A modular multilevel converter (MMC) is regarded as a promising topology in high-voltage direct current systems. However, the MMC consists of numerous submodules (SMs) and switching devices, which lead to a considerable switching loss, and increased cost and size of the heat sink. To mitigate these issues, this paper presents a novel modulation method composed of fundamental frequency modulation (FFM) and multicarrier-based sinusoidal pulsewidth modulation schemes. The main purpose of this modulation method is the reduction of switching loss while maintaining good harmonic performance. However, the FFM scheme leads to the unbalanced capacitor voltage of each SM in the MMC. Accordingly, this paper additionally proposes the rotation method and selective voltage balancing control for SMs to ensure effective performance of the method. Simulation and experimental results verify the effectiveness and performance of the proposed modulation scheme through switching loss and spectral analyses.
Manuscript received November 24, 2017; revised February 5, 2018 and April 11, 2018; accepted May 31, 2018. Date of publication June 17, 2018; date of current version February 20, 2019. This work was supported by the KEPCO under the project entitled by \u201cDemonstration Study for Low Voltage Direct Current Distribution Network in an Island\u201d under Grant D3080, and in part by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) and the Ministry of Trade, Industry and Energy (MOTIE) of the Republic of Korea under Grant 20171210201100. Recommended for publication by Associate Editor C. Shu. (Corresponding author: Kyo-Beum Lee.) S.-M. Kim and K.-B. Lee are with the Department of Electrical and Computer Engineering, Ajou University, Suwon 16499, South Korea (e-mail:, smkim@ajou.ac.kr; kyl@ajou.ac.kr).
