Hybrid Modular Multilevel Converter based on Si and SiC Devices with Level Multiplier Circuit

This paper presents a Modular Multilevel Converter (MMC) variant that can obtain greater number of output voltage levels than the conventional MMC while using smaller number of Submodule (SM). It is called as Level Multiplier Circuit for MMC (LMMMC). It is a Hybrid MMC made up of Half-bridge Submodule (HB-SM) and Full-bridge Submodule (FB-SM). In comparison to the HB-SM cell, the FB-SM cell has a different voltage value. The number of FB-SMs connected in the arm determines the value of each FB-SM voltage. To achieve the same number of levels in the output voltage, LMMMC employs fewer semiconductor switches than the conventional MMC. The switching loss of the LMMMC increases because the switching frequency of FB-SM is significantly higher than the HB-SM. To compensate for this, Silicon Carbide (SiC) switches are utilized instead of Silicon (Si) switches in the FB-SM. This is due to the fact that SiC devices have lower switching losses than Si devices. The operational principle of LMMMC is described, as well as comparison of its power loss to that of a conventional MMC is presented. The conventional MMC and LMMMC models are simulated in MATLAB Simulink to verify the effectiveness of the proposed converter topology.