Analysis and Design of the Split-Capacitor-Based Sub-Modules Equipped for Hybrid Modular Multilevel Converter

The hybrid modular multilevel converter (MMC) is always featured and profited by the merits of the equipped power valves. Referring to this, a novel hybrid MMC topology equipped with the split-capacitor-based sub-modules (SCSMs) on the AC side is proposed. It aims to increase the utilization of the DC bus voltage with DC fault blocking capability. Especially compared to the hybrid MMC equipped with the full-bridge-based sub-modules (FBSMs) on the AC side, smaller power losses can be achieved for the proposed hybrid MMC, due to the reason that only one semiconductor device of the SCSM is inserted into the current flow route. Structurally, the proposed converter mainly consists of the half-bridge-based sub-module (HBSM) stacks and SCSM stacks. The HBSMs located on the DC converter side of the proposed hybrid MMC are in charge of exchanging active powers, while the SCSMs located on the AC converter side are in charge of shaping the circuit waveforms. Additionally, profited by the specific structure of the SCSM, the DC fault current could be cut off by imposing inversed voltages collected from the SCSM capacitor voltages on the uncontrollable diodes of the IGBTs. For the deep study, a detailed mathematical model and modulation control of the proposed hybrid MMC are analyzed. In addition, an analysis of the balancing control for SCSMs is also provided. Finally, the simulation and experimental results are proposed to verify the effectiveness of the theoretical analysis