simple and effective equation for designing the DC-link capacitor has been proposed, since design guidelines only for the flying capacitors are reported in literature. Numerical simulations have been carried out by Matlab/Simulnik in order to verify the proposed developments.