An Improved Phase-Shifted Carrier Modulation Scheme for a Hybrid Modular Multilevel Converter

Abstract

This paper presents an improved phase-shifted carrier pulse width modulation (PSC-PWM) scheme for the hybrid modular multilevel converter (MMC) consisting of half-bridge submodules (HBSMs) and full-bridge submodules (FBSMs). When the traditional PSC-PWM schemes for the HBSMs-based MMC and the FBSMs-based MMC are directly applied to the hybrid MMC, some mismatch pulses will occur on the arm voltages because the HBSMs and the FBSMs have different characteristics. These mismatch pulses not only generate undesirable harmonics on the output voltages, but also induce the significantly uneven loss distributions between the HBSMs and the FBSMs. Therefore, an improved PSC-PWM scheme for the hybrid MMC is proposed in this paper to deal with these issues. The improved PSC-PWM scheme can eliminate the mismatch pluses in the output voltages, alleviate the uneven loss distributions between the HBSMs and the FBSMs, and reduce the total switching loss of the converter. The mathematical analysis of the improved PSC-PWM scheme for the hybrid MMC is conducted and its harmonic characters are investigated. The analysis results are verified and compared with the traditional PSC-PWM scheme by the simulated and experimental results.