Abstract
The modular multilevel converter (MMC) has been a crucial component for medium/high-power energy conversion systems due to its modular structure. In the literature, the harmonic analysis of MMC with different modulation methods, including the conventional carrier phase-shifted pulse width modulation (CPS-PWM) method, have been extensively investigated. However, the influence of the carrier displacement angles between three-phase legs on the output performance of an MMC is normally ignored. This paper proposes a dual-phase-shifted PWM (DPS-PWM) for a three-phase MMC which further enhances the performance of the conventional CPS-PWM scheme through proper selection of carrier displacement angles between three phases. First, the operation principle and implementation of the proposed DPS-PWM method is described. Then a two-dimensional (2D) Fourier model is derived to analyze how the carrier displacement angles between stacks and legs affect the harmonics of output voltage and circulating current. It is found that DPS-PWM can suppress specific harmonics in the line-to-line voltage by coordinating the carriers' phase shifting between the three-phase legs without affecting phase voltage and circulating current. Finally, the effectiveness of the DPS-PWM method is verified by simulation and experimental results.
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