A Hybrid Modular Multilevel Converter Comprising Si Submodules and SiC Submodules with Its Specialized Capacitor Voltage Balancing Strategy

Abstract

In medium voltage modular multilevel converter (MMC), modulation strategies with high equivalent switching frequency such as PSC-PWM are usually used, and the switching loss are particularly prominent when many of Si devices such as Si-IGBT operated at a higher switching frequency. SiC devices have received widespread attention for their outstanding switching performance, which is characterized by high switching frequency and can reduce switching loss effectively. However, the on-resistance of SiC devices of the same grade is greater than that of Si devices, and the cost is also higher than that of Si devices, which means that the reduction of switching loss may increase the conduction loss at the same time, and the higher cost will also reduce the competitiveness of the product market. This paper proposes a hybrid MMC comprising Si submodules and SiC submodules to reduce switching loss and improving MMC operational efficiency without significantly increasing cost and conduction loss.